Esther Sanz Sanz
email: esther.sanz-sanz@inrae.fr

Aurélie Cardona

Claude Napoléone

Motivations of Public Officials as Drivers of Transition to Sustainable School Food Provisioning: Insights from Avignon, France

Keywords: Multi-level perspective, Public service motivation, Farm-to-school, Implementation of local food policies, Public school food procurement

A large body of experience and expertise on the implementation of sustainable public school food procurement policies has developed in recent years. However, there has been little investigation of the values and motivations of the public officials implementing the policies. To address this gap, we examine how the city of Avignon (France) took a step toward transition to local fresh food procurement for public schools, under French government calls for sustainable food products in public canteens. Our analysis combines the Multi-Level Perspective (MLP) on sustainable transitions with the Public Service Motivation construct. Unlike other studies addressing the MLP at a macro level, we focus on individual motivations behind public action. We demonstrate that staff motivations have a major impact on how policies supporting transition to local fresh food procurement for public schools are implemented. These public officials' approach to food shows concern for the public interest regardless of financial return. It is not the rational choice (utilitarian or monetary rewards) that primarily drives the implementation of urban food policies, but normative conformity (equity, education, fairness) and affective bonding (health, environmental convictions). Interestingly, we conclude that the success of Avignon's politically-driven school food procurement policy is essentially due to the catering and procurement staff who overcame the barriers to its implementation.

Introduction: Transitions in the Public School Food Procurement Movement

The practice of weaving food into local policy is well underway in Europe. The re-localization of local food supply is viewed as enhancing human health through the freshness, seasonality, and "distinctive" quality of local food [START_REF] Wiskerke | On places lost and places regained: Reflections on the alternative food geography and sustainable regional development[END_REF], despite critical debate on the capacity of local food systems to curb the energy and pollution costs associated with the transportation of food (i.e. "food miles") [START_REF] Coley | Local food, food miles and carbon emissions: A comparison of farm shop and mass distribution approaches[END_REF]. Thus, local food policy usually views "food from somewhere" [START_REF] Campbell | Breaking new ground in food regime theory: Corporate environmentalism, ecological feedbacks and the 'food from somewhere' regime?[END_REF]) not as a commodity market or a commercial service, but as an investment in the health and welfare of the citizens of tomorrow. Furthermore, there is a rising awareness of the power of the public sector to enhance sustainable consumption and production practices, in particular related to food procurement and its social, economic, environmental, and health implications [START_REF] Lehtinen | Sustainability and local food procurement: A case study of Finnish public catering[END_REF][START_REF] Løes | Increasing organic consumption through school meals-Lessons learned in the iPOPY project[END_REF][START_REF] Morgan | Empowering consumers: the creative procurement of school meals in Italy and the UK[END_REF][START_REF] Rimmington | Corporate social responsibility and sustainable food procurement[END_REF]. Indeed, public school food procurement is recognized as a driver of food and nutrition security [START_REF] Filippini | Sustainable school food procurement: What factors do affect the introduction and the increase of organic food?[END_REF]. For some children, the school lunch is the only well-balanced meal of the day [START_REF] Caldeira | Public Procurement of Food for Health[END_REF]. Both children's health and environmental sustainability are relevant goals that can motivate public bodies to move toward the introduction and diversification of local or certified-origin food [START_REF] Filippini | Sustainable school food procurement: What factors do affect the introduction and the increase of organic food?[END_REF].

In the US context, local food procurement efforts largely come under the heading of farm-to-school initiatives [START_REF] Izumi | Farm to school programs: Exploring the role of regionally-based food distributors in alternative agrifood networks[END_REF]. In European countries, public food procurement is constrained by EU law (Directive 2014/24/EU). This encourages the use of the most economically advantageous tender and enables the contracting authority to take into account other criteria than low price: quality, social, environmental, and innovative aspects, delivery conditions such as delivery date, delivery process, and delivery period. Nevertheless, an obstacle to increasing local supply may be local public managers' difficulties interpreting the European regulations on free competition [START_REF] Morgan | Greening the realm: Sustainable food chains and the public plate[END_REF]. Several ways to promote the transition have been suggested, such as introducing seasonal products and splitting contracts into lots to encourage local producers and discourage big international companies [START_REF] Nölting | Providing organic school food for youths in Europe-Policy strategies, certification and supply chain management in Denmark, Finland, Italy and Norway[END_REF][START_REF] Stein | Public sector food procurement in UK local authorities: ethics and sustainability[END_REF][START_REF] Maietta | School meals and pupil satisfaction. Evidence from Italian primary schools[END_REF]. Success factors are identified as the specific structures of national laws, the maturity of implementation, and the general management and organization of public canteens [START_REF] Soldi | Sustainable public procurement of food[END_REF].

However, identifying the objectives and the obstacles does not explain how public food procurement practices actually change. Studies inspired by the Multi-level Perspective (MLP) framework have shown that transition to sustainable agri-food systems depends on coordination between different actors and institutions (farmers, intermediaries, processors, civil society organizations, agricultural institutions, public policy-makers, etc.) having their own norms, modes of governance, scale of action, motivations, and routines [START_REF] Lamine | Sustainability and resilience in Agrifood systems: reconnecting agriculture, food and the environment: Sustainability and resilience in Agrifood systems[END_REF]. Large-scale decisions or local initiatives can either positively influence the transition processes or produce lock-in effects that need to be overcome [START_REF] Bui | Sustainability transitions: Insights on processes of nicheregime interaction and regime reconfiguration in agri-food systems[END_REF].

The role of committed local public bodies has been shown to be fundamental for the transition to sustainability. The success of "school food reform" can be attributed to the people working to order, deliver, prepare the food and to design the menus [START_REF] Morgan | The school food revolution: public food and the challenge of sustainable development[END_REF]. Research shows that motivating and acknowledging kitchen and catering staff is key to success [START_REF] Darly | La demande en produits locaux de la restauration collective: Quels liens avec l'offre de proximité dans une région d'agriculture industrielle? Le Cas De L'ile-De-France[END_REF]. Recent studies on the emergence and framing of farm-to-school initiatives highlight the crucial role of individual motivations in bringing more fresh locally-produced foods into school meals [START_REF] Bagdonis | The emergence and framing of farm-to-school initiatives: Civic engagement, health and local agriculture[END_REF]. The commitment of public procurers is acknowledged as key to sustainable public procurement behavior [START_REF] Grandia | It is not easy being green: Increasing sustainable public procurement behaviour[END_REF]. Research over the past 30 years on Public Service Motivation (PSM) and related constructs in public administration and in the social and behavioral sciences has supported the idea that individuals tend to act in the public domain with the aim of doing good for others and society [START_REF] Perry | The motivational bases of public service[END_REF][START_REF] Perry | Revisiting the motivational bases of public service: Twenty years of research and an agenda for the future[END_REF].

The core of our analysis concerns changing practices and norms, or regime changes, and how a public school catering department in Avignon (France) developed strategies to successfully re-localize food procurement. Little is known about how motivations (i.e. moral approaches to satisfying human emotional and psychological needs) may underpin the actions of the public officials implementing public school food procurement re-localization policies. To address this gap, we combine the Multi-Level Perspective (MLP) concerning sociotechnical transitions with the Public Service Motivation (PSM) framework. We present this Analytical framework" and the "Methodology" in the homonymous sections. "Results" section highlighs how the motivations of public officials drive the school food procurement policy implementation. The "Discussion" section contextualizes these results within the local food system and explores the role of the public plate. The paper concludes with the prospect of co-construction of public actions with the actors responsible for their implementation.

Analytical Framework

The Multi-Level Perspective is a heuristic framework that allows different levels of actions contributing to a transition process to be considered together [START_REF] Geels | Technological transitions as evolutionary reconfiguration processes: A multi-level perspective and a case-study[END_REF]. It works on three analytical levels: the niche level, where small networks of actors develop radical innovations or new technology on the margins of the regime [START_REF] Geels | Typology of sociotechnical transition pathways[END_REF] (small firms processing local products in our case); the regime level, where established practices and norms maintain existing sociotechnical systems (classical canteen food procurement systems relying on industrial catering services in our case); and the landscape level, representing the exogenous economic, political, and cultural context (the different policies framing food procurement at the EU and national levels in our case) [START_REF] Geels | Technological transitions as evolutionary reconfiguration processes: A multi-level perspective and a case-study[END_REF][START_REF] Rip | Technological change. In: Human choice and climate change: An international assessment[END_REF]. The MLP as defined by [START_REF] Geels | Technological transitions as evolutionary reconfiguration processes: A multi-level perspective and a case-study[END_REF] considers that the transition processes result from landscape-level pressure impacting the regime level, creating opportunities for radical innovations developed at the niche level, resulting in changes at the regime level (Fig. 1). We use the MLP as an analytical framework here to distinguish between the effects of the landscape level and of the niche level on the established regime of food procurement in Avignon. The MLP framework also helped us to track changes that occurred during the transition process, focusing our analysis on the following components of the regime level:

• Norms (here, applicable standards and current regulations concerning hygiene, nutrition, public procurement procedure), • Routines [START_REF] Geels | Technological transitions as evolutionary reconfiguration processes: A multi-level perspective and a case-study[END_REF] (here, organizational inertia, e.g. the presentation of food, purchase ordering, type of meals served, etc.), • Motivations [START_REF] Smith | Innovation studies and sustainability transitions: The allure of the multi-level perspective and its challenges[END_REF].

The MLP literature points to motivations as components of the regime level by considering that different individual motivations can support a transition process [START_REF] Geels | Co-evolution of technology and society : The transition in water supply and personal hygiene in the Netherlands (1850-1930)-A case study in multi-level perspective[END_REF]. However, this framework views the most important triggers of change as interactions with other actors, organizational decision-making, and economic and social contexts. Consequently, the nature of motivations and the role they play in transitions are not the MLP focus. To address how both these interactions and individual motivations impact the process of transition, we combine the MLP Fig. 1 Multi-level perspective on transitions (from Geels & Schot, 2007, p. 401) framework with a framework from the Public Service Motivation (PSM) literature in analyzing this case study.

According to the literature, [START_REF] Knoke | Individual motives and organizational incentive systems[END_REF] distinguish between three categories of officials' motivations:

• "Rational choice": self-interest leading individuals to promote policies to optimize their own interests, such as financial return.

• "Normative conformity": based on social norms of what is proper and appropriate arising from a sense of duty to one's government and community, such as enhancing social justice. • "Affective bonding": individual emotional basis for commitment behavior with regard to a program -in this case sustainable public food procurement-through a genuine belief in its importance and the desire to participate. For example, a nature-loving public procurer with an environmentally-friendly lifestyle might be more committed to implementing sustainable food procurement than a procurer who does not care about nature.

Rational, affective, and normative motivations combine to influence an individual's aggregate motivation to contribute effort or resources towards collective action (i.e. a group of like-minded people who have joined forces to pursue a common goal) (Perry & Hondeghem, 2008). Individual motivations coalesce to shared motivations, and both are influenced by external factors (e.g. policies, popular framings, etc.).

Our analytical framework is summarized in Fig. 2 below, showing specific focal points of analysis in red.

Methodology

Research Context: Avignon's Public School Food Procurement

This paper focuses on the public procurement of food for nursery and primary schools in Avignon. For several years, the French government has spotlighted procurement in public canteens, seeking to increase the proportion of sustainable products used including local and environmentally-friendly quality products. In 2010, a national plan for nutrition ("Plan national pour l'Alimentation") was established to encourage the use of local products in public and private catering. In 2012, the French government set an objective of 20% organic food in public canteens. Local procurement is also an objective: in 2013, the Ministry of the Interior announced the government's intention to enable farmers to participate in public contracts. In 2015, the French Senate defined local procurement by setting a maximum spatial distance between the site of production and the point of sale. This distance is not normative and depends on the type of food production: 30 km for fresh fruits and vegetables, 80 km for processed products. In 2016, there was a move to demand that public canteens procure at least 20% organic food products and 40% local food products, but in the end this was not adopted. In 2017, during the General Assembly on Food (Etats généraux de l'alimentation), the French Ministry of Agriculture stated that its objective was to make public canteens use at least 50% organic products by 2022. Currently, the national Law #Egalim1 on Agriculture and Food adopted by the French government on 1 st November 2018 to support local products requires public canteens to use at least 50% sustainable or high-quality certified-origin food products, including 20% organic products, by 1st January 2022. In response to the French government's call for a greater proportion of sustainable high quality food products in public canteens, many municipal governments attempting to anticipate these future requirements have taken steps to increase the local and organic products used in their school canteens. 2The local government in Avignon is running an ongoing project to improve the quality of school meals by increasing the proportion of local fresh fruits and vegetables, to replace frozen and tinned foodstuffs. School food procurement, as part of the city catering service, was contracted out in 2000 to the private firm Scolarest, Fig. 2 Focal points of analysis based on combining MLP and PSM frameworks a branch of Sodexo, one of the biggest French food services and facilities companies. Some parents complained about the quality of meals served, although school food issues are not discussed in the school councils. In March 2014, the new mayor decided to place school catering under municipal control, fulfilling a campaign promise. The main objective was to improve the quality of the meals served to children (i.e. by introducing local fresh products) and to educate children in good eating habits, with school food considered a "service with a social function meeting needs in the public interest" (25/03/2015, Cécile Helle, Mayor of Avignon, during the municipal council session). With the return to municipal management of catering, a new head of the central kitchen and a new kitchen manager interested in working with unprocessed quality food were hired. The latter, seeking to differentiate himself from his predecessor, said "a cook is not a warmer-up".

The characteristics of Avignon school food catering and procurement are described in Table 1.

Furthermore, a "Commission to promote good eating habits" (Commission du "Bien-Manger") was created in 2014 to encourage healthy eating practices among schoolchildren through activities like pedagogic exhibitions during the school day about food sources, flexibility in menus to account for pupils' cultural or religious preferences (e.g. pork-free menus) or specific health needs (e.g. allergies, diabetes), vegetarian meals twice a month, or a competition between schools to reduce food Cost of a meal School meals cost parents a maximum €2.95 per meal and minimum €1.02 per meal for families with low incomes. The price paid by parents has not changed over the last 4 years, although the food alone (ingredients) costs around €2.00.

Total cost of meals

The decision to place school catering under municipal control eliminated fees and commissions charged by the food services and facilities company and enabled the total cost of meals to be reduced from 2.4 to 2 million euros, 60% funded by the city.

Schedule

Meals are served on the 4 full school days per week (Monday, Tuesday, Thursday and Friday).

Origin of school food Roughly 18% of meal components are local, roughly 28% of meal components are organic.

Local-sourced procurement Local fresh products are mainly fruits. Vegetables are mainly either "raw ready for use" (classed as 4th range under the public procurement code) or "cooked ready for use (5th range). There is little production of animalsource foods (ex. meat, eggs, dairy products) in the Avignon area so local sourcing is limited.

Strategy for procurement of local products

The main contract with a large food-service provider is supplemented by ad-hoc orders on the virtual intermediary platform Agrilocal to provide seasonal fresh products (mainly fruits and vegetables) from local suppliers without tender documents.

waste on-site (Les Olympiades de l'anti-gaspi). New menus are being introduced, based on fresh and seasonal local food with reduced additives, in consultation with the Menus Committee composed of the catering department, procurement officers, councillors, representatives of parent-teacher associations and school canteens. Surprisingly, the councillor responsible for Schooling and Youth does not regularly attend the Menus Committee and the city has not appointed another specific delegate. However, the councillor responsible for Agriculture handles this subject because he has a good knowledge of locally-sourced food and the farmers producing it. In addition, it should be noted that the catering department has received no additional financial or human resources from the city specifically to facilitate the transition to locally-sourced procurement of fresh products.

Qualitative Methodology

Our research team has been engaged in the field since 2012 in various ways which contribute to our comprehensive analysis [START_REF] Katz | Playing the field: Questions of fieldwork in geography[END_REF]. First, some of us were engaged in our case study in an immersive way as inhabitants of Avignon town and as parents directly concerned by food provisioning in schools (2016)(2017)(2018)(2019)(2020)(2021)(2022). Second, our research team has also worked since 2012 in partnership with local stakeholders involved in urban planning linked to periurban farming management [START_REF] Sanz Sanz | Planification urbaine et agriculture. Méthodologie systémique de caractérisation de l'agriculture périurbaine à partir d'une recherche empirique en France et en Espagne[END_REF]. Consequently, our study is partly based on this accumulated knowledge of Avignon's history of agricultural and food strategies.

To investigate the process of change in food provisioning between 2015 and 2018, we combined several methods yielding different kinds of evidence [START_REF] Becker | Problems of inference and proof in participant observation[END_REF]) so as to cross-validate our provisional hypothesis about the role of individual motivations of public officials in the process of change (See "Appendix 1"). We consulted grey literature about the management of public food procurement in Avignon. Between 2016 and 2018, we were participant observers in two meetings of the Menus Committee and twelve meetings on locally-sourced school food procurement. In parallel, between 2017 and 2019, we conducted twenty-five semi-structured interviews with the different actors and stakeholders in public food procurement in Avignon. The aim of the interviews was to elucidate the chain of actions involved in implementing the re-localization policies for public school food procurement, from the production side (local supply) to the consumption side (central kitchen needs), through the intermediate stages (processing, packaging, storage, transport).

In 2018, we held two half-day workshops with people involved in Avignon school food preparation and supply, most of whom had previously been interviewed. The workshops were organized as focus group interviews, with small groups discussing topics selected for investigation under the guidance of a facilitator [START_REF] Morgan | Focus groups[END_REF]. This allowed participants to interact with one another, favoring the emergence of views on a bottom-up basis [START_REF] Fallon | Focusing on focus groups: Lessons from a research project involving a Bangladeshi community[END_REF]. The first focus group interview (16/01/2018) involved eight participants: seven members of the Menus Committee and a consultant working for the public food procurement department of a nearby city. It focused on the changes entailed in adding the criterion of proximity of origin of the ingredients of school meals to the existing criteria concerning price and nutritional balance. During the first part of the focus group interview, participants were asked to examine two existing weekly menus (one from winter 2018, week 15-19/01/2018 and another from summer 2017, week 13-17/06/2017) and to adapt them to the requirements of re-localization. Participants had to replace the vegetables and fruits in the menu with local products according to seasonal availability.

The second focus group interview took place a week later (23/01/2018) and involved not only the members of the Menus Committee but also seven local farmers or delegates of farming cooperatives and partners in re-establishing the distribution network for local farm produce. One of the partners was the intermediary platform Agrilocal, created in Avignon in 20153 to connect public catering services and farmers in support of short food circuits. Another was Local en Bocal, a small firm also created in 2015 in Avignon, which prepares soups and fruit purées using organic and local products from a perimeter of 150 km around the factory. A third small local firm represented was Les jardins de Solène, created in 2017, which collects and processes downgraded vegetables from local farms to provide catering services with peeled fresh vegetables ready to cook. Discussions centered on the two menus adapted in the previous workshop in the light of the constraints of local farmers and entrepreneurs already working, or interested in working, with Avignon's public school food procurement services. This interview's objective was to identify the motivational factors enabling the transition to public school local fresh food procurement.

Both focus group interviews were filmed and participants' contributions were transcribed to enable further qualitative analysis. Focus group interview participants (n = 14) answered a questionnaire-based survey including closed-ended and openended questions (see "Appendix 2") aimed at revealing their individual position with regard to the new policy. Statistical analyses were conducted, using keywords to code responses to open-ended questions. All interviews and transcriptions were coded according to our analysis grid combining the MLP and PSM frameworks; illustrative remarks from the transcriptions are cited below. Our analysis of the discourse of interviewees and participants covered routines, norms, and motivations concerning public food procurement, and their recent changes. We identified and coded three different motivations: rational choice (e.g. potential salary increase), normative conformity (e.g. commitment to the municipal Commission aim of promoting good eating habits, including access to fresh and healthy food), and affective bonding (e.g. environmental convictions concerning local products seen as environmentally-friendly).

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Results

"Changes at the regime level" section presents observations from applying the Multi-Level Perspective at the regime level. It identifies changes to norms and routines involved in this step toward transition to more local fresh products taken by Avignon public school food procurement between 2015 and 2018. The followingsection analyzes the individual motivations of public officials as drivers of public school food procurement policy implementation, applying the Public Service Motivation framework. Table 2 summarizes the results.

Changes at the Regime Level

Our results highlight how barriers can be overcome, shedding light on how procurement works in practice through both formal and informal procedures, and on the role of individuals in changing entrenched norms (summarized in Table 2). Norms were easily bypassed by individuals, especially public procurement norms that did not allow local food to be specified in contracts. The catering department got around the tendering system regulated by the Public Procurement Code (Code des marchés publics) by creating a "direct supply or no intermediaries" award combined with a "guaranteed freshness or carbon criterion" award to promote food from local crops. In addition, the ceiling price of €25,000 pre-tax per year for each purchase order lot (using a simplified competitive call without tender documents) was raised to €90,000 through a deal with the legal department of Agrilocal. Furthermore, the regulatory body GEM-RCN (Groupement d'Etude des Marchés en Restauration Collective et de Nutrition) stipulated the proportion and frequency of the different "components" of a school meal in a monthly menu (e.g. 10 out of 20 side dishes principally composed of vegetables, at least 8 desserts out of 20 fresh fruit). In terms of hygiene, sanitary standards meant that meals had to be delivered to school canteens by cold transfer the day after being cooked in the central kitchen.

Routines were easily changed, or at least challenged, as follows.

• New kitchen management effectively promoted local fresh products (enhanced capabilities). Up to 2015, routines carried on due to the previous management's failure to promote the use of fresh products: "the problem with using fresh local produce is that the kitchen manager has to know how to make the most of it, which we didn't until recently" (a member of the catering department during the 1st focus group interview, 16/01/2018). Through the recruitment of a new kitchen manager, the staff was encouraged to gradually use more local fresh products: "we had a long period where our kitchen manager was not a driving force" (a member of the catering department during the 1st focus group interview, 16/01/2018).

-New recipes were chosen according to the children's tastes. Meals cooked with fresh and seasonal products are not always appreciated by schoolchildren, who are not used to this kind of food: home meals may just be "micro- wave cooking". The nutritionist and the central kitchen staff worked out new recipes suited to the tastes of young children, incorporating the feedback of food service assistants (e.g. adding popular processed cheese "Kiri" to the zucchini gratin, grating carrots directly in the central kitchen to preserve their organoleptic properties). This policy also reduced on-site food waste (measured daily as part of the game Les Olympiades de l'anti-gaspi), since the children actually eat the meals served. -External partnerships were set up to deal with processing. Processing routines were one of the main barriers to the use of local fresh ingredients, since the central kitchen was not equipped with a vegetable processing area to pre-prepare (e.g. peel) raw vegetables before cutting them (e.g. slice, julienne). A plan to equip the kitchen in this way was examined but the cost (€700,000) and the additional labor required seemed disproportionate. Instead, new partnerships were created with local small and medium-sized firms processing local fresh vegetables and fruits (Local en Bocal and Les jardins de Solène), to circumvent the need for technical equipment and labor that raw products involve: "We are currently testing new methods of placing orders for other processed fruit and vegetables. For the moment, there is no commitment, but we are in the process of setting up contracts." (a local firm manager during the 2nd focus group interview, 23/01/2018). -Quantities were properly estimated and communicated to clearly-identified potential local producers (provisioning). Avignon is situated in an urban context, and the catering department in 2016 knew little about seasonality, local farmers, and which local products were available at a given time. For example, they did not know the exact quantity of fresh vegetables per month that they would need a year ahead, so they estimated them. They went to local farmers and specified their needs. For instance, they estimated the quantities of specific vegetables required per month; they tested mixed green salads to identify one the schoolchildren liked so that a local market-gardener could grow it; they tested fruit purées with Local en bocal to define the amount of sugar to be added. Farmers adjusted their production to meet the requirements of the catering department: "What's enabled us to use local fruit and vegetables is that we (the catering department) have encouraged farmers upstream, and farmers who used to be very wary now come to us" (a member of the catering department during the 1st focus group interview, 16/01/2018). -Organizational procedures on purchasing were adjusted. There is usually no contractual agreement, just a handshake and a promise by the head of the central kitchen to purchase the produce grown specifically to meet catering department needs. The local food provisioning system is mostly informal and based on mutual trust: "For the moment, farmers trust my word without a signed contract" (head of central kitchen, 09/02/2017). However, both the catering and procurement departments are seeking ways to secure local food from local suppliers while providing them with a longer-term perspective. Furthermore, tendering system requirements are tedious for farmers, while the simplified competitive call without tender documents under the platform Agrilocal is too time-consuming for the head of procurement, required to advertise, monitor response, analyze tenders, communicate with farmers, and validate the purchase order. Different binding arrangements are being explored to find solutions that are simple and rapid for both sides, like a contract under a framework agreement with a cascade system, or providing farmers with a single interlocutor to centralize orders for different products. -Payment terms were adjusted. Long provider-payment terms of 3 or 4 months discouraged small farmers from continuing to work with the catering department. The Finance Department therefore made arrangements enabling providers to be paid at the end of each month.

Individual Motivations of Public Officials as Drivers of Public School Food Procurement Policy Implementation

The above findings raise the question of what may underlie such remarkable changes in routines and bypassing of stable norms. Intuitively, considering the current policy of many local governments, the municipal government should be the prominent institution in urban food and nutrition security issues [START_REF] Dubbeling | Assessing and planning sustainable city region food systems: insights from two Latin American Cities[END_REF]. However, in our case it was not the main driving force in the successful implementation of the public procurement policy of local food supply, because budget constraints prevented it from providing supplementary funding or human resources. Moreover, the municipal government gave no official guidelines on developing local food procurement, although the policy represented the Mayor's fulfillment of an election promise. Thus, motivations were the main driving force behind the changes in routine surrounding the local sourcing of school food. Critically, although driven by politicians, the policy's success was due to catering staff overcoming barriers to its implementation. More than a third of focus group interview participants considered "individual motivation" to be the main driver of the project's success, before political willingness ("Appendix 3.2.7"). Furthermore, the participants' discussions revealed the trust-based partnerships existing with local farmers and entrepreneurs: "for us, local means quality food produced by nearby farmers that we trust" (a member of the catering department during a semi-structured interview, 05/12/2017). They provided a rich source of insights into the common shared motivations underpinning these business relationships and the changes in catering department routines. It was these motivations that enabled the food supply system to begin transitioning from a regime largely based on frozen and tinned "Food from Nowhere" [START_REF] Campbell | Breaking new ground in food regime theory: Corporate environmentalism, ecological feedbacks and the 'food from somewhere' regime?[END_REF] to one increasingly integrating local fresh products. Considering that individual motivations of public officials are at the heart of how urban food polices are implemented, and based on the public service motivation framework (cf. "Introduction: Transitions in the public school food procurement movement" section of this paper), we looked at three kinds of motivations: rational choice, normative conformity, and affective bonding.

(a) Rational choice (i.e. based on utilitarian or monetary rewards) in the catering department staff (i.e. the people working to order, deliver, prepare the food and to design the menus) remained stable. First, the local government decided not to raise the cost of school meals to parents. Second, no additional resources -financial, labor, or technical-were allocated to the catering department, so the cost of preparing school meals was maintained. Third, salaries in the catering department remained unchanged even though the perceived workload increased. Fourth, most public officials have no personal interest in a utilitarian approach, not being involved in non-profit organizations promoting food or supporting campaigns on environmental issues; nor do most have children at school. This means that they are not driven by monetary or utilitarian rewards. Furthermore, price is not the only criterion considered in the tendering process: "for us, price is not the only selection criterion, it's the quality of products" (a member of the catering department during a meeting with an organic food wholesaler, 05/12/2017). The catering department staff do not see purchasing local food products as generating any positive or negative financial return ("Appendix 3.2.10"). Nevertheless, for councillors, introducing fresh local products into school meals involves a utilitarian benefit: "For a politician, it looks good if his/her vegetables come from a local socially-aware and solidarity-based firm" (councillor, 05/12/2017). (b) With regard to normative conformity (i.e. based on social norms), the objectives of the "Commission to promote good eating habits" are highlighted as major concerns. Indeed, social equity and a sense of duty to offer children of low socioeconomic status access to healthy food are the main motivations underpinning the actions of the catering department staff: "What (the food) we offer (to poor children) at school is light years away from what they are used to"; "We even considered giving parents a taste of the leftovers from the children's meals" (various participants in the 2 nd focus group interview, 23/01/2018). Beyond improving access to healthy food for vulnerable populations, there is a desire to improve education on food and nutrition. The catering department staff consider that the young generation's taste is "formatted" by ultra-processed foodstuffs that always taste the same and are of low nutritional quality. They are aware of French nutritional recommendations (ex. GEM-RC norm) and know that good dietary habits in childhood reduce the risk of overweight and obesity in adulthood, which they consider the public health challenge of our time. In response, they organize different pedagogical activities and events to make schoolchildren aware of good food (e.g. a school canteen "taste week" "La semaine du gout"). They exhibit a sense of duty to positively influence the dietary habits of both children and parents in order to improve the health status of their community. Their leitmotiv is "raise awareness of food and nutrition issues among schoolchildren, to raise awareness among parents" (a participant in the 2nd focus group interview, 23/01/2018).

Catering department staff also explicitly express their commitment to the actions undertaken by the "Commission to promote good eating habits" to reduce on-site food waste: "We're committed to reducing food waste […] It needs to wind up in their stomachs and not in the litter bins" (a member of the catering department during the 2nd focus group interview, 23/01/2018). Finally, fairness toward food producers and suppliers is also mentioned as a concern, both regarding the negotiated price and the payment terms. Concerns about the business model of their partners, and a will to avoid making them wholly dependent on school food procurement, are often mentioned. They are committed to participat-ing in the municipal action with a view to developing local agriculture (questionnaire 2.11). Words like "common ground" (terrain d'entente) and "arrangement" (arrangement) are often used to define the various existing informal partnerships based on mutual trust.

(iii) Affective bonding (i.e. based on personal convictions and individual emotions) also underpins catering staff actions. The most frequently mentioned affective motivations are related to health, also identified by 85% of the catering department participants in focus group interviews as the main objective of a good quality diet ("Appendix 3.1.5"). The catering department staff show a real commitment to ensuring that the children's meals are healthy, nutritious, and tasty. Because of their frequent contact with the children, they know that their home diet is poor: "Only a quarter of the children eat meals at a table at home, that's all", "they eat mostly ultra-processed fast food", "the children don't eat well at home" (various participants in 1 st focus group interview, 16/01/2018). In the absence of a specific municipal programme to improve the nutritional status of children, the catering staff altruistically seeks to improve children's health through their action in the school canteens. Actually, in the second focus group interview questionnaire, catering department staff members identify their "personal satisfaction" as the keystone of the success of the ongoing introduction of fresh, local products into school meals (average of 9 "very satisfied" on a 1 to 10 scale). Environmental concern is identified by more than half of the catering department participants as the second affective motivation behind their actions ("Appendix 3.1.5"): "We try to work in a rational way, which means juggling what children consume with the vitamin content and with an environmental approach" (interview with a key informant, 13/10/17). Local fresh products are perceived by most participants as healthy and of higher nutritional quality (e.g. containing more vitamins than tinned food). But local products are also seen as much more environmentally-friendly than even organic non-local food products, involving lower transportation-related carbon emissions ("Appendix 3.1.6"): "Local doesn't mean organic […] local is our main objective […] I can't see the point of getting organic pears from the other side of the world" (a member of the catering department during a working session on estimated fresh vegetable needs, 14/03/2018). Moreover, the people who work in the catering department are committed to knowing where the fresh products they order come from, and to developing an "ultra-local" sourcing network: "It is not acceptable for us not to know where the products come from" (head of food procurement, 05/12/2017). The expression "it is not acceptable for us" points to the shared, emotional, and genuine conviction underpinning the action.

To conclude, the motivations of the catering department staff appear to be a strong driving force behind the changes in routines surrounding the introduction of fresh local products into school meals and the improved quality of the food served.

These results highlight the role that motivations play in the process of transition to sustainable school food provisioning.

Discussion

Public School Food Procurement and the Motivations of Public Officials

This study confirms the importance of public officials' beliefs and motivations when striving toward sustainable public school food procurement. Motivations rooted in affective bonding (i.e. emotional attachments) and normative conformity (i.e. social norms) have been shown in this study to lie at the heart of policy implementation. Our results are similar to the conclusions of other studies finding that procurement managers' personal commitment is crucial in overcoming obstacles to the preparation, award, and management of more sustainable and healthier food procurement contracts [START_REF] Soldi | Sustainable public procurement of food[END_REF][START_REF] Sonnino | Quality food, public procurement, and sustainable development: The school meal revolution in Rome[END_REF]. The successful implementation of food policies hinges on a well-trained and highly-motivated catering staff, who find recognition, worth, and value in service [START_REF] Darly | La demande en produits locaux de la restauration collective: Quels liens avec l'offre de proximité dans une région d'agriculture industrielle? Le Cas De L'ile-De-France[END_REF]. Despite the small number of comparable studies, similar findings were obtained, for instance, in a school food reform project in Gloucester, UK: "the staff needs to have "an ownership, a value, an understanding" […] "school food reform primarily became an issue of labour" (Morgan & Sonnino, 2008, 116). Similar results were obtained in the USA by examining the perspectives of foodservice workers in the context of values-based procurement shifts, specifically to more healthful and regionally-sourced foods [START_REF] Rosenthal | Bringing school foodservice staff back in: accounting for changes in workloads and mindsets in K-12 values-based procurement[END_REF]. Based on data from interviews with 21 cafeteria managers and 147 completed staff surveys in 23 schools collected in 2 school years (2016 and 2017), the research concludes that successful values-based procurement changes depend on cafeteria staff recognizing the importance of serving local and healthy foods [START_REF] Rosenthal | Bringing school foodservice staff back in: accounting for changes in workloads and mindsets in K-12 values-based procurement[END_REF]. Their motivation to make new initiatives work for the good of the students is key to successful implementation of values-based purchasing initiatives, despite constraints due to the correlated more labor-intensive and complex food preparation techniques. Furthermore, the theory of public service motivation shows that staff motivated by concern for the public interest are high performers, with high levels of achievement, job commitment, and job satisfaction [START_REF] Brewer | Whistle blowers in the federal civil service: new evidence of the public service ethic[END_REF]. Our experience of Avignon and our 3-year immersion in the Avignon school food procurement project enabled us to thoroughly grasp the context, with the challenges and motivations it involved. This understanding informs our analysis of a step in the transition toward more local fresh products.

These findings should be of interest to urban food policymakers, planners and stakeholders. The theoretical literature has highlighted the need for multi-level governance that increases the degree of contact with the beneficiaries of policies. From a social psychology perspective, there has been a call to use co-productive arrangements among a range of parties, from "street-level bureaucrat" to elected policymaker able to implement an effective public policy [START_REF] Wirth | Responding to citizen needs: from bureaucratic accountability to individual coproduction in the public sector[END_REF]. The economics approach has involved arguing that a policy-maker's strategy on governing environmental issues should include dialogue among stakeholders, officials, and scientists [START_REF] Dietz | The struggle to govern the commons[END_REF]. In the policy sciences, it has been pointed out that the beneficiaries should be allowed to play a role in policy-building [START_REF] Orsini | Les acteurs non étatiques dans les négociations multilatérales[END_REF]. This multi-level governance could be achieved in transitional situations like our study case by means of training programs that enlist catering staff as front-line implementers of public school food policies.

Moreover, our results could be used to convince policy-makers of the need to provide public officials with adequate resources to implement urban food policies. Their societal relevance also extends to food producers, who could refer to them when constructing the messages they send to procurement managers. Furthermore, these findings could be used to foster parent involvement in activities promoting healthy food in the school framework. Despite the important role parents can play [START_REF] Clelland | Challenges of parental involvement within a health promoting school framework in New Zealand[END_REF], the parents in our study case were not involved in such activities, and the representatives of the Federation of Parent-Teacher Associations did not participate in the Menus Committee even when invited. Against this background, some studies recommend that food education campaigns be aimed not only at pupils but also at families [START_REF] Morgan | The school food revolution: public food and the challenge of sustainable development[END_REF]. Finally, we suggest that a territorial alliance between families, private companies, and committed local public bodies is fundamental to increase the supply of local food [START_REF] Filippini | Sustainable school food procurement: What factors do affect the introduction and the increase of organic food?[END_REF], and more generally, to successfully implement urban food policies.

Contextualizing School Food Procurement Within the Local Food System

However, even if individual-level motivations seem to be driving the success of this step in Avignon's public school food procurement transition toward more local fresh products, relying on such motivations for systems change would be unwise. There is evidence that change is very hard to sustain when individual "champions" -highly motivated by emotional attachments and social norms-leave their positions; for instance, there may be a perception of safety risks attributable to local foods [START_REF] Thompson | You can't manage with your heart": Risk and responsibility in farm to school food safety[END_REF]. Beyond individual-level motivations, changes at the landscape and niche levels are also essential in maintaining this type of change. In our Avignon case, the previous kitchen manager was not motivated to move toward more local fresh products, and it took a personnel shift to make the difference; but the catering department staff was not the only force behind the change. Since 2010, the French government has sought to increase the proportion of local and organic products in school meals through measures (cf. "Analytical framework" section of this paper) several of which affect the landscape level as defined by the MLP framework. These measures supported the public school food procurement transition process in Avignon. For example, the measure enabling local producers to participate in public tendering since 2013 allowed public procurement departments to use intermediary platforms such as Agrilocal as an aid to local sourcing. Moreover, the national plan for nutrition ("Plan national pour l'Alimentation") in force since 2010, then the #Egalim Law in 2018, acted as powerful drivers of municipal changes to management of food procurement. In parallel, change can also be linked to local initiatives (e.g. Local en Bocal, Les jardins de Solène) that emerged when school catering was placed under municipal control. The creation of these firms, which can be considered as radical niche innovations in the MLP framework, helped Avignon take a step in the process of public school food procurement transition to more local fresh products. More broadly, these new local firms contributed to the Avignon-area movement to re-localize food supply at the territorial level. As another study on agri-food systems pointed out [START_REF] Bui | Sustainability transitions: Insights on processes of nicheregime interaction and regime reconfiguration in agri-food systems[END_REF], when public officials share common visions or common motivations with private food sector entrepreneurs or organizations, the process of transition is smoother. Furthermore, these motivations drive stakeholders to go beyond the established norms and routines which maintain the existing local food system [START_REF] Geels | Typology of sociotechnical transition pathways[END_REF]. It is often the combination of private initiatives with a political project that generates the change.

Nevertheless, implementing food supply re-localization policies does not simply involve broadening and deepening the norms and criteria behind food tendering and procurement processes. Midscale food chains need to be developed and this requires new forms of organization among all the stakeholders in the food chain. For instance, new viable regional market opportunities for small and medium-sized farmers (e.g. Agrilocal), a new tendering system and bidding process suited to them (e.g. joint standing-order contract), and new regional infrastructure/equipment (e.g. creation of small-scale pre-processing facilities) (Sanz Sanz, 2021). Furthermore, the great variety of territorial situations does not make best practices easily replicable everywhere, and it often takes years for public canteens to gradually move to more sustainable food [START_REF] Caldeira | Public Procurement of Food for Health[END_REF][START_REF] Soldi | Sustainable public procurement of food[END_REF]. Against this background, our results contribute insights into the form and nature of institutional responses to food system issues at local level, which need to be bolstered by planning and policy initiatives at regional, national, and even global levels [START_REF] Pothukuchi | Placing the food system on the urban agenda: The role of municipal institutions in food systems planning[END_REF]. The role of public bodies is fundamental in the sharing of motivations contributing to the development of sustainable procurement strategies [START_REF] Day | Buying green: The crucial role of public authorities[END_REF]European Commision, 2015).

The Role of the Public Plate in the Implementation of Local Food Policies

Finally, our study shows that, while until recently governments treated food as a commercial service, their policy perspective is shifting toward investment in the health and welfare of future citizens. Service provision has become a major government responsibility in many welfare states, which raises the issue of how it can legitimately be fulfilled. The state school system imported the neo-liberal values of the market to shape a "cheap food" catering culture [START_REF] Morgan | The school food revolution: public food and the challenge of sustainable development[END_REF]. However, school meals are now acknowledged to contribute to education regarding sustainable dietary habits, the protection of children's health, and the orientation of the production system [START_REF] Caldeira | Public Procurement of Food for Health[END_REF][START_REF] Galli | Co-producing sustainability: Involving parents and civil society in the governance of school meal services. A case study from Pisa. Italy[END_REF][START_REF] Løes | Increasing organic consumption through school meals-Lessons learned in the iPOPY project[END_REF]. Thus, public school food procurement is seen as a driver of food and nutrition security, particularly concerning the alignment between local food demand and local supply that is needed to better address sustainability [START_REF] Filippini | Sustainable school food procurement: What factors do affect the introduction and the increase of organic food?[END_REF]. This is especially relevant in urban areas, which largely rely on imported food. However, we should remember that school food reform challenges the ethics of the foodscape, the "goodness" and "badness" of the various foods available to be cooked in or delivered to schools [START_REF] Moragues-Faus | El horizonte ético alimentario: La política del cuidado[END_REF][START_REF] Morgan | Greening the realm: Sustainable food chains and the public plate[END_REF], and raises questions about the role of the state and the public realm. How powerful is the public plate and what role should it play in the implementation of local food policies? What are the prospects for a transition from sustainable school food provisioning using locally-sourced food to community food planning? What role will school food procurement play in the recently launched Farm-to-Fork Strategy that is at the heart of the European Green Deal and aims to make food systems fair, healthy, and environmentally-friendly? To address these questions, deepening and broadening our results from the Avignon school food procurement case, we plan to conduct a survey in several European cities participating in an ongoing project.

Conclusion

Public school food procurement is considered one of the main targets of the local food policy movement. We argue in this article that the individual motivations of public officials are central to how sustainable public school food procurement policies are implemented. Our work focuses on individual motivations behind public action, thus differing from other studies on the multi-level perspective at a macro level. Conducting a 3-year immersion study of municipal re-localization of public school food procurement, we found that the changes in routines involved in this step in the transition process were largely driven by the motivations of public officials. We conclude that utilitarian or monetary rewards are not the main drivers of such policy implementation. Motivations related to normative conformity-equity, education, fairness-and affective bonding-health, environmental convictions -take precedence over them. Public officials appear to approach food with concern for the public interest regardless of financial return. The fresh, locally-sourced food policy was initiated by politicians, but its success was due to highly-motivated catering and procurement staff overcoming the barriers to implementation. In other words, political will is necessary but not sufficient to promote the transition to sustainable school food provisioning; motivation and training of public officials is essential to the policy's success.

This opens up the perspective of co-construction of public actions with the actors responsible for their implementation, as well as the beneficiaries. The long-standing interest in the modes of participation of the various actors or beneficiaries of public action (see for example [START_REF] Arnstein | A ladder of citizen participation[END_REF] has not been sufficiently disseminated in practice. In some countries, the result of this neglect has been challenges to the legitimacy of public action (see for example [START_REF] Rosanvallon | La légitimité démocratique. Impartialité, réflexivité, proximité. Seuil[END_REF] for France). Formally, the example we provide here illustrates the difficulty of implementing the co-construction of public actions. There is room for improvement in our study case, even though it involves elected officials who are open to this type of mechanism, staff who want it, and beneficiaries who are willing to participate. The work that remains to be done is therefore an internal reform of the institutions that will allow them to be adapted to this mode of decision-making-for instance, by loosening the Public Procurement Code constraints [START_REF] Caldeira | Public Procurement of Food for Health[END_REF].

Further research in two directions will be useful. First, it would be interesting to clarify how motivations are informed by multi-level contextual issues. A broader focus could shed light on how individual motivations coalesce to shared motivations and how both are influenced by external factors (policies, popular framings, etc.). The second area that deserves more attention is the policy-making process. Future research might suggest methods of reforming institutions or decision-making so as to incorporate local stakeholders.

Strongly agree

The city of Avignon is taking important action for children's nutrition

The city of Avignon is taking important action to boost agriculture.

The city of Avignon has many partnerships with civil society (associations and entrepreneurs).

The city of Avignon has a strong policy of commitment to social issues Appendix 3: Outstanding results of the analysis of responses to the questionnaire

Table 1

 1 Characteristics of Avignon school food catering and procurement in 2018

	Item	Description of the item
	Preparation of school meals A central kitchen delivers between 4000 and 5000 lunches to 58 child-care
		centers and primary state schools, as well to the private homes of elderly
		people on request.

Table 2

 2 Results synthesis: norms, routines, and motivations involved in a step in the transition process of Avignon public school food procurement toward more local fresh

products NORMS Nutritional norms Hygiene and sanitary standards Public procurement norms

	The GEM-RCN regulates the proportion Obligatory delivery by cold liaison the day after The Public Procurement Code imposes a codified	and frequency of the different cooking, from the central kitchen to the school tendering system with a bidding process (contract, lots,	"components" of school meals per month canteens award criteria) open to public competition. But rules do	not allow local origin of food to be specified in contracts	Baseline situation (2015) Local adjustment (2018)	Enhancing Lack of leadership of the kitchen manager New kitchen manager competent to promote local fresh products	Schoolchildren's Meals cooked with fresh and seasonal products are not New recipes suited to the tastes of young children incorporating	tastes always to the children's taste and thus not eaten feedback from cafeteria assistants	Processing Central kitchen does not have a raw vegetable processing area External partnerships established with local firms (Les jardins de Solène and Local en bocal)	Provisioning Catering department knows little about local farmers and precise availability of local products at a given time Catering department estimates exact quantities of fresh vegetables needed monthly a year ahead and informs identified local producers	-No contract agreement, just a handshake when -Work in progress to secure local food from local suppliers and to	Purchasing purchasing local produce -Tendering system requirements are tedious and provide them with a longer-term perspective -Organizational adjustments are being explored (e.g. framework	alternative platform Agrilocal is too time-consuming agreement with a cascade system)	Payment Overly long payment terms are a disincentive to small farmers supplying the catering department Corporate Credit Card instituted by Finance department enables payment to suppliers at the end of each month	Rational choice Normative conformity Affective bonding	-Not monetary rewards: cost of meals, Committed to the objectives of: -Emotional desire to enhance children's health	resources allocated, and salaries remain -the Commission to promote good eating habits: through good quality school meals underpinned by	stable equity in access to fresh and healthy food, own experience of the children's poor home diet	-Not utilitarian approach: catering education on food and nutrition -Environmental convictions concerning local products	department staff do not have children at -the municipal action to develop local agriculture: seen as environmentally-friendly due to lower	school in Avignon fairness toward local food producers and suppliers transportation-related carbon emissions
										ROUTINES						MOTIVATIONS	of the catering	department staff

  Do you agree or disagree with the following statements (only one answer per statement, please)?

	Method of investigation 2.11. Statements	Date 23/01/2018	Stakeholders involved Public officials, councillor, rep-resentative of parent-teacher associations, local farmers and Level of agreement Description of the event Discussion on the two menus adapted in the previous focus-group interview in the light of I don't know Strongly Somewhat Somewhat
			delegates of farming coopera-disagree disagree	the constraints of local farmers disagree
			tives, local firms (n = 15)	and entrepreneurs already in or
				interested in a business relation-
				ship with Avignon's public
				school food procurement system
	Long semi-structured interviews
	(n = 7)

https:// agric ulture. gouv. fr/ egalim-ce-que-conti ent-la-loi-agric ulture-et-alime ntati on.

In France, the public procurement of food for nursery and primary schools is the responsibility of municipal authorities.

Developed since 2012 in other parts of France, Agrilocal is a free website helping local farmers to directly contact public procurement services with a collective catering mission (schools, hospitals, retirement homes, etc.). The platform shows the buyer all the relevant products available locally, and each supplier has a personal farm presentation page. https:// www. agril ocal. fr/.

Acknowledgements

We thank Marjorie Sweetko for editing the English of this paper.

Author Contributions All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by ESS. The first draft of the manuscript was written by ESS and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Funding This work was supported by FONDATION DE FRANCE [Grant Number E 00061222].

Declarations


Yohan Pillon

Faridah Qamaruz-Zaman

Michael F Fay

Frédéric Hendoux

Yves Piquot

GENETIC DIVERSITY AND ECOLOGICAL DIFFERENTIATION IN THE ENDANGERED FEN ORCHID (LIPARIS LOESELII) Running Title: Liparis loeselii conservation genetics

Keywords: Liparis loeselii, conservation genetics, AFLP, clonality, autogamy

Liparis loeselii is a rare and endangered orchid occurring in Europe and north-east America. Genetic diversity and structure of this species in north-west France and the United Kingdom were investigated using amplified fragment length polymorphisms (AFLPs). Although clonality and autogamy are common in L. loeselii, we found moderate to important variability within populations. We observed a significant genetic differentiation between populations occurring in dune slacks and fens. This may be correlated with leaf shape as dune slack individuals are sometimes treated as the distinct variety L. loeselii var. ovata. Genetic differentiation between populations was generally low suggesting that gene flow can occur over long distances and possibly across the English Channel. These results show that populations from dune slacks and fens should be managed separately and that geographically distant populations may be equivalent.

INTRODUCTION

Appropriate conservation of biodiversity requires evaluation of the conservation value of populations, species, ecosystems and areas, and a determination of priorities at each scale. The species is the most commonly used measure for biodiversity [START_REF] Purvis | Getting the measure of biodiversity[END_REF] and the main unit in conservation. However the conservation of wild species requires a good knowledge of their delimitation and distinctiveness from their closest relatives [START_REF] Vane-Wright | What to protect?--Systematics and the agony of choice[END_REF]. Systematics is an important issue to take into account in conservation [START_REF] May | Taxonomy as destiny[END_REF]) so that cryptic species are not neglected (e.g. for the tuatara, [START_REF] Daugherty | Neglected taxonomy and continuing extinctions of tuatara (Sphenodon)[END_REF] or to clarify the status of taxa of dubious distinctiveness (e.g. the red wolf, [START_REF] Wayne | The problematic red wolf[END_REF].

In spite of extensive work, European orchids are still the subject of major taxonomic issues, as shown by the differences between treatments by [START_REF] Delforge | Guide des Orchidées d'Europe[END_REF] (2001) and, for example, [START_REF] Pedersen | Species concept and guidelines for infraspecific taxonomic ranking in Dactylorhiza (Orchidaceae)[END_REF], with substantial differences in the number of species recognised. Because of the ease of hybridisation, morphological variability within species and their popularity, taxonomic splitting may have been particularly common in orchids. Taxonomic clarification in this charismatic group is therefore an essential condition for efficient conservation plans. Taxonomic issues have already been raised in the British Isles concerning the conservation of rare species in taxonomically difficult genera such as Dactylorhiza [START_REF] Bateman | Evolution and classification of European orchids: insights from molecular and morphological characters[END_REF][START_REF] Hedrén | Conservation priorities in Dactylorhiza, a taxonomically complex genus[END_REF][START_REF] Pillon | Species diversity versus phylogenetic diversity: a practical study in the taxonomically difficult genus Dactylorhiza (Orchidaceae)[END_REF] and Epipactis [START_REF] Squirrell | Taxonomic complexity and breeding system transitions: conservation genetics of the Epipactis leptochila complex (Orchidaceae)[END_REF].

The fen orchid, Liparis loeselii, is a declining species throughout its distribution, a large part of Europe and North America. This species occupies two types of habitats: dunes slack on the coast and neutral to alkaline fens in plains and mountains. Suitable habitats have become scarce due to coastal urbanisation and the draining of wetlands. The species is protected in most European countries where it occurs and is listed on Annex II of the European directive 92/43/EEC on the conservation of natural habitats and of wild fauna and floras.

In Britain, the species is now only known to occur at three sites in eastern England [START_REF] Wheeler | Liparis loeselii (L.) Rich. in eastern England: constraints on distribution and population development[END_REF]) and four in southern Wales [START_REF] Jones | Aspects of the population biology of Liparis loeselii (L.) Rich. var. ovata Ridd. ex Godfery (Orchidaceae) in the dune slacks of South Wales, UK[END_REF]. In France, L. loeselii was the first plant species to be the subject of a national conservation plan [START_REF] Hendoux | Plan national de conservation du Liparis de Loesel (Liparis loeselii (L.) L.C.M. Rich.). Ministère de l'aménagement du territoire et de l'environnement. Jaccard P[END_REF]. Compared with other European countries, the species is still relatively well represented in France, especially on the coast of Northern France and in the Alps. However, most populations have drastically reduced in size, and the majority of continental lowland populations have completely disappeared.

Within the species, Welsh populations in dunes are characterised by rounded leaves and have been described as Liparis loeselii var. ovata [START_REF] Riddlesdell | Liparis loeselii Rich. var. ovata[END_REF]. This variety was later identified in Brittany, and coastal populations of northern France may also belong to this taxon [START_REF] Hendoux | Plan national de conservation du Liparis de Loesel (Liparis loeselii (L.) L.C.M. Rich.). Ministère de l'aménagement du territoire et de l'environnement. Jaccard P[END_REF]. However, the delimitation of the var. ovata and var. loeselii remains unclear. There is continuous variation between ovate and more lanceolate shapes [START_REF] Hendoux | Plan national de conservation du Liparis de Loesel (Liparis loeselii (L.) L.C.M. Rich.). Ministère de l'aménagement du territoire et de l'environnement. Jaccard P[END_REF], and leaf shape has not been compared critically across populations under controlled conditions. Therefore leaf shape variation could be the result of environmental variance due to biotic (e.g. interspecific competition for light) or abiotic (e.g. soil trophic richness) differences among habitats. However, seedlings germinated in vitro appear to maintain differences in leaf shape (M. Ramsay, pers. comm.).

Because vegetative reproduction and autogamy are common in Liparis loeselii, genetic drift probably affects diversity within populations. The severe fragmentation of its habitat is expected to contribute to genetic impoverishment as well as differentiation between populations. Also, because in the area investigated here, the English Channel region, L. loeselii occurs in two readily distinguishable habitats (dune slacks and alkaline fens), genetic differentiation may be expected between the two habitats.

A good knowledge of the genetic diversity and structure is a necessary prerequisite for the conservation of a species as it reflects the status and survival potential of populations [START_REF] Lande | Genetics and demography in biological conservation[END_REF]. This requires the use of molecular markers, which can also reveal the dispersal capacity of a species [START_REF] Ouborg | Population genetics, molecular markers and the study of dispersal in plants[END_REF]) and infraspecific structure [START_REF] Soltis | Molecular systematics and the conservation of rare species[END_REF]. Amplified fragment length polymorphisms (AFLPs) are recently developed multilocus markers [START_REF] Vos | AFLP: a new technique for DNA fingerprinting[END_REF] that have already shown their usefulness in population genetics of rare or endangered species [START_REF] Juan | Patterns of variability and gene flow in Medicago citrina, an endangered endemic of islands in the western Mediterranean, as revealed by amplified fragment length polymorphism (AFLP)[END_REF][START_REF] Maunder | The genetic status and conservation managment of two cultivated bulb species extinct in the wild: Tecophilaea cyanocrocus (Chile) and Tulipa sprengeri (Turkey)[END_REF][START_REF] Travis | An analysis of genetic variation in Astragalus cremnophylax var. cremnophylax, a critically endangered plant, using AFLP markers[END_REF]. Although L. loeselii probably has a relatively large genome (the congeneric L. rostrata has a C-value of 9.7 pg, [START_REF] Bennett | Angiosperm DNA C-values database[END_REF] that could affect the quality of AFLP results [START_REF] Fay | The effects of nuclear DNA content (C-value) on the quality and utility of AFLP fingerprints[END_REF], they have been previously used successfully in L. loeselii [START_REF] Qamaruz-Zaman | Conservation genetics of rare and endangered British orchids PhD thesis[END_REF].

In the present study, we investigated genetic variation within L. loeselii with a sampling covering Britain and northwestern France and including both varieties and habitat types. We tested for genetic differentiation between varieties and habitats and a possible match between them. We searched for putative geographical structure of genetic diversity and evaluated the genetic differentiation between populations revealing the eventual capacity of the species to disperse in a fragmented habitat.

The plant species

Liparis loeselii is a perennial plant that can live for up to eight years but generally less [START_REF] Jones | Aspects of the population biology of Liparis loeselii (L.) Rich. var. ovata Ridd. ex Godfery (Orchidaceae) in the dune slacks of South Wales, UK[END_REF][START_REF] Wheeler | Liparis loeselii (L.) Rich. in eastern England: constraints on distribution and population development[END_REF]. Individual plants consist of a pseudobulb, one or generally two leaves in adult plant and a central inflorescence with up to twenty green scentless flowers. Vegetative reproduction is achieved though the development of one or two small pseudobulbs from an adult one. The species is generally considered to be selfpollinated and rain drops may facilitate self fertilization (Catling 1980). As for most orchids, Liparis seeds are small (less than one millimetre long) and produced in great number, probably several thousand per fruit [START_REF] Arditti | Numerical and physical properties of orchid seeds and their biological implications[END_REF]. Liparis loeselii is generally associated with early succession stages of vegetation in dune slacks and fens.

Population demography can be irregular, but dormancy is believed to be negligible in this species [START_REF] Jones | Aspects of the population biology of Liparis loeselii (L.) Rich. var. ovata Ridd. ex Godfery (Orchidaceae) in the dune slacks of South Wales, UK[END_REF][START_REF] Wheeler | Liparis loeselii (L.) Rich. in eastern England: constraints on distribution and population development[END_REF].

Sampling

Our sampling covers 12 populations (see figure 1): the three remaining English populations (Catfield, Sutton and Upton), two southern Welsh populations (Whiteford and Kenfig), four populations from northern France (Merlimont, Stella, Villiers and Wimereux), two populations from Brittany (Guidel and Guisseny) and one population from Michigan (North America), used as an outgroup. In the northern French population of Stella, two subpopulations were distinguished corresponding to two non-adjacent dune slacks.

Our sampling includes dune slack and fen populations and regions where plants are classically referred to as var. loeselii (England) and var. ovata (Wales). A total of 155 individuals were included, with an average of 12 individuals per population, but this varies from one to 31, as small populations could not be extensively sampled. No more than half a leaf was collected from two-leaved adult plants. Observations on greenhouse grown plants showed that this had no apparent deleterious effect on the plants; sampling was less drastic than snail or rabbit predation frequently observed in the field. Leaves were dried in silica gel [START_REF] Chase | Silica gel: an ideal material for field preservation of leaf samples for DNA studies[END_REF].

Molecular Procedure

DNA was extracted using a 2CTAB protocol or with the Nucleospin® 96 Plant kit (Macherey-Nagel) and a Microlab Star robot (Hamilton). Genomic DNA was quantified on agarose gel using DNA dilution, and 300 ng of DNA was used for the AFLP reaction using the standard protocol recommended by LI-COR. Two pairs of selective primers were used as they showed appropriate levels of polymorphism (i.e. allowing detection of within and between population variations) in an earlier study of L. loeselii (Qamaruz-Zaman 2000): E-AGC and M-CTG, E-ACT and M-CAA. Fragments were separated on a 41 cm denaturing acrylamide gel in a LI-COR sequencer. Fragment lengths were measured using the software AFLP-SCAN; only bands between 50 and 500 bp were scored as present (1) or absent (0). Electrophoregrams were read twice to guarantee the accuracy of the results.

Data analysis

A principal coordinate analysis (PCOA) was used to look for groupings of the different genotypes observed using the R package for Multivariate Analysis version 4.0 [START_REF] Casgrain | The R Package for Multivariate Analysis, Montreal. Catling PM (1980) Rain-assisted autogamy in Liparis loeselii (L.) L. C. Rich. (Orchidaceae)[END_REF]) using Jaccard's coefficient (Jaccard 1908). To reconstruct relationships between populations, genetic distances between each pair of populations were calculated using AFLP-SURV [START_REF] Vekemans | AFLP-SURV. Laboratoire de Génétique et Ecologie Végétale[END_REF]. Allele frequencies were calculated with the assumption that the species was fully autogamous as this has generally been observed (Catling 1980). A neighbor-joining tree was then built using PHYLIP [START_REF] Felsenstein | PHYLIP (Phylogeny Inference Package)[END_REF]) and NJPLOT [START_REF] Perrière | WWW-Query : an on-line retrieval system for biological sequence banks[END_REF]. Genetic diversity within populations were measured using the Nei and Shannon diversity indices (based on allele frequencies), as calculated with POPGENE 1.31 [START_REF] Yeh | POPGENE, microsoft window-based freeware for populations genetic analysis[END_REF]. To take into account the sampling effects we used a rarefaction procedure to compare the populations that were unevenly sampled [START_REF] Kalinowski | Counting alleles with rarefaction: private alleles and hierarchical sampling designs[END_REF]. For populations for which more than 10 individuals were analysed, ten samples were randomly chosen and the numbers of genotypes and of polymorphic loci were measured and averaged for one hundred replicates.

Genetic structure was tested by AMOVA [START_REF] Excoffier | Analysis of Molecular Variance inferred from metric distances among DNA haplotypes: application to human mitochondrial DNA restriction data[END_REF]) with the software ARLEQUIN 2.0 [START_REF] Schneider | ARLEQUIN: a software for population genetics data[END_REF]. We tested for genetic differentiation between the four areas sampled (England, Wales, northern France and Brittany), between Britain and France and between dune slack and fen populations.

Overall genetic differentiation (F ST ) was estimated using AFLP-SURV with 1000 permutations. Genetic isolation through distance was tested by the mean of a Mantel test using the software PASSAGE 1.0 [START_REF] Rosenberg | PASSAGE. Pattern Analysis, Spatial Statistics, and Geographical Exegesis[END_REF].

The Upton population, for which only a single individual was analysed, was excluded from all analyses except AMOVA.

RESULTS

Amplifications for both pairs of primers tested were successful in 155 individuals.

With the primer pair E-AGC M-CTG and E-ACT M-CAA an average of 37 and 39 bands per individual was revealed. In total 108 bands were scored. Bands that were either present or absent in single accessions were excluded as they were likely to be artefactual.

With both primer pairs, a total of 44 unambiguous polymorphic bands were selected, of which four were polymorphic above the 5% level. When combining these 44 bands, we could distinguish 51 genotypes.

The numbers of genotypes observed, number of polymorphic loci, Nei's diversity index and Shannon's diversity index are given for each population in Table 1. Often one genotype was dominant within the populations, but all the populations for which at least four individuals were sampled showed variability.

Genetic diversity was particularly high for the American population from

Michigan and the northern French population of Merlimont. In all the other populations the most frequent genotype was found in half or more of the individuals. The number of genotypes observed per population and genotypic Shannon index were significantly correlated with the number of accessions analysed (Spearman's rank test, n=12, p<0.01 and p<0.05). The correlation between the number of polymorphic loci and the number of accessions was also close to significance (0.05<p<0,1). However the number of genotypes and the number of polymorphic loci were no more correlated to sample size after rarefaction (n=8; p>0;1). Neither Nei's nor Shannon's diversity index showed significant correlation with sampling effort (p>0.1) or with estimated population size (n=9, p>0.1).

The relationships between the 51 genotypes observed according to the PCOA are shown in Figure 2. The American accessions were clearly distinguishable from the European individuals. Three genotypes were present on both sides of the English Channel. One genotype was found in both fen and dune slack populations, but otherwise genotypes from these two habitats tended to cluster in two groups, although there are exceptions.

The neighbor-joining tree showing the relationships between the populations (Fig. 3) indicates that the dune slack populations form a cluster, to which the fen populations form successive branches, but no geographical structure was apparent. For instance, although the fen population of Villiers is only ca. 10 km away from the dune slack population of Merlimont, it is genetically closer to the fen populations in England.

AMOVA indicates a significant genetic differentiation between dune slack and fen populations (p=0.023). With AMOVA we did not find any significant differentiation between Britain and France (p=0.23) or between the four regions sampled (northern France, Brittany, Wales and England; p=0.44). When both fen and dune slack populations were considered separately, the differentiation between the regions was again not significant (p=0.52 and p=0.91).

There was a significant genetic differentiation between populations overall (F ST =0.382, p<0.01). When considering the two habitat types separately genetic differentiation was high between fen populations (F ST =0.370, p<0.01) but non-significant between dune slack populations (F ST =0.146; p>0.05).

The Mantel test did not reveal any evidence of genetic isolation through distance (p=0.073). When the structure of the sampling into two habitat types was taken into account (partial Mantel test), the correlation was even weaker (p=0.25).

DISCUSSION

Genetic diversity within L. loeselii

The genetic variability revealed by our markers is relatively limited as only 40 percent of the bands scored were polymorphic and only four bands were polymorphic above the 5% level. Trials of other primer pairs showed fewer bands and less variability than the two presented here (data not shown). However the primer pairs used were sufficient to distinguish clearly all the individuals from the population of Michigan.

Therefore the lack of variability observed may be explained by a limited genetic diversity of the European populations, which is not unexpected considering the biology of the species. Although the limited variability of the markers may affect the power of the analyses, it was sufficient to reveal some significant genetic structure (i.e. between fen and dune slack populations). However the variability was not sufficient to reveal any significant biogegraphic structure.

Although L. loeselii is known to be autogamous, capable of vegetative reproduction and in decline, we found a higher level of genetic variation than expected.

More than one genotype was found in all populations that had been appropriately sampled. This observation is consistent with the non-negligible genetic diversity observed in other clonal plants [START_REF] Ellstrand | Patterns of genotypic diversity in clonal plant species[END_REF]. Generally one genotype was dominant in most populations, with a frequency often exceeding 50%. This could be interpreted as evidence of extensive clonality in Liparis populations, although the genetic variability observed could be explained by founding by multiple individuals or gene flow via seeds.

At equal population size, fen populations may be less variable than dune slack populations, but our sampling did not allow to test this. Before rarefaction, the numbers of genotypes and polymorphic loci were clearly correlated with sampling effort and therefore these raw figures should not be used to compare the diversity between populations. After rarefaction the difference between unevenly sampled populations was greatly diminished and only the Merlimont population remained clearly more polymorphic than the others.

Although poorly sampled, the only North American population sampled here displays a comparatively high level of variability. The distribution of L. loeselii does not overlap with any other species of the genus containing over 600 species (World Checklist of Monocots 2004) mostly found in the Tropics. The nearest species in distribution is probably L. lilifolia, found in North America in more southern locations than L. loeselii [START_REF] Luer | The Native Orchids of the United States and Canada, excluding Florida[END_REF]. A close relationship between the two species is further supported by molecular data [START_REF] Cameron | Leave it to the leaves: a molecular phylogenetic study of Malaxideae (Epidendroideae, Orchidaceae)[END_REF]. Therefore a North American origin of L. loeselii seems reasonable and could explain the higher genetic diversity found there.

Genetic differentiation between habitats

Our markers reveal that the populations cluster according to habitat type rather than geographical location, with dune slack populations from Northern France clustering with dune slack populations from Britain rather than with the northern France fen populations. The separation is not perfect at the individual level (Fig. 2) as one genotype (A) was found in both habitats (and in Britain and France: Merlimont, Villiers, Catfield and Kenfig). Therefore the separation between these two groups is probably recent or some gene flow may still be occurring between the two forms. The genetic differentiation between these two putative ecotypes could potentially be linked with adaptation to dune slack and fen environments and the concomitant differences in nutrients, light and humidity or association with different mycorrhizal fungi [START_REF] Bidartondo | Changing partners in the dark: isotopic and molecular evidence of ectomycorrhizal liaisons between forests orchids and trees[END_REF][START_REF] Taylor | Populations, habitat and genetic correlates of mycorrhizal specialization in the 'cheating' orchids Corallorhiza maculata and C. mertensiana[END_REF]. Distinct races only found in dune slacks have also been described in other European orchid genera, e.g. Dactylorhiza [START_REF] Pedersen | Late-flowering dune populations of Dactylorhiza incarnata (Orchidaceae): variation patterns and taxonomic inferences[END_REF] or Epipactis [START_REF] Squirrell | Taxonomic complexity and breeding system transitions: conservation genetics of the Epipactis leptochila complex (Orchidaceae)[END_REF]), but so far genetic studies do not support their distinctiveness from commoner varieties or species [START_REF] Hedrén | Amplified fragment length polymorphisms (AFLP) reveal details of polyploid evolution in Dactylorhiza (Orchidaceae)[END_REF], Squirrell et al. 2002, respectively).

The differentiation between dune slack and fen populations matches in some way the distinction between var. ovata and var. loeselii. Liparis loeselii var. ovata was originally described from Wales and then recorded from Brittany in the 1990s.

Morphometric studies based on ratios of leaf width and length [START_REF] Hendoux | Plan national de conservation du Liparis de Loesel (Liparis loeselii (L.) L.C.M. Rich.). Ministère de l'aménagement du territoire et de l'environnement. Jaccard P[END_REF] indicate that all dune slack populations from Northern France and Northern Brittany have broad leaves and could be unambiguously attributed to var. ovata. The fen population of Villiers in Northern France, and some continental French fen populations have longer leaves and should be placed in var. loeselii, along with the English fen populations. Thus leaf shape, similarly to genetics, tends to separate fen and dune forms. All the Liparis populations in Brittany are coastal and occur in dunes. The two populations analysed here, Guisseny and Guidel (from southern and northern Britanny, respectively) both cluster genetically with other dune populations. However, morphometric data indicate that Guisseny plants have narrower leaves typical of var. loeselii and represent an exception among the sampled populations. However, [START_REF] Hendoux | Plan national de conservation du Liparis de Loesel (Liparis loeselii (L.) L.C.M. Rich.). Ministère de l'aménagement du territoire et de l'environnement. Jaccard P[END_REF] expressed some concerns regarding the accuracy and the potential bias in their data due to the observer as leaf length cannot be clearly defined in L. loeselii.

More precise data are needed to clarify the status of the var. ovata and var. loeselii, for example with the application of Fourier's ellipses [START_REF] Jensen | Lines, outlines, and landmarks: morphometric analysis of leaves of Acer rubrum, Acer saccharinum (Aceraceae) and their hybrid[END_REF].

Furthermore, studies under controlled conditions would be necessary to rule out direct effects of biotic and abiotic factors in the different habitats on the morphology of the plants.

Genetic structure within habitats

Beyond the split between habitats, the genetic differentiation between populations is limited and not significant for dune populations, and the limited variability of the markers used may explain this lack of the structure. The F ST value observed for this habitat (0.146) is below any other value obtained with similar markers (AFLPs or RAPDs) in orchids [START_REF] Forrest | Population genetic structure in European populations of Spiranthes romanzoffiana set in the context of other genetic studies on orchids[END_REF]). Similarly no obvious geographical structure was observed (Fig. 3) and we did not find any evidence for isolation through distance.

Although this lack of differentiation may be linked with the limited variability that we observed, this may have a real biological explanation. As for most orchids, the seed of L. loeselii are minute [START_REF] Arditti | Numerical and physical properties of orchid seeds and their biological implications[END_REF]. Because this species is often found in coastal environments, dispersal by wind is even more likely. The populations sampled in this study could also have a recent and common origin, rendering any structure invisible.

Genetic differentiation was greater and more significant in the fen populations; this may be due to limited exposure to winds and/or higher habitat fragmentation, although our sampling for this habitat is more limited, thus making any conclusions more speculative.

Implications for conservation and perspectives.

Our study reveals a genetic distinction between the dune slack and the fen forms of L. loeselii. These two forms should thus be considered separately in any conservation plan in Britain and nortwestern France at least. Further morphological studies are needed to clarify the delimitation of var. ovata and var. loeselii, and whether or not they match the two ecological forms. Further sampling is also desirable, for instance on the coast of the North Sea and the Baltic Sea, the Alps region and North America. Our results emphasize the need for preserving the fenland form, which has undergone the most dramatic decline and for which population sizes are generally small. As for the dune slack form, the lack of genetic differentiation between populations studied here suggests a possible exchangeability of individuals within this area, which could facilitate reintroduction efforts, if required.

Figure 1 :

 1 Figure 1: Map of southern Britain and north-western France showing the location

Figure 2 .

 2 Figure 2. Principal Component Analysis based on AFLP data separating the 51

Figure 3 .

 3 Figure 3. Neighbor joining tree depicting relationships between the populations studied,

Table 1 :

 1 Results of the genetic analysis for each population. For populations for which more than ten accessions had been analysed the number of genotypes and the number of polymorphic loci were recalculated after rarefaction (random selection of ten individuals with one hundred replicates).

	Population	Estimated	Habitat	Num	Number	Frequenc	Number	Number	Num	Nei's	Shan	Shan
		size		ber	of	y of main	of	of	ber	index	non's	non's
				of	genotype	genotype	polymorp	genotype	of		index	index
				acce	s		hic loci	s after	poly	(alleli		(gen
				ssion				rarefactio	morp	c)	(alleli	otypi
				s				n	hic		c)	c)
									loci
									after
									raref
									actio
									n
	Michigan	unknown	opening	5	5	1	16	-	-	0,146 0,213 2,32
			in forest
	Guidel	unknown	dune	2	2	1	3	-	-	0,034 0,047	1
			slack
	Guisseny	unknown	dune	3	1	3	0	-	-	0	0	0
			slack
	Merlimont	>10000	dune	31	15	6	18	7.3	9.4	0,063 0,109 3,51
		(2004)	slack
	Stella A	272 (2002)	dune	12	4	9	10	3.4	8.0	0,038 0,069 1,21
			slack
	Stella B	~ 60 (2004)	dune	15	4	11	4	3.2	2.8	0,046 0,084 1,24
			slack
	Wimereux	~ 144	dune	14	6	7	6	4.9	5.4	0,042 0,064 2,06
		(2004)	slack
	Kenfig	22000	dune	10	5	6	8	5	8	0,039 0,067 1,77
		(1992)	slack
	Whiteford	90 (1992)	dune	4	2	3	2	-	-	0,017 0,026 0,81
			slack
	Villiers	94 (2003)	fen	18	6	11	6	4.2	4.0	0,02 0,038 1,79
	Catfield	147 (1998)	fen	17	6	10	7	4.3	4.6	0,024 0,045 2,23
	Sutton	24 (1998)	fen	23	7	14	9	4.2	4.6	0,023 0,044 1,86
	Upton	2 (1999)	fen	1	1	1	0	-	-	0	0	0

Acknowledgments : This work was partly funded by the operational programme for the Franco-British area of cross-border co-operation interreg III A. The authors wish to thank Adeline Courseaux, Cécile Godé, Glenda Willems, Pierre Saumitou-Laprade and Robyn Cowan for help and advice in the laboratory. Jean-François Arnaud, Stéphane Fénart, Maxime Pauwels and Xavier Vekemans also provided valuable help with data analyses.