Organisation spatiale de la diversité génétique et flux polliniques dans une chênaie mixte

L’organisation de la diversité génétique a été décrite dans le cas d’un peuplement mélangé de chêne sessile et pédonculé constitué de 355 arbres adultes répartis sur une surface de 6 ha. La diversité a été appréhendée à l’aide de 6 loci microsatellites manifestant un polymorphisme très élevé (de 15 à 32 allèles par locus). L'organisation a été décrite à l’aide de deux paramètres : la différenciation (Fst) entre différentes subdivisions spatiales de la parcelle étudiée et l’autocorrélation spatiale (I) entre les génotypes présents sur la parcelle. Les deux espèces se caractérisent par une différenciation génétique faible mais significative, quelle que soit la taille des subdivisions spatiales considérées (à l’exception des faibles tailles < 10 m chez le chêne pédonculé). L’autocorrélation est significative aux faibles distances chez le chêne sessile alors qu’une structuration plus faible apparaît chez le chêne pédonculé. Ces valeurs sont interprétées en fonction des flux de gènes chez les deux espèces, dont des indications sont données pour les flux de pollen. En effet des recherches de paternité à l’aide des données multilocus sur les microsatellites ont permis d’identifier les parents pollinisateurs de treize descendances récoltées dans la parcelle. Ces résultats suggèrent que les flux de pollen cumulent une dispersion à courte distance et des transports à longue distance. La faible structuration spatiale est interprétée comme le résultat de l’asymétrie de flux entre graines et pollen. La structure mise en place par la dispersion réduite des graines est érodée par les flux de pollen à longue distance.The spatial genetic structure was analysed in a 6 ha mixed stand of 355 adult oaks trees (Quercus petraea (Matt.) Liebl. and Quercus robur L.). The genetic diversity was investigated with six highly polymorphic microsatellite loci (15 to 32 alleles per locus). Two parameters of the spatial genetic structure were used: the genetic differentiation (Fst), for different spatial scales within the stand, and the spatial autocorrelation (7) between the genotypes in the stand. Both species are characterised by a low but significant genetic differentiation, whatever the spatial scale of observation (except for the smallest scale of < 10 m for Quercus robur). The autocorrelation values are significant for the smallest scales for Quercus petraea and the spatial structure appears weaker for Quercus robur. Results are interpreted in terms of gene flow for both species. Paternity analysis based on multilocus microsatellite data made it possible to identify the paternal parents of progenies collected on 13 mother trees in the stand. Results of the paternity analysis indicate that pollen flow combines dispersion at short distances and transport at long distances. As a result, the spatial structure observed is seen as the consequence of the asymmetry of pollen versus seed flow. Restricted seed movement is likely to build up spatial structures that are disrupted by long distance pollen movements

Pleistocene origins of chorusing diversity in Mediterranean bush-cricket populations (Ephippiger diurnus)

International audienceWe studied the Pleistocene diversification of a relatively endemic Mediterranean insect (Ephippiger diurnus ; Orthoptera: Tettigoniidae) to understand how species with restricted range may nonetheless exhibit the complex phylogeography normally associated with broad distribution. A time-calibrated molecular phylogeny based on two mitochondrial genes showed that E. diurnus diverged into two major clades, distinguished largely be male song, before or early during the Pleistocene. Several subclades also diverged before the most recent glacial period. Data from 20 microsatellite loci indicated higher genetic diversity in populations along the Mediterranean coast in France, consistent with the hypothesis that glacial refuges were located there. ‘Isolation by distance’ accounts for much genetic differentiation between populations, but some adjacent populations are highly differentiated. A Bayesian approach defined genetically distinct clusters and assigned individuals to their most probable cluster. Clusters corresponded to clades in the phylogenetic tree, and we used cluster assignments to estimate inter-clade gene flow in areas of potential secondary contact. Gene flow is negligible in potential contact areas in the Pyrenees, but a narrow hybrid zone featuring a steep cline exists on the coast. This hybrid zone suggests that the major clades represent distinct species that diverged within a restricted area during the Pleistocene

Pleistocene origins of chorusing diversity in Mediterranean bush-cricket populations (Ephippiger diurnus)

International audienceWe studied the Pleistocene diversification of a relatively endemic Mediterranean insect (Ephippiger diurnus ; Orthoptera: Tettigoniidae) to understand how species with restricted range may nonetheless exhibit the complex phylogeography normally associated with broad distribution. A time-calibrated molecular phylogeny based on two mitochondrial genes showed that E. diurnus diverged into two major clades, distinguished largely be male song, before or early during the Pleistocene. Several subclades also diverged before the most recent glacial period. Data from 20 microsatellite loci indicated higher genetic diversity in populations along the Mediterranean coast in France, consistent with the hypothesis that glacial refuges were located there. ‘Isolation by distance’ accounts for much genetic differentiation between populations, but some adjacent populations are highly differentiated. A Bayesian approach defined genetically distinct clusters and assigned individuals to their most probable cluster. Clusters corresponded to clades in the phylogenetic tree, and we used cluster assignments to estimate inter-clade gene flow in areas of potential secondary contact. Gene flow is negligible in potential contact areas in the Pyrenees, but a narrow hybrid zone featuring a steep cline exists on the coast. This hybrid zone suggests that the major clades represent distinct species that diverged within a restricted area during the Pleistocene

Animal choruses emerge from receiver psychology OPEN

National audienceSynchrony and alternation in large animal choruses are often viewed as adaptations by which cooperating males increase their attractiveness to females or evade predators. Alternatively, these seemingly composed productions may simply emerge by default from the receiver psychology of mate choice. This second, emergent property hypothesis has been inferred from findings that females in various acoustic species ignore male calls that follow a neighbor's by a brief interval, that males often adjust the timing of their call rhythm and reduce the incidence of ineffective, following calls, and from simulations modeling the collective outcome of male adjustments. However, the purported connection between male song timing and female preference has never been tested experimentally, and the emergent property hypothesis has remained speculative. Studying a distinctive katydid species genetically structured as isolated populations, we conducted a comparative phylogenetic analysis of the correlation between male call timing and female preference. We report that across 17 sampled populations male adjustments match the interval over which females prefer leading calls; moreover, this correlation holds after correction for phylogenetic signal. Our study is the first demonstration that male adjustments coevolved with female preferences and thereby confirms the critical link in the emergent property model of chorus evolution

De novo transcriptomic resources for two sibling species of moths: Ostrinia nubilalis and O. scapulalis.

Background: This study aimed at enhancing the transcriptomic resources for two sibling species of moths, Ostrinia scapulalis (Adzuki bean borer) and Ostrinia nubilalis (European corn borer), as a foundation for future researches on their divergence history. Previous works on these species had shown that their genetic divergence was low, while they were reproductively isolated in natura and specialized on different host plants. Comparative genomic resources will help facilitate the understanding of the mechanisms involved in this isolation and adaptation to the host plants. Despite their fundamental interest, these species still lack the genomic resources to thoroughly identify candidate genes for functions of interest. We present here a high throughput sequencing and de novo transcriptome assembly for these two sibling species in line with this objective of comparative genomics. Results: Based on 322,504 and 307,622 reads of 454 sequencing for O. scapulalis and O. nubilalis respectively, we reconstructed 11,231 and 10,773 transcripts, of which 40% were functionally annotated by BLAST analyzes. We determined the level of completeness of both assemblies as well as the recovery level of published Ostrinia genomic resources. Gene ontology (GO) of common and species-specific de novo transcripts did not reveal GO terms significantly enriched in one or the other species. By applying stringent homology searches on transcripts common to O. scapulalis and O. nubilalis, we identified a set of homologous transcripts, with a mean nucleotide identity value of 98.1%. In this set, the most divergent transcripts revealed candidate genes involved in developmental, sensorial and pathogen defense processes. Conclusions: This data greatly increases the genomic resources of Ostrinia species and constitute a solid skeleton for future comparative analyzes of expression or diversity, despite we show that the transcriptomes for both species have not been assembled at full completion. In addition, we provide a set of homologous transcripts together with their annotation as a source of candidate genes for comparative analyzes. Keywords: NGS, 454 sequencing, Tanscriptome, Moth, European corn borer, Adzuki bean borer, Sibling species, Ostrinia nubilalis, Ostrinia scapulali

Data from: Microsatellite evolutionary rate and pattern in Schistocerca gregaria inferred from direct observation of germline mutations

Unravelling variation among taxonomic orders regarding the rate of evolution in microsatellites is crucial for evolutionary biology and population genetics research. The mean mutation rate of microsatellites tends to be lower in arthropods than in vertebrates, but data are scarce and mostly concern accumulation of mutations in model species. Based on parent-offspring segregations and a hierarchical Bayesian model, the mean rate of mutation in the orthopteran insect Schistocerca gregaria was estimated at 2.1e-4 per generation per untranscribed dinucleotide locus. This is close to vertebrate estimates and one order of magnitude higher than estimates from species of other arthropod orders, such as Drosophila melanogaster and Daphnia pulex. We also found evidence of a directional bias towards expansions even for long alleles and exceptionally large ranges of allele sizes. Finally, at transcribed microsatellites, the mean rate of mutation was half the rate found at untranscribed loci and the mutational model deviated from that usually considered, with most mutations involving multistep changes that avoid disrupting the reading frame. Our direct estimates of mutation rate were discussed in the light of peculiar biological and genomic features of S. gregaria, including specificities in mismatch repair and the dependence of its activity to allele length. Shedding new light on the mutational dynamics of grasshopper microsatellites is of critical importance for a number of research fields. As an illustration, we showed how our findings improve microsatellite application in population genetics, by obtaining a more precise estimation of S. gregaria effective population size from a published data set based on the same microsatellites