Lucas Leclère
email: leclere@obs-vlfr.fr

Richard R Copley

Tsuyoshi Momose

Evelyn Houliston

Hydrozoan insights in animal development and evolution

The fresh water polyp Hydra provides textbook experimental demonstration of positional information gradients and regeneration processes. Developmental biologists are thus familiar with Hydra, but may not appreciate that it is a relatively simple member of the Hydrozoa, a group of mostly marine cnidarians with complex and diverse life cycles, exhibiting extensive phenotypic plasticity and regenerative capabilities. Hydrozoan species offer extensive opportunities to address many developmental mechanisms relevant across the animal kingdom. Here we review recent work from non-Hydra hydrozoans -hydromedusae, hydroids and siphonophores -shedding light on mechanisms of oogenesis, embryonic patterning, allorecognition, stem cell regulation and regeneration. We also highlight potential research directions in which hydrozoan diversity can illuminate the evolution of developmental processes at micro-and macro-evolutionary time scales.

Introduction

Although the relationships between non-bilaterian animals are currently somewhat controversial, the position of cnidarians as the closest relatives of bilaterians seems relatively undisputed. This has helped to establish the anthozoan cnidarian Nematostella vectensis as a key model for molecular studies in evolutionary aspects of developmental biology. Anthozoa is one side of the deepest split in the cnidarian lineage, the other being Medusozoa, a group united by the presence of a medusa (i.e. a jellyfish) stage in their life-cycle. Medusae show high morphological complexity, including features such as striated muscle and elaborate sensory structures, and in some instances even camera eyes.

Medusozoa is composed of four clades: Hydrozoa, Staurozoa, Cubozoa and Scyphozoa (Figure 1a) [1•]. Hydrozoa is the biggest and most diverse of these, comprising more than 3500 species.

Detailed observation and experimentation on marine hydrozoan species fueled many discoveries and conceptual advances in the second half of the 19 th century, relating notably to germ plasm theory, evolution of germ layers, and regeneration. Weismann, Haeckel, Morgan, Huxley, Driesch, the Hertwig brothers and Metchnikov all worked extensively on marine hydroids and hydromedusae.

During the 20 th century, studies in the freshwater polyp Hydra dominated hydrozoan research in cell and developmental biology, resulting in important findings related to organizer activity, morphogen gradients, pluripotent stem cells, and more recently, evolution of aging (e.g. [START_REF] Boehm | FoxO is a critical regulator of stem cell maintenance in immortal Hydra[END_REF]) and tumorigenesis (e.g. [START_REF] Domazet-Lošo | Naturally occurring tumours in the basal metazoan Hydra[END_REF]), and interactions between animals, symbionts and microbiota (see [START_REF] Bosch | Rethinking the role of immunity: lessons from Hydra[END_REF]). Hydra is still, at the time of writing, the only hydrozoan for which a genome sequence has been published [START_REF] Chapman | The dynamic genome of Hydra[END_REF]. Several excellent recent reviews have covered Hydra research (see [4,6-12•]) and so here, we will focus on current work on other hydrozoan species to highlight their contribution and potential for understanding fundamental developmental processes and evolutionary questions. Unlike Hydra, some of these species allow easy experimental access to sexual reproduction and embryonic development.

In recent years, marine hydrozoan species have been used increasingly for molecular studies, notably Clytia hemisphaerica [START_REF] Houliston | Clytia hemisphaerica: a jellyfish cousin joins the laboratory[END_REF], Hydractinia echinata and its close American relative Hydractinia symbiolongicarpus [START_REF] Plickert | Hydractinia, a pioneering model for stem cell biology and reprogramming somatic cells to pluripotency[END_REF], Cladonema radiatum [START_REF] Suga | Evolution and functional diversity of jellyfish opsins[END_REF] and Podocoryna carnea [START_REF] Schmid | Isolated, mononucleated, striated muscle can undergo pluripotent transdifferentiation and form a complex regenerate[END_REF]. Improved molecular technologies and decreasing sequencing costs are aiding emergence of additional models such as Turritopsis dohrnii [START_REF] Schmich | Induction of reverse development in two marine hydrozoans[END_REF][START_REF] Piraino | Reversing the Life Cycle: Medusae Transforming into Polyps and Cell Transdifferentiation in Turritopsis nutricula (Cnidaria, Hydrozoa)[END_REF], Eleutheria dichotoma [START_REF] Kamm | Axial patterning and diversification in the cnidaria predate the Hox system[END_REF][START_REF] Jakob | Changing hydrozoan bauplans by silencing Hox-like genes[END_REF] and the siphonophore Nanomia bijuga [21,22•,23] (summarized in Table 1).

Phenotypic plasticity and life cycle complexity

The typical hydrozoan life cycle comprises three basic forms: the motile 'planula' larva, sessile polyps (which typically propagate to form extensive colonies by asexual reproduction), and the pelagic medusa, a sexual form usually generated by budding from a polyp (in contrast to the scyphozoan medusa, which forms by a process known as strobilation [24••]). The evolutionary plasticity of this presumably ancestral program is remarkable, as illustrated by the loss of the medusa in the lineages leading to Hydra and Hydractinia. Molecular based phylogenies imply more than 50 independent losses of the medusa and at least 2 losses of the polyp within Hydrozoa, and show that major changes in life cycles and in colonial organization have occurred over short evolutionary time-scales [25-35•] (Figure 1b-c). Hydrozoan life cycles can include sexual and asexual reproduction at almost any stage, and the transitions can occur in atypical sequences, such as the famous medusa to polyp transformation ('reverse development') of Turritopsis dohrnii [START_REF] Schmich | Induction of reverse development in two marine hydrozoans[END_REF]. Determining the molecular mechanisms (including epigenetic modifications and response to environmental factors), and evolutionary processes triggering morphological and life cycle plasticity are important challenges for future research [START_REF] Bosch | How do environmental factors influence life cycles and development? An experimental framework for early-diverging metazoans[END_REF]. The history of genes expressed preferentially in the medusa (relating for instance to striated muscle or sense organs) has started to be addressed [START_REF] Nawrocki | Expression of Wnt pathway genes in polyps and medusa-like structures of Ectopleura larynx (Cnidaria: Hydrozoa)[END_REF][START_REF] Sanders | Patterns of Wnt signaling in the life cycle of Podocoryna carnea and its implications for medusae evolution in Hydrozoa (Cnidaria)[END_REF], and the first comparisons of transcriptomes from Podocoryna and Hydractinia, related species with and without medusae respectively, have been made [39•]. A successful approach that allowed identification of cnidarian-specific genes regulating tentacle patterning in Hydra involved subtractive hybridization between cDNAs from morphologically distinct Hydra strains, followed by functional validation via transgenesis [START_REF] Khalturin | A novel gene family controls species-specific morphological traits in Hydra[END_REF].

Additional life cycle complexity in hydrozoans arises via the formation in many species of complex benthic or pelagic colonies comprising connected polyps specialized for different functions (e.g. budding, feeding, defense). The siphonophores are pelagic colonies which have attained extreme complexity including many different polyp types, but also specialized attached medusa forms serving distinct functions (e.g. reproduction, swimming) [21,22•,41]. Very little is known about how the polyp and medusa components of complex colonies acquire different forms and functions during development and evolution, although the advent of molecular analysis in siphonophores is promising [22•,23]. New transcriptomic data for several polyp types in Hydractinia [START_REF] Soza-Ried | The transcriptome of the colonial marine hydroid Hydractinia echinata[END_REF][START_REF] Sanders | Differential gene expression between functionally specialized polyps of the colonial hydrozoan Hydractinia symbiolongicarpus (Phylum Cnidaria)[END_REF][START_REF] Plachetzki | Gene coexpression modules underlying polymorphic and monomorphic zooids in the colonial hydrozoan, Hydractinia symbiolongicarpus[END_REF] provide many candidates for future investigations of the developmental mechanisms leading to a division of labor between polyps within a colony (see Table 1).

In some hydrozoans groups, polyp colonies of the same species in close contact can fuse or reject depending on how closely genetically related they are. This phenomenon has been successfully dissected at the molecular level in Hydractinia, starting with the seminal work of von Hauenschild in the 1950s (see [START_REF] Rosengarten | Model systems of invertebrate allorecognition[END_REF]). A long and outstanding genetic investigation, involving crosses of many related and unrelated strains [START_REF] Cadavid | An invertebrate histocompatibility complex[END_REF], led to the discovery of an allorecognition complex composed of two genetic loci, alr1 [START_REF] Nicotra | A hypervariable invertebrate allodeterminant[END_REF] and alr2 [START_REF] Rosa | Hydractinia allodeterminant alr1 resides in an immunoglobulin superfamily-like gene complex[END_REF]. The Alr1 and Alr2 proteins show huge diversity in natural populations [49••,50]. They have recently been shown to be homophilic ligands binding only to themselves [51••]. In natural populations additional genetic factors may also be involved in the allorecognition process [START_REF] Powell | Genetic background and allorecognition phenotype in Hydractinia symbiolongicarpus[END_REF].

Allorecognition regulation has important consequences for individual and colonial biology and genotype survival. Fusion between sexually generated polyps has recently being proposed as the mode of colony formation in the genus Ectopleura [35•]. Rejection between colonies can induce necrosis in Hydractinia [START_REF] Buss | Allorecognition triggers autophagy and subsequent necrosis in the cnidarian Hydractinia symbiolongicarpus[END_REF]. Contact between genetically distinct colonies results in mixing of stem cells, which can lead to invasion, takeover and eventually changes in morphology. A fascinating corollary is that evolutionary selection in this context might act at the level of the stem cells, as also proposed in the colonial ascidian Botryllus [START_REF] Laird | Stem cells are units of natural selection in a colonial ascidian[END_REF].

Medusa evolution and development

Cnidarians are often represented as having a simple morphology and relatively few cell types, reflecting the situation in the common bilaterian-cnidarian ancestor. The medusa form, however, has a sophisticated organization, including specialized sensory and reproductive organs and the fastcontracting striated muscle of the bell for swimming [START_REF] Suga | Evolution and functional diversity of jellyfish opsins[END_REF][START_REF] Houliston | Clytia hemisphaerica: a jellyfish cousin joins the laboratory[END_REF][START_REF] Koizumi | The nerve ring in cnidarians: its presence and structure in hydrozoan medusae[END_REF] (Figure 2a), providing an opportunity to compare the developmental and evolutionary origins of these structures in cnidarians and bilaterians. Molecular studies of hydrozoan medusae sensory structures have so far focused mainly on light detection. Eyes of Cladonema medusae express Opsin photoproteins and Six/Pax/Eya transcription factors [START_REF] Suga | Evolution and functional diversity of jellyfish opsins[END_REF][START_REF] Suga | Flexibly deployed Pax genes in eye development at the early evolution of animals demonstrated by studies on a hydrozoan jellyfish[END_REF][START_REF] Graziussi | The "eyes absent" (eya) gene in the eye-bearing hydrozoan jellyfish Cladonema radiatum: conservation of the retinal determination network[END_REF], suggesting a common origin of the molecular mechanisms of eye development and convergence of the eyes as complex structures between Hydrozoa and Bilateria.

The medusa stage itself has been the subject of historical dispute, with opposing camps regarding it as a primitive cnidarian trait lost in Anthozoa, or a derived feature of Medusozoa. From a phylogenetic perspective, recent debate has revolved around potential paraphyly of Anthozoa and the position of Staurozoa (so-called 'stalked jellyfish'). It is now widely accepted that the medusa is a derived character of Medusozoa, although the most recent phylogeny recovers monophyletic Anthozoa, as sister to Medusozoa, with Hydrozoa (rather than Staurozoa) as sister group to the other

medusozoans [1•].
Gene expression data relating to medusa development is accumulating gradually (e.g. [58-61•]), but remains scarce compared to planula and polyp data, while gene function studies in the medusa are still largely lacking [START_REF] Jakob | Changing hydrozoan bauplans by silencing Hox-like genes[END_REF]. Detailed comparative anatomical, molecular and functional studies between medusae of the different medusozoan groups will be insightful for deciphering the origin(s) of the medusa form. The evolutionary origin of hydrozoan striated muscle, traditionally considered homologous between cnidarians and bilaterians [START_REF] Seipel | Evolution of striated muscle: jellyfish and the origin of triploblasty[END_REF], was addressed by Steinmetz and coworkers 2a). Genomic analyses and in situ hybridization approaches showed that key bilaterian striated muscle proteins, notably components of the Z-disk, are not present in Clytia, while most of the bilaterian striated muscle genes are either expressed broadly or in other cell types. This study thus provides compelling evidence for convergent evolution of striated muscle in hydrozoans and bilaterians.

[63••] (Figure

Gametogenesis and spawning

The transparency and accessibility of many hydrozoan sexual forms makes them particularly good models for studying the widely conserved regulatory mechanisms of animal gametogenesis, and dissecting the mechanisms of oocyte maturation, spawning and fertilization (discussed in detail in [START_REF] Amiel | Clytia hemisphaerica: a cnidarian model for studying oogenesis[END_REF], Figure 2b). Studies in several medusae including Cladonema, Cytaeis and Clytia are allowing analysis of successive regulatory steps. For technical reasons (notably access to microinjection of Morpholinos/mRNAs/indicators), the main research focus so far has been on the fully grown oocyte and spawned egg. Spawning in both males and females is triggered by light, which induces somatic cells of the gonad to secrete a small diffusible hormone that awakens the dormant gametes. Recent studies suggest that neuropeptide-related molecules participate in this process [START_REF] Takeda | Neuropeptides trigger oocyte maturation and subsequent spawning in the hydrozoan jellyfish Cytaeis uchidae[END_REF]. The essential downstream response of oocytes to the hormone is an immediate rise in cytoplasmic cAMP levels and PKA activation [START_REF] Takeda | Increase in intracellular cAMP is a prerequisite signal for initiation of physiological oocyte meiotic maturation in the hydrozoan Cytaeis uchidae[END_REF]. This stimulates both release of meiotic arrest and entry into the meiotic divisions and parallel activation of the Mos-MAP kinase pathway responsible for regulation of oocyte-specific processes such as polar body formation and post-meiotic cell cycle arrest [START_REF] Amiel | Conserved functions for Mos in eumetazoan oocyte maturation revealed by studies in a cnidarian[END_REF]. MAP kinase pathway inactivation following fertilization, along with cytoplasmic Ca ++ release, is also involved in regulating polyspermy [68•]. Concerning the regulation of early steps of gametogenesis such as entry into meiosis and oocyte growth, which represent major bottlenecks in research in reproductive biology, the advent of gene editing techniques is opening the powerful possibility of combining gene function analysis and imaging using transparent hydrozoan gonads.

Body axis evolution and development

Studying axis formation in a range of cnidarians, including hydrozoans, offers an informative perspective for the understanding of body plan evolution in metazoans. It is still debated whether the oral-aboral axis of cnidarians is homologous to any of the body axes of bilaterians, but it seems very likely that localized Wnt signaling was a feature of the gastrulation pole of the last common ancestor of these major animal groups.

Each hydrozoan form, planula, polyp and medusa, is organized with respect to a principal axis of polarity termed oral-aboral (Figure 3a). For instance the planula larva has an aboral specialization of the nervous system [START_REF] Piraino | Complex neural architecture in the diploblastic larva of Clava multicornis (Hydrozoa, Cnidaria)[END_REF], and the medusa has integrating nerve rings around the bell margin [START_REF] Koizumi | The nerve ring in cnidarians: its presence and structure in hydrozoan medusae[END_REF]. Key to establishment and maintenance of this axis is the oral pole organizer. The key molecular pathway of oral organizer activity in Hydra is Wnt/-catenin signaling [START_REF] Bode | The head organizer in Hydra[END_REF], activated by the diffusible ligand Wnt3 and maintained at the oral tip by a complex auto-feedback loop [START_REF] Nakamura | Autoregulatory and repressive inputs localize Hydra Wnt3 to the head organizer[END_REF]. Oral organizers have now been described at the oral pole of the planula larvae and polyp in several marine hydrozoan species [START_REF] Stumpf | An organizing region in metamorphosing hydrozoan planula larvae -stimulation of axis formation in both larval and in adult tissue[END_REF][START_REF] Mayorova | Organizer regions in marine colonial hydrozoans[END_REF], with the Wnt/-catenin pathway established as a key player in the regulation of the planula and polyp organizer.

In Clytia larvae, functional studies involving morpholino and mRNA injection into the egg have shown that axis formation is initiated by maternal mRNAs coding for the ligand Wnt3 (Figure 3a,b), and for two Frizzled family receptors [START_REF] Momose | Two oppositely localised frizzled RNAs as axis determinants in a cnidarian embryo[END_REF][START_REF] Momose | A maternally localised Wnt ligand required for axial patterning in the cnidarian Clytia hemisphaerica[END_REF] which become localized in the egg during oocyte growth and maturation [START_REF] Amiel | Three distinct RNA localization mechanisms contribute to oocyte polarity establishment in the cnidarian Clytia hemisphaerica[END_REF]. During early development, Wnt3 and Fz1 together activate the Wnt/-catenin pathway at the oral pole, while Fz3 acts as a negative regulator at the aboral pole. In parallel, the transmembrane protein Strabismus interacts with Fz1 across neighboring cell boundaries to direct morphogenesis along the oral-aboral axis via a typical PCP mechanism [76••]. PCP coordinates the alignment of the ectodermal cilia to ensure unidirectional swimming, and orients cell movements participating in elongation of the developing larva (Figure 3b). Common involvement of Frizzled proteins in establishing a Wnt/-catenin activity gradient and PCP is likely to be an ancestral mechanisms to couple morphological and molecular polarity during development [76••]. A transcriptomic study identified potential Wnt/-catenin downstream targets and genes regulated by the PCP pathways [77••], providing several promising candidates for roles in organizer activity.

Analyses of Wnt pathway regulation in Hydractinia have focused mainly on the polyp. Wnt3 signaling via a TCF transcription factor induces development of oral structures [START_REF] Duffy | Wnt signaling promotes oral but suppresses aboral structures in Hydractinia metamorphosis and regeneration[END_REF]. Other studies in Hydractinia have addressed the dramatic metamorphosis that transforms the planula into the polyp, and notably the extensive caspase dependent apoptosis at the oral pole during metamorphosis [START_REF] Seipp | Apoptosis -a death-inducing mechanism tightly linked with morphogenesis in Hydractina echinata (Cnidaria, Hydrozoa)[END_REF][START_REF] Seipp | Neuronal cell death during metamorphosis of Hydractina echinata (Cnidaria, Hydrozoa)[END_REF][START_REF] Wittig | Evidence for an instructive role of apoptosis during the metamorphosis of Hydractinia echinata (Hydrozoa)[END_REF][START_REF] Duffy | A heat shock protein and Wnt signaling crosstalk during axial patterning and stem cell proliferation[END_REF]. This apoptosis is essential for the formation of the primary polyp [START_REF] Seipp | Metamorphosis of Hydractinia echinata (Cnidaria) is caspase-dependent[END_REF], playing a constructive role [START_REF] Wittig | Evidence for an instructive role of apoptosis during the metamorphosis of Hydractinia echinata (Hydrozoa)[END_REF][START_REF] Duffy | Instructive reconstruction: a new role for apoptosis in pattern formation[END_REF] as it does during regeneration in Hydra [START_REF] Chera | Apoptotic cells provide an unexpected source of Wnt3 signaling to drive Hydra head regeneration[END_REF]. Interestingly, Wnt5a expressing cells at the oral pole of Hydractinia larvae appear to be protected from apoptosis during metamorphosis [START_REF] Stumpf | An organizing region in metamorphosing hydrozoan planula larvae -stimulation of axis formation in both larval and in adult tissue[END_REF].

Cell type plasticity and stem cell systems in Hydrozoa

Hydrozoans characteristically exhibit a very strong ability to regenerate one or all their phenotypic forms, a capacity underpinned by extreme cell type plasticity. This includes bone fide transdifferentiation, as demonstrated using Podocoryna carnea by Schmid and collaborators, who convincingly showed transdifferentiation of striated muscle cells isolated from the medusa into several cell types including smooth muscle, sensory cells, gland cells and nematocytes (stinging cells characteristic of Cnidaria) [START_REF] Schmid | Isolated, mononucleated, striated muscle can undergo pluripotent transdifferentiation and form a complex regenerate[END_REF].

Hydrozoan regeneration involves active stem cell systems, first characterized in Hydra, where three types of stem cell coexist: ectodermal epithelial stem cells, endodermal epithelial stem cells and 'insterstitial' cells (i-cells) (see [START_REF] Hobmayer | Stemness in Hydra -a current perspective[END_REF]) (Figure 3c). The first two basic epithelial cell types support the constant renewal of the ectodermal and endodermal epithelia. I-cells are a hydrozoan-specific type of undifferentiated multipotent stem cell that can differentiate into nerve cells, nematocytes, gland cells and also germ cells. I-cell developmental potential varies between species. Thus, in Hydractinia echinata, i-cells can differentiate not only into nerve cells and nematocytes, but also into epithelial cells, as demonstrated using mutants, BrdU labeling and grafting experiments [START_REF] Müller | Totipotent migratory stem cells in a hydroid[END_REF], and confirmed using transgenic tools [START_REF] Künzel | Migration and differentiation potential of stem cells in the cnidarian Hydractinia analysed in eGFP-transgenic animals and chimeras[END_REF] (Figure 3c).

Progress in understanding the molecular regulation and cellular dynamics of hydrozoan stem cells was greatly accelerated by the development of transgenic lines both in Hydractinia [88••] and Hydra [START_REF] Wittlieb | Transgenic Hydra allow in vivo tracking of individual stem cells during morphogenesis[END_REF], which allowed tracking of stem cells in vivo, notably during regeneration [88••] (Figure 3d).

Pioneering studies in

Conclusion

Hydrozoans have much to contribute to our understanding of basic developmental and cell biology processes and their evolution, as well as to relatively neglected areas of biological complexity such as colony level organization and asexual reproduction. Rapid technological advances mean that it is now feasible with quite modest budgets to undertake genome sequencing, large scale gene expression/transcriptomics studies, functional analyses at all life cycle stages via gene editing, as well as cell/molecule tracking using transgenic lines carrying diverse fluorescent reporters. With these accumulating resources, we expect in the next few years that a wide range of marine hydrozoan species will emerge as valuable experimental models.

•• This study demonstrates a highly conserved role for the transmembrane protein Strabismus in setting up the Planar Cell Polarity (PCP) required for oriented ciliogenesis and embryo elongation. Common involvement of Frizzled family proteins in PCP and Wnt/β-catenin signaling ensures intimate coupling of morphological and molecular polarity along the developing axis, a key feature which may date back to the origins of metazoans. 77. Lapébie P, Ruggiero A, Barreau C, Chevalier S, Chang P, Dru P, Houliston E, Momose T: Differential responses to Wnt and PCP disruption predict expression and developmental function of conserved and novel genes in a cnidarian. PLoS Genet 2014, 10:e1004590.

•• A screen based on transcriptome comparisons between Wnt and PCP manipulated embryos allowed systematic prediction of gene sets expressed in oral versus aboral territories, and a set expressed in ingressing cell populations at the gastrulation pole. Many members of the expected families of developmental regulators known from bilaterians were identified, but also many taxonspecific genes, reminding us that evolution of development in cnidarians has probably not solely relied on the 'shared metazoan toolkit'. an early medusa bud composed of ectoderm (ect), endoderm (end), and a third layer, the entocodon (ent), which generates the striated muscle of the medusa. The entocodon is a unique feature of hydrozoan medusae; homology to mesoderm has been proposed but is not widely accepted (see [START_REF] Seipel | Evolution of striated muscle: jellyfish and the origin of triploblasty[END_REF]). (b) Clytia oocyte maturation [START_REF] Amiel | Clytia hemisphaerica: a cnidarian model for studying oogenesis[END_REF][START_REF] Amiel | Conserved functions for Mos in eumetazoan oocyte maturation revealed by studies in a cnidarian[END_REF][START_REF] Amiel | Three distinct RNA localization mechanisms contribute to oocyte polarity establishment in the cnidarian Clytia hemisphaerica[END_REF]. Note: development of extensive transcriptome and genome resources are underway for most of these species.

In situ hybridization technique and/or transcriptome resources have been developed for a few others species (e.g. [START_REF] Zapata | Phylogenomic analyses support traditional relationships within Cnidaria[END_REF][START_REF] Nawrocki | Expression of Wnt pathway genes in polyps and medusa-like structures of Ectopleura larynx (Cnidaria: Hydrozoa)[END_REF][START_REF] Hroudova | Diversity, phylogeny and expression patterns of Pou and Six homeodomain transcription factors in hydrozoan jellyfish Craspedacusta sowerbyi[END_REF]).

  Hydra have compared molecular signatures of different cell types by transcriptome analysis of fluorescence-tagged sorted cells from transgenic lines [90] and established proteomic methods [91••]. In Hydractinia a POU-domain containing transcription factor of the class 3/5 involved in regulating pluripotency has been identified [92•], of particular interest given the role of the (class 5) POU-domain factor Oct 4 in mammals. Similarly, in Clytia, several Sox family transcription factors (groups B, C, E and F) were found expressed either in stem-cells or differentiated cells, suggesting a regulatory role in multipotency maintenance operating widely across the animal kingdom [93]. A recent study has shown a correlation between nuclear localization of the Hippo pathway component Yorkie and cell division in Clytia medusae [94], suggesting that regulation of cell proliferation by this transcriptional cofactor is conserved between Cnidaria and Bilateria. I-cells in Clytia [95,96•] and Hydractinia [88••,92•,97,98], as in Hydra (e.g. [90,99]), also express orthologues of genes typically associated with germ line or stem cell function such as Piwi, Nanos1, and Vasa. I-cell formation during embryogenesis was addressed in Clytia, and appears to involve both determinant inheritance and inductive mechanisms [96•]. I-cells originate at the onset of gastrulation in a region inheriting localized Piwi, Nanos1, Vasa and Pl10 mRNAs from the animal pole of the egg, evoking the 'preformation' mode of germ-line specification by maternal 'germ plasm' well known in insects and frog embryos. I-cells can also form in Clytia planulae in the absence of the key egg animal pole region, implying the involvement of inductive mechanisms [96•].

Figure 1 .

 1 Figure 1. Hydrozoan phylogeny and life cycle diversity and evolution. (a) Phylogeny of Cnidaria following [1•], with Bilateria as the outgroup. Hydrozoa is sister to the other medusozoans (Staurozoa, Scyphozoa and Cubozoa). Red, orange and blue dots indicate presence of planula, polyp or medusa stages respectively in the last common ancestor of these groups. Acquisitions of the medusa and polyp stages are indicated by orange and blue diamonds respectively. Staurozoa adult stages show a mix of polyp and medusa characters. (b) Phylogeny and evolution of Hydrozoa following [32]. The groups 'Filifera', 'Trachymedusae' and 'Limnomedusae' are probably not monophyletic [30, 32]. Losses of the polyp stage in the clade Trachylina are indicated by white diamonds. The planula stage was likely lost in the common ancestor of Aplanulata [35•]. It is still equivocal whether the medusa stage was lost concomitantly, or later, within this clade [35•]. Mature siphonophores are composed of specialized polyps and medusae that remain attached within the colony. (c) Examples of the four main life cycle types found in Hydrozoa. In all cases sexual reproduction generates planula larvae. (i) Clytia hemisphaerica; polyps develop from planulae bymetamorphosis; medusae by budding from polyps. Two polyp types co-exist within the colony, specialized for medusa budding (gonozoid; left) and feeding (gastrozoid; right). Image from[START_REF] Houliston | Clytia hemisphaerica: a jellyfish cousin joins the laboratory[END_REF]. (ii) Aglantha digitale; the planula larva metamorphoses directly into a medusa. (iii) Hydractinia echinata;The colony contains four types of polyp (from left to right): gonozooid, gastrozooid, dactylozooid, tentaculozooid. The common part of the colony also includes protective spines. (iv) Nanomia bijuga; the larva develops into a complex polygastric colony comprising different types of medusa-(e.g. nectophores, propelling the colony -in blue) and polyp-(e.g. gastrozooid -in orange) derived structures, distributed in ordered arrays. Image in (c-i) reproduced from[START_REF] Houliston | Clytia hemisphaerica: a jellyfish cousin joins the laboratory[END_REF]. Images courtesy of Alexander Semenov (c-ii), Uri Frank (c-iii), Brad Gemmell (c-iv).

Figure 2 .

 2 Figure 2. Clytia medusa: muscle and egg formation. (a) Medusa organization and development. (i) Diagram of a mature Clytia jellyfish; cc: circular canal, ex-u: ex-umbrella, go: Gonad, ma: manubrium tb: tentacle bulb, te: tentacle, rc: radial canal, sub-u: sub-umbrella surface, ve: velum. (ii) Convergent evolution of striated muscles in Bilateria and Cnidaria [63••]. (iii) Subumbrellar striated muscle of a young medusa stained with phalloidin (red in iii and iv; grey in v and vi) and nuclei stained with Hoechst (blue). (iv) Newly budded medusa -at this stage the striated muscle layer (sm) covers most of the sub-umbrella surface and is sandwiched between an endodermal (end) and ectodermal smooth muscle (ect) layers. gp: gonad primordium, other labels as in (i). Image courtesy of Johanna Kraus [61•]. (v) Confocal section of a medusa bud within the gonozoid. Prominent features are the

  (i) Female gonad containing fully grown oocyte ready to mature (FGO). (ii) Fully-grown oocyte with germinal vesicle (GV) close to the cell surface on the ectoderm side (ect), opposite the contacts with endodermal cells (end). (iii) The same oocyte about 15 min after a light cue, undergoing germinal vesicle breakdown (GVBD). A light cue initiates the release of maturating inducing factor (MIH) by the gonad ectoderm, which unblocks the oocyte's meiotic arrest at prophase I via an cytoplasmic cAMP release / PKA activation, leading to activation both of MPF and of the Mos-MAPK pathway. (iv) Spawning of the same oocyte, about 100 min after light; involves rupture of the ectodermal epithelium just after second polar body (pb) emission. (v) Clytia egg with the heads of attracted sperm (sp) visible in the surrounding jelly. Fertilization induces MAPK inactivation and increase of intracellular calcium, shown in Cytaeis to prevent polyspermy [68•]. Scales bars: 100 µm, except for (a-iii): 10 µm.

Figure 3 .

 3 Figure 3. Embryonic axis establishment and stem cell plasticity. (a) Schematic representation of Wnt3 expression at five embryonic stages in Clytia. From left to right: fertilized egg, blastula, early gastrula, late planula, primary polyp. Wnt3 mRNA is localized at the egg animal pole, and oral (top in all figure parts) expression is maintained at all stages. Drawings modified from [13]. (b) Wnt3 Morpholino injected embryos show no oral-aboral polarity. Images reproduced from [74]. Strabismus Morpholino larvae show disrupted PCP and ciliogenesis. Images reproduced from [76••]. Arrowheads indicate microvilli marking sites where ciliogenesis has failed. (c) Schematic representation of cell lineages in Hydra (top) and Hydractinia (bottom). Epithelial cells (EC) can be generated from interstitial stem cells (i-cells) in Hydractinia, but not in Hydra. Intermediate differentiation stages are not represented [86]. (d) Summary of Hydractinia polyp head regeneration. Proliferating i-cells (blue dots) migrate towards the oral pole after bisection and participate in the formation of the new head structures. Tools routinely used in Hydractinia regeneration studies include stable transgenic fluorescent reporter lines and proliferation assays (BrDU). Images from [88••]. Scales bars: 100 µm, except the four right panels in (b): 5 µm.

Figure 1 Figure 2 Figure 3

 123 Figure 1

Table 1 -Hydrozoans used for genetic/molecular studies Clade/Species Available techniques Main research topics Aplanulata

 1

	Hydra spp.	In situ hybridization; RNAi; egg	Stem cell; regeneration; pattern
		micro-injection; transgenesis;	formation; organizer; budding;
		mutagenesis; proteomic; RNAseq	symbiosis; sex determination; aging
		of fluorescent-tagged sorted cells	[2-12,40,70, 85,89-91,99]
	Capitata
	Cladonema radiatum	In situ hybridization	Specification of sensory cells; eye
			development and regeneration
			[15,56,57]
	Eleutheria dichotoma	In situ hybridization; RNAi	Hox genes; patterning [19,20]
	Filifera
	Cytaeis uchidae	Manipulation of oocytes and eggs Reproductive biology [65,66,68]
	Hydractinia echinata	In situ hybridization; RNAi,	Polyp regeneration; stem cells;
		Morpholino and mRNA injection;	colony development [14,42,71,78-
		transgenesis	83,86-88,92,97,98]
	H. symbiolongicarpus	In situ hybridization; genetics	Allorecognition; polyp
			polymorphism [14,39,43-53]
	Podocoryna carnea	In situ hybridization;	Colony development; medusa
		manipulation of medusa tissues	development; muscle
			transdifferentiation [16,17,38,60]
	Turritopsis dohrnii	'reverse development'	Life cycle plasticity [17,18]
	Leptothecata
	Clytia hemisphaerica	In situ hybridization; Morpholino	Larval development; polarity
		and mRNA injection;	establishment and maintenance;
		manipulation of oocytes and	stem cells; oocytes; muscle
		eggs; CRISPR and TALEN gene	evolution; medusa formation
		editing (unpublished)	[13,58,61,63,64,67,73-77,93-
			96,100]
	Siphonophorae
	Nanomia bijuga	In situ hybridization	Colony development [21-
			23,27,101]

Acknowledgements

Our recent research on hydrozoans has been funded by grants from the ANR (MEDUSEVO -ANR-13-PDOC-0016 and OOCAMP -ANR-13-BSV2-0008), Sorbonne Universités («Convergence» program and the André Picard Network), the EMBRC-Fr Infrastructure project and CNRS core funding to the LBDV.

We thank Chiara Sinigaglia and Michaël Manuel for helpful comments on the manuscript.


Delphine Eoche-Bosy
email: delphine.eoche-bosy@rennes.inra.fr

Yannick Outreman

Thiago Oliveira

Liliane Krespi

Joan Van Baaren

Seasonal variations of host resources influence foraging strategy in parasitoids

Keywords: aphid parasitoids, generalist, opportunist, optimal foraging theory, specialist, switch, Hymenoptera, Aphididae, Hemiptera, cereal aphids, Braconidae, Aphidius spp

Many species have to cope with decreased resource availability and life expectancy during winter. The optimal foraging theory predicts that under these conditions, generalist foraging strategies should be favoured, via the acceptance of suboptimal resources. In contrast, during favourable seasons, specialist foraging strategies, i.e., a preferential consumption of the most profitable resources, should be favoured instead. Although spatial and fine-scale temporal dimensions of the influence of resource distribution on foraging strategies have long been studied in individual species, guild-level, large-scale temporal approaches (over multiple seasons) have rarely been considered. Parasitoids which can remain active during winter are an interesting model system which allows direct testing of resource profitability and reaching conclusions about foraging strategies from an evolutionary point of view. Here, we analysed how temporal variations of host resource availability in northwestern France impact the foraging strategies of parasitoid wasps. The foraging behaviours of dominant cereal aphid parasitoid species in relation to the two most abundant aphid host species were observed in winter and in spring. Because of a seasonal change in the host-parasitoid community and of a few species present in the fields each season, we were unable to confirm our hypothesis at the species level for all the studied species. Nevertheless, this study brought results consistent with our assumptions at the guild level, indicating that different species of a guild favour similar foraging strategies. In winter, female parasitoids generally adopted an opportunistic strategy, accepting all aphid hosts encountered, even if they were suboptimal. In spring, parasitoids displayed a specialist strategy by selecting preferentially a host species, but the better quality of preferentially-selected species remains to be fully demonstrated.

Introduction

Temperature strongly influences physiological mechanisms in ectotherms such as insects [START_REF] Bale | Insect cold hardiness: a matter of life and death[END_REF][START_REF] Bale | Insects and low temperatures: from molecular biology to distributions and abundance[END_REF][START_REF] Ramløv | Aspects of natural cold tolerance in ectothermic animals[END_REF][START_REF] Sinclair | Insects at low temperatures: an ecological perspective[END_REF], and consequently conditions many behavioural strategies [START_REF] Hance | Impact of extreme temperatures on parasitoids in a climate change perspective[END_REF]. Under temperate climates, some insects avoid unfavourable winter conditions by migrating or diapausing, whereas others endure them [START_REF] Kimura | Climatic adaptations in the Drosophila immigrans species group: seasonal migration and thermal tolerance[END_REF][START_REF] Polgár | Induction of dormancy in aphid parasitoids: implications for enhancing their field effectiveness[END_REF][START_REF] Danks | Key themes in the study of seasonal adaptations in insects I. Patterns of cold hardiness[END_REF][START_REF] Danks | Key themes in the study of seasonal adaptations in insects II. Life-cycle patterns[END_REF][START_REF] Colinet | Cold-induced expression of diapause in Praon volucre: fitness cost and morpho-physiological characterization[END_REF]. In addition to the climatic constraint, active organisms must also deal with another winter challenge: the resources essential for their survival are often less readily available [START_REF] Danks | The elements of seasonal adaptations in insects[END_REF]. As searching for resources can generate high energetic costs, there is a positive selective pressure for appropriate strategies for habitat exploitation in order to optimize net energy gain. According to the optimal foraging theory (OFT) [START_REF] Macarthur | On optimal use of a patchy environment[END_REF], this depends on the energy content of the resource, but also on other factors such as the rate at which the resource is encountered and the handling time [START_REF] Bolnick | The ecology of individuals: incidence and implications of individual specialization[END_REF]. The selection of resource items should therefore correspond to an optimization of different factors, inducing potentially divergent strategies between seasons as resource density varies. Indeed, the OFT predicts that if the encounter rate with more profitable resources is low, suboptimal resources should always be accepted [START_REF] Heller | On optimal diet in a patchy environment[END_REF][START_REF] Stephens | Foraging Theory[END_REF]. This prediction suggests that under winter conditions, organisms may enlarge their resource range, by being opportunistic through the exploitation of both optimal and suboptimal resources. Surprisingly, although spatial (patches) and fine-scale temporal (minutes or hours) dimensions of the influence of resource distribution on foraging strategies have long been studied [START_REF] Heller | On optimal diet in a patchy environment[END_REF][START_REF] Owen-Smith | Foraging theory upscaled: the behavioural ecology of herbivore movement[END_REF], large-scale temporal approaches (over multiple seasons) seem to have been more neglected. Only studies focusing precisely on one or few species, not necessarily insects, and aiming at studying their diet have been found to address the topic of seasonal resource availability [START_REF] Sidorovich | Seasonal and annual variation in the diet of the raccoon dog Nyctereutes procyonoides in northern Belarus: the role of habitat type and family group[END_REF][START_REF] Zhou | Dietary shifts in relation to fruit availability among masked palm civets (Paguma larvata) in central China[END_REF][START_REF] Clulow | Resource predictability and foraging behavior facilitate shifts between nomadism and residency in the eastern grass owl[END_REF]. These studies led to results that seem to follow OFT predictions, as they show foraging-strategy adjustments depending on the availability of resources [START_REF] Riechert | Nutritional ecology of spiders[END_REF][START_REF] Wetherbee | Diet, feeding habits, digestion, and consumption in sharks, with special reference to the lemon shark, Negaprion brevirostris. Elasmobranchs as Living Resources: Advances in the Biology, Ecology, Systematics, and the Status of the Fisheries[END_REF]. For example, several studies on sharks revealed that many species show seasonal dietary shifts and fit the description of 'opportunistically selective feeders', i.e., they are selective when resources are abundant, and become more opportunistic when resource density decreases [START_REF] Wetherbee | Diet, feeding habits, digestion, and consumption in sharks, with special reference to the lemon shark, Negaprion brevirostris. Elasmobranchs as Living Resources: Advances in the Biology, Ecology, Systematics, and the Status of the Fisheries[END_REF]. Similar results have been found in spiders [START_REF] Riechert | Nutritional ecology of spiders[END_REF]), which present an unselective feeding behaviour most of the time, but become seasonally selective when prey are present in excess A c c e p t e d m a n u s c r i p t in the environment. However, in most of these studies, the biological model studied does not easily allow an assessment of the impact of resource profitability on an individual's fitness. It is therefore not possible to conclude from an evolutionary point of view that organisms are opportunistic because they feed on several suboptimal resources, and become selective when they feed on one or few types of resources which are more profitable in the environment.

Host-parasitoid interactions represent a unique case of dependence between fitness of an organism and its exploitation of food resources. The life cycle of parasitoids includes a free-living adult stage, during which females actively search for hosts on or in which to lay its eggs, and an immature stage, during which the larva develop inside or on the host, feeding (only) on host tissues and killing the host at the end of the its larval development [START_REF] Godfray | Parasitoids: Behavioral and Evolutionary Ecology[END_REF]. Due to this particular life history, the development of a parasitoid is intimately related to the quality of the selected and exploited host, which can depend on factors such as the species, development stage, size, or parasitic status of the host [START_REF] Brodeur | Functional ecology of immature parasitoids[END_REF].

There is therefore a direct link between the foraging behaviour of female parasitoids, i.e., their host choices, and the quality of the progeny produced, i.e., their fitness.

Aphid parasitoids are insects able to remain active during winter, provided winter conditions are sufficiently mild [START_REF] Hance | Impact of extreme temperatures on parasitoids in a climate change perspective[END_REF]. Their winter persistence is made possible through the availability of hosts, which remain active as well. However, these host resources are scarce and highly patchily distributed. In addition, parasitoids have to face other environmental factors, such as a limited time horizon, because the mortality risk grows with the strong environmental stochasticity during winter [START_REF] Roitberg | Seasonal dynamic shifts in patch exploitation by parasitic wasps[END_REF], and a decrease of temperature and day duration that may restrict their activity, but also reduce competition. In these unfavourable winter conditions, the OFT suggests that female parasitoids should adopt an opportunistic strategy and always oviposit in the encountered hosts, regardless their profitability, whereas in spring, they should be more selective by choosing the host species with the highest profitability. The close link between female parasitoid fitness and host quality [START_REF] Godfray | Parasitoids: Behavioral and Evolutionary Ecology[END_REF] makes the assessment of host choice impact on female parasitoid fitness easier and direct. This makes parasitoid insects a choice model in this study, in which we investigate the hypothesis of a resource-exploitation switch according to resource seasonality by analysing host-selection strategies in multiple parasitoid species exploiting natural host populations.

The insect parasitoids of cereal aphids were considered in the present study. In winter, they can exploit anholocyclic aphid populations, which reproduce asexually throughout the year [START_REF] Polgár | Induction of dormancy in aphid parasitoids: implications for enhancing their field effectiveness[END_REF][START_REF] Dedryver | Coexistence in space and time of sexual and asexual populations of the cereal aphid Sitobion avenae[END_REF]. Host abundance reaches a seasonal peak in A c c e p t e d m a n u s c r i p t spring and summer, and then drastically declines in winter due to lower reproductive rates [START_REF] Dixon | Parthenogenetic reproduction and the rate of increase in aphids[END_REF][START_REF] Krespi | Variability in the development of cereal aphid parasitoids and hyperparasitoids in oceanic regions as a response to climate and abundance of hosts[END_REF]. We took into account in our experiments, at each season studiedwinter and springthe aphid parasitoids guild and their associated hosts found in cereal fields. We tested the two most abundant species each season to determine whether the same or different strategies would be observed in parasitoids undergoing the same evolutionary pressure. For each period, we studied (1) the host preference choice made by female parasitoids between the two most frequent aphid host species, and (2) the consequences of this host selection in terms of fitness (i.e., survival, developmental time, and size of offspring produced), in order to determine their performance in the host individuals selected. Our hypotheses were (1) winter parasitoids will display no preference, even if the various host species have different profitability values, and (2) if host species present different profitability values, then spring parasitoids will oviposit preferentially in the species resulting in the higher fitness.

Materials and methods

Sampling and species studied

Sampling was conducted in Brittany (northwestern France), where different parasitoid species are present in cereal crops throughout the year. In winter, Aphidius matricariae Haliday and Aphidius rhopalosiphi De Stefani-Perez (Hymenoptera: Braconidae, Aphidiinae) are the dominant species in the guild. In spring, A. rhopalosiphi remains numerous, but A. matricariae is not frequently found in cereal crops; other species, such as Aphidius avenae Haliday and Aphidius ervi Haliday, become more frequent [START_REF] Krespi | Étude de la Biocénose Parasitaire des Pucerons des Céréales dans le Bassin de Rennes: Cas Particulier d'Aphidius uzbekistanicus Luz[END_REF][START_REF] Krespi | Variability in the development of cereal aphid parasitoids and hyperparasitoids in oceanic regions as a response to climate and abundance of hosts[END_REF][START_REF] Andrade | Winter host exploitation influences fitness traits in a parasitoid[END_REF][START_REF] Andrade | Spatiotemporal variations in aphid-parasitoid relative abundance patterns and food webs in agricultural ecosystems[END_REF]. Whereas A. matricariae, A. avenae, and A. ervi have been shown to exploit wide aphid host ranges, A. rhopalosiphi specializes in cereal aphid species [START_REF] Starý | A review of the Aphidius species (Hymenoptera: Aphidiidae) of Europe[END_REF]. All these species are solitary pro-ovigenic koinobiont endoparasitoids which exclusively parasitize aphids.

Concerning aphid hosts, three species are common in cereal crops in the study site: Rhopalosiphum padi L., Sitobion avenae Fabricius, and Metopolophium dirhodum Walker (all Hemiptera: Aphididae) [START_REF] Dedryver | Biologie, Écologie et Dynamique des Populations de Pucerons des Céréales en Climat Océanique[END_REF]. Observations over the last decades indicate that during winter, population densities are very low, and R. padi is the dominant species in the aphid community, followed by S. avenae, then M. dirhodum, both being rare during winter [START_REF] Krespi | Étude de la Biocénose Parasitaire des Pucerons des Céréales dans le Bassin de Rennes: Cas Particulier d'Aphidius uzbekistanicus Luz[END_REF][START_REF] Andrade | Winter host exploitation influences fitness traits in a parasitoid[END_REF]. During spring, total aphid population densities increase, with S. avenae and M. dirhodum becoming the dominant species, whereas R. padi nearly A c c e p t e d m a n u s c r i p t disappears from the community in cereal fields [START_REF] Krespi | Étude de la Biocénose Parasitaire des Pucerons des Céréales dans le Bassin de Rennes: Cas Particulier d'Aphidius uzbekistanicus Luz[END_REF][START_REF] Fievet | Aphid colony turnover influences the spatial distribution of the grain aphid Sitobion avenae over the wheat growing season[END_REF]. Aphid and parasitoid densities are low in winter, but parasitism rate can reach 38% [START_REF] Andrade | Winter host exploitation influences fitness traits in a parasitoid[END_REF]. During spring, the density of aphids increases rapidly, and parasitism rates decrease accordingly [START_REF] Andrade | Spatiotemporal variations in aphid-parasitoid relative abundance patterns and food webs in agricultural ecosystems[END_REF].

All experiments were done with parasitoid individuals collected from cereal fields at the immature stage in order to avoid any laboratory-induced alteration of foraging behaviour after some generations under rearing conditions. These experimental individuals have been collected in various cereal crops in the Long Term Ecological Research (LTER-Europe) site 'Armorique', around the city of Rennes, during both winter (in January and February) and spring (in April) in 2013. Within each field, the sampling sessions were performed during 1 h and all aphid mummies (i.e., dead aphids containing an immature parasitoid close to emergence) found were collected and placed individually in gelatine capsules (1.5 cm long, 0.5 cm diameter) until parasitoid emergence. Parasitoid emergences were checked twice every day, at 9:00 and 18:00 hours. Newly-emerged parasitoids were identified based on morphological traits and for each species, individuals were placed together for 48 h in 'micro-cages' (9 cm long, 1.4 cm diameter) containing moistened cotton and droplets of honey to allow mating. Then females were collected for experiments and each female was tested only once.

In winter, 402 parasitoids emerged from sampled mummies, 42% were A. matricariae and 52% were A. rhopalosiphi. These two most abundant species were therefore considered in our experiments (Table 1). In spring, 274 parasitoids emerged from sampled mummies and a change in community structure was observed: the two most abundant species were A. rhopalosiphi and A. avenae, with 17 and 81% relative abundance, respectively (A. matricariae individuals were no longer found) (Table 1).

Of the aphid community, R. padi and S. avenae were the two most frequent species found in crops in winter, R. padi being highly dominant (>90% of the community) (Table 1).

During spring, S. avenae and M. dirhodum were the most frequent species found (Table 1).

During field samplings, at least 20 live aphids of each species available each season were also sampled. Each species was reared during only one generation in the laboratory on winter wheat (Triticum aestivum L. cv. Boston, Poaceae) in separated Plexiglas cages (50 × 50 × 50 cm), after a quarantine period of 10 days in plastic tubes (16 cm long, 4 cm diameter) to ensure they were not parasitized, in order to produce host resources for the experiments. Maintenance of experimental individuals (aphids and parasitoids) and all experiments were done at 20 ± 1 °C, 60 ± 10% r.h., and L16: D8 photoperiod. We chose to standardize the experimental conditions used for both seasons, because the parasitoids are known to be active in the field only at the highest temperatures of the day in winter, which can exceed 20 °C where we sampled [START_REF] Tougeron | Comparing thermal tolerance across contrasting landscapes: first steps towards understanding how landscape management could modify ectotherm thermal tolerance[END_REF]. The parasitoids used will have experienced more days in natural than in experimental conditions, as they were close to emergence at the time of collection of the mummies, and experiments were performed only few days after emergence.

Seasonality of host preference

For each season, the two most abundant aphid species were considered in experiments. The experimental setup consisted of introducing one aphid individual of each aphid species in a common 4-cm-diameter Petri dish, isolated on a piece of winter wheat leaf. A female parasitoid of a given species was then introduced in the arena. For each choice test, we recorded the (1) aphid species first encountered, in order to test whether parasitoid choice could be made from a distance (as already shown for A. ervi; Le Lann et al., 2011a), and (2) outcome of the encounter, i.e., host acceptance (ovipositor insertion) or host rejection (no ovipositor insertion). Female parasitoids were allowed to encounter only one aphid between both hosts presented. After each choice test, both aphids were replaced by two equivalent ones, until the female parasitoid had attacked a total of 20 aphids. At the end of each experiment, attacked aphids were isolated on winter wheat plantlets under rearing conditions, until their mummification. Each mummy was then isolated in a gelatine capsule until parasitoid emergence. For each season, 10 females of each parasitoid species were tested.

Overall, 400 host choice tests were performed for each season. After attack of 20 hosts out of the aphids introduced into the arena, each female was put in Petri dishes with several aphids of both species during several minutes to allow them to parasitize more hosts, ensuring that a sufficient number of emerging offspring would be obtained for subsequent life-history-trait measurements. Aphids attacked were treated the same way as aphids from the choice experiment. In this experiment, absence of host preference does not mean absence of host discrimination. The host species are very different in size, colour, and defensive behaviour (alarm pheromones) [START_REF] Dixon | Parthenogenetic reproduction and the rate of increase in aphids[END_REF], and there is no doubt that parasitoid females are able to discriminate between aphid species (Le [START_REF] Ralec | Inter-specific variation in the reactive distance of different aphid-parasitoid associations: analysis from automatic tracking of the walking path[END_REF].

A c c e p t e d m a n u s c r i p t

Seasonality of host performance

Three life-history traits have been measured on the offspring emerging from all attacked aphidsparasitic success rate, development time, and hind tibia length -, which are common proxies used in the literature to describe the fitness of parasitoid individuals. Parasitic success rate is defined as the number of accepted aphids leading to emerging parasitoids divided by the total number of accepted aphids. Development time is the total time needed for the parasitoid offspring to develop from oviposition to adult emergence. It determines the generation time, which is inversely related to the growth rate of the parasitoid population [START_REF] Tripathi | Fecundity, reproductive rate, longevity, and intrinsic rate of increase of an aphidiid parasitoid Lysiphlebia mirzai[END_REF]: a shorter development time could allow for a faster population growth. It could also contribute to reducing the predation pressure on parasitoids in mummies, a phase during which they are more vulnerable, according to the slow growth/high mortality hypothesis [START_REF] Ishihara | Reproductive inactivity and prolonged developmental time induced by seasonal decline in host plant quality in the willow leaf beetle Plagiodera versicolora (Coleoptera: Chrysomelidae)[END_REF]. Hind tibia length has been measured following the protocol used by Le Lann et al. (2011b). It is an indicator of the overall size and mass [START_REF] Godfray | Parasitoids: Behavioral and Evolutionary Ecology[END_REF], being positively correlated [START_REF] Roitberg | Fitness, parasitoids, and biological control: an opinion[END_REF].

Statistical analysis

Host preference experiment. For each choice test, each female parasitoid was exposed to two aphid hosts of different species. The effect of host species on the probability of encounter by the parasitoid (i.e., aphid species choices) was analysed by a binomial non-parametric test (see details in [START_REF] Outreman | Can imperfect host discrimination explain partial patch exploitation in parasitoids?[END_REF]. The null hypothesis was that the probability of encounter for a given aphid species was 0.5 (i.e., female parasitoids have no preference for a host species at distance). Once encountered, an aphid host was either accepted or rejected for oviposition. The effect of host species (i.e., fixed factor with two levels) on the acceptance rate was then analysed. In this experiment, several host individuals were attacked by the same female parasitoid. Then, the female parasitoid individual was considered as a random independent variable in statistical modelling. Generalized linear mixed models (GLMMs) were then fitted by assuming a binomial error and a logit-link function. All statistical modelling was performed by the 'lme4' package in R v.3.0.2 (R Development Core Team,

2013).

Host performance experiment. The dependent variables studied were parasitic success rate, development time, and tibia size of the offspring. The effect of host species was tested on each dependent variable. In our experiments, several offspring originated from the same female parasitoid. The female parasitoid individual was then considered as a random A c c e p t e d m a n u s c r i p t independent variable in our statistical modelling. The effect of sex on offspring tibia size was also included in the models. GLMMs were fitted by assuming either a binomial, gamma, or Gaussian error according to the dependent variable and a logit or identity link function, respectively. To assess the significance of the individual model terms we used likelihood ratio tests.

Results

Seasonality of host preference

In winter, for the two parasitoid species studied, no significant differences were found for the encounter rate (binomial test, A. rhopalosiphi: P = 0.60; A. matricariae: P = 0.071) nor for the host acceptance rate (GLMM, A. rhopalosiphi: χ 2 = 1.044, P = 0.31; A. matricariae: χ 2 = 0.012, P = 0.91, both d.f. = 1) (Figure 1A). Thus, both A. matricariae and A. rhopalosiphi did not exhibit preference, neither remotely nor after contact, towards R. padi or S. avenae.

In spring, the two parasitoid species studied were not found to differ in encounter rate of S. avenae and M. dirhodum each being encountered half of the time (binomial test, A.

rhopalosiphi: P = 0.60; A. avenae: P = 0.071) (Figure 1B). Thus, both parasitoids did not select their hosts from a distance. Both parasitoids displayed a significantly higher acceptance rate towards S. avenae (GLMM, A. rhopalosiphi: χ 2 = 44.668; A. avenae: χ 2 = 67.790, both d.f. = 1, P<0.001) (Figure 1).

Seasonality of host performance

In winter, the parasitic success rate of the two parasitoid species was not different between S. avenae and R. padi (GLMM, A. rhopalosiphi: χ 2 = 0.004, P = 0.95; A. matricariae: χ 2 = 0.131, P = 0.72, both d.f. = 1) (Figure 2A). Aphidius rhopalosiphi showed a parasitic success rate of 37.7 ± 3.7% in S. avenae and 35.5 ± 3.7% in R. padi, whereas A. matricariae showed a parasitic success rate of 35.5 ± 3.7% in S. avenae and 34.8 ± 3.6% in R. padi. However, both parasitoids developed faster on S. avenae (A. rhopalosiphi: χ 2 = 12.032, P<0.001; A. matricariae: χ 2 = 4.9313, P = 0.026, both d.f. = 1) and had longer hind tibia (χ 2 = 16.856 and 14.771, respectively, both d.f. = 1, P<0.001) (Figures 2B andC). In winter, S. avenae hosts resulted in larger parasitoids than R. padi and faster parasitoid development, with the same parasitism success. The size of the offspring produced by the winter parasitoid wasps was not affected by their sex (A. rhopalosiphi: χ 2 = 3.124, P = 0.077; A. matricariae: χ 2 = 0.460, P = 0.50, both d.f. = 1).

A c c e p t e d m a n u s c r i p t

In spring, as in winter, the two aphids had no specific effect on the parasitic success rate of A. rhopalosiphi: 46.3 ± 3.8% in S. avenae and 55.5 ± 4.4% in M. dirhodum (GLMM, χ 2 = 0.0261, d.f. = 1, P = 0.87) (Figure 3A). However, aphid species did affect the parasitism success of A. avenae: 38.7 ± 3.9% in S. avenae vs. 23.4 ± 4.1% in M. dirhodum (χ 2 = 6.803, d.f. = 1, P = 0.009) (Figure 3A). Aphid host species had no effect on development time of A. rhopalosiphi (χ 2 = 1.1236, d.f. = 1, P = 0.29), whereas development of A. avenae was significantly slower in S. avenae (χ 2 = 4.6567, d.f. = 1, P = 0.030) (Figure 3B). Aphid host species had no effect on hind tibia length of either parasitoid (A. rhopalosiphi: χ 2 = 0.001, P = 0.98; A. avenae: χ 2 = 0.939, P = 0.33, both d.f. = 1) (Figure 3C). The size of the offspring produced by the spring parasitic wasps depended on their sex (A. rhopalosiphi: χ 2 = 4.580, P = 0.032; A. avenae: χ 2 = 13.219, P<0.001, both d.f. = 1).

Discussion

Our results indicate that winter and spring female parasitoids show contrasting reactions when confronted with hosts. In winter, the two most abundant species in the parasitoid guild, A. matricariae and A. rhopalosiphi, when exposed to the dominant aphid hosts available, R. padi and S. avenae, did not express any preference for the host resources, exploiting both host species equally, as predicted. This absence of preference would not be associated with a lack of host species discrimination by parasitic wasps, as S. avenae and R. padi are highly different in terms of morphology, colour, and behaviour [START_REF] Dixon | Parthenogenetic reproduction and the rate of increase in aphids[END_REF]. In spring, the two most frequent parasitoid species, A. avenae and A. rhopalosiphi, showed a preference towards the same aphid species, S. avenae. However, to evaluate the adaptive value of these contrasted foraging strategies by female parasitoids, it is necessary to link host species selection to host profitability in terms of offspring quality. In winter, it appears that S. avenae was a host of better quality than R. padi for both parasitoid species. Although both aphid species led to an equivalent parasitic success rate, development time was shorter and offspring tibia length larger in S. avenae. As expected, during the harsh winter season the two major parasitoid species of the guild are opportunistic, exploiting all host species available regardless of their quality. As predicted, the spring female parasitoids expressed a selective behaviour with regards to the available resources and this strategy could be related to host resources profitability: A. avenae prefers to parasitize S. avenae, which appears to be a host of better quality than M. dirhodum. Indeed, S. avenae allows a shorter development time and also leads to a higher parasitic success rate than M. dirhodum. Females of the second most A c c e p t e d m a n u s c r i p t frequent species in the parasitoid guild, A. rhopalosiphi, preferred to oviposit in one aphid species rather than the other, yet a better performance in the preferred aphid species has not been detected. Perhaps a difference in host quality was not necessarily reflected by the traits considered here, and concerns potentially other trait(s). For example, longevity, lipid reserves at emergence, and fecundity (estimated as the number of eggs contained in ovarioles) have not been considered. Another explanation would be that the more profitable host could also be more easily accessible under field conditions because, e.g., the host expresses less defensive behaviour or is easier to find in the environment (S. avenae is known to be more present on wheat heads whereas M. dirhodum is more often hidden on leaves).

The present study suggests that the optimal host acceptance strategy in parasitoids may depend on the host resources seasonality. These results are consistent with those of [START_REF] Roitberg | Seasonal dynamic shifts in patch exploitation by parasitic wasps[END_REF], who also found that female parasitoids show variable foraging strategies according to the season. Females of the Drosophila spp. parasitoid Leptopilina heterotoma (Thomson) generally reject hosts that are already parasitized, as they are considered to be poor hosts. However, [START_REF] Roitberg | Seasonal dynamic shifts in patch exploitation by parasitic wasps[END_REF] showed that superparasitism (parasitism of a host by more than one individual of a single species) rate increases in females reared under autumn conditions, i.e., when individuals have a short life expectancy and therefore when time available for searching becomes limited, as is the case in winter for cereal aphid parasitoids. Nonetheless, this study considered the same host species and focused on the impact of the host parasitic status on the parasitoid foraging strategy.

Two out of the three parasitoid species studied were only present during one season:

A. matricariae during winter and A. avenae during spring. Due to this seasonal change in the parasitoid guild, our study is not a strong test of our hypotheses even if our results are consistent with these assumptions. Even if no global switch of foraging strategies can be demonstrated here, our results indicate that the winter parasitoid guild did not exhibit any host preference, whereas in spring host species specialization could be generally favourable considering the higher host density. In addition, A. rhopalosiphi, the common species between the winter and the spring guild, displayed contrasting foraging strategies depending on the season. The adequacy of the host acceptance strategy to the ecological conditions can be achieved in two ways: balanced polymorphism (i.e., genotypes in the parasitoid population differ with time; some genotypes are frequent in winter and decline in spring) or phenotypic plasticity (i.e., the ability of one genotype to develop different phenotypes in different environments). To our knowledge, polymorphism in host acceptance strategy in parasitoids

has not yet been demonstrated. Conversely, some experimental studies have demonstrated A c c e p t e d m a n u s c r i p t that wasps could change their host acceptance strategy in response to current environmental conditions experienced [START_REF] Godfray | Parasitoids: Behavioral and Evolutionary Ecology[END_REF][START_REF] Babendreier | Superparasitism in the solitary ectoparasitoid Aptesis nigrocincta: the influence of egg load and host encounter rate[END_REF][START_REF] Goubault | Selection strategies of parasitized hosts in a generalist parasitoid depend on patch quality but also on host size[END_REF][START_REF] Outreman | Effects of within-and among-patch experiences on the patch-leaving decision rules in an insect parasitoid[END_REF]. Further investigations are therefore needed to exlain this strategy change.

Aphid parasitoids are of great importance in biological control against cereal aphids, which are serious crop pests in temperate regions [START_REF] Schmidt | Relative importance of predators and parasitoids for cereal aphid control[END_REF]. They represent an alternative or complementary control method to insecticides, which can be harmful to the environment and to human health. It is therefore essential to understand the interactions between aphid parasitoids and their hosts, and this study contributes to the comprehension of the seasonal dynamics of these interactions. Moreover, aphid-parasitoid systems have scarcely been studied in winter, because of sampling difficulties and low densities, despite the importance of parasitoids for the biological control of spring pest populations [START_REF] Plantegenest | Assessment of the relative impact of different natural enemies on population dynamics of the grain aphid Sitobion avenae in the field[END_REF]. Indeed, winter is a crucial season for aphid population dynamics and therefore for the occurrence of spring outbreaks. The results of this study suggest that, as aphid parasitoids do not exhibit any host preference between aphid species in winter and attack all encountered aphids, they are potentially of use during winter for pest control in cereal crops.

  From these populations, only third instars were used for the experiments, as intermediate stages are known to be of better quality and usually preferred by female parasitoids(Colinet

  A c c e p t e d m a n u s c r i p t et al., 2005; Tahriri et al., 2007).

Figure 1

 1 Figure captionsFigure 1 Mean (± SE; n = 10) relative host encounter and acceptance rate in (A) winter (Aphidius rhopalosiphi and A. matricariae were exposed to aphid species Sitobion avenae and Rhopalosiphum padi) and (B) spring (A. rhopalosiphi and A. avenae were exposed to S. avenae and Metopolophium dirhodum). Asterisks indicate significant differences (***P<0.001; ns, not significant).

Figure 2

 2 Figure 2 Influence of host species (Sitobion avenae and Rhopalosiphum padi) on mean (± SE) (A) parasitic success rate [number of attacked aphids (ovipositor inserted) leading to emerged parasitoids divided by the total number of aphids attacked, %], (B) development time (days), and (C) hind tibia length (mm) of males (M) and females (F) of the two

Figure 3

 3 Figure 3 Influence of host species (Sitobion avenae and Metopolophium dirhodum) on mean (± SE) (A) parasitic success rate [number of attacked aphids (ovipositor inserted) leading to emerged parasitoids divided by the total number of aphids attacked, %], (B) development time (days), and (C) hind tibia length (mm) of males (M) and females (F) of the two parasitoids species, Aphidius rhopalosiphi and A. avenae in spring. Asterisks indicate significant differences (*0.01<P<0.05, **P<0.01; ns, non-significant). Means are based on 72 M and 8 F A. rhopalosiphi on S. avenae, 41 M and 8 F A. rhopalosiphi on M. dirhodum, 52 M and 6 F A. avenae on S. avenae, and 21 M and 3 F A. avenae on M. dirhodum.

  Figure 1

Table 1

 1 Parasitoid and aphid species dominant in winter and spring season

		Winter	Spring
	Parasitoids	Aphidius matricariae	Aphidius avenae
		Aphidius rhopalosiphi	A. rhopalosiphi
	Aphids	Rhopalosiphum padi	Metopolophium dirhodum
		Sitobion avenae	S. avenae

Acknowledgements

This work was supported by the French National Research Agency Landscaphid program (grant number ANR-09-STRA-05) and by 'Région Bretagne'. All field and laboratory work conducted in this study comply with French legal code requirements. We are grateful to Philippe Louâpre, Lucy Alford, Franck Hieronimus, Philippe Vernon, and Josselin Montarry for the technical support provided and the comments on an earlier version of the manuscript. Special thanks to Stéphanie Llopis for the technical support provided for the aphids rearing.


Bernard Grabot
email: bernard.grabot@enit.fr

Raymond Houé

Fabien Lauroua
email: fabien.lauroua@sap.com

Anne Mayère
email: anne.mayere@iut-tlse3.fr

Introducing "2.0" functionalities in an ERP

Keywords: Web 2.0, ERP 2.0, business processes

Introduction

The use of "Web 2.0" tools (including wikis, forums and social networks), which give an active role to Internet users, has dramatically increased during the last few years, creating a great interest from companies and organisations (including governments), all looking for new ways to better involve their stakeholders in their daily activities. Therefore, new paradigms like "Government 2.0" or "Enterprise 2.0" have been suggested for describing organisations re-structured in order to take full benefit of the "2.0" technologies. At the operational level, the idea of "ERP 2.0" (Enterprise Resource Planning 2.0) has been introduced, and several software editors have launched new version of their ERPs that include "2.0" functionalities. In this quickly evolving context, the first objective of this communication is to make a panorama on recent applications of the 2.0 technologies in industry, illustrated on the example of the new version of the SAP ERP "Business By Design". We also show that existing applications only loosely integrate the 2.0 aspects to the existing business processes and we suggest guidelines for allowing to really design "2.0 processes" using an "ERP 2.0".

F o r P e e r R e v i e w O n l y

A P M S 2 0 1 2 2
The "Web 2.0" tools

The term "Web 2.0" refers to the new generation of Internet, characterised by innovative applications that break the barrier between creators and users of web sites. The Web 2.0 mainly include wikis, blogs, tagging, syndication, mashups and social networks: Wikis: A wiki is a web site which content can be edited by any user. Blogs: A blog is a Web site containing inputs (posts) written on a specific subject by an individual or a group.

Social bookmarking (tagging):

A tag (or bookmark) is a key word added to a numerical object, which can be stored on a distant server and shared with other users [Millen et al., 2005]. RSS and syndication: Syndication is the process that allows to make accessible information coming from a web site on another web site. Social networks: A social network is composed of people or organisations interacting in order to share mutual interests, contents, knowledge, etc. Mashups: A "mashup" is a new applications, data or web page built on the base of multiple and heterogeneous sources.

These tools are of course of interest for companies, which permanently seek for new ways to more efficiently involve into their business processes their employees, but also their customers and suppliers. Especially, these new applications could address some of the problems linked to the use of ERP systems, often considered as creating social tensions within the companies by an increased centralized control and by imposing a standardised communication between employees, based on external "best practices" [START_REF] Light | Contradictions and the appropriation of ERP packages. In "ERP systems and organisational change[END_REF].

"2.0" functionalities in companies: some examples

Different uses of Web 2.0 tools can be noticed in companies:

The Web 2.0 as a tool to improve the relationships with the partners. An already classical use of the social networks in companies is to create links with potential customers [START_REF] Edwards | Using social media to sell products, effectively! Blog[END_REF], using the web site of the company, or existing social networks like Facebook, or blogs and topics in Twitter [START_REF] Goodbaum | How Media Networking can help your manufacturing business[END_REF]. Web 2.0 tools can also be used for supplier support [START_REF] Doan-Huy | Getting the right information to the right people at the right time[END_REF] and market places can be complemented with "chat" facilities [START_REF] Williams | New software makes live chat an affordable reality for aviation component vendors[END_REF], or by adding 2.0 functionalities to CRM tools [START_REF] Sigala | eCRM 2.0 applications and trends: The use and perceptions of Greek tourism firms of social networks and intelligence[END_REF]. In a context close to B2B (Business To Business), the Web 2.0 can also allow to gather partners for creating a "social" supply chain [START_REF] Hinchcliffe | The Advent of the social Supply Chain[END_REF]. Adebanjo [START_REF] Adebanjo | Analysis of web 2.0 enabled e-clusters: a case study[END_REF] underlines the interest of these tools for creating "e-clusters" of SMEs.

The Web 2.0 as a mean to create an employees' network. The goal is here a better interactivity between employees [9-10], like at Lockheed Martin for sharing purchase practices [START_REF] Rosen | Lockheed Martin Sets up private social network[END_REF] or at EDF (Electricité de France) for allowing knowledge exchange [START_REF] Passant | Case Study: Enhancement and Integration of Corporate Social Software Using the Semantic Web (EDF)[END_REF]. At Dassault Systèmes, a platform of internal blogs has been implemented for facilitating the information transfer [START_REF] Bourdier | Enjeux et apports du Web 2.0 pour la circulation de l'information dans l'entreprise: le cas du service de veille stratégique du groupe Yves Rocher[END_REF]. At HP, a "2.0" platform including bookmarking, tagging, RSS and social network allows employees to contact people with useful expertise. In [START_REF] Lynch | FONA wins a CIO 100 award for use of Enterprise Social Networking software from Socialtext[END_REF] is presented an application in a company manufacturing flavours for the agro-food industry: the SocialText software, including microblogging, social networks and widgets, is used for creating networks allowing a fully decentralised management of tests of flavours by employees.

The Web 2.0 as a tool for knowledge coproduction. Content management tools are of specific interest for knowledge coproduction [START_REF] Goodbaum | Wikis in use in Manufacturing sector[END_REF][START_REF] Iversen | Social Networking Tools Penetrate Manufacturing, Blog[END_REF]. A wiki dedicated to the creation of "trade encyclopaedia" has been implemented at Atos Origin [START_REF] Bourdier | Enjeux et apports du Web 2.0 pour la circulation de l'information dans l'entreprise: le cas du service de veille stratégique du groupe Yves Rocher[END_REF] while Emerson Process Management and IFS North America use 2.0 tools for transferring knowledge from a generation of employees to another [START_REF] Goodbaum | Wikis in use in Manufacturing sector[END_REF]. The improvement of an on-line support is mentioned in [START_REF] Iversen | Social Networking Tools Penetrate Manufacturing, Blog[END_REF]. Carbone et al. [START_REF] Carbone | Open Innovation in an Enterprise 3.0 framework: Three case studies[END_REF] also describe results obtained in several Spanish companies on knowledge structuration through 2.0 tools, but Passant [START_REF] Passant | Case Study: Enhancement and Integration of Corporate Social Software Using the Semantic Web (EDF)[END_REF] emphasizes on the EDF case the problem of making exploitable the information recorded in a wiki.

The Web 2.0 as a way to open the company on its environment. Some applications aim at creating a link between the company and external entities, outside formal working relations: at IFB, the access to "external users' wisdom" allows the employees to be aware of the practices promoted by other companies [START_REF] Iversen | Social Networking Tools Penetrate Manufacturing, Blog[END_REF]. This need is also mentioned in [START_REF] Williams | Facebook in the factory: manufacturers want social software, too. Blog[END_REF].

The Web 2.0 as a tool for collaborative work. Web sites can be turned into collaborative working platforms using Web 2.0 functionalities [START_REF] Neil | Teamwork 2.0. Blog[END_REF]. At Ford, the factory manager can publish the planning and may authorise on line improvements by other users [START_REF] Neumann | From a social wiki to a social workflow system[END_REF]. In an operational way, social bookmarking tools like del.icio.us or "My Web 2.0" from Yahoo may allow users to share their bookmarks, and associated notes [START_REF] Millen | Dogear: social bookmarking in the Enterprise[END_REF].

The Web 2.0 as a mean to increase individual productivity. In [21], an annotation system applied on the IBM Intranet is suggested for improving the performance of the search engines.

The Web 2.0 as a social experiment in the company. 4000 employees of British Telecom were participating to a FaceBook group called "BT". The company decided to create internally a similar initiative, without any precise idea on its finality. A comprehensive set of tools including wiki/blog/social network was opened, and was massively adopted by the employees, with 1500 blogs opened in few days [START_REF] Ferron | Analyzing collaborative networks emerging in Enterprise 2.0: the Taolin platform[END_REF]. Nevertheless, no link seems to have been created with the existing information system of the company. A similar experience is described in [START_REF]ChessMedia: State of Enterprise 2.0 Collaboration[END_REF], with the implementation of Taolin, a 2.0 platform, in the FBK research foundation in Italy.

In 2011, according to the ChessMedia survey [START_REF] Andersson | Enterprise 2.0 and social media coming to ERP[END_REF], the 2.0 tools currently used in the organizations were Blogs (70%) and microblogs (58%), Full-feature collaboration platforms (60%), Videos (53%), Forums (51%), RSS feeds (34%) and Mashups (22%), in all the departments of the companies. In next section will be investigated more precisely how 2.0 functionalities could be introduced in companies, and more specifically in their main information systems: the ERP.

4

The "ERP 2.0"

4.1

From Enterprise 2.0 to ERP 2.0

The flexibility that could be given to an the ERP by the Web 2.0 is often discussed in blogs. For Andersson [START_REF] Botta-Genoulaz | A recent survey on the research literature on ERP systems[END_REF], the integration of tools like wikis and blogs to an ERP is firstly useful for "canalising" a tendency that may lead to a loss of productivity of the employees and to security breaches if not correctly addressed. For Botta-Genoulaz et al. [START_REF] Hawryszkiewycz | Perspectives for Integrating Knowledge and Business Processes through Collaboration, Enterprise, Business-Process and Information Systems Modeling[END_REF], the "2.0" functionalities should participate to re-create the social links damaged by the standardisation of the exchanges between actors which may follow the ERP implementation, while Hawryszkiewycz [START_REF] Kimberling | ERP 2.0: Social Media and Enterprise Software[END_REF] suggests an evolution of the corporate information systems towards a real "2.0" version for allowing "knowledge workers" to permanently update their social work connections. Kimberling [28] wonders whether these two technologies can really be aligned: on the one hand, 2.0 technologies (and especially social networks/wikis) group informal and unstructured social media tools allowing anyone to say anything without any real control or structure. On the other hand, ERPs are large, structured, enterprise systems with controls surrounding master data, security profiles, and standard workflows.

Few ERPs have at the moment publicized on the term "2.0". The example of "Business By Design", edited by SAP, is taken in next section for giving operational illustrations of what could be an "ERP 2.0".

4.2

The example of "Business By Design"

Business By Design (ByD) has been launched by SAP in 2007 as a SaaS product (Software as a Service); it includes several functionalities of the Web 2.0: RSS, allowing to have access to external information. Mashups: Pre-configured mashups include communications with Google Map, Bing, Route planners (Google and Bing), search for a person (Tweeter, Facebook), and search for a company (Tweeter).

Tagging and bookmarking: Tags can be associated to each object (customer, materials, customer order...). Other users will be able to access the tagged object via hyperlinks.

Web services: ByD can create links with external Web services.

Collaboration tools: a new tool, "Feed", allows group discussions and instant messaging.

Groupware integration: a special add-on has been developed for Outlook for creating a direct link with ByD.

Examples of use

Even if these functionalities have only been recently added, some real applications can already be listed: Mashup Embedded Map: maps provided by Google Map have been used by several users in order to get information on their customer's environment.

Web Services: Web Services are often used for getting information on order delivery from other systems (Freight Forwarder). Such links have also been used for creating orders in a remote Online Sales service (an Internet based company linking retailers and consumers), the order being then automatically created in ByD. Tags: some project managers have tagged their Projects with the technology that has been implemented. It is then easy to find people who have a comparable experience for other projects based on same technology. RSS feeds: users often select and filter feeds according to a customer name or product. Each time the user opens the "customer screen", RSS feeds are selected according to the on-line customer and sent to him. A SAP customer has also created two RSS feeds in order to inform his employees on IT maintenance and on company events.

In spite of several interesting applications, no clear methodology for developing 2.0 applications within Business by Design has yet emerged, and only "local" developments have been performed. The draft of a more systematic approach supporting the development of more comprehensive applications is suggested in next section.

Guidelines for development of 2.0 applications in an ERP

Some basic questions should be considered:

1. What is the main target of the project in the ERP context? ERP systems can be considered according to (at least) two dimensions: the functions they address (broadly speaking: Customer Relationship Management, Logistics, Finances, Human Resource Management, Business Intelligence) and the steps of their life cycle (project organisation, training, process modelling, tests, go-live, optimisation). Additionally, an ERP has close connections with peripheral functions like Enterprise Modelling, Knowledge Management and Product LifeCycle Management. The goal is here the identification of a couple (step of implementation, function), called "Target" in what follows; for instance: CRM function in the Activity modelling phase.

What are the stakeholders involved in the Target?

The answer should be a list of roles for the people involved in the Target. For instance: customers and employees for the Marketing area, logisticians and suppliers in the "Logistic" function, key users and consultants in the "Optimisation phase" of the implementation, etc. 4. Which 2.0 tools should be relevant for meeting these objectives? A decision tree has been developed for summarizing the criteria that should orientate on a given tool rather than on another, the objective of the introduction of the 2.0 tools being the root of this decision tree (see a part of the tree in Figure 1). 5. In reference to the pre-selected tools, what are the roles of the Stakeholders? Example: in the "CRM" function, the goal is to disseminate news from the Marketing employees to the Customers. Marketing employees may so be the producers of one or several blogs, while the Customers will be the readers. If a formal group has to be built, a Social Network may encapsulate the process. 6. Develop the application inside the ERP, or choose external software.

In that purpose, it will be necessary to specify precisely what type of information or knowledge should be coproduced by each stakeholder according to his role. 7. Model the business processes based on the use of the "2.0" application. The development of the "2.0" application should allow to reformulate the concerned business process and activities. The validation of this step-by-step approach on real implementations of Business By Design is now in progress, promising initial results having already been obtained. to the companies. Many "minimal" implementations, often highly publicised, are a consequence of this "high-tech" image. Nevertheless, many interesting applications have also shown that these tools have a real potential for improving business processes, especially those related to coproduction of information or knowledge, which is a critical issue for the companies. In order to maximize the impact of these tools, it is therefore important to integrate them into the existing information system of the companies, the ERP. In that purpose, ERP editors begin to include "2.0" functionalities in their products, but a clear methodology for the definition of "2.0" business processes, supported by the ERP, is still missing. On the base of real applications using the new version of the ERP "Business by Design", edited by SAP, we suggest in this article to consider two dimensions in which the "2.0" tools could support ERP-based processes: the implementation project of the ERP, and the functions addressed by the ERP. This approach only provides some guidelines, and should be adapted to specific cases but we think that such methodology could allow to increase the use of these promising tools in industrial applications.

F

F

F

3 .

 3 Inside the Target and between these Stakeholders, what are the objectives of the project?The points listed in section 3.1 are examples of such objectives.

Fig. 1 .

 1 Fig. 1. Decision tree for the choice of a "2.0" tool (partial)

F

Acknowledgments

B. Grabot, A. Mayère and R. Houe would like to thank the partners of the SyGeo Project (MLState, HEC, Scan & Target), especially Layth Sliman, for their help.