domain: phys spi

text:
W Aouimeur

S Lepilliet

C Gaquière

E Lauga-Larroze

J.-D Arnould

J Moron-Guerra

T Quemerais

D Gloria

A Serhan

A Fully In-Situ Reflectometer in G band in 55 nm SiGe BiCMOS

Keywords: Built In Self Test, VNA, G Band, S-parameters, Frequency multiplier, Coupler, Mixer, SiGe BiCMOS 55 nm. I

This paper describes an in-situ reflectometer for one port VNA in 160 to 200 GHz band (G Band). The proposed system is fabricated in 55 nm SiGe BiCMOS technology from STMicroelectronics. Measured performances of system shown 110 mW of power DC consumption from a 1.2 V supply. A 180 GHz nMOS is measured as the device-under-test (DUT) after an in-situ calibration. The results obtained using this fully integrated VNA have been compared to a commercial VNA. A discrepancy of 0.3 dB is noted between the two systems on magnitude over a wide frequency range 172-192 GHz. Without calibration, the "raw" dynamics range of the system is limited by the directivity of the coupler which is 20 dB at 140-220 GHz. This dynamic will be improved after the calibration. The SiGe chip size is 3.3 mm 2 . To our best knowledge, the presented in-situ VNA have the first results compared to the recently published and are the first with an in-situ calibration integrated in SiGe or CMOS technologies.

INTRODUCTION

Microelectronic

applications such as wireless communications, radar or space detections require higher data rate resolutions, implying the use of millimeter wave and submillimeter frequencies. Thanks to the silicon technologies improvement, some microelectronic circuits are emerging working in the frequency range of 140-220 GHz (G-band) but they suffer from a lack of complete characterization tools involving costly investment. To date, there are few papers in the literature that deal with the miniaturization of in-situ VNA [START_REF] Laemmle | A 122 GHz Multiprobe Reflectometer for Dielectric Sensor Readout in SiGe BiCMOS Technology[END_REF]- [START_REF] Ku | A 70-110 GHz single-chip SiGe reflectometer with integrated local oscillator quadrupler[END_REF] and even fewer integrated in-situ VNAs for Bist application from 1 to 125 GHz. All these papers deal with measuring systems. In the literature we distinguish two types of reflectometer: 6-ports and separation of signal [START_REF] Laemmle | A 122 GHz Multiprobe Reflectometer for Dielectric Sensor Readout in SiGe BiCMOS Technology[END_REF]- [START_REF] Ku | A 70-110 GHz single-chip SiGe reflectometer with integrated local oscillator quadrupler[END_REF]. [START_REF] Laemmle | A 122 GHz Multiprobe Reflectometer for Dielectric Sensor Readout in SiGe BiCMOS Technology[END_REF]- [START_REF] Laemmle | A 62 GHz reflectometer for biomedical sensor readout in SiGe BiCMOS technology[END_REF] presents the first in-situ 6-port reflectometer using for biomedical detector but with narrow-band and with small area. The reflectometer in [START_REF] Ku | A 70-110 GHz single-chip SiGe reflectometer with integrated local oscillator quadrupler[END_REF] is fabricated with separation of signal topology and present high bandwidth and huge area (6 mm 2 ). Therefore, the work developed in this paper aimed to integrate in the die the measurement systems that would measure small signals "S-parameters" of the device under test (DUT). Being closer to the DUT makes it possible to reduce the insertion losses, to reduce the amplitude of the error vectors and thus the residual errors after calibration. Moreover, it is possible to better control the power of the signal sent and to consider calibration methods using integrated loads, which reduces the time and cost processing.

The solution developed consists on connecting the wafer with some probes and driving it with an external signal that spans the 35-55 GHz band. Once into the die, this signal is then quadrupled in frequency and amplified to reach good power level in G band at the DUT input. S11 is extracted from the DUT thanks to a very directive coupler designed at the input of the DUT. The outputs of the coupler are then converted to low frequencies (IF =0.

A. G band frequency quadrupler [4]

A solution to generate those high frequencies is to use a lower frequency source and to cascade it with a frequency multipliers chain.

In this part, we present a frequency quadrupler in G band based on single ended doubler fed by a Marchand Balun and balanced frequency doubler [START_REF] Aouimeur | A G band frequency quadrupler in 55 nm BiCMOS for bist applications[END_REF]. An external frequency source supplies a RF signal at a frequency f0between 35 and 55 GHz. This input signal is doubled and amplified to W band thanks to an original Marchand balun based on Slow-wave CPW couplers. Next, the balanced frequency doubler followed by a power amplifier (PA) generates the output signal in the G band. The design of this G band quadrupler and its simulated performances and experimental results are described and compared at the state of art in [START_REF] Aouimeur | A G band frequency quadrupler in 55 nm BiCMOS for bist applications[END_REF].

B. Coupler

The presented coupler, placed between the quadrupler and the DUT, is used to extract the S11 parameters of the DUT (Fig. 1). In order to obtain a compact design with a high isolation, a flat performance, the coupler used a Side Cut Coupled Slow-wave Coplanar Waveguides (SC-CS-CPWs) topology [START_REF] Lugo-Alvarez | High-directivity compact slow-wave CoPlanar waveguide couplers for millimeter-wave applications[END_REF].

The different parameters of the SC-CS-CPW coupler are determined in order to reach 50 Ohm of impedance in each port, the lowest insertion losses and 10 dB of coupling over the whole frequency bandwidth 140-220 GHz. The top metal strips are composed of a stack of the two top metal levels (M7 and M8). The thin ribbons placed below the strips are fabricated in M5 metal layer (the gap between M5 and M7 is h=2.1 µm). The optimum dimensions have been defined following the method in [START_REF] Lugo-Alvarez | High-directivity compact slow-wave CoPlanar waveguide couplers for millimeter-wave applications[END_REF] and confirmed by an HFSS EM simulation. The resulting dimensions are WS=15 µm, Wg=12 µm, S=5 µm, SL=0.16 µm, SS=0.64 µm, the cuts and the length of SC-CS-CPW lines are 2 µm and 160 µm respectively. The measured performances of this coupler in standalone after pad and access lines de-embedding are: Isolation=30 dB, Coupling=10 dB and directivity=20 dB at 180 GHz.

C. Mixer in G band

In this part, we present a single-ended passive downconversion mixer in G band. The schematic of this mixer is detailed in (Fig. 3). This mixer is used at the output of the insitu reflectometer like detector (Fig. 1). To reduce the complexity of the system (Fig. 1). a simple passive topology is proposed. This circuit is optimized to achieve the best compromise between conversion losses, linearity, and the power level required for LO access. When applying the LO to the gate of the nMOS, the sizing of the cold (without Vds) nMOS transistor is done by varying the width, length, and the number of fingers. All of these parameters are set to minimize the ratio Zon/Zoff (Zon and Zoff are the impedances presented by the nMOS in the ON and OFF states respectively) [START_REF] Yhland | Simplified Analysis of Resistive Mixers[END_REF]. The size of the nMOS transistor (width W=30 µm, length L=0.06 µm) and its bias voltage (Vgate=0.5 V) are set to obtain a good tradeoff between conversion loss and the 1 dB compression point at output IF=2.4 GHz (Fig. 3).The measured performances of this mixer in standalone are Conversion loss = 14 dB and RF-LO isolation around 20 dB.

D. DUT in G band

This integrated 50 Ω load utilized like DUT is composed of an nMOS transistor M1 and a stub placed at the RF input to suppress the imaginary part of M1 impedance. The real part of the transistor impedance is adjusted with Vgate=0.7 V to get 50 Ω at 180 GHz (Fig. 4). A very good agreement between measurements with commercial VNA and our in-situ reflectometer is noted (Fig. 7). The magnitude measured of Z4 (impedance of DUT at (Vgate=0.9 V of nMOS DUT) shown difference is < 0.3 dB at 172-192 GHz.

III. CONCLUSION

In this paper, we have presented a fully integrated G band heterodyne in-situ reflectometer for one-port vector network analyzers (design and characterization). This reflectometer is composed of a wide band frequency quadrupler made up of two frequency doublers for RF and LO chains, cold downconverters and a very directive coupler based on slow wave topology. First measurements on an in-situ DUT show good agreement compare to commercial VNA.

  5-2.4 GHz) through passive frequency mixers (Fig 1). One of the obvious advantages of this heterodyne integrated test solution is the use of off-chip and low frequency a low cost VNA (<3 GHz) that allow for quick and inexpensive verification of circuits or components. A study of each block standalone have been evaluated (Fig 1).

Fig. 1 .

 1 Fig. 1. Block diagram of proposed in-situ reflectometer In this paper, we present a frequency in-situ reflectometer in G band frequency based on signal separation technic with a coupler (Fig 1). The design of each blocs and its simulated performances are detailed in Section II, while the experimental results of in-situ reflectometer are described and compared at the measured with commercial VNA in Section III. Finally, the conclusion is presented in Section IV I. DESIGNThis system has been designed in the 55 nm SiGeBiCMOS technology developed by STMicroelectronics for mmW and sub-mmW applications. This work is supported by the project ANR-14-CE26-0027-BISCIG of the French National Research Agency (ANR) supported by ECSEL TARANTO project toward advanced BiCMOS nanotechnology platforms for RF and THz application

Fig. 2 .

 2 Fig. 2.Chip photo of the fabricatedof in-situ reflectometer in G band

Fig. 3 .

 3 Fig. 3. Schematic of down conversion mixer in G band.

Fig. 4 .

 4 Fig. 4. Schematic (left), Chip photo (right) of the fabricated nMOS used as 50 Ω load at 180 GHz.

Fig. 5 .

 5 Fig. 5. Comparison between simulated and measured of nMOS load with and without pad and access lines in G band

Fig. 6 .

 6 Fig. 6. Setup of measured magnitude of in-situ reflectometer At nominal power supply (1.2 V), the maximum DC power consumption is 110 mW and constitutes the consumption of the two frequency quadruplers in G band. The reflectometer is first calibrated by using a three known impedances Z1, Z2 and Z3 from the DUT in standalone, at the reference plane and calculating the 3-terms errors matrix [7]. Then, S11of in-situ DUT are obtained from the corrected a1 and b1 values.

Fig. 7 .

 7 Fig. 7. Measured input return loss: in-situ refelectomter versus commercial VNATABLE I PERFORMANCES SUMMARY OF REFLECTOMETER Ref Process Bandwidth [GHz] Topology PDC [mW] Type (DUT) Area [mm 2 ] [3] BiCMOS 70-110 separation -Offsitu 6 This work 55nm BiCMOS 172-192 separation 110 In-situ 3.3

  Table I presents a comparison with other previous studies in different technologies, frequency range and in-situ, off-situ DUT. This in-situ reflectometer presents good performances in terms of magnitude accuracy and bandwidth frequency.

ACKNOWLEDGMENT

The authors wish to acknowledge A. Silligaris from CEA-Leti for his help in design.


Philippe Ninnin
email: philippeninnin@hotmail.fr

Institutional Innovations for Organic Agriculture in Africa (IIABA) Work Package 3: Participatory Guarantee Systems (PGS) 2021 Field report -Governance of the Kilimo Hai PGS in Tanzania

The presented study was performed during a Master 2 internship led by CIRAD as part of the Work Package 3 of the IIABA project. The main objective of the internship was to develop and put to the test a questionnaire aiming to identify the governance characteristics of a Participatory Guarantee System (PGS). To do so, it was decided to try out the questionnaire in Tanzania, in collaboration with TOAM. However, the sanitary restrictions of the Covid pandemic reduced drastically the time for field work, passing from 5 months on the field to only 1,5 months, from July to August 2021. The contribution of TOAM agents and local NGO workers was a great help to gather enough data in this reduced time period.

 12 PGS groups have been visited in four regions of Tanzania (Zanzibar, Masasi, Arusha, Morogoro) and interviews have been performed with 59 producers.  Development stages of local organic markets is very heterogeneous among regions, going from an infancy stage in Zanzibar to a stabilized market in Morogoro.  PGS producers are well involved in the organization of internal inspections, which fosters a shared responsibility and transfers of knowledge between producers.  Local group members are free to choose how to organize their governance, which allows the adaptation of each group to its specific needs.  Women seem to have equal access to decision-making bodies in local groups.  Producers are not involved in the management of the contents of the standard, which induces a risk of lack of adaptation of the rules of production.  Surveyed producers were mostly motivated to participate in PGS by the transmission of knowledge (vertical and horizontal), an increased income and improved social linkage.  The main challenges to face for individual certification are pests and diseases, water management, inputs and access to market.  The main challenges to face for collective action are lack of participation, pests and diseases and market failures.  Local groups are relatively isolated from each other and receive no support from public authorities.  The management of Kilimo Hai has a top-down structure which allow for an efficient and lowcost certification, but leaves limited space for producers' implication.

Introduction

In 2007, three countries in the East African Community (Kenya, Tanzania and Uganda, later joined by Burundi and Rwanda) adopted the East African Organic Product Standard (EAOPS), a regional standard for organic plant, animal and bee production, harvesting and processing of wild products [START_REF] Eaops | East African Organic Product Standards[END_REF]. EAOPS is the first regional standard to be developed through a collaborative process between public, private and non-profit organizations (UNEP, 2010), which gives the opportunity to associate the political and legal authority of governments to the technical expertise of National Organic Agriculture Movements (NOAMs) [START_REF] Pekdemir | On the regulatory potential of regional organic standards: Towards harmonization, equivalence, and trade?[END_REF]. The aim of the partners was to use this standard to certify products for the regional organic market. In 2010, the OSEA II project was set up to develop and support a Participatory Guarantee System (PGS) to manage the use of the East African Organic Mark (Kilimo Hai) [START_REF] Katto-Andrighetto | Participatory Guarantee Systems in East Africa. Case studies from Kenya[END_REF]. PGS certification represents a viable alternative to third party certification, especially for the development of domestic and region organic markets in low agricultural income countries, where third party is only economically viable for export [START_REF] Lundberg | Report: Organic Farming in Brazil: Participatory Certification and Local Markets for Sustainable Agricultural Development[END_REF][START_REF] Niederle | Social movements and institutional change in organic food markets: Evidence from participatory guarantee systems in Brazil and France[END_REF]. In 2011, the first PGS groups were established in Tanzania under the supervision of Tanzania Organic Agriculture Movement (TOAM). Today, the standards are applied by over 2000 PGS-certified producers across the country. However, little documentation is available on the actual functioning of the system, and the various decision making processes regarding PGS governance in the country. This study aims to provide elements of understanding of the Kilimo Hai PGS and of its impacts.

Research questions and method

The questions raised across the study were the following:

1) What is the institutional context of PGS certification in Tanzania?

2) What are the collective decision making processes in PGS groups of Tanzania? What are the forms of internal / external inspections? Who is involved and how are rights and power distributed? 3) What is the impact of Kilimo Hai PGS perceived by its members? What do they expect from participating? What are the main challenges faced by PGS certified producers?

Elements of context [Q1] and general governance [Q2] were gathered remotely by semi-structured interviews with five NGO representatives and by a review of scientific literature and regulatory texts. Afterwards, semi-structured interviews were performed on the field with PGS producers in order to understand the diversity of governance structures in local groups [Q2], the perception of producers and their main challenges [Q3]. Surveys were conducted with 59 members (31 women and 28 men) from 12 local groups located in four regions (Figure 1) to collect qualitative as well as quantitative data.

Figure 1 -Map of visited areas

For each group, members of the board or decision-making committee as well as regular producers were interviewed. Open-ended interviews were also conducted with external institutions (government, NGOs, etc.) to ensure the integrity of the information gathered and a good understanding of the links between the organizations and their respective institutional environments. Internal rules of producer groups were analyzed in different situations involving collective decisionmaking, with a focus on horizontality of decision and repartition or roles. Based on the major dynamics that emerged during the interviews, we attempted to identify the major impacts of the PGS on producers. Finally, a focus group was organized at the end of the fieldwork with TOAM agents to discuss the results of the surveys and what they reveal about the benefits and vulnerabilities of the system.

Results

Institutional context of PGS certification in Tanzania

Main stakeholders

The institutional framework for organic agriculture in Tanzania consists of several organizations, both public and private. Tanzania Organic Agriculture Movement (TOAM) is a federation of 115 member institutions and organizations (farmers' associations, cooperatives, business companies, NGOs and Individuals) as well as external partners (foreign NGOs, etc.). TOAM's role is to provide a link between local NGOs, to distribute information on organic food to its members and other stakeholders in the sector, and to coordinate and promote the development of organic agriculture at national scale. It is also the accrediting body which assesses the viability of the monitoring carried out by PGS groups to obtain Kilimo Hai certification (TOAM, 2021).

The main role of government institutions is to set up policies and regulations, which can support organic farming, such as the National Agricultural Policy of 2013 and Agriculture Sector Development Programme (ASDP 2) which aims to improve the availability of organic inputs for farmers, facilitate the accreditation of organic products by public authorities in order to reduce the costs of certification, promote initiatives in favour of organic farming, and strengthen effective coordination between organic farming stakeholders.

Finally, local NGOs (Milele Foundation in Zanzibar, Swiss Aid in Masasi, Mesula in Arusha and Sustainable Agriculture Tanzania in Morogoro) promote organic production, organize producers into local groups and facilitate the recognition and marketing of their products. Bringing producers together in groups facilitates the certification process, access to training in good production practices, and access to organic inputs. It also allows for the joining of production and the achievement of sufficient volumes to open up new market opportunities [START_REF] Mbapila | Institutional Framework: Status and Prospects for Tanzania Organic Sector Development -Policy Brief[END_REF]. SwissAid works in order to promote agroecology and sustainable livelihoods in Tanzania. As "implementing partners" of TOAM, they have started to use PGS certification in Masasi as a means to facilitate access to village markets. Products are sold through baskets, organic shops with premium prices in Dar el Salam and Masasi, restaurants and regular markets. According to one respondent (TZ2), access to synthetic inputs is very scarce and expensive in these regions, so producers are already inclined to produce organically. This year they expected a total of 40 certified PGS groups, of which 3 were visited: Ma A (Temeke), Ma B (Moroco) and Ma C (Upendo).

Local contexts

Meru Sustainable Land Co. (MESULA) is a company created by the Italian NGO Oikos Institute as a project to promote sustainable agricultural production and livestock breeding in Arusha [START_REF] Mesula | Mesula -Meru Sustainable Land[END_REF]. PGS are well established in the area, with outlets in hotels and expat communities through Mesula. However, producers have struggled finding a market since the Covid outreach. Mesula plans to improve sales conditions by establishing a centralized point of sale in town, as well as an ecommerce website. It has a large PGS that brings together all the producers in the district (Joint KB). Two sub-groups of the Joint KB, each with its own governance, were visited: Ar A (Kitchari pinda) and Ar B (Overgrow).

Sustainable Agriculture Tanzania (SAT) is the main support organization for PGS groups in Tanzania based in Morogoro. In 2019, they supported 835 certified farmers (spice, vegetable and fruit producers) on 525.6 acres of land dedicated to organic farming (SAT, 2020). The number of PGScertified producers continues to grow, and a cooperative of several organic producer groups is currently being formed to implement an internal third-party control system recognized for export (TZ4). More than 50 groups are already certified in Morogoro, and 4 of them were visited: Mo A (Upatachu), Mo B (Tughese), Mo C (Vijana Amikendi) and Mo D (Mungano Mazigira Viungo MMO).

Surveyed groups

The level of development of PGS groups varies widely by region. The first groups surveyed in Zanzibar (Za A-B) were formed by Milele in 2018 and have yet to be certified. Those in Masasi (Ma A-C) were composed by Swiss Aid between 2015 and 2017, and then first certified between 2019 and 2020. SAT is the longest-standing organization involved in PGS certification, but the groups surveyed in Morogoro (Mo A-D) were initiated between 2009 and 2017, for first certification between 2014 and 2019. The groups surveyed in Arusha (Ar A-B) are the oldest, having been trained by other NGO projects in 1996 and 2006, and then certified with Mesula support in 2012. Some of the groups surveyed have therefore had Kilimo Hai certification for over 9 years, while others have not yet obtained it. Group membership varies relatively little, with the majority of groups between 15 and 30 members. Only the Joint KB federation, which includes all the subgroups in Arusha District (including Ar A and Ar B), deviates from this range, with 98 members in total. Ar B has its own governance structure and organizes its own inspections in parallel with those of the federation, whereas Ar A has only the federation structure.

The interviews with Ar A will therefore be counted as representative of Joint KB in the following.

Collective decision-making processes and repartition of rights and powers

Structure of the PGS and access to decision-making bodies

The Tanzanian PGS, certifying compliance with East African Organic Products Standards (EAOPS) through the "Kilimo Hai" mark, operates at two scales: producer groups are independent and have full authority over their own governance, committees for oversight and monitoring of compliance with the standards, while remaining accredited by TOAM (Figure 2). The employees of TOAM are recruited through formal procedures and managed by the CEO, who applies the policy of the governing board. Members of the governing board are themselves appointed by the General Assembly of organic initiatives members of the umbrella organization (NGOs, merchants, farmers' associations…).

Most PGS groups have an average size of 25-30 farmers. They all have the same basic governance structure: an executive board, a marketing committee, a production committee and an internal control/evaluation committee. Some have additional groups (finance, planning...) as needed (Ar A).

Committee and board members are elected by the group as a whole for a period of one to four years. In some cases, board members appoint the committees and/or have the right to exclude their members (Mo B+D). The composition of the groups is relatively balanced in terms of the number of female and male group members. Since one of the objectives of the study was to analyze the distribution of power according to the gender of SPG members, we tried to identify potential disparities in access to leadership positions. However, the participation to decision-making committees appears to be fairly balanced (Figure 3). Nevertheless, we do not have data on the concrete application of these powers and the possible problems of authority that gender issues may induce.

Figure 3 -Composition of local group offices (left) and committees (right) for each group, discriminated by gender: the number of female members appears in blue and male appear in yellow.

Organization of internal inspections

The certification process of Kilimo Hai has two steps: certification of individual producers by the local group, and accreditation of the group by TOAM (Figure 4). Internal inspections are usually supervised by a dedicated committee (production/internal control/quality committee), which is responsible for the quality of the system and has the rights to manage the control system. In some cases, members of the board or marketing committee (Za A, Ma B+C, Mo D) also participate in the inspection. In sufficiently small groups (Mo A), the whole group can decide together on the control plan.

Inspections are usually carried out by the same members as those who organize them (except for Mo C, which involves members of another committee), who can usually be joined by other group members. Thus informally, every member has the right to participate to inspections. For groups interviewed in Arusha, inspections are unannounced and performed by a single inspector from the monitoring committee. The inspection rights are therefore held by only a few peer inspectors. During the inspection, peer inspectors ask about inputs used, waste management, expected yields, quantities, selling prices, etc., as guided by the checklist. In case of non-compliance, the inspector gives recommendations for corrective action to the producer and writes a report.

Governance structures chosen by the groups depend little on the region, and therefore on the NGOs that formed them. In contrast, the mode of inspection organization appears to be strongly related to group size. The large size of Ar A makes it difficult to organize collectively and involve all members in inspections. Having managers assigned to carry out the visits therefore greatly limits the coordination and transportation costs associated with carrying them out. In contrast, Mo A producers are very few in number. They can not only afford to involve regular members in the inspections but also share the responsibility for their proper conduct and coordination.

Certification and sanction process

Even though the conformity with EAOPS is a mandatory basis for PGS certification, some groups may add more or less strict rules in terms of collective action (involvement in group activities) or production (production specific crops and practices). If a nonconformity is observed by internal inspectors, recommendations are noted in the reports (Figure 4). If corrected within a short period of time, farmers may retain their certification with a warning. However, if a producer has a major noncompliance, the group can sometimes decide to directly suspend the certification for a few months with a trusteeship (Ar A, Mo B+C) or until the group collectively decides to reinstate the producer (Mo A). In the other groups, if the producer does not apply the corrections, he receives a first and then a second warning. At the second warning, if there is still no improvement, the case is discussed in the general assembly in most cases (Za A, Ma A+C, Ar A+B). All the members of the group have the right to be excluded during these deliberations, and can participate in the decision to sanction by voting. In other groups, upon receipt of the inspection report, the board members alone decide whether or not to sanction the non-compliant producer (Za B, Ma B), with the advice of the production committee in the case of Mo D. The sanction can range from supervision by a peer to exclusion from the group without the possibility of appeal. It would seem that sanction decision models depend more on the relationships of trust between members and the methods of sanction chosen than on the size of the groups. Groups that have delegated the decision on whether or not to sanction non-compliant producers to closed bodies only sanction them after several warnings, in a gradual manner and on the basis of formal inspection reports, which limits the risk of arbitrary punishment.

Once the groups are ready, upon a call for certification, the organic guarantee system (OGS) officer from TOAM will go through the internal inspection reports and randomly select 20% of the total group members who attended the inspection to visit their farms. If the OGS officer finds major nonconformities among farmers who had been approved by the peer review, a dialogue takes place between TOAM approval committee (composed of the CEO, the finance and administration manager, the program manager and representatives from the OGS department who did not conduct the inspection), the group and the host NGO. If the capacity for good control of the group cannot be assessed, none of the group members would be allowed to use the Kilimo Hai label until corrections have been made to ensure that the group's governance and certification processes are in line with EAOPS.

Figure 4 -Inspection and decision process for Kilimo Hai certification

Adaptation of local governance and operating rules

The small size of producer groups allows for simplicity in the collective decision-making processes. Many discussions are done informally, during meetings or collective tasks. If a group member wants to make a change to the rules of procedure of a group, he or she can usually make the proposal at a general meeting (Za A, Ma A-C, Ar B, Mo A+B), or go through the office, which acts as an intermediary, having the right to control the suggestions made at the meetings (Za B, Ar A, Mo C+D). The suggestions are then discussed and adopted, or not, by the vote of the whole group.

Modification of production rules

The EAOPS standard is administered by NOAMs from the East African Community, but it is owned by the governments of the member countries. A modification can be suggested by a NOAM member. If the suggestion is deemed appropriate, a proposal for change is drafted by the NOAMs' council and presented to the EAC council. The EAC Board representatives then make a final decision on whether to adopt the change. Since the EAOPS standard is owned by the governments of the East African Community, decisions to change it can only be made with their agreement. However, there is no formal mechanism for producers to contribute by suggesting changes. Producers therefore only have a right of access to the content of the standard, and only 43% of respondents said they were aware of EAOPS. This reveals a lack of ownership of the standard on the one hand (issues, interests and scale of the standards, implications, etc.), but also strong differences between the level of training of the different groups.

Impacts of the Kilimo Hai PGS on producers

Implication in collective action

Producers who are members of PGS groups have very heterogeneous levels of investment, going from a few hours per year to several days per week. The time invested in the group depends largely on the position occupied in the group, the organization of internal inspections and the auxiliary activities practiced by the group (collective farm, animal husbandry, beekeeping...). On the other hand, this variable degree of investment does not seem to be related to the socio-economic characteristics assessed. 31 women and 28 men were interviewed, with ages ranging from 19 to 72 years (average 48.8 years). Of the 59 producers surveyed, only 36% were dedicated solely to their farms, 51% had a secondary activity (crafts, trade, etc.) and 13% had another activity that provided them with the majority of their income (businesses, restaurants, etc.). The producers surveyed have areas ranging from 0.1ha to 8 hectares in production (1.2ha on average). Most of the producers surveyed own their land (14% have a title deed, 51% have informal ownership). The others produce on family land (17%), rented land (15%) or public land (3%). However, there does not seem to be any correlation between the involvement of producers in PGS groups and the gender of the members, their age, pluriactivity or the ownership of their farms.

Collective activities

All groups have a collective demonstration plot, which provides income for all members. Some groups have other joint activities, such as chicken and beekeeping (Mo C+D), fish farming (Mo D), processing (Ma A-C) or handicrafts (Ma C). Certified production is relatively homogeneous within the groups. The Masasi region produces a majority of seeds and nuts (sunflower, cashew nuts, peanuts...), and the Mo C and Mo D groups specialize in spices, but most groups produce fruits and vegetables (banana, papaya, tomato, carrot...) with some livestock (rabbits, pigs, goats...).

Market outlets

Zanzibar does not yet have a specifically organic market outlet (Figure 5). Production in the area is still too low and unstable, with insufficient volumes to maintain sustainable contracts with local businesses. Conversely, markets are sometimes saturated in Morogoro (for spices) and Arusha (for carrots), with insufficient local demand to absorb production. 61.7% of the producers interviewed have access to an outlet at a premium price (organic stores, hotels, restaurants, etc.), but these outlets are insufficient (problems of transport, volumes, quality, etc.). Direct sales (in the village or on the farm) remain the majority. On these local markets, the producers do not use the label and do not benefit from a premium price, but the superior quality of their products allows them to sell off their stocks more quickly and to better manage the time needed for sales.

Figure 5 -Market outlets used by surveyed producers sorted by decreasing average (N=59).

Relations with institutional environment

Apart from training, donations of equipment (greenhouses, processing units, etc.) and business facilitations from local support NGOs, local groups have few relationships with other organizations. Support from public authorities is non-existent. Inter-group cooperation is only observed in the Arusha region where groups are federated into one (Ar A+B), and in the Morogoro region where groups organize themselves into cooperatives for joint marketing (Mo C), transport of goods (Mo A+B) or collective savings (Mo C). There is no cooperation between groups in different regions, but exchanges are underway between the various NGOs to share organic marketing opportunities (notably through the few organic stores established throughout the country).

Individual benefits from PGS certification

We seek to identify the motivations of producers to become involved in the system through the way in which the groups respond to their needs, difficulties and future prospects. On average, 85% of the 59 producers interviewed said that access to information on "good agricultural practices" was one of the main benefits of participating in PGS groups (Figure 6). This transfer of information is achieved through access to training, but also through collective reflection and sharing of experiences between members of the same group during inspections or meetings. Access to information is perceived as more important than increasing income (83% of respondents on average), the links formed within the community (58%) or limiting the side effects of industrial agriculture on health (35%). Overall, the responses indicate that producers see PGS as an opportunity to improve their living conditions, acquire new skills and improve their practices, and develop a network within their communities and beyond.

Challenges for individual certification

In spite of PGS benefits, there are barriers to participation in the groups, which are often related to production barriers (Figure 7). On mainland farms, disease and pests are the main problem cited by the farmers surveyed. It is notable that this problem does not affect any of the Zanzibar farmers, who have much more difficulty with water management and irrigation systems. Presumably, access to biopesticides is better in this region, or the Indian Ocean acts as a natural barrier to the spread of disease in the region. Overall, access to appropriate inputs, equipment, and stable markets are the main challenges that groups face in facilitating production for their members.

Challenges for collective action

Within the groups, producers face recurring difficulties and obstacles to collective action (Figure 8). The major difficulty is the lack of participation in common tasks (collective farm, beekeeping, meetings, etc.), which generally operate on the basis of a compulsory weekly schedule for all members, but which suffer from absenteeism, lateness, low personal investment, etc. Production difficulties, in particular the management of diseases and pests, are sometimes an obstacle to the proper functioning of the group, as drops in yields lead to a drop in motivation. Some groups seem to have difficulty enforcing their internal rules and agreeing on collective decisions, which can create tensions. The lack of a market is seen as an obstacle to the smooth functioning of the groups in Arusha and Masasi. In Arusha, commercial agreements with supermarkets or direct consumers have been facilitated by Mesula (mobile application, advertising...). Groups in the district were severely affected by the epidemic, as they depended on hotels and expatriate communities to market their products. Since these outlets have not reopened, producers must sell their products on conventional markets and therefore have no interest in investing in certification, although most continue to produce according to the organic standard due to a lack of material possibility (cost and difficult access of synthetic inputs), to a concern for health issues, or in the hope for markets to reopen. Finally, distance is a problem for some groups with members from different villages.

Figure 8 -Aggregated answers of main difficulties within surveyed groups (N=12).

Evolution perspectives of farmers

43% of the 56 respondents plan to increase their farm production and income in the near future (Figure 9). 23% and 14% plan to expand their farms and invest in new equipment, respectively, reflecting confidence in the return on investment. 14% and 11% plan to diversify into new crop or livestock production, respectively, revealing untapped work capacity. Finally, 9% of the producers plan to open a new market outlet and 9% plan to raise awareness of AB issues in their communities, revealing the importance of the network for PGS members.

Conclusion

The organization of the Tanzanian PGS has many advantages. The structuring of the system into local groups greatly favors vertical knowledge transfer through access to collective training (NGO training agents, extension agents), but also the possibility of fostering entrepreneurship and empowerment of members, especially women (Ma C). Collective involvement in the process of enforcing organic standards leads to a shared responsibility, albeit limited, on the part of producers for the management of the label. Participation in inspections and collective decision-making allows for a very important horizontal transfer of knowledge (collective reflection in the event of a problem on a group farm, sharing of advice and experiences during visits, etc.). Because of this better understanding of organic agriculture and its issues, PGS members are better able to adapt and improve their production practices, and to make their families and communities aware of the importance of the quality of the products consumed (Mo B and Za B). Finally, by pooling production volumes and sales efforts, the formation of producer groups opens up new commercial outlets (organic sales outlets planned in each region). As local governance issues are fully delegated to producers, the PGS requires limited bureaucracy for certification and management of the standard's content. It thus provides the opportunity for a gradual and inexpensive transition to organic agriculture.

The relevance of a guarantee system may be questioned in regions where the organic market is in its infancy, as the presence of a label may be of limited interest in direct sales. When the consumer and the producer have the opportunity to interact, trust is built through dialogue; even more so when they are part of the same community and consumers have the opportunity to see the farm by themselves. Labels become useful in supply chains with intermediaries, or in markets where organic production represents a real advantage and where the risk of opportunism from producers/intermediaries who want to take advantage of the market without respecting production rules (EAOPS) is high. However, this risk does not yet exist in Masasi and Zanzibar, and a "healthy and local" label is sufficient for now in Arusha. As of today, the PGS seems to have more benefits in terms of dissemination of knowledge and creation of networks than it has in terms of market added value.

Producer groups suffer from weak insertion in their institutional environment (markets, consumers, public authorities...). Even though organic farming has many benefits for society (less hazardous for health, ecologically sustainable, low production costs…), it may be difficult for producers to bear the constraints of environment-friendly production and to invest time and efforts in PGS certification without incentives. As we saw, there are numerous sources of motivation for farmers to contribute in such systems. Nonetheless, most farmers rely on agriculture for their income, and neither markets nor public authorities provide stable financial incentive for now. On the national market, volumes are inadequate: production is insufficient to establish a stable market in some regions (Zanzibar, Masasi), and demand is saturated in others (Arusha, Morogoro); the number of commercial outlets with premium prices is limited, which leads to low market resilience (Arusha, Zanzibar); and the population is not very aware of the issues of organic agriculture. The opening of specifically organic outlets (already existing in Dar es Salaam, Morogoro and Masasi, under development in Arusha and Zanzibar) is a necessary prerequisite for the establishment of a stable market, and facilitating the establishment of contracts between producer groups and private actors (processors, restaurants, hotels, shops, etc.) or public actors in the sector (canteens, schools, hospitals, etc.) would allow for the multiplication of commercial outlets while ensuring the economic viability of the supply chains. In this sense, the label could be much better promoted if PGS groups could market their products collectively both at district level (already the case in Arusha and Morogoro) and nationally (under development) through specific supply chains. The connection of the multiple Kilimo Hai production pools, along with the improvement of transport and storage conditions for the products, would help to maintain and enhance their quality, diversify the supply of certified products, and distribute production surpluses and gaps within the territory, while multiplying the number of possible commercial outlets.

In addition, the formation of a national PGS network would open the possibility for new actors to join the system (transporters, processors, businesses, associations, etc.) and to contribute to the extent of their capacities. In fact, as consumers are not involved in the PGS, this model does not produce a link between producers and consumers. The proper functioning of the control system is guaranteed by the accreditation performed by TOAM employees. Although this model allows for a certain administrative efficiency, the lack of consumer involvement does not allow them to take ownership of the standard. An appropriation of the PGS by local actors could allow for a better acknowledgement of the label in the communities, but would require a greater coordination effort between the different groups. The insertion of the standard in its environment is all the more necessary since the support of public authorities for the PGS is non-existent.

The EAOPS standard is publicly owned by EAC governments, but there is very little awareness or recognition of PGS certification. This may be due to very low availability of information. There is a distinct lack of transparency that does not facilitate understanding of how the PGS works, what is at stake, and what the interests are, which may explain the low level of investment by most stakeholders.

A direct relationship with local authorities or government could be a legitimacy factor and a potential source of funding. However, it could also reinforce the "top down" structure of the system and a redistribution of rights that would not allow for initiative and innovation by participants.

Ultimately, the PGS has a vertical organization that leaves relatively little room for producer empowerment. The groups are not formed by the initial will of the producers, but by the intervention of NGOs. They are accredited by a higher authority (TOAM) over which they have no control (except for a right of appeal during the accreditation process). Producers have to comply with production standards (EAOPS) over which they have no rights (and about which they are not very well informed).

Similarly, the groups rely heavily on the support of local NGOs for their operational activities (marketing, training, etc.). This top-down organization leads to several structural risks. Some producers may have difficulty seeing the relevance of a guarantee system in which they are only marginally involved. There is therefore a risk of a mismatch between the requirements of the standard and the expectations of its members. Because producers have no right to contribute to the content of the standard, the EAOPS and associated training may not be adapted to local production conditions (lack of water, raw material for compost, etc.). Finally, the entire certification system depends on TOAM employees who, in spite of a shuttling process with local supporting NGOs during the accreditation process, have the final right to opt out for local group certification. The entire system thus relies on a small number of people and could collapse if they ran out of external funding or defaulted, as was the case in Uganda with the NOGAMU crisis. To establish a real common property regime at the level of the PGS as a whole, representation and involvement of producer members would be necessary in decisions regarding the management of the standard on a large scale (producer representatives at the TOAM General Assembly, bridges between PGS groups and the TOAM board...). A more horizontal governance structure may allow the voice of producers to be heard and ensure that the system is well adapted to local conditions.

Contents

  Foreword ................................................................................................................................................. 2 1. Introduction ..................................................................................................................................... 4 2. Research questions and method ......................................................................................................... 4 3. Results ................................................................................................................................................ 5 3.1. Institutional context of PGS certification in Tanzania .................................................................. 5 3.2. Collective decision-making processes and repartition of rights and powers ............................... 7 3.3. Impacts of the Kilimo Hai PGS on producers .............................................................................. 10 References ............................................................................................................................................. 16 Key elements

Figure 2 -

 2 Figure 2 -Tanzanian PGS structure

Figure 6 -

 6 Figure 6 -Main benefits of PGS participation according to surveyed producers (N=59).

Figure 7 -

 7 Figure 7 -Main difficulties for organic certification according to surveyed producers (N=56).


S G O U T T E

A Dubois

S D Howard

R M Ar Q U E Z ‡

J J L Rowley § ¶

J M Dehling

P Grandcolas

R C Xiong

F L E G E N D R E

How the environment shapes animal signals: a test of the acoustic adaptation hypothesis in frogs

.

Based on the AAH, bioacousticians have predicted which call features should be selected in a given environment, focusing primarily on vegetation structure

Introduction

Long-distance acoustic communication is used in many species of insects, birds, mammals and anurans and is of paramount importance for reproductive success in many of these taxa. When travelling from sender to receiver, acoustic signals face environmental constraints [START_REF] Ey | The "acoustic adaptation hypothesis" -a review of the evidence from birds, anurans and mammals[END_REF]. In forested areas, signals with lower dominant frequency, narrower frequency range, longer duration and low amplitude or frequency modulation are less attenuated or distorted and should therefore be favoured for long-distance communication. In open spaces, short, frequency-modulated signals should be selected [START_REF] Morton | Ecological sources of selection on avian sounds[END_REF][START_REF] Morton | On the occurrence and significance of motivation-structural rules in some bird and mammal sounds[END_REF][START_REF] Marten | Sound transmission and its significance for animal vocalization[END_REF][START_REF] Wiley | Physical constraints on acoustic communication in the atmosphere: implications for the evolution of animal vocalizations[END_REF][START_REF] Richards | Reverberations and amplitude fluctuations in the propagation of sound in a forest: implications for animal communication[END_REF]. In addition, the ground attenuates or reflects sound waves depending on their frequency and on ground porosity. This 'ground effect' favours signals with frequencies above 0.5-1.0 kHz, whereas lower frequencies are attenuated [START_REF] Morton | Ecological sources of selection on avian sounds[END_REF][START_REF] Wiley | Physical constraints on acoustic communication in the atmosphere: implications for the evolution of animal vocalizations[END_REF]. Finally, ambient noise may partially or totally mask an acoustic signal if the frequency ranges of the two sounds overlap, and would thus favour signals with frequencies outside of the ambient noise frequency range [START_REF] Klump | Bird communication in the noisy world[END_REF][START_REF] Nemeth | Blackbirds sing higher-pitched songs in cities: adaptation to habitat acoustics or side-effect of urbanization?[END_REF][START_REF] Cunnington | Plasticity in the vocalizations of anurans in response to traffic noise[END_REF][START_REF] Goodwin | Shift of song frequencies in response to masking tones[END_REF]. All these call features are thus potentially adaptive to the environment they are produced in.

Studies of the AAH in birds, mammals and anurans have so far yielded inconsistent results with some studies verifying the predictions mentioned above and others finding no impact of the environment on call features or even an opposite relationship to the expected trends (see references in [START_REF] Ey | The "acoustic adaptation hypothesis" -a review of the evidence from birds, anurans and mammals[END_REF]. For example, in [START_REF] Bertelli | Body mass and habitat correlates of song structure in a primitive group of birds[END_REF], the songs of tinamous living in open habitats were higher-pitched and had a wider frequency bandwidth than those of their relatives living in closed habitats, in accordance with the AAH. However, [START_REF] Blumstein | Can the acoustic adaptation hypothesis predict the structure of Australian birdsong?[END_REF] and [START_REF] Saunders | The evolution of song structure in southern African birds: an assessment of the acoustic adaptation hypothesis[END_REF] found only weak support of the AAH when examining spectral and temporal characteristics of songs and controlling for phylogenetic effect in 121 and 40 bird species, respectively. [START_REF] Peters | Long-distance call evolution in the Felidae: effects of body weight, habitat, and phylogeny[END_REF] examined long-distance roars of 27 species of Felidae (taking into account body size and phylogenetic relationships) and found that their dominant frequency was lower in open than in closed habitats, contradicting the AAH prediction. These contradictory results are, at least partially, explained by a very broad categorization of habitats, such as 'open' vs. 'closed', which oversimplifies complex habitat conditions [START_REF] Bosch | Are frog calls modulated by the environment? An analysis with anuran species from Bolivia[END_REF][START_REF] Goutte | Environmental constraints and call evolution in torrent-dwelling frogs[END_REF]. Thus, testing predictions stemming from the AAH requires examination of the acoustic constraints in a microhabitat-specific context [START_REF] Goutte | The importance of ambient sound level to characterise anuran habitat[END_REF][START_REF] Goutte | Environmental constraints and call evolution in torrent-dwelling frogs[END_REF] when it is not possible to measure the transmission properties of all the habitats [START_REF] Penna | Frog call intensities and sound propagation in the South American temperate forest region[END_REF][START_REF] Penna | Effect of natural and synthetic noise on evoked vocal responses in a frog of the temperate austral forest[END_REF][START_REF] Llusia | Call transmission efficiency in native and invasive anurans: competing hypotheses of divergence in acoustic signals[END_REF]. Using continuous measurements of the habitat, [START_REF] Maddieson | Human spoken language diversity and the acoustic adaptation hypothesis[END_REF] showed a correlation between habitat characteristics and the number and cluttering of consonants in 663 local human languages, which are comparable to the complexity and the importance of high-frequency components in animal vocalizations.

In torrent habitats, the noise of flowing water masks low-frequency vocalizations (usually below 2 kHz), and most anurans call below 5 kHz (e.g. [START_REF] Hoskin | Ecology and taxonomy-driven deviations in the frog call-body size relationship across the diverse Australian frog fauna[END_REF]Gingras et al., 2013a,b;[START_REF] Goutte | Environmental constraints and call evolution in torrent-dwelling frogs[END_REF]. Many anuran calls are therefore masked by torrent noise (Dubois, 1977a,b). Based upon the AAH, one would expect vocalizations of torrent-breeding frogs to be adapted to these noisy conditions, and also to the surrounding vegetation structure of these streams. Consequently, all other things being equal, advertisement calls emitted by torrent-breeding frogs should differ from those produced by frogs calling in other habitats because they are subject to different acoustic constraints, particularly high ambient noise level [START_REF] Goutte | The importance of ambient sound level to characterise anuran habitat[END_REF].

Torrent-breeding ranids generally produce shorter and higher-pitched advertisement calls than other closely related frogs [START_REF] Arch | Ultrasonic signalling by a Bornean frog[END_REF][START_REF] Boonman | Evolution of high-frequency communication in frogs[END_REF][START_REF] Goutte | Environmental constraints and call evolution in torrent-dwelling frogs[END_REF], although there appears to be no single typical advertisement call type for torrent-breeding frogs. Investigating habitat characteristics at a finer scale, [START_REF] Goutte | Environmental constraints and call evolution in torrent-dwelling frogs[END_REF] identified call characteristics in ranids, which could be adaptive to high ambient noise levels in torrent-breeding frogs: high dominant frequency, short note duration and marked frequency modulations. To investigate these call features further, morphological, environmental and phylogenetic information should be integrated into evolution and adaptation analyses because they may include confounding factors (e.g. [START_REF] Martins | Adaptation and the comparative method[END_REF][START_REF] Olson | How to study adaptation (and why to do it that way)[END_REF]. Indeed, factors linked with the anatomy and physiology of the structures involved in call production directly impact call properties, and body size and air temperature are among these factors for anurans. The dominant frequency (DF) of acoustic signals is generally negatively correlated with body size (e.g. [START_REF] Ryan | The role of body size, phylogeny, and ambient noise in the evolution of bird song[END_REF][START_REF] Ryan | Selection on long-distance acoustic signals[END_REF]Gingras et al., 2013a), and body temperature, directly influenced by air temperature in ectotherms, has an effect on some temporal parameters of the calls produced by these organisms (e.g. [START_REF] Walker | Factors responsible for intraspecific variation in the calling songs of crickets[END_REF][START_REF] Navas | Thermal dependency of calling performance in the eurythermic frog Colostethus subpunctatus[END_REF]. In addition, closely related species are more likely to share similar traits than more distantly related species, owing to common ancestry (e.g. [START_REF] Felsenstein | Phylogenies and the comparative method[END_REF]. All these factors may affect the evolution of acoustic signals, and they should be considered when investigating correlations between habitat and signal characteristics.

In this study, we investigated potential adaptations in the advertisement calls of torrent frogs using a comparative method that includes potential confounding factors (i.e. body size and air temperature). This method complements the historical approach of ancestral state reconstruction used on the same data set in [START_REF] Goutte | Environmental constraints and call evolution in torrent-dwelling frogs[END_REF]. [START_REF] Goutte | Environmental constraints and call evolution in torrent-dwelling frogs[END_REF] reconstructed the evolutionary history of call characteristics and tested whether it followed models of evolution determined by environmental constraints. Ancestral state reconstructions, as used in [START_REF] Goutte | Environmental constraints and call evolution in torrent-dwelling frogs[END_REF], provide hypotheses on the chronology of habitat and call feature changes. Changes in calls can be inferred as historically concomitant with a change in habitat, but it does not mean that they are necessarily adaptive. Here, to complement the results found in [START_REF] Goutte | Environmental constraints and call evolution in torrent-dwelling frogs[END_REF], we statistically test specific predictions derived from the AAH. We examined the correlation between putatively adaptive vocalization characteristics (i.e. dominant frequency, frequency and amplitude modulation, bandwidth, note duration and number of notes per call; [START_REF] Goutte | Environmental constraints and call evolution in torrent-dwelling frogs[END_REF] and (i) ambient noise level, as suggested in [START_REF] Goutte | Environmental constraints and call evolution in torrent-dwelling frogs[END_REF], and (ii) in conjunction with vegetation density, as hypothesized under the AAH paradigm [START_REF] Morton | Ecological sources of selection on avian sounds[END_REF][START_REF] Morton | On the occurrence and significance of motivation-structural rules in some bird and mammal sounds[END_REF][START_REF] Marten | Sound transmission and its significance for animal vocalization[END_REF][START_REF] Wiley | Physical constraints on acoustic communication in the atmosphere: implications for the evolution of animal vocalizations[END_REF][START_REF] Richards | Reverberations and amplitude fluctuations in the propagation of sound in a forest: implications for animal communication[END_REF].

Thus, after reconstructing a molecular phylogeny and identifying the changes in calls that occurred concurrently with habitat changes [START_REF] Goutte | Environmental constraints and call evolution in torrent-dwelling frogs[END_REF], we now investigate whether frogs calling in habitats with similar constraint profiles produce similar calls as our current understanding of the AAH suggests. In other words, whereas [START_REF] Goutte | Environmental constraints and call evolution in torrent-dwelling frogs[END_REF] tested whether changes in calls historically followed changes in calling habitats, here we test predictions derived from the AAH on whether and how calls vary according to environmental conditions. Each approach provides complementary information regarding the adaptive nature of call traits. We conducted these analyses both with broad habitat categories and with a fine-scale habitat description as suggested in [START_REF] Goutte | Environmental constraints and call evolution in torrent-dwelling frogs[END_REF].

Materials and methods

Study sites and specimen collection

Sampling efforts were primarily focused on torrentdwelling species, these being the most time-consuming taxa to record. We targeted species of the family Ranidae because this large clade includes four torrent-dwelling groups: Amolops [START_REF] Cope | Sketch of the primary groups of Batrachia s[END_REF]Odorrana Fei, Ye & Huang, 1990;Staurois Cope, 1865;and the clade composed of Clinotarsus Mivart, 1869, Huia Yang, 1991and Meristogenys Yang, 1991. Fieldwork was conducted in Asia, as most torrent-dwelling ranid species occur in this region. Data were collected at 11 localities within five Asian territories: Preah Vihear Province, Cambodia, from 11 to 20 December 2010; West Kalimantan Province, Indonesia, from 9 June to 3 August 2011; Sichuan, Hunan and Hainan provinces, China, from 7 June to 19 July 2012; and Sabah Province, Malaysia, from 8 to 24 August 2012 (Fig. S1 and Table S1). We collected a total of 112 individuals referred to 37 species of the families Ranidae, Rhacophoridae, Dicroglossidae and Microhylidae for which we recorded vocalizations and fine-scale measurements characterizing their calling sites (Table S2). In addition, we recorded and collected 18 individuals of 10 other species within these families, but without any precise data about their calling sites (Table S2). We measured snout-vent length (SVL) of each specimen to the nearest 0.1 mm with a SPI dial calliper (Table S3).

Vocalization recording and analysis

Advertisement calls were recorded from a distance between 0.5 and 2 m with a Marantz PMD671 recorder and a Sennheiser ME64 microphone or an Avisoft CM16 microphone. Sampling rate was 44.1 or 96 kHz at 16 bits. The Avisoft CM16 microphone and sampling rate of 96 kHz allowed recording sounds up to 44 kHz (whereas the other setting allowed recording up to 22 kHz); this equipment was used to record species with particularly high call frequencies (up to 23 kHz for Huia cavitympanum (Boulenger, 1983)) to ensure we captured all spectral components of the calls.

To supplement our data set, recordings of 38 species were gathered from scientific sound collections or extracted from commercial compact discs (Table S4). In total, the recordings of 225 individuals in 79 species were used in this analysis, representing about 21,500 advertisement call notes. We measured the following acoustic traits with the software Praat [START_REF] Boersma | Praat, a system for doing phonetics by computer[END_REF] and the package seewave [START_REF] Sueur | Seewave, a free modular tool for sound analysis and synthesis[END_REF] in the R environment (R Core Team, 2013): dominant frequency (DF), frequency band width (FBW), DF modulation (DFM), amplitude modulation (AM), note duration and number of notes per call (Table S5).

Habitat measurements and categorization

Once an individual had been captured, we measured habitat descriptors shown to be of importance in anuran habitat and calling site choice [START_REF] Gillespie | Herpetofaunal richness and community structure of offshore islands of Sulawesi, Indonesia 1[END_REF][START_REF] Keller | The importance of environmental heterogeneity for species diversity and assemblage structure in Bornean stream frogs[END_REF][START_REF] Goutte | The importance of ambient sound level to characterise anuran habitat[END_REF]: depth, width and average slope of the closest water body, air temperature, canopy coverage, ambient noise sound pressure level (SPL) at the exact individual calling location and maximal SPL in a 2 m radius around the frog calling post (Table S2). Ambient noise levels were measured with an American Recorder Technologies SPL meter on A-weighting (precision: 1 dB at 1 kHz) and one-second integration time. Ambient air temperature was measured with a probe-K digital thermometer (Hanna) to the nearest 0.1 °C. The canopy coverage was measured the day following the capture with a convex-A spherical densitometer. We measured maximal depth and mean diameter for ponds and the width of the water body, and the maximum depth across that width at the focal male level for streams.

We produced a broad-type coding for calling sites based on these precise measurements with multifactorial analysis and cluster analysis following [START_REF] Goutte | The importance of ambient sound level to characterise anuran habitat[END_REF]. It resulted in four categories of calling sites: 'torrents', 'ponds', 'rivers/lakes' and 'forest' (Table S2).

Molecular phylogeny

We used the phylogenetic hypothesis reconstructed in Bayesian inference based on five molecular markers and 148 taxa [START_REF] Goutte | Environmental constraints and call evolution in torrent-dwelling frogs[END_REF]Fig. S2, Table S6). This phylogeny includes the species for which we collected environmental and acoustic data, and it does not differ significantly from previously published phylogenies of the group (e.g. [START_REF] Pyron | A large-scale phylogeny of Amphibia including over 2800 species, and a revised classification of extant frogs, salamanders, and caecilians[END_REF].

Association of vocalization characteristics with habitats

All statistical analyses were conducted in the R environment (R Core Team, 2013). To test the hypothesis that vegetation density and ambient noise level affected the evolution of vocalization characteristics, we ran phylogenetic generalized least square (PGLS) multiple regression models using the function pgls in the R package caper [START_REF] Orme | Issues in the classification of multimodal communication signals[END_REF] including noise level (SPL) and canopy coverage (used as a proxy for vegetation density) as predictor variables. Given that temperature and body size influence temporal properties of calls and dominant frequency, we included body size and air temperature as predictors in the corresponding models: body size was incorporated in the PGLS model with dominant frequency as dependent variable, and air temperature was incorporated in the PGLS models with note duration and number of notes as dependent variables. We also tested whether vocalization traits differed among calling site categories (i.e. 'forests', 'ponds', 'rivers/lakes' and 'torrents'). Vocalization characteristics were averaged for each individual and for all individuals in a species.

Multiple regression models require uncorrelated predictor variables. If this condition is not met, estimates become unstable [START_REF] Quinn | Experimental Design and Data Analysis for Biologists[END_REF] and the risk of type II error increases. Therefore, we tested each pair of variables for correlation prior to running the models. All acoustic variables were log-transformed and the square root of body size was used to meet or approach normality of the regression residuals for each model.

Behavioural traits are supposedly more labile than morphological traits [START_REF] Blomberg | Testing for phylogenetic signal in comparative data: behavioral traits are more labile[END_REF], but that does not necessarily mean that they do not retain any trace of their evolutionary history and therefore lack phylogenetic signal [START_REF] De Queiroz | The usefulness of behavior for phylogeny estimation: levels of homoplasy in behavioral and morphological characters[END_REF][START_REF] Legendre | The evolution of social behaviour in Blaberid cockroaches with diverse habitats and social systems: phylogenetic analysis of behavioural sequences[END_REF]. The strength of the phylogenetic signal (k) in the residuals of the models was optimized by maximum likelihood when running the models using the function pgls as implemented in caper.

Species of the genus Staurois use visual displays in addition to vocalizations during advertisement [START_REF] Grafe | Multimodal signaling in male and female foot-flagging frogs Staurois guttatus (Ranidae): an alerting function of calling[END_REF][START_REF] Preininger | Communication in noisy environments Ii: visual signaling behavior of male foot-flagging frogs Staurois Latopalmatus[END_REF][START_REF] Grafe | Multimodal communication in a noisy environment: a case study of the Bornean rock frog Staurois parvus[END_REF], which may alter the selection strength on vocalizations and thus decrease the potential adaptive signal contained in calls (see [START_REF] Goutte | Environmental constraints and call evolution in torrent-dwelling frogs[END_REF]. However, the low incidence of visual communication in the sampled species (visual communication for five species forming a monophyletic group) prevents us from including it as a variable in the analyses [START_REF] Mundry | Statistical Issues and Assumptions of Phylogenetic Generalized Least Squares[END_REF].

Results

Associations between habitats and vocalization characteristics

Half of the PGLS models contained significant phylogenetic signal (Tables 1 and2). Frog vocalization dominant frequency, frequency modulation and frequency bandwidth were significantly different among calling site categories (Fig. 1 and Table 1). All three spectral characteristics had higher values in vocalizations of torrent-dwelling species than in species vocalizing in other categories of calling sites, although call frequency bandwidth was not significantly different between torrent and forest frogs. Call temporal characteristics (note duration, amplitude modulation and number of notes per call) were not significantly different among calling site categories (Fig. 1 and Table 1).

As expected, call dominant frequency was significantly correlated with noise level (Fig. 2 and Table 2). Frequency modulation was also significantly correlated with noise level, which did not correspond to a prediction stemming from the AAH. None of the call characteristics examined was correlated with canopy coverage (Fig. 2 and Table 2), contradicting the AAH.

Discussion

The present study supports several, but not all, predictions inferred from the acoustic adaptation hypothesis as defined by [START_REF] Rothstein | Vocal dialects and their possible relation to honest status signalling in the brownheaded cowbird[END_REF]. Within our data set, the spectral properties of vocalizations were correlated with habitat categories and ambient noise level, but the temporal properties of calls were not significantly correlated with habitat, noise level or canopy coverage.

Spectral properties of calls as possible adaptations to noise

The impact of noise on communication efficiency and evolution has been increasingly studied lately [START_REF] Brumm | Acoustic communication in noise[END_REF][START_REF] Slabbekoorn | Birdsong and anthropogenic noise: implications and applications for conservation[END_REF][START_REF] Barber | The costs of chronic noise exposure for terrestrial organisms[END_REF][START_REF] Pijanowski | Soundscape ecology: the science of sound in the landscape[END_REF]. Noise, like that produced by fast-flowing water, constitutes an important constraint for acoustically signalling animals, partially or completely masking the signals of many species. Consequently, animals signalling in noisy environments are expected to produce higher-frequency sounds than animals signalling in quieter habitats. Spectral characteristics (dominant frequency, frequency modulation and frequency bandwidth) differ significantly between torrent-dwellers' calls and calls of species living in other habitats, whereas temporal characteristics do not vary significantly between habitats. N = number of species included in the model; DF = dominant frequency; DFM = dominant frequency modulation; FBW = frequency bandwidth; AM = amplitude modulation. Habitat categories 'pond', 'river/lake' and 'forest' are compared to the habitat category 'torrent'. For each model, the estimated value for the phylogenetic signal (k), AICc and log-likelihood are reported. For each independent variable, the parameter estimate (b) and its associated standard error (SE), t-statistic and P-value are given. Significant correlations are indicated by asterisks (*). 1). Unsurprisingly, our results show that spectral properties of frog calls are related to the level of ambient noise at the calling site. Even when considering body size and phylogenetic nonindependence, call dominant frequency was strongly correlated with noise level, with torrent-breeding species calling at higher frequencies than species calling in other habitats. Ranid species advertising in the noisy environment of fast-flowing streams would thus escape noise masking with their higher-pitched calls. Given that high dominant frequencies seem to have evolved when these ranids started to occupy noisy habitats [START_REF] Goutte | Environmental constraints and call evolution in torrent-dwelling frogs[END_REF], this correlation is congruent with an adaptation hypothesis, even though it does not prove it [START_REF] Martins | Adaptation and the comparative method[END_REF].

The correlation between ambient noise and dominant frequency of animal acoustic signals has been explored in a few studies, yielding heterogeneous results. For example, urban great tits were found to sing at higher frequencies than rural populations [START_REF] Slabbekoorn | Birds sing at a higher pitch in urban noise[END_REF]. In anurans, positive [START_REF] Hoskin | Road impacts on abundance, call traits, and body size of rainforest frogs in northeast Australia[END_REF] and negative [START_REF] Hoskin | Ecology and taxonomy-driven deviations in the frog call-body size relationship across the diverse Australian frog fauna[END_REF] correlations were found, but body size and phylogenetic relationships among species, two important factors, were not considered in these studies. Taking into account these two factors, Vargas-Salinas & Am ezquita (2014) found no significant difference in call dominant frequency between stream-and nonstream-dwelling species, whereas R€ ohr et al. (2016) found higher dominant frequencies in stream-dwelling frogs. This discrepancy in results may be attributed to the broad categorization of habitats ('stream' vs. 'other'), a limitation we tried to overcome in our study using precise values of ambient noise levels.

Noise was also correlated with calls' frequency modulation: torrent-dwelling species produced calls with more pronounced frequency modulations. This result deviates from predictions derived from the AAH literature [START_REF] Wiley | Physical constraints on acoustic communication in the atmosphere: implications for the evolution of animal vocalizations[END_REF][START_REF] Richards | Reverberations and amplitude fluctuations in the propagation of sound in a forest: implications for animal communication[END_REF]. Either of the two hypotheses could explain our results: (i) by widening the frequency range, modulation in call frequency reduces the extent to which signals are masked by noise-the signal would thus only be affected for frequencies overlapping with the noise; (ii) a third variable is correlated with both frequency modulation and noise, resulting in a spurious correlation in this particular data set. The third variable could be the amount of air turbulence: [START_REF] Wiley | Physical constraints on acoustic communication in the atmosphere: implications for the evolution of animal vocalizations[END_REF] predicted more pronounced frequency modulation in vocalizations of species calling in turbulent habitats, and turbulence is linked to noise here because the most important noise source in our data set is fast-flowing water, which creates air turbulence. It would be worth investigating air turbulence further, as it may explain the variability found in frequency modulation within habitat categories (high variability in ponds, rivers and lakes, and low variability in forests and torrents).

The calls of torrent species showed a significantly broader frequency bandwidth than those of species calling in other microhabitats, except for forest species. However, frequency bandwidth was not correlated with noise level. This suggests that a broad frequency bandwidth may be selected for in torrent species, but not only due to the high noise level of torrents, or, conversely, that a narrow frequency bandwidth could be selected in other habitats. For example, in lakes or ponds, the presence of several species signalling simultaneously likely results in acoustic competition, which may drive each species to call within a narrow spectral 'niche' within this phonocenosis [START_REF] Amiet | A new Leptopelis of the Cameroon forest zone (Amphibia, Anura, Hyperoliidae)[END_REF], that is at a specific frequency range (e.g. Dubois, 1977a;[START_REF] Duellman | Acoustic resource partitioning in anuran communities[END_REF][START_REF] Amiet | Some aspects of the biology of the Cameroonian anurans[END_REF][START_REF] Sinsch | Acoustic niche partitioning in an anuran community inhabiting an Afromontane wetland (Butare, Rwanda)[END_REF]. This hypothesis has been called 'acoustic niche hypothesis' [START_REF] Krause | Bioacoustics, habitat ambience in ecological balance[END_REF] and should be explored further.

No acoustic adaptation to vegetation structure

Vegetation reflects and absorbs sound waves, creating interference. The density and the height of vegetation modify the amount of air turbulence, which also impact sound waves. Vegetation density is thus supposed to be a factor of prime importance for vocalization adaptations to the environment [START_REF] Morton | Ecological sources of selection on avian sounds[END_REF][START_REF] Morton | On the occurrence and significance of motivation-structural rules in some bird and mammal sounds[END_REF][START_REF] Marten | Sound transmission and its significance for animal vocalization[END_REF][START_REF] Wiley | Physical constraints on acoustic communication in the atmosphere: implications for the evolution of animal vocalizations[END_REF][START_REF] Richards | Reverberations and amplitude fluctuations in the propagation of sound in a forest: implications for animal communication[END_REF]. Here, we used canopy coverage as a proxy for vegetation density because the vegetation profiles of the study sites fell mostly into two categories: either rather dense tropical forests with limited understory vegetation and numerous high trees, or completely open spaces with vegetation limited to patchy grasses and shrubs. In other words, each canopy coverage value corresponded roughly to a single vegetation profile and we thus consider this proxy appropriate for this data set.

Our results show no correlation between canopy coverage and call characteristics in the present data set. We expected species calling in more open microhabitats to produce calls with higher dominant frequency, broader frequency bandwidth and more frequency modulations [START_REF] Wiley | Physical constraints on acoustic communication in the atmosphere: implications for the evolution of animal vocalizations[END_REF], which was not the case. This suggests that other environmental constraints, such as noise level, may constitute stronger selective pressures than vegetation density for vocalization transmission in the habitats we studied. [START_REF] Weir | The role of ecological constraint in driving the evolution of avian song frequency across a latitudinal gradient[END_REF] pointed out, for instance, that in addition to excess attenuation in tropical forests (due to dense vegetation), the high-frequency noise produced by insects and acoustic competition were important constraints on song evolution in tropical birds.

The importance of confounding variables and phylogenetic information in the study of acoustic adaptations

As expected from previous studies (e.g. [START_REF] Hoskin | Ecology and taxonomy-driven deviations in the frog call-body size relationship across the diverse Australian frog fauna[END_REF][START_REF] Gillooly | The energetic basis of acoustic communication[END_REF], we showed here that body size and air temperature were significantly correlated with some of the vocalization characteristics we investigated. These correlations may alter the relationships found between environmental conditions and call characteristics, as well as the conclusions drawn for the adaptive nature of vocalizations. These results underline the importance of considering these confounding factors when studying potential adaptations in anuran vocalizations, and likely in other characters and taxa.

In addition, we emphasized the need to incorporate phylogenetic information in the analyses when testing the AAH, regardless of the supposed phylogenetic signal of a trait. The presence of phylogenetic signal within frog calls has been debated in previous studies. [START_REF] Cannatella | Phylogeny of frogs of the Physalaemus pustulosus species group, with an examination of data incongruence[END_REF] 2010) also demonstrated how choices in acoustic character delimitation may alter the outcome of phylogenetic signal analyses. The detection of a phylogenetic signal in frog vocalization thus appears to be group-or method-dependent.

Towards more integrative tests of the acoustic adaptation hypothesis

The role of environmental constraints on acoustic communication has been widely investigated but yielded mixed results regarding the support of the acoustic adaptation hypothesis. Here, the spectral characteristics of torrent frog advertisement calls were found to be potentially adaptive and noise level appeared to be the major acoustic constraint impacting their evolution. Torrent frogs seem to have evolved higher-frequency vocalizations in response to high ambient noise levels, similarly to urban great tits [START_REF] Slabbekoorn | Birds sing at a higher pitch in urban noise[END_REF], ecotone little greenbuls [START_REF] Slabbekoorn | Habitat-dependent song divergence in the little greenbul: An analysis of environmental selection pressures on acoustic signals[END_REF] or pygmy marmosets (de la [START_REF] De La Torre | Environmental correlates of vocal communication of wild pygmy marmosets, Cebuella pygmaea[END_REF]. However, predictions based on the AAH regarding the topology of habitats were not corroborated by the outcome of our analyses.

This mixed support for the AAH concurs with previous investigations in other groups of frogs (e.g. Vargas-Salinas & Am ezquita, 2014), birds (e.g. [START_REF] Saunders | The evolution of song structure in southern African birds: an assessment of the acoustic adaptation hypothesis[END_REF][START_REF] Blumstein | Can the acoustic adaptation hypothesis predict the structure of Australian birdsong?[END_REF] and mammals (e.g. [START_REF] Peters | Long-distance call evolution in the Felidae: effects of body weight, habitat, and phylogeny[END_REF]. A mixed support is unsurprising given the complex nature of acoustic signals and constraints, the number of factors shaping signal evolution, and their intertwined roles. Although a call is perceived as a single signal, decomposing it into spectral and temporal characteristics reveals that these features may evolve in a decoupled manner. Most acoustic properties of a given habitat are frequencydependent, so that the environment is expected to constrain mainly call spectral properties. Temporal characteristics, on the other hand, may be more affected by other selection pressure, such as sexual selection.

Our mixed results also demonstrate the need to simultaneously consider factors directly (air temperature) or indirectly (body size, phylogenetic position) affecting signal production when testing the AAH. Other factors, not included here, should be considered in the future such as the roles of (inter-or intra)sexual selection, sensory and physiological limitations (in the signaller and receiver), predation or heterospecific acoustic competition. For example, a limited hearing range or a marked preference for a given call feature in females may overrule environmental constraints on call evolution and need to be considered. Signals evolve as an integrated element of a communication system in a complex environment and in a historical context. More integrative tests of the AAH should also consider factors not directly linked to signal production or environmental acoustic constraints but that may nonetheless impact signal evolution.

In our data set, species of the genus Staurois advertise in torrents both acoustically and visually [START_REF] Grafe | Multimodal signaling in male and female foot-flagging frogs Staurois guttatus (Ranidae): an alerting function of calling[END_REF][START_REF] Preininger | Communication in noisy environments Ii: visual signaling behavior of male foot-flagging frogs Staurois Latopalmatus[END_REF][START_REF] Grafe | Multimodal communication in a noisy environment: a case study of the Bornean rock frog Staurois parvus[END_REF]. The use of an additional communication channel offers new possibilities for communication but also presents new constraints [START_REF] Orme | Issues in the classification of multimodal communication signals[END_REF]. [START_REF] Grafe | Multimodal signaling in male and female foot-flagging frogs Staurois guttatus (Ranidae): an alerting function of calling[END_REF] suggested that vocalizations of Staurois guttatus (G€ unther, 1858) have an alerting function prompting a general orientation towards the caller but mostly lacking informative content, which is delivered visually. These vocalizations may thus be less constrained by the environment than those of species using only acoustic communication. However, the rarity of visual communication in the present data set prevents us from drawing conclusions on its impact on call evolution because of the lack of statistical power. It would be worth investigating call evolution in other frogs using bimodal communication during advertisement, such as Micrixalus Boulenger, 1888 or Hylodes Fitzinger, 1826 [START_REF] Preininger | Multimodal signaling in the Small Torrent Frog (Micrixalus saxicola) in a complex acoustic environment[END_REF][START_REF] De S A | Sophisticated Communication in the Brazilian Torrent Frog Hylodes japi[END_REF], and comparing the results with other taxa using bimodal communication to better understand the evolution of multimodal communication in animals [START_REF] Rosenthal | Visual and acoustic communication in non-human animals: a comparison[END_REF].

The latest tests of the AAH, including ours, have brought mixed outcomes supporting some aspects of the acoustic adaptation hypothesis and refuting others. At this point, the task is not so much to continue testing the AAH, but rather to assess more comprehensively the extent to which the environment has shaped signal evolution. To do so, we suggest that future investigations on the evolution of communication should be as integrative as possible, considering potentially confounding selection pressure such as sexual selection or sensory biases together with the factors included here. The organisms studied must also be more taxonomically diversified than they are now if one wants to obtain a general understanding on the evolution of animal communication [START_REF] Rosenthal | Taxonomic bias in animal behaviour publications[END_REF][START_REF] Troudet | Taxonomic bias in biodiversity data and societal preferences[END_REF].

Fig. 1

 1 Fig. 1 Vocalization characteristics for each calling site category. (a) Dominant frequency (DF), (b) dominant frequency modulation (DFM), (c) frequency bandwidth (FBW), (d) note duration, (e) amplitude modulation (AM) and (f) number of notes per call. Stars indicate a significant difference to the 'torrent' calling site category in the corresponding PGLS model (see Table1).

Fig. 2

 2 Fig. 2 Relationships between vocalization parameters and calling site characteristics. Regressions from PGLS results are represented by solid red lines.

Table 1

 1 PGLS models for call characteristics and habitat types.

				Variable statistics			Model statistics
	N	Dep. var.	Indep. var.	b	SE	t	P -value	k	AICc	Loglik
	39	DF	Size	À0.25	0.07	À3.79	0.00***	0.73	63.53	À25.88
			Pond	À1.02	0.26	À3.91	0.00***
			River/lake	À1.11	0.23	À4.80	0.00***
			Forest	À1.25	0.44	À2.80	0.01**
	39	DFM	Pond	À1.46	0.58	À2.51	0.02*	0.00	154.07	À72.46
			River/lake	À2.17	0.68	À3.21	0.00**
			Forest	À4.10	0.98	À4.18
	39	FBW	Pond	À0.44	0.19	À2.29	0.03*	0.92	30.07	À10.46
			River/lake	À0.50	0.16	À3.18	0.00**
			Forest	À0.47	0.33	À1.42	0.16
	39	AM	Pond	0.39	0.62	0.62	0.54	0.00	159.43	À75.14
			River/lake	À0.14	0.72	À0.20	0.85
			Forest	1.38	1.05	1.32	0.20
	36	Notes per call	Air temp.	0.00	0.06	À0.06	0.95	1.00	85.35	À35.90
			Pond	0.03	1.08	0.02	0.98
			River/lake	À0.47	0.80	À0.59	0.56
			Forest	À0.03	2.10	À0.02	0.98
	28	Note duration	Air temp.	0.09	0.06	1.63	0.12	0.00	76.24	À31.75
			Pond	0.16	0.38	0.43	0.67
			River/lake	À0.15	0.43	À0.35	0.73
			Forest	0.35	0.88	0.39	0.70

Table 2

 2 PGLS models for call characteristics and environmental variables.

				Variable statistics			Model statistics
	N	Dep. var.	Indep. var.	b	SE	t	P -value	k	AICc	Loglik
	28	DF	Size	À0.19	0.12	À1.58	0.13	0.46	46.69	À18.39
			SPL	0.04	0.01	3.49	0.00**
			Canopy cover	0.02	0.03	0.63	0.54
	28	DFM	SPL	0.07	0.03	2.32	0.03*	0.00	107.93	À50.49
			Canopy cover	À0.04	0.08	À0.43	0.67
	28	FBW	SPL	0.01	0.01	0.61	0.55	0.92	29.33	À11.19
			Canopy cover	0.02	0.02	1.26	0.22
	28	AM	SPL	À0.01	0.03	À0.30	0.77	0.00	110.78	À51.91
			Canopy cover	À0.12	0.09	À1.41	0.17
	27	Notes per call	Air temp.	À0.01	0.06	À0.18	0.86	0.97	93.31	À41.74
			SPL	0.00	0.03	0.03	0.98
			Canopy cover	À0.02	0.06	À0.41	0.69
	28	Note duration	Air temp.	0.07	0.04	1.61	0.12	0.80	68.66	À29.46
			SPL	À0.01	0.02	À0.45	0.66
			Canopy cover	À0.04	0.04	À1.03	0.31

Calls' dominant frequency and frequency modulation are significantly correlated with ambient noise level. The other call characteristics are not correlated with ambient noise level or canopy cover. N = number of species included in the model; DF = dominant frequency; DFM = dominant frequency modulation; FBW = frequency bandwidth; AM = amplitude modulation; SPL = ambient noise level. For each model, the estimated value for the phylogenetic signal (k), AICc and log-likelihood are reported. For each independent variable, the parameter estimate (b) and its associated standard error (SE), t-statistic and P-value are given. Significant correlations are indicated by asterisks (*).

  found no phylogenetic signal in vocalizations in nine species of the Physalaemus pustulosus(Cope, 1864) group (now Engystomops pustulosus; see Nascimento et al., 2005), and Tobias (2011) found very weak signal in two genera of African clawed frogs (Xenopus Wagler, 1827). However, Cocroft & Ryan (1995), Wollenberg et al. (2007) and Gingras et al. (2013b) found a phylogenetic signal within the calls of other anuran groups. Robillard et al. (2006) and Goicoechea et al. (

Acknowledgments

We are very thankful to D. Bickford, W. Bin, U. Grafe, D. Iskandar, J. Jianping, W. Jichao, L. Maklarin, A. Ohler and P. Yambun who helped in the field and with the permits; and to A. Boonman and D. Preininger who shared their recordings. We are very thankful to W. H€ odl, C. Miaud, E. Paradis and A. Pyron for their comments on earlier versions of the manuscript. We also thank the Fonoteca Zoologica (www.Fono Zoo.com), Museo Nacional de Ciencias Naturales -CSIC Madrid, for providing frog recordings. Finally, we thank the associate editor, A. Gonzalez-Voyer, and the two anonymous reviewers for their comments on the manuscript.

Funding

This project was supported by internal grants (ATM 'Biodiversit e fossile et actuelle' supported by P. Janvier and S. Peign e) from MNHN, the Ecole Normale Sup erieure de Lyon, the National University of Singapore, the Soci et e des Amis du Mus eum, the Ministerio de Ciencia e Innovacion, Spain (projects TATANKA CGL2011-25062, CGL2010-09700), and the Ministerio de Economia y Competitividad, Spain (project CGL2011-16159-E; PI. R. M arquez).

Data archiving

Raw data of body size, calls and phylogenetic inference will be deposited in a Dryad public repository.

Supporting information

Additional Supporting Information may be found online in the supporting information tab for this article: Figure S1 Map of sampled localities. Figure S2 Phylogenetic hypothesis from the Bayesian Inference analysis with two partitions (arithmetic mean of marginal likelihood = À58545.67). Table S1 Sampled localities. Table S2 Habitat measurement averaged per species. Table S3 Average adult male snout-vent length (SVL), number of specimens (N) and source of data for the anuran species investigated in our study. Table S4 List of species recordings provided by recor-ders other than [initials of the first author]. Table S5 Call variables average values per species. Table S6 GenBank accession numbers.