Coalescence 2.0: a multiple branching of recent theoretical developments and their applications

Population genetics theory has laid the foundations for genomics analyses including the recent burst in genome scans for selection and statistical inference of past demographic events in many prokaryote, animal and plant species. Identifying SNPs under natural selection and underpinning species adaptation relies on disentangling the respective contribution of random processes (mutation, drift, migration) from that of selection on nucleotide variability. Most theory and statistical tests have been developed using the Kingman coalescent theory based on the Wright-Fisher population model. However, these theoretical models rely on biological and life-history assumptions which may be violated in many prokaryote, fungal, animal or plant species. Recent theoretical developments of the so called multiple merger coalescent models are reviewed here ({\Lambda}-coalescent, beta-coalescent, Bolthausen-Snitzman, {\Xi}-coalescent). We explicit how these new models take into account various pervasive ecological and biological characteristics, life history traits or life cycles which were not accounted in previous theories such as 1) the skew in offspring production typical of marine species, 2) fast adapting microparasites (virus, bacteria and fungi) exhibiting large variation in population sizes during epidemics, 3) the peculiar life cycles of fungi and bacteria alternating sexual and asexual cycles, and 4) the high rates of extinction-recolonization in spatially structured populations. We finally discuss the relevance of multiple merger models for the detection of SNPs under selection in these species, for population genomics of very large sample size and advocate to potentially examine the conclusion of previous population genetics studies.Comment: 3 Figure

Survival Rate and Transcriptional Response upon Infection with the Generalist Parasite Beauveria bassiana in a World-Wide Sample of Drosophila melanogaster

The ability to cope with infection by a parasite is one of the major challenges for any host species and is a major driver of evolution. Parasite pressure differs between habitats. It is thought to be higher in tropical regions compared to temporal ones. We infected Drosophila melanogaster from two tropical (Malaysia and Zimbabwe) and two temperate populations (the Netherlands and North Carolina) with the generalist entomopathogenic fungus Beauveria bassiana to examine if adaptation to local parasite pressures led to differences in resistance. Contrary to previous findings we observed increased survival in temperate populations. This, however, is not due to increased resistance to infection per se, but rather the consequence of a higher general vigor of the temperate populations. We also assessed transcriptional response to infection within these flies eight and 24 hours after infection. Only few genes were induced at the earlier time point, most of which are involved in detoxification. In contrast, we identified more than 4, 000 genes that changed their expression state after 24 hours. This response was generally conserved over all populations with only few genes being uniquely regulated in the temperate populations. We furthermore found that the American population was transcriptionally highly diverged from all other populations concerning basal levels of gene expression. This was particularly true for stress and immune response genes, which might be the genetic basis for their elevated vigor

Universality of neutral models: decision process in politics

Abstract Political elections exemplify complex decision processes in human populations. Data of proportional elections show a striking feature at different spatial scales, across years, and for several democracies: when ranking the parties according to their number of voters, the amount of votes grows exponentially with the party’s rank. We develop a mechanistic mathematical model of birth and death of parties and voter grouping based only on word of mouth and not on political contents, close to neutral models used in evolutionary biology (Ewens sampling formula), or Hubbell’s model of species biodiversity. Data and model agree strikingly well. The model explains, for instance, the steady loss of big-tent parties in France and Germany by the increasing number of parties standing for elections. A cannibalism effect (parties/candidates at a given rank systematically withdraw votes from others) can be identified. The interpretation and consequences of the rational or lack thereof of voters’ choices for modern democracies are discussed

Approximate Bayesian Computation Untangles Signatures of Contemporary and Historical Hybridization between Two Endangered Species

Contemporary gene flow, when resumed after a period of isolation, can have crucial consequences for endangered species, as it can both increase the supply of adaptive alleles and erode local adaptation. Determining the history of gene flow and thus the importance of contemporary hybridization, however, is notoriously difficult. Here, we focus on two endangered plant species, Arabis nemorensis and A. sagittata, which hybridize naturally in a sympatric population located on the banks of the Rhine. Using reduced genome sequencing, we determined the phylogeography of the two taxa but report only a unique sympatric population. Molecular variation in chloroplast DNA indicated that A. sagittata is the principal receiver of gene flow. Applying classical D-statistics and its derivatives to whole-genome data of 35 accessions, we detect gene flow not only in the sympatric population but also among allopatric populations. Using an Approximate Bayesian computation approach, we identify the model that best describes the history of gene flow between these taxa. This model shows that low levels of gene flow have persisted long after speciation. Around 10 000 years ago, gene flow stopped and a period of complete isolation began. Eventually, a hotspot of contemporary hybridization was formed in the unique sympatric population. Occasional sympatry may have helped protect these lineages from extinction in spite of their extremely low diversity

Microsatellite loci to recognize species for the cheese starter and contaminating strains associated with cheese manufacturing

UMR BGPI Equipe 5International audienceWe report the development of 17 microsatellite markers in the cheese fungi Penicillium camemberti and P. roqueforti, using an enrichment protocol. Polymorphism and cross-amplification were explored using 23 isolates of P. camemberti, 26 isolates of P. roqueforti and 2 isolates of each of the A chtysogenum and P. nalgiovense species. used to produce meat fermented products. The markers appeared useful for differentiating species, both using their amplification sizes and the sequences of their flanking regions. The microsatellite locus PC4 was particularly suitable for distinguishing contaminant species closely related to P. camemberti and for clarifying the phylogenetic relationship of this species with its supposed ancestral form, P. commune. We analyzed 22 isolates from different culture collections assigned to the morphospecies P commune, most of them occurring as food spoilers, mainly from the cheese environment. None of them exhibited identical sequences with the ex-type isolate of the species P. commune. They were instead distributed into two other distinct lineages, corresponding to the old species P. fuscoglaucum and P. biforme, previously synonymised respectively with P. commune and P. camemberti. The ex-type isolate of P. commune was strictly identical to P. camemberti at all the loci examined. P. caseifulvum, a non toxinogenic species described as a new candidate for cheese fermentation, also exhibited sequences identical to P. camemberti. The microsatellite locus PC4 may therefore be considered as a useful candidate for the barcode of these economically important specie