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The distribution of neutral genetic variation in subdivided populations is driven by the interplay between genetic drift, migration, local extinction and colonization. The influence of environmental and demographic factors has also been increasingly examined in empirical studies, but generally focusing on a single species. An open question is whether these factors will similarly, or idiosyncratically, affect a guild of species occupying the same, though exhibiting different traits, mating systems and histories. We addressed it by comparing the population genetic structure of the four most common species of hermaphroditic freshwater snails in Guadeloupe (Lesser Antilles), which occupy a network of patchily distributed sites experiencing temporal variation in water availability. We analyzed microsatellite variability in 21 to 43 populations per species, and built predictions on how several environmental and demographic variables, quantified from a long-term annual survey, as well as species traits, may affect the distribution of genetic variation. These species displayed similarities, such as fairly high levels of variation, but with marked differences among sites, as well as strong genetic differentiation and limited isolation by distance, which can be explained by passive dispersal (strong role of site connectivity), extinction/colonization dynamics and variation in local population size. They also exhibit differences, largely due to the mating system with less genetic diversity and more genetic differentiation in the two selfing species when compared to the two outcrossing ones. These differences can also be attributed to interspecific interactions resulting from the ongoing invasion of Guadeloupe by one of the species studied, which affects the demography of other species, and, to a limited extent, to local environmental factors. Our comparative approach shows both differences and uniqueness in the way species occupy the same landscape, and provides a possible entry to interspecific interactions in community assembly.

Combining the analysis of spatial and temporal variation when investigating population structure enhances our capacity for unravelling the biotic and abiotic factors responsible for microevolutionary change. This work aimed at measuring the spatial and temporal genetic structure of populations of the freshwater snail Biomphalaria pfeifferi (the intermediate host of the trematode Schistosoma mansoni) in relation to the mating system (self-fertilization), demography, parasite prevalence and some ecological parameters. Snail populations were sampled four times in seven human-water contact sites in the Man region, western Côte d'Ivoire, and their variability was measured at five microsatellite loci. Limited genetic diversity and high selfing rates were observed in the populations studied. We failed to reveal an effect of demographic and ecological parameters on within-population diversity, perhaps as a result of a too small number of populations. A strong spatial genetic differentiation was detected among populations. The temporal differentiation within populations was high in most populations, though lower than the spatial differentiation. All estimates of effective population size were lower than seven suggesting a strong effect of genetic drift. However, the genetic drift was compensated by high gene flow. The genetic structure within and among populations reflected that observed in other selfing snail species, relying on high selfing rates, low effective population sizes, environmental stochasticity and high gene flow.

We studied the population genetic structure of the freshwater snail Galba schirazensis (Küster, 1862), a potential vector of infectious diseases such as fascioliasis. Galba schirazensis has now a worldwide distribution but a poorly known origin because this species has been distinguished only recently from the morphologically similar and cosmopolitan Galba truncatula (O.F. Müller, 1774). We developed specific microsatellite markers and sequenced a mitochondrial gene (cytochrome oxidase subunit I (CO1)) to study individuals of G. schirazensis from the Old World and the New World. We found very low genetic diversity within populations, no heterozygotes, and marked population structure — a pattern observed in other highly selfing lymnaeid species with recently enlarged distributions as a result of biological invasions. The total lack of observed heterozygosity in the few populations of G. schirazensis that displayed some allelic diversity suggests high selfing rates. We also found that the center of diversity, and by extension the origin area of this species, should be found in the New World, whereas Old World populations should rather result from a recent introduction of a genetically uniform population. The microsatellite markers developed here will help to clarify the history of expansion of G. schirazensis and might help to understand its role as a potential vector of infectious diseases. Fil: Lounnas, Manon. Université de Montpellier. Maladies Infectieuses et Vecteurs: Ecologie, Génétique, Evolution et Contrôle; Francia. Centre National de la Recherche Scientifique. Institut de Recherche pour le Développement; Francia Fil: Correa, Ana Cristina. Centre National de la Recherche Scientifique. Institut de Recherche pour le Développement; Francia. Université de Montpellier. Maladies Infectieuses et Vecteurs: Ecologie, Génétique, Evolution et Contrôle; Francia Fil: Alda, Maria del Pilar. Centre National de la Recherche Scientifique. Institut de Recherche pour le Développement; Francia. Université de Montpellier. Maladies Infectieuses et Vecteurs: Ecologie, Génétique, Evolution et Contrôle; Francia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Estudios Parasitológicos y de Vectores. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Estudios Parasitológicos y de Vectores; Argentina Fil: David, Patrice. Université de Montpellier. Centre d’Ecologie Fonctionnelle et d’Evolution; Francia Fil: Dubois, Marie Pierre. Université de Montpellier. Centre d’Ecologie Fonctionnelle et d’Evolution; Francia Fil: Calvopiña, Manuel. Universidad Central del Ecuador, Carrera de Medicina; Ecuador Fil: Caron, Yannick. Université de Liège; Bélgica Fil: Celi Erazo, Maritza. Universidad Central del Ecuador; Ecuador Fil: Bui, Dung Thi. Université de Liège; Bélgica Fil: Jarne, Philippe. Université de Montpellier. Centre d’Ecologie Fonctionnelle et d’Evolution; Francia Fil: Loker, Eric. University Of New Mexico. Department Of Biology; Estados Unidos Fil: Noya, Oscar. Universidad Central de Venezuela; Venezuela Fil: Rodríguez Hidalgo, Richar. Universidad Central del Ecuador; Ecuador Fil: Toty, Céline. Université de Montpellier. Maladies Infectieuses et Vecteurs: Ecologie, Génétique, Evolution et Contrôle; Francia Fil: Uribe, Nelson. Universidad Industrial Santander; Colombia Fil: Pointier, Jean Pierre. Université de Perpignan; Francia. Centre National de la Recherche Scientifique; Francia Fil: Hurtrez Boussès, Sylvie. Université de Montpellier. Maladies Infectieuses et Vecteurs: Ecologie, Génétique, Evolution et Contrôle; Francia

International audience; Biological invasions offer interesting situations for observing how novel interactions between closely related, formerly allopatric species may trigger phenotypic evolution in situ. Assuming that successful invaders are usually filtered to be competitively dominant, invasive and native species may follow different trajectories. Natives may evolve traits that minimize the negative impact of competition, while trait shifts in invasives should mostly reflect expansion dynamics, through selection for colonization ability and transiently enhanced mutation load at the colonization front. These ideas were tested through a large-scale common-garden experiment measuring life-history traits in two closely related snail species, one invasive and one native, co-occurring in a network of freshwater ponds in Guadeloupe. We looked for evidence of recent evolution by comparing uninvaded or recently invaded sites with long-invaded ones. The native species adopted a life history favoring rapid population growth (i.e., increased fecundity, earlier reproduction, and increased juvenile survival) that may increase its prospects of coexistence with the more competitive invader. We discuss why these effects are more likely to result from genetic change than from maternal effects. The invader exhibited slightly decreased overall performances in recently colonized sites, consistent with a moderate expansion load resulting from local founder effects. Our study highlights a rare example of rapid life-history evolution following invasion.

Modeling the dynamics of competition and coexistence between species is cru- cial to predict long-term impacts of invasive species on their native congeners. However, natu- ral environments are often fragmented and variable in time and space. In such contexts, regional coexistence depends on complex interactions between competition, niche differentia- tion and stochastic colonization–extinction dynamics. Quantifying all these processes at land- scape scale has always been a challenge for ecologists. We propose a new statistical framework to evaluate metapopulation parameters (colonization and extinction) in a two-species system and how they respond to environmental variables and interspecific competition. It requires spatial surveys repeated in time, but does not assume demographic equilibrium. We apply this model to a long-term survey of two snails inhabiting a network of freshwater habitats in the West Indies. We find evidence of reciprocal competition affecting colonization or extinction rates, modulated by species-specific sensitivity to environmental variables. Simulations using model estimates allow us to predict species dynamics and explore the role of various coexis- tence mechanisms described by metacommunity theory in our system. The two species are pre- dicted to stably coexist, because niche partitioning, source–sink dynamics and interspecific differences in extinction–colonization parameters all contribute to reduce the negative impacts of competition. However, none of these mechanisms is individually essential. Regional coexis- tence is primarily facilitated by transient co-occurrence of the two species within habitat patches, a possibility generally not considered in theoretical metacommunity models. Our framework is general and could be extended to guilds of several competing species.

1. In a rapidly changing world, ecology has the potential to move from empirical and conceptual stages to application and management issues. It is now possible to make large-scale predictions up to continental or global scales, ranging from the future distribution of biological diversity to changes in ecosystem functioning and services. With these recent developments, ecology has a historical opportunity to become a major actor in the development of a sustainable human society. With this opportunity, however, also comes an important responsibility in developing appropriate predictive models, correctly interpreting their outcomes and communicating their limitations. There is also a danger that predictions grow faster than our understanding of ecological systems, resulting in a gap between the scientists generating the predictions and stakeholders using them (conservation biologists, environmental managers, journalists, policymakers). 2. Here, we use the context provided by the current surge of ecological predictions on the future of biodiversity to clarify what prediction means, and to pinpoint the challenges that should be addressed in order to improve predictive ecological models and the way they are understood and used. 3. Synthesis and applications. Ecologists face several challenges to ensure the healthy development of an operational predictive ecological science: (i) clarity on the distinction between explanatory and anticipatory predictions; (ii) developing new theories at the interface between explanatory and anticipatory predictions; (iii) open data to test and validate predictions; (iv) making predictions operational; and (v) developing a genuine ethics of prediction.

Bottleneck episodes may occur in small and isolated animal populations, which may result in decreased genetic diversity and increased inbreeding, but also in mating strategy adjustment. This was evaluated in the vulnerable and socially monogamous Monteiro's Storm-petrel Hydrobates monteiroi, a seabird endemic to the Azores archipelago which has suffered a dramatic population decline since the XVth century. To do this, we conducted a genetic study (18 microsatellite markers) in the population from Praia islet, which has been monitored over 16 years. We found no evidence that a genetic bottleneck was associated with this demographic decline. Monteiro's Storm-petrels paired randomly with respect to genetic relatedness and body measurements. Pair fecundity was unrelated to genetic relatedness between partners. We detected only two cases of extra-pair parentage associated with an extra-pair copulation (out of 71 offspring). Unsuccessful pairs were most likely to divorce the next year, but genetic relatedness between pair mates and pair breeding experience did not influence divorce. Divorce enabled individuals to improve their reproductive performances after re-mating only when the new partner was experienced. Re-pairing with an experienced partner occurred more frequently when divorcees changed nest than when they retained their nest. This study shows that even in strongly reduced populations, genetic diversity can be maintained, inbreeding does not necessarily occur, and random pairing is not risky in terms of pair lifetime reproductive success. Given, however, that we found no clear phenotypic mate choice criteria, the part played by non-morphological traits should be assessed more accurately in order to better understand seabird mating strategies. Fundação para a Ciência e Tecnologia (PRAXIS/C/BIA/13194/98 and POCTI-BIA-13194/98 to MB, PTDC/BIABDE/67286/2006 to JB, and SFRH/BPD/88914/2012 to VCN); Fundo Europeu de Desenvolvimento Regional (Programme COMPETE, ref. FCOMP-01-0124-FEDER-007061); Programmes ‘MARE’ (Life contract B4-3200/98-509), ‘OGAMP’ (Interreg IIIB-MAC/4.2/A2), ‘MARMAC’ (Interreg IIIB/FEDER/MARMAC/003-4/2005-6 and Interreg IIIB-05/MAC/4.2/A4), MoniAves (Programme launched by the Regional Environment Directorate from the Azores); Luso-French Integrated Actions Programmes (PESSOA 4.1.1/França and PAUILF F-30/07) info:eu-repo/semantics/publishedVersion

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; Community genetics aims at understanding how within-species variation, species diversity and environmental factors interact to shape community assembly. An approach that emerged a few years ago has been to quantify the correlation between the neutral genetic diversity of a focal species and species diversity of the surrounding community (species–genetic diversity correlations, or SGDCs). We here review this approach and discuss its interpretative framework in a community ecology context. First, we show that the case for mostly positive SGDCs is probably overstated due to publication bias – only 11% are significantly positive, a fraction comparable to the significantly negative ones. This suggests that variation in area and connectivity among habitat patches, theoretically leading to positive SGDCs, is not the only factor affecting SGDCs. Second, building upon previous contributions, we propose a general framework to identify the multiple factors underpinning SGDCs, and argue that it will help deepen our understanding of community assembly, especially with regard to the ecological factors playing at metacommunity scale. Our framework distinguishes between site and community factors which can affect SGDCs either positively or negatively, depending on whether the focal species and the rest of the community are similar or dissimilar, in terms of realized niches and dispersal abilities. Empirical studies should thus go beyond simply computing SGDCs, and we provide statistical methods (e.g. structural equation modelling) to decompose SGDCs into the multiple contributions of site and community factors. As an example, we use a published dataset (freshwater snail metacommunity), and show how the role of focal population size on SGDCs had hitherto not been detected. We further discuss how considering several focal species and various delimitations of the community may help one to identify clusters of ecologically similar species. We eventually highlight the benefit that SGDC studies would get from integrating beta-diversities.

Sexual selection operates on a sequence of events, from mating to offspring production. Which stages in this sequence undergo stronger selection, especially the relative importance of pre- versus postcopulatory processes, are intensely debated issues. Unequal siring success among mates of polyandrous females is classically taken as evidence for a large contribution of postcopulatory processes to the variance in male reproductive success (var(RSm )). However, paternity skews also depend on the timing and number of copulations, a source of variation that should be considered precopulatory rather than postcopulatory. We develop a method for decomposing var(RSm ) accounting for copulatory activity and apply it to experimental mating groups of the snail Physa acuta. In our experiment, 40% of var(RSm ) emerges at the precopulatory stage, only half of which depends on variation in mating success (number of partners). Ignoring copulation characteristics can therefore lead to severe underestimation of precopulatory sexual selection. Moreover, although only 36% of var(RSm ) arises at the postcopulatory stage, this is when sexual selection on body weight mostly occurs. Finally, trade-offs were detected between different components of precopulatory success, whereas pre- and postcopulatory success appear independent. Our study opens the way to a detailed quantitative understanding of sexual selection in polyandrous species.

Quantifying metapopulation dynamics is a challenging task. Difficulties particularly arise in species that possess unobservable resistance forms that bias the estimation of colonization and persistence rates. Here, we develop a general multistate occupancy model that allows estimation of species persistence for both normal and resistant forms, even when the latter are not detectable. We apply this model to an 11-year data set on the tropical freshwater snail Drepanotrema depressissimum in a network of 229 ponds. These ponds frequently dry out, and the snails can persist by aestivating in the ground, where they are not detected. Our model adequately captures this feature because it infers a high persistence rate for the resistant form, while models ignoring aestivation tend to overestimate extinction and colonization. In addition, we find that, surprisingly, colonization and persistence are even higher in sites prone to desiccation and during years with low rainfall than in more humid sites and years, suggesting that D. depressissimum favors unstable sites where competitors are rare and where it can rely on aestivation to persist. Our model has the potential to provide valuable insights into the metapopulation dynamics of many species that otherwise could hardly be studied because of the existence of undetectable life forms.

Population differentiation was investigated by confronting phenotypic and molecular variation in the highly selfing freshwater snail Biomphalaria pfeifferi, the intermediate host of Schistosoma mansoni. We sampled seven natural populations separated by a few kilometers, and characterized by different habitat regimes (permanent/temporary) and openness (open/closed). A genetic analysis based on five microsatellite markers confirms that B. pfeifferi is a selfer (s≈0.9) and exhibits limited variation within populations. Most pairwise FST were significant indicating marked population structure, though no isolation by distance was detected. Families from the seven populations were monitored under laboratory conditions over two generations (G1 and G2), allowing to record several life-history traits, including growth, fecundity and survival, over 25 weeks. Marked differences were detected among populations for traits expressed early in the life cycle (up to sexual maturity). Age and size at first reproduction had high heritability values, but such a trend was not found for early reproductive traits. In most populations, G1 snails matured later and at a larger size than G2 individuals. Individuals from permanent habitats matured at a smaller size and were more fecund than those from temporary habitats. The mean phenotypic differentiation over all populations (QST) was lower than the mean genetic differentiation (FST), suggesting stabilizing selection. However, no difference was detected between QST and FST for both habitat regime and habitat openness.

The metapopulation concept is a cornerstone in the recent history of ecology and evolution. However, determining whether a natural system fits a metapopulation model is a complex issue. Extinction-colonization dynamics are indeed often difficult to quantify because species detectability is not always 100%, resulting in an imperfect record of extinctions. Here, we explore whether combining population genetics with demographic and ecological surveys can yield more realistic estimates of metapopulation dynamics. We apply this approach to the freshwater snail Drepanotrema depressissimum in a fragmented landscape of tropical ponds. In addition to studying correlations between genetic diversity and demographical or ecological characteristics, we undertake, for the first time, a detailed search for genetic signatures of extinction-recolonization events using temporal changes in allele frequencies within sites. Surprisingly, genetic data indicate that extinction is much rarer than suggested by demographic surveys. Consequently, this system is better described as a set of populations with different sizes and immigration rates than as a true metapopulation. We identify several cases of apparent extinction owing to nondetection of low-density populations, and of aestivating individuals in desiccated ponds. More generally, we observed a frequent mismatch between genetic and demographical/ecological information at small spatial and temporal scales. We discuss the causes of these discrepancies and show how these two types of data provide complementary information on population dynamics and history, especially when temporal genetic samples are available.

International audience; Classical ecological theory has proposed several determinants of food chain length, but the role of metacommunity dynamics has not yet been fully considered. By modelling patchy predator-prey metacommunities with extinction-colonization dynamics, we identify two distinct constraints on food chain length. First, finite colonization rates limit predator occupancy to a subset of prey-occupied sites. Second, intrinsic extinction rates accumulate along trophic chains. We show how both processes concur to decrease maximal and average food chain length in metacommunities. This decrease is mitigated if predators track their prey during colonization (habitat selection) and can be reinforced by topdown control of prey vital rates (especially extinction). Moreover, top-down control of colonization and habitat selection can interact to produce a counterintuitive positive relationship between perturbation rate and food chain length. Our results show how novel limits to food chain length emerge in spatially structured communities. We discuss the connections between these constraints and the ones commonly discussed, and suggest ways to test for metacommunity effects in food webs

Numerous models have been designed to understand how dispersal ability evolves when organisms live in a fragmented landscape. Most of them predict a single dispersal rate at evolutionary equilibrium, and when diversification of dispersal rates has been predicted, it occurs as a response to perturbation or environmental fluctuation regimes. Yet abundant variation in dispersal ability is observed in natural populations and communities, even in relatively stable environments. We show that this diversification can operate in a simple island model without temporal variability: disruptive selection on dispersal occurs when the environment consists of many small and few large patches, a common feature in natural spatial systems. This heterogeneity in patch size results in a high variability in the number of related patch mates by individual, which, in turn, triggers disruptive selection through a high per capita variance of inclusive fitness. Our study provides a likely, parsimonious and testable explanation for the diversity of dispersal rates encountered in nature. It also suggests that biological conservation policies aiming at preserving ecological communities should strive to keep the distribution of patch size sufficiently asymmetric and variable.

Most bird species are socially monogamous. However, extra-pair copulations (EPCs), resulting in extra-pair paternity (EPP), commonly occur. EPCs should allow females to adjust social mate choice and allow males that fail to obtain a nest a chance to avoid missing a breeding season, especially when poor nest supply constrains social mate choice. Procellariiformes (albatrosses and petrels) are socially monogamous seabirds which seldom divorce, even when nest availability constrains social mate choice. In Cory's shearwater Calonectris diomedea, a burrow-nesting petrel, two studies conducted in the Mediterranean, where competition for nests is weak, detected no EPP. EPP remains to be investigated at localities where competition for nests is much stronger, such as Vila islet, Azores archipelago, Atlantic Ocean. We conducted a genetic (microsatellites) study over two successive years on Vila, involving the breeding pairs of the same 65 nests each year and their single chick. EPPs occurred each year, the overall rate being 11.6%. Coupling genetic analyses to a 7-year demographic survey provided additional data on pair bonds and competition for nests. Overall, cuckoldry was unrelated to divorce, nest density and inbreeding avoidance, but was more frequent when the social male was small. Nest changes were more costly for males than for females, and some apparently unpaired males attempted to dislodge social males during within-pair copulations. These results are compatible with the existence of a link between poor nest availability and EPP and confirm that even species considered strongly monogamous can adopt flexible mating strategies.

We characterized 15 new variable microsatellites in the freshwater snail Pseudosuccinea (Lymnaea) columella, as well as conditions for multiplexing and simultaneously genotyping sets of loci. Two to six alleles were detected per locus over the six populations studied. Gene diversity ranged from 0.000 to 0.498, but essentially no heterozygous individuals were observed. This resulted in extremely high F(IS) estimates, and therefore high selfing rates. The F(ST) estimates ranged from 0.18 to 1 among populations, but was generally high. These markers will constitute efficient tools for investigating the population structure of this invasive species. Cross-species amplification was on the whole unsuccessful.

Current evolutionary forces and historical processes interact to shape the distribution of neutral genetic variability within and among populations. Focusing on the genetics of recently introduced organisms offers a good opportunity to understand the relative importance of these factors. This study concerns variation at 8 polymorphic microsatellite loci in 30 populations of Biomphalaria pfeifferi. The sampling area spans most of the species’ range in Madagascar where it was probably introduced recently. Extremely low variation was found within all populations studied, which may partly result from high selfing rates. However, this cannot account for the variance of variation across populations, which is better explained by habitat openness (that reflects environmental stochasticity), the prevalence of the parasitic trematode Schistosoma mansoni and historical demography (colonization and subsequent bottlenecks). Large global differentiation was also observed, suggesting that current gene flow among populations is limited to small distances, within watersheds and to few individuals. Our data set also allowed us to test several hypotheses regarding colonization, based on bottleneck and admixture tests. The observed pattern requires at least two independent introductions from slightly differentiated genetic sources in the western part of Madagascar. Another introduction, from a very different genetic origin, should also be postulated to explain the genetic composition of eastern populations. That this introduction occurred recently suggests that the colonization of Madagascar by B. pfeifferi is an ongoing process.

[Notes_IRSTEA]Article référencé sous : Article number 20160548 [Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; Difference in dispersal ability is a key driver of species coexistence in metacommunities. However, the available frameworks for interpreting species diversity patterns in natura often overlook trade-offs and evolutionary constraints associated with dispersal. Here,we build a metacommunity model accounting for dispersal evolution and a competition-dispersal trade-off. Depending on the distribution of carrying capacities among communities, species dispersal values are distributed either around a single strategy (evolutionarily stable strategy, ESS), or around distinct strategies (evolutionary branching, EB). We show that limited dispersal generates spatial aggregation of dispersal traits in ESS and EB scenarios, and that the competition-dispersal trade-off strengthens the pattern in the EB scenario. Importantly, individuals in larger (respectively (resp.) smaller) communities tend to harbour lower (resp. higher) dispersal, especially under the EB scenario.We explore how dispersal evolution affects species diversity patterns by comparing those from our model to the predictions of a neutral metacommunity model. The most marked difference is detected under EB, with distinctive values of both alpha and beta diversity (e.g. the dissimilarity in species composition between small and large communities was significantly larger than neutral predictions). We conclude that, from an empirical perspective, jointly assessing community carrying capacity with species dispersal strategies should improve our understanding of diversity patterns in metacommunities.

Snails (Mollusca: Gastropoda) are a diverse class of mollusks inhabiting marine, terrestrial, and freshwater ecosystems. Although the most common reproductive system is gonochorism, an astounding diversity of other systems have repeatedly evolved, including apomictic parthenogenesis, protandrous hermaphroditism, and simultaneous hermaphroditism. Some snails have evolved specific mechanisms of sex determination (e.g., sex chromosomes), while others show that environmental contaminants can induce changes in reproductive anatomy (e.g., imposex). Despite the diversity of reproductive systems and strategies that has been observed, and the fact that Gastropods serve as model systems for addressing a wide range of questions, a great deal remains to be discovered.

Although 92% of avian species are socially monogamous, extra-pair copulation (EPC), resulting in extra-pair paternity (EPP), is a common reproductive strategy in birds. Among seabirds, in which the rate of social monogamy reaches 100%, Procellariiformes (albatrosses and petrels) show low EPP rates, with the noticeable exception of the only albatross investigated in this regard, the Waved Albatross Phoebastria irrorata . This species, in which forced copulations are known to occur, showed a surprisingly high rate of EPP (25% of chicks). We investigate here EPP rates in another albatross species, the Wandering Albatross Diomedea exulans , subject to a demographic survey conducted for 38 years. We combined data on pair bonds with analysis of ten microsatellite loci and found that 10.7% of 75 chicks had an extra-pair sire. Although there was some evidence for inbreeding avoidance, within-pair and extra-pair chicks showed similar levels of heterozygosity, and the incidence of EPP was independent of age, experience or past reproductive success. Hence, we found no evidence that females benefit from EPCs. Owing to the male-biased sex ratio in adults, widowed and divorced males required more time to find a new mate (+28 and +72%, respectively) than did females. Combined with high sexual size dimorphism, this phenomenon might promote the forced copulations observed in this species. Our data therefore suggest that EPC is beneficial to unpaired males but occurs at random in females, consistent with the hypothesis that EPP results solely from forced EPCs. However, the importance of the latter for EPP and the part played by solitary males require further investigation.

Correspondance: Benoit.Facon@unil.ch; International audience; Studies of bioinvasions have revealed various strategies of invasion, depending on the ecosystem invaded and the alien species concerned. Here, we consider how migration (as a demographic factor), as well as ecological and evolutionary changes, affect invasion success. We propose three main theoretical scenarios that depend on how these factors generate the match between an invader and its new environment. Our framework highlights the features that are common to, or differ among, observed invasion cases, and clarifies some general trends that have been previously highlighted in bioinvasions. We also suggest some new directions of research, such as the assessment of the time sequence of demographic, genetic and environmental changes, using detailed temporal surveys

Delayed selfing allows self-fertile organisms to reproduce even in the absence of mate, and is thought to have evolved as a reproductive assurance strategy. In animal species with strong inbreeding depression, the time during which selfing should be postponed in the absence of mates (referred to as the waiting time) is predicted to have evolved as a function of inbreeding depression, resource reallocation and survival. Under the same theoretical perspective, variation in population density should trigger the evolution of a plastic adjustment of the waiting time. A condition is that individuals should be able to perceive environmental cues (e.g. chemicals) of the density of potential mates. These predictions were tested here using the hermaphroditic freshwater snail Physa acuta, based on two experiments in which rearing water was conditioned such as to manipulate the probability of mate encounter through chemical signals emitted by snails. First, a choice trial experiment showed that the exploration behaviour of individuals is sensible to chemical signals. The second experiment aimed at documenting fitness components (age at first reproduction, growth before and after reproduction, and fecundity over a three-week period) under five treatments (20 individuals per treatment) with different water-conditioning and access to mate. As predicted theoretically, this experiment detected the occurrence of a waiting time (11 days) and resource reallocation to growth when comparing individuals from pure water (no chemicals) and outcrossing individuals. However, the waiting time and resource reallocation to future fecundity did not increase with increasing chemical cues of conspecifics density. There is therefore no evidence that delayed selfing is plastic and adjusted according to mate encounter probability.

Nine sites were sampled 19 times over 2 years in an irrigation system in Morocco in order to study species abundance in a snail community in relation to environmental parameters (including human activities) and migration (geographic distance) among sites. Each site was made of a sink and the first meters of the downstream canal. The snail community included four species (Bulinus truncatus, Lymnaea truncatula, Mercuria similis and Physa acuta). Strong spatial variation in species occurrence and abundance was detected which might be partly due to variation in water availability. However abundance in sinks and canals in which water availability differs were correlated. There was, as predicted, limited evidence in favor of isolation by distance which might be due to fast water current. Dispersal might therefore be an important factor structuring this community. On the other hand, the temporal variation was much more limited. This is consistent with the analysis of individual size distributions in B. truncatus, since no clear-cut cohorts were detected. The environmental parameters recorded (e.g. temperature, occurrence of macrophytes or cleaning of sinks) were extremely variable in time and space, except temperature. Analyzing their association with species through multidimensional methods indicated that P. acuta is ubiquitous and B. truncatus positively associated with macrophytes. These two species were associated in sinks. Less clear trends were detected for the two other species. Annual cleaning of sinks affected all species, but population recovery was fast in B. truncatus and P. acuta.

Schistosoma mansoni is the most widespread of the human-infecting schistosomes, present in 54 countries, predominantly in Africa, but also in Madagascar, the Arabian Peninsula, and the Neotropics. Adult-stage parasites that infect humans are also occasionally recovered from baboons, rodents, and other mammals. Larval stages of the parasite are dependent upon certain species of freshwater snails in the genus Biomphalaria, which largely determine the parasite's geographical range. How S. mansoni genetic diversity is distributed geographically and among isolates using different hosts has never been examined with DNA sequence data. Here we describe the global phylogeography of S. mansoni using more than 2500 bp of mitochondrial DNA (mtDNA) from 143 parasites collected in 53 geographically widespread localities. Considerable within-species mtDNA diversity was found, with 85 unique haplotypes grouping into five distinct lineages. Geographical separation, and not host use, appears to be the most important factor in the diversification of the parasite. East African specimens showed a remarkable amount of variation, comprising three clades and basal members of a fourth, strongly suggesting an East African origin for the parasite 0.30-0.43 million years ago, a time frame that follows the arrival of its snail host. Less but still substantial variation was found in the rest of Africa. A recent colonization of the New World is supported by finding only seven closely related New World haplotypes which have West African affinities. All Brazilian isolates have nearly identical mtDNA haplotypes, suggesting a founder effect from the establishment and spread of the parasite in this large country.

Many invasive taxa are hybrids, but how hybridization boosts the invasive process remains poorly known. We address this question in the clonal freshwater snail Melanoides tuberculata from Martinique, using three parental and two hybrid lines. We combine an extensive field survey (1990-2003) and a quantitative genetic experiment to show that hybrid lines have outcompeted their parents in natural habitats, and that this increased invasiveness co-occurred with pronounced shifts in life-history traits, such as growth, fecundity and juvenile size. Given the little time between hybrid creation and sampling, and the moderate standing genetic variance for life-history traits in hybrids, we show that some of the observed trait changes between parents and hybrids were unlikely to arise only by continuous selection. We therefore suggest that a large part of hybrid advantage stems from immediate heterosis upon hybridization.

Although self-fertilization and its evolutionary consequences have been widely studied, the relative influence of genetic and environmental factors on the determination of mixed-mating systems remains poorly known. In 1999 and 2000, we surveyed the mating system, the population dynamics and some life-history traits of four populations of the freshwater snail Biomphalaria pfeifferi, the major intermediate host of Schistosoma mansoni in Africa, in two areas of Madagascar (Itasy and Antananarivo). We confirmed that B. pfeifferi is a predominant selfer, with selfing rates ranging between 80 and 100%. Temporal and geographical variation of the selfing rate was observed at both local and large spatial scale. Historical processes of colonization and invasion of B. pfeifferi in Madagascar could explain the geographical variation of the mating system observed at regional scale. Pure selfing has probably evolved in the two populations of Antananarivo area as a reproductive assurance strategy in a metapopulation where extinction is frequent and migration rare. The reproductive assurance hypothesis does not explain the spatio-temporal mating system variations observed in Itasy area. However genetic factors including inbreeding depression-the expression of which can be environmentally mediated-and metapopulation dynamics could influence the mating system in both populations sampled in Itasy and lead to different levels of evolutionary stable intermediate selfing rate in this region. Our results therefore highlight the influence of environmental heterogeneity and stochasticity on mating system.

The respective role of factors acting on population functioning can be inferred from a variety of approaches, including population genetics and demography. We here investigated the role of four of these factors (mating systems, population size, bottlenecks and migration) in the hermaphroditic freshwater snail Physa acuta. Twenty-four populations were sampled either around Montpellier (local scale), or at the scale of France (global scale). At local scale, eight populations were sampled twice, before and after summer drying out. The genetic structure of these populations was studied using microsatellite loci. Populations were classified according to openness (ponds vs. rivers) and water regime (permanent vs. temporary) allowing predictions on genetic patterns (e.g. diversity within populations and differentiation). At local scale, progeny-arrays analysis of the selfing rate was conducted, and size distributions of individuals were followed over two years. Results with regard to the four factors mentioned above were: (i) Estimates of population selfing rates derived from inbreeding coefficients were only slightly higher than those from progeny-arrays. (ii) More variation was detected in rivers than in ponds, but no influence of water regime was detected. One reason might be that permanent populations are not going less often through low densities than those from temporary habitats at the time scale studied. (iii) There was limited evidence for genetic bottlenecks which is compatible with the fact that even marked reduction in water availability was not necessarily associated with demographic bottlenecks. More generally, bottlenecks reducing genetic variation probably occur at population foundation. (iv) Lower genetic differentiation was detected among rivers than among ponds which might be related to limitations on gene flow. Demographic and temporal genetic data further indicates that flooding in rivers is unlikely to induce marked gene flow explaining the strong genetic differentiation at short geographical scale in such habitats. Finally, the demographic data suggest that some populations are transitory and subject to recurrent recolonization, a pattern that was also detected through genetic data.

Inbreeding depression was simultaneously studied under contrasted environments, laboratory and natural conditions, using individuals originating from 14 families of the freshwater snail Physa acuta. Both survival and growth of juveniles showed inbreeding depression under laboratory conditions. The same fitness components were monitored with mature snails either kept under laboratory conditions or released at a natural site and analysed using capture-mark-recapture models. Genetic composition of both samples was similar. Inbreeding depression on survival was highest in the laboratory while strong outbreeding depression was revealed in the field. Thus inbreeding depression may not be always higher under natural conditions, at the opposite of what is commonly assumed. We suggest that inbreeding depression is dependent on metabolic requirements imposed by the environment. Other evidences showing that inbreeding depression is environment-dependent are reviewed. We conclude that genetic models should include both genetic and environmental variance in inbreeding depression for studying mating system evolution.

We study the influence of mate availability on the mating behavior of the self-fertile, preferentially outcrossing freshwater snail Physa acuta. Previous optimization theory indicated that mating system interacts with life-history traits to influence the age at first reproduction, providing three testable predictions. First, isolated individuals should reproduce later than individuals with available mates in the expectancy of finding a partner and avoiding the cost of inbreeding. Second, resource reallocation to future fecundity is needed for such reproductive delays to evolve. Third, the reproductive delay can be optimized with respect to life-history traits (e.g., survival, growth) and the mating system (inbreeding depression). Our results largely validate these predictions. First, reproduction is significantly delayed in isolated individuals ("selfers") as compared with individuals frequently exposed to mates ("outcrossers"). Second, delayed reproduction is associated with reallocation to future growth, survival, and fecundity, although fecundity is also affected by the mating system (selfing vs. outcrossing). Third, the reproductive delay found (approximately 2 wk) is consistent with quantitative predictions from optimization models. The delay is largely heritable, which might be partly explained by among-family differences in the amount of inbreeding depression (mating system) but not growth or survival.

The population biology of the schistosome-vector snailBulinus truncatuswas studied in an irrigation area near Marrakech, Morocco, using demographic approaches, in order to estimate life-history parameters. The survey was conducted using 2 capture-mark-recapture analyses in 2 separate sites from the irrigation area, the first one in 1999 and the second one in 2000. Individuals larger than 5 mm were considered. The capture probability varied through time and space in both analyses. Apparent survival (from 0·7 to 1 per period of 2–3 days) varied with time and space (a series of sinks was considered), as well as a square function of size. These results suggest variation in population intrinsic rate of increase. They also suggest that results from more classical analyses of population demography, aiming, for example at estimating population size, should be interpreted with caution. Together with other results obtained in the same irrigation area, they also lead to some suggestions for population control.

Spatial patterns of biological diversity have been extensively studied in ecology and population genetics, because they reflect the forces acting on biodiversity. A growing number of studies have found that genetic (within-species) and species diversity can be correlated in space (the so-called species-gene diversity correlation [SGDC]), which suggests that they are controlled by nonindependent processes. Positive SGDCs are generally assumed to arise from parallel responses of genetic and species diversity to variation in site size and connectivity. However, this argument implicitly assumes a neutral model that has yet to be developed. Here, we build such a model to predict SGDC in a metacommunity. We describe how SGDC emerges from competition within sites and variation in connectivity and carrying capacity among sites. We then introduce the formerly ignored mutation process, which affects genetic but not species diversity. When mutation rate is low, our model confirms that variation in the number of migrants among sites creates positive SGDCs. However, when considering high mutation rates, interactions between mutation, migration, and competition can produce negative SGDCs. Neutral processes thus do not always contribute positively to SGDCs. Our approach provides empirical guidelines for interpreting these novel patterns in natura with respect to evolutionary and ecological forces shaping metacommunities.

Biomphalaria glabrata is the main intermediate host of Schistosoma mansoni in America and one of the most intensely studied species of freshwater snail, yet very little is known about its population biology. Here, we used seven highly polymorphic microsatellite loci to analyse genetic diversity in populations from three regions (Lesser Antilles, Venezuela and southern Brazil). Considerable genetic variation was detected, with an average (s.d.) H(0) = 0.32 (0.24). More diversity per population was found in the Valencia lake basin in Central Venezuela, which suggests an influence of dispersal (via inter-population connectivity) on the restoring of genetic diversity after the demographic bottlenecks recurrently experienced by populations. A marked population structure was detected and there seems to be a relationship between mean differentiation and genetic diversity within regions. There is also a significant isolation-by-distance pattern. The Lesser Antilles populations appear clearly differentiated from the rest, which suggests a single colonisation event followed by local radiation within these islands or multiple colonisation events from the same source area. Our results indicate that B. glabrata essentially cross-fertilises, with little variation in selfing rates among populations. However, significant deficits in heterozygotes and linkage disequilibria were detected in two Venezuelan populations suggesting a mixture of at least two different genetic entities, probably with differences in their respective mating systems.

Biomphalaria glabrata is the main intermediate host of Schistosoma mansoni in America and one of the most intensely studied species of freshwater snails, yet very little is known about its population biology. Here, we used seven highly polymorphic microsatellite loci to analyse genetic diversity in the Valencia lake basin, which represents the core of the endemic area for schistosomiasis in Venezuela. Populations were sampled at short spatial scale (a few kilometres), both inside the lake and in ponds or rivers near the lake. Our results indicate that B. glabrata essentially cross-fertilizes, with little variation in selfing rates among populations. Our markers detected considerable genetic variation, with an average heterozygosity of 0.60. More diversity per population was found within than outside the lake, suggesting an influence of connectivity among populations on the levels of genetic diversity. A marked population structure was detected and lake populations were less structured than other populations. Most individuals were assigned to their population of origin using an assignment test. No strong demographic signal (e.g. bottleneck) was detected, though lake populations are likely to experience bottlenecks more frequently than the other populations analysed. Differences in gene flow therefore seem to play an important role in population differentiation and in the restoring of genetic diversity in demographically unstable populations.

Combining genetic and demographic data is a powerful approach to study adaptation process and evolutionary forces acting in natural populations. We focus on the freshwater snail Biomphalaria pfeifferi, the intermediate host of Schistosoma mansoni. Twenty-one populations sampled in the south of Madagascar were genotyped at six microsatellite loci. Demographic parameters and parasitic prevalence were estimated monthly over the year preceding the genetic sampling. Our results indicate that populations experience recurrent bottlenecks and size fluctuations, which strongly depresses the genetic diversity within population. The recolonization of depleted sites involves genetically differentiated immigrants. We detected frequent migration events along rivers and rare migration events between watersheds. This explains the high level of differentiation observed among populations. The negative regression observed between the prevalence of S. mansoni and the genetic diversity of B. pfeifferi populations indicates that host consanguinity may affect prevalence through the genetic mechanisms involved in resistance. Coevolutionary outcomes are also influenced by the relative migration rates of snails and flukes, but the parasite local adaptation may be prevented by rare long distance dispersal in snails and the phylogeographical patterns of colonization of both hosts and snails.

An important parameter in the evolution of sexual polymorphisms in hermaphroditic organisms is the way resources are allocated to male and female functions by various morphs. Detecting differences in allocation between morphs may not always be possible under optimal conditions and may require stressful conditions. Here we investigate the allocation to various functions in the hermaphroditic, highly selfing, freshwater snail Bulinus truncatus, in relation to phally polymorphism. In natural populations, two morphs, euphallic individuals (regular hermaphrodites) and aphallic individuals (missing the male copulatory organ), co-occur at various ratios. To quantify whether the loss of the male organ in aphallics may be compensated for by other functions, we compared the fecundity, size, and survival of 123 aphallic and 111 euphallic snails originating from 53 families and three natural populations under optimal (25°C) and stressful (19°C and 30°C) temperatures. We also compared the hatching rate and survival of offspring of 10 aphallic and 10 euphallic snails per population at these three temperatures. Firstly, we confirmed a strong effect of temperature on the determination of the sexual morph. Secondly, we found that the two morphs did not differ in size, fecundity, hatching rate, or survival of offspring, suggesting no obvious cost of the male function in isolated snails, even under stressful conditions. However, a trade-off was observed: aphallic individuals laid more capsules, though with fewer eggs per capsule, than euphallic individuals. Thirdly, we found a linear variation of some parameters with the family aphally ratio, suggesting that fitness may be perceived in a frequency-dependent way. Our results are discussed with regard to the relative strength of selective and stochastic factors in the evolution of phally polymorphism.

We followed the invasion dynamics of the Oriental thiarid snail Thiara granifera on the Martinique island, French Antilles. This freshwater species was first discovered in 1991 in the Charpentier River, and its spread has since been analysed based on a yearly survey of the malacological fauna at more than 100 sites covering the whole island and representing 50 river systems and three pools. Four river systems were sampled at many sites. Thirteen river systems were colonized by 1997. Colonization within river systems occurred at a speed greater than 1km per year, probably resulting from both active and passive dispersal. Our results can, on the whole, be explained by a simple diffusion process. However, stratified diffusion has to be invoked in at least one river. Moreover, colonization was faster downstream than upstream, suggesting that current velocity plays a significant role in dispersal. Dispersal also occurred between river systems at a mean distance of almost 10km, though with a large variance, in accordance with the scattered colony model of stratified diffusion. The relative frequencies of T. granifera and Melanoides tuberculata, another recent invader of Martinique, were followed at three sites on the Lezarde River. The first species quickly outnumbered the second, though never wiped it out. The data therefore do not support any exclusion phenomena between these two parthenogenetic invaders. Our analysis does not indicate any obvious influence of the rise of T. granifera on the local freshwater fauna.

We describe nine new variable di- and trinucleotide microsatellites in the plant Crepis sancta, as well as conditions for multiplexing and simultaneous genotyping sets of loci. Their variability was assessed in four populations. Four to 33 alleles were detected per locus; two to 23 alleles per population. Significant deviations from Hardy–Weinberg equilibrium could be attributed either to a mating system involving partial selfing or to null alleles. Genetic differentiation over all loci was significant among the four populations studied. These markers will constitute an efficient tool for investigating dispersal patterns in fragmented landscapes. Cross-species amplification provided few loci variability in three other Crepis species (C. pulcra, C. foetida and C. rubra).

It is commonly observed that reproduction decreases with age, often at a different rate in males and females. This phenomenon is generally interpreted as senescence. Such reproductive declines may stem from at least two sources: a change in resource allocation and a decline in the ability to convert resources into offspring. This distinction is important because a shift in resource allocation may be favoured by selection, while reduced efficiency is purely deleterious. We propose a way to distinguish whether a decline in reproduction is purely deleterious based on estimating reproductive investment, output, and their ratio, efficiency. We apply this approach to the hermaphroditic snail Physa acuta and demonstrate that both male and female functions decline with age. The male decline largely stems from reduced investment into male activity while female decline is due to increased reproductive inefficiency. This shows that age-related declines in reproduction can occur for a number of different reasons, a distinction that is usually masked by the general term ‘senescence’. This approach could be applied to any species to evaluate age-related reproductive decline. We advocate that future studies measure age trajectories of reproductive investment and output to explore the potential processes hidden behind the observation that reproduction declines with age.

International audience; Whether bioinvasions are associated with a loss of genetic diversity and a change in mating system is instrumental for understanding the evolutionary fate of invasive species. Little loss is expected under strong propagule pressure which might be a general situation in widespread, efficient invader. In hermaphroditic species, we have few examples of a transition between outcrossing and selfing as a consequence of invasion, though this is classically predicted (as a corollary to Baker's law). We estimated microsatellite variation in 44 populations of the widespread freshwater snail Physa acuta sampled at worldwide scale (including several populations from its native North America). Neither loss of variation (or bottleneck), nor increase in selfing rate was detected in invaded areas. Moreover there was no isolation by distance at large geographic scale, and limited geographic coherence in genetic patterns was detected using STRUCTURE software-the West Mediterranean area being an exception. Such patterns might be explained by (1) multiple introductions in the invaded areas, presumably fostered by aquarium trade, followed by regional spread in some cases-in which case mating partners might be numerous enough to prevent transition towards higher selfing rates, and (2) invasions from the whole native area. This suggests that P. acuta is an exceptionally efficient invader (which is not true of related species), but the reasons of its success remain elusive.

The distribution of neutral genetic variability within and among sets of populations results from the com- bined actions of genetic drift, migration, extinction and recolonization processes, mutation, and the mating system. We here analyzed these factors in 38 populations of the hermaphroditic snail Bulinus truncatus. The sampling area covered a large part of the species range. The variability was analyzed using four polymorphic microsatellite loci. A very large number of alleles (up to 55) was found at the level of the whole study. Observed heterozygote deficiencies within populations are consistent with very high selfing rates, generally above 0.80, in all populations. These should depress the variability within populations, because of low effective size, genetic hitchhiking, and background selection, whatever the model of mutation assumed. However, that some populations exhibit much more variability than others suggests that historical demographic processes (e.g., population size variation, bottlenecks, or founding events) may play a significant role. A hierarchical analysis of the distribution of the variability across populations indicates a strong pattern of isolation by distance, whatever the geographical scale considered. Our analysis also illustrates how the mutation rate may affect population differentiation, as different mutation rates result in different levels of homoplasy at microsatellite loci. The effects of both genetic drift and gene flow vary with the temporal and spatial scales considered in B. truncatus populations.

Density-dependent and density-independent processes have been shown to influence the population dynamics of marine invertebrates, especially recruitment. However, their relative importance has not been evaluated in natural populations. High adult densities have been suggested to inhibit recruitment, especially in suspension-feeders which may ingest incoming larvae. Age structure and juvenile abundance were investigated in the bivalve Spisula ovalis in order to evaluate the importance of density dependence in generating spatial patterns. Age structure is readily established in this species owing to annual shell lines. An extensive sample (from about 100 sites a few hundred meters apart over 4 consecutive years) was analyzed in the statistical framework of spatial analyses, avoiding spurious correlations due to non-independence between neighboring sites. The area studied supports about ten annual cohorts, though only a few occur at each site. The overall picture is a mosaic of kilometer-scale patches of contrasted age structures, as revealed by highly significant spatial autocorrelations. To our knowledge, such large-scale spatial patterns in age structure have not previously been described in benthic invertebrates. Strong patterns are detected even for juveniles, and are independent of the adult biomass present before settlement. Therefore, patchy patterns of age structure mainly reflect density-independent effects, such as spatial variations in larval supply, passive transport of juveniles, or predation on recruits. In the absence of detailed spatial analyses, such patterns have been misinterpreted previously as negative effects of adult density on settlement success.

A population genetic study using starch gel electrophoresis was performed on populations of several species of lymnaeid snails acting as intermediate hosts for Fasciola hepatica (Trematoda, Plathyhelminth). Lymnaea viatrix was collected in 16 sites from the Bolivian Northern Altiplano. L. cubensis were obtained in one site from Venezuela, one site from Guadeloupe, three sites from Cuba and one site from the Dominican Republic. L. truncatula were collected in one site from France, one from Portugal and one from Morocco. Multilocus enzyme electrophoresis (MEE) were determined for 282 snails at 18 loci. A complete monomorphism was encountered at each geographic site. However, among these 18 loci, 13 are polymorphic and low and high levels of genetic divergence were observed between samples. Two genotypic groups can be differentiated by their multilocus genotypes. The western genotypic group associates together samples from Venezuela, Guadeloupe, Cuba and Dominican Republic ( L. cubensis ) while samples from France, Portugal and Morocco ( L. truncatula ) belong to the eastern genotypic group. Surprisingly, the Northern Bolivian Altiplano populations ( L. viatrix ) do not present any genetic divergence with the Portuguese sample. Therefore, the Bolivian snails belong entirely to the eastern genetic group. Within each group, slight genetic divergences were observed. These results strongly support the European origin of the lymnaeid snails from the Northern Bolivian Altiplano.

We describe 10 new variable dinucleotide microsatellites in the wandering albatross Diomedea exulans , as well as conditions for multiplexing and simultaneous genotyping sets of loci. Their variability was assessed in two and one populations from the Crozet and Kerguelen archipelagos (southern Indian Ocean), respectively. Two to 13 alleles were detected per population, and the mean gene diversity was around 0.4. The low genetic differentiation suggests that these populations constitute a single panmictic unit. Cross-species amplification provided some variability at three and five loci in two other marine birds ( Bulweria bulwerii and Pagodroma nivea ), but none in Calonectris diomedea .

In the hermaphrodite freshwater snail Bulinus truncatus, two sexual morphs, euphallic (regular hermaphrodites) and aphallic individuals without a male copulatory organ, co-occur at various ratios in natural populations. Both aphallic and euphallic individuals can reproduce by selfing, but when outcrossing aphallic individuals can only play the female role. A comparison of life-history traits and sex allocation in these two forms provides the opportunity to investigate the evolution and maintenance of sexual polymorphisms. This study was performed to test whether a reallocation of resources from the lost male function to the female function occurs in aphallic snails at the level of both sex organs (sex allocation) and life-history traits. In a first experiment we compared life-history traits over a whole life-cycle under selfing between the two sexual morphs. In a second experiment, the sex organs were weighed to test for a difference in sex allocation between the two morphs. No difference in resource allocation to female function between the two morphs was observed in either experiment. This is in contrast to patterns frequently observed in sexually polymorphic plants, and in a previous study performed on aphally in the same snail species. We discuss the genetic and physiological hypotheses that could explain these results, and their consequences for the evolution and maintenance of phally polymorphism in B. truncatus.

An increasing number of studies are simultaneously investigating species diversity (SD) and genetic diversity (GD) in the same systems, looking for ‘species– genetic diversity correlations’ (SGDCs). From negative to positive SGDCs have been reported, but studies have generally not quantified the processes underlying these correlations. They were also mostly conducted at large biogeographical scales or in recently degraded habitats. Such correlations have not been looked for in natural networks of connected habitat fragments (metacommunities), and the underlying processes remain elusive in most systems. We investigated these issues by studying freshwater snails in a pond network in Guadeloupe (Lesser Antilles). We recorded SD and habitat characteristics in 232 ponds and assessed GD in 75 populations of two species. Strongly significant and positive SGDCs were detected in both species. Based on a decomposition of SGDC as a function of variance–covariance of habitat characteristics, we showed that connectivity (opportunity of water flow between a site and the nearest watershed during the rainy season) has the strongest contribution on SGDCs. More connective sites received both more alleles and more species through immigration resulting in both higher GD and higher SD. Other habitat characteristics did not contribute, or contributed negatively, to SGDCs. This is true of the desiccation frequency of ponds during the dry season, presumably because species markedly differ in their ability to tolerate desiccation. Our study shows that variation in environmental characteristics of habitat patches can promote SGDCs at metacommunity scale when the studied species respond homogeneously to these environmental characteristics.

One of the main advantages of self-fertilization is to provide reproductive assurance when pollen or mates are scarce. In plants, partial or facultative selfing limits the risk of pollination failure. In preferentially outcrossing species, this may result in mixed-mating. In hermaphroditic animals, recent studies suggest that mixed mating might be much rarer than in plants. However more studies are required to substantiate this claim, especially focusing on species whose lifestyle entails a high potential benefit of reproductive assurance via selfing. We studied a hermaphroditic snail, Drepanotrema depressissimum, which inhabits very unstable and fragmented freshwater habitats. Individuals often have to recolonize newly refilled ponds after long droughts, a situation of low population density and hence low mate availability in which selfing could be an advantage. We estimated selfing rates in natural populations from Guadeloupe (Lesser Antilles), and used laboratory experiments to characterize the reproductive behaviour and success of individuals with or without mates. We detected no sign of selfing in natural populations. Even when given no other option, isolated individuals were extremely reluctant to self. They produced either no or very small clutches, and in the latter case initiated egg-laying later than non-isolated individuals. Self-fertilized clutches suffered near-total (98%) inbreeding depression at the juvenile stage. The example of D. depressissimum therefore shows that a species can overcome periods of mate shortage and habitat instability without the potential to rely on facultative selfing. We hypothesize that metapopulation persistence in this landscape is probably related to a form of dormancy (aestivation in dry ground) rather than to recolonization by rare immigrants and reproductive assurance.

Bulinus globosus, one of the intermediate hosts of the genus Schistosoma, is an hermaphrodite freshwater snail species. This species occupies different kinds of environments in Africa, which are generally subjected to large variations in water availability. The mating system of this species is outcrossing, although selfing has been suggested for one population. Here we investigate the genetic structure of populations of B. globosus in natural and human-modified environments from Niger and Ivory Coast using protein electrophoresis. Our goal is to analyse the respective role of the environment (genetic drift and gene flow), the mating system and human activities. Our results indicate a low intrapopulation polymorphism. A large differentiation among populations occurs on the scale of the whole study area whereas neighbouring populations can show little differentiation. These results point to the role of genetic drift and gene flow as the main factors shaping the genetic structure, with human activities playing a role occasionally.

We present data for seven new markers isolated from a microsatellite-enriched DNA library from the freshwater snail Physa acuta. Six of them appear to be conserved in Physa cubensis. These loci might be useful for analysing population structure and reconstructing the story of invasion of freshwaters on a worldwide scale by P. acuta.

Correspondance: Molecular Ecology Resources Primer Development Consortium, E-mail: editorial.office@molecol.com; International audience; This article documents the addition of 512 microsatellite marker loci and nine pairs of Single Nucleotide Polymorphism (SNP) sequencing primers to the Molecular Ecology Resources Database. Loci were developed for the following species: Alcippe morrisonia morrisonia, Bashania fangiana, Bashania fargesii, Chaetodon vagabundus, Colletes floralis, Coluber constrictor flaviventris, Coptotermes gestroi, Crotophaga major, Cyprinella lutrensis, Danaus plexippus, Fagus grandifolia, Falco tinnunculus, Fletcherimyia fletcheri, Hydrilla verticillata, Laterallus jamaicensis coturniculus, Leavenworthia alabamica, Marmosops incanus, Miichthys miiuy, Nasua nasua, Noturus exilis, Odontesthes bonariensis, Quadrula fragosa, Pinctada maxima, Pseudaletia separata, Pseudoperonospora cubensis, Podocarpus elatus, Portunus trituberculatus, Rhagoletis cerasi, Rhinella schneideri, Sarracenia alata, Skeletonema marinoi, Sminthurus viridis, Syngnathus abaster, Uroteuthis (Photololigo) chinensis, Verticillium dahliae, Wasmannia auropunctata, and Zygochlamys patagonica. These loci were cross-tested on the following species: Chaetodon baronessa, Falco columbarius, Falco eleonorae, Falco naumanni, Falco peregrinus, Falco subbuteo, Didelphis aurita, Gracilinanus microtarsus, Marmosops paulensis, Monodelphis Americana, Odontesthes hatcheri, Podocarpus grayi, Podocarpus lawrencei, Podocarpus smithii, Portunus pelagicus, Syngnathus acus, Syngnathus typhle,Uroteuthis (Photololigo) edulis, Uroteuthis (Photololigo) duvauceli and Verticillium albo-atrum. This article also documents the addition of nine sequencing primer pairs and sixteen allele specific primers or probes for Oncorhynchus mykiss and Oncorhynchus tshawytscha; these primers and assays were cross-tested in both species.