Genetic variability and reproductive modalities in European populations ofTriops cancriformis(Crustacea, Branchiopoda, Notostraca)

Pleistocene allopatric differentiation followed by recent range expansion explains the distribution and molecular diversity of two congeneric crustacean species in the Palaearctic

Pleistocene glaciations had a tremendous impact on the biota across the Palaearctic, resulting in strong phylogeographic signals of range contraction and rapid postglacial recolonization of the deglaciated areas. Here, we explore the diversity patterns and history of two sibling species of passively dispersing taxa typical of temporary ponds, fairy shrimps (Anostraca). We combine mitochondrial (COI) and nuclear (ITS2 and 18S) markers to conduct a range-wide phylogeographic study including 56 populations of Branchinecta ferox and Branchinecta orientalis in the Palaearctic. Specifically, we investigate whether their largely overlapping ranges in Europe resulted from allopatric differentiation in separate glacial refugia followed by a secondary contact and reconstruct their postglacial recolonization from the inhabited refugia. Our results suggest the existence of distinct refugia for the two species, with genetic divergence among intraspecific lineages consistent with late Pleistocene glacial cycles. While B. ferox lineages originated from Mediterranean refugia, the origin of B. orientalis lineages was possibly located on the Pannonian Plain. We showed that most dispersal events predominantly happened within 100 km, coupled with several recent long-distance events (> 1000 km). Hence the regional habitat density of suitable habitats in Central Europe is possibly a key to the co-existence of the two species. Overall, our study illustrates how isolation in combination with stochastic effects linked to glacial periods are important drivers of the allopatric differentiation of Palaearctic taxa.

Comparative genomics of tadpole shrimps (Crustacea, Branchiopoda, Notostraca): Dynamic genome evolution against the backdrop of morphological stasis

This analysis presents five genome assemblies of four Notostraca taxa. Notostraca origin dates to the Permian/Upper Devonian and the extant forms show a striking morphological similarity to fossil taxa. The comparison of sequenced genomes with other Branchiopoda genomes shows that, despite the morphological stasis, Notostraca share a dynamic genome evolution with high turnover for gene families' expansion/contraction and a transposable elements content comparable to other branchiopods. While Notostraca substitutions rate appears similar or lower in comparison to other branchiopods, a subset of genes shows a faster evolutionary pace, highlighting the difficulty of generalizing about genomic stasis versus dynamism. Moreover, we found that the variation of Triops cancriformis transposable elements content appeared linked to reproductive strategies, in line with theoretical expectations. Overall, besides providing new genomic resources for the study of these organisms, which appear relevant for their ecology and evolution, we also confirmed the decoupling of morphological and molecular evolution.

Discriminating between the effects of founding events and reproductive mode on the genetic structure of Triops populations (Branchiopoda: Notostraca)

Crustaceans that initially colonize a freshwater temporary pond can strongly bias the subsequent genetic composition of the population, causing nearby populations to be genetically distinct. In addition, these crustaceans have various reproductive modes that can influence genetic differentiation and diversity within and between populations. We report on two species of tadpole shrimp, Triops newberryi and Triops longicaudatus "short", with different reproductive modes. Reproduction in the tadpole shrimp can occur clonally (parthenogenesis), with self fertilization (hermaphroditism), or through outcrossing of hermaphrodites with males (androdioecy). For all these reproductive modes, population genetic theory predicts decreased genetic diversity and increased population differentiation. Here we use mitochondrial control region (mtCR) sequences and nuclear microsatellite loci to determine if the difference in reproductive mode affects the high genetic structure typical of persistent founder effects. Previous authors indicated that T. newberryi is androdioecious because populations are composed of hermaphrodites and males, and T. longicaudatus "short" is hermaphroditic or parthenogenetic because males are absent. In our data, T. newberryi and T. longicaudatus "short" populations were highly structured genetically over short geographic distances for mtCR sequences and microsatellite loci (T. newberryi: ΦST = 0.644, FST = 0.252, respectively; T. l. "short": invariant mtCR sequences, FST = 0.600). Differences between the two Triops species in a number of diversity measures were generally consistent with expectations from population genetic theory regarding reproductive mode; however, three of four comparisons were not statistically significant. We conclude the high genetic differentiation between populations is likely due to founder effects and results suggest both species are composed of selfing hermaphrodites with some level of outcrossing; the presence of males in T. newberryi does not appreciably reduce inbreeding. We cannot exclude the possibility that males in T. newberryi are non-reproductive individuals and the two species have the same mating system.

Mitochondrial and nuclear markers highlight the biodiversity of Kalotermes flavicollis (Fabricius, 1793) (Insecta, Isoptera, Kalotermitidae) in the Mediterranean area

The biodiversity of the European termite Kalotermes flavicollis is here studied through the analysis of mitochondrial (303 bp of control region and 912 bp of COI/tRNA(Leu)/COII) and nuclear (five microsatellite and 20 Inter-SINE loci) markers on 18 colonies collected in Southern France, Corsica, Sardinia, peninsular Italy, the Balkans and Greece. Different statistical analyses (Bayesian phylogenetic analysis,parsimony network, F-statistics, PCA) were performed. Mitochondrial sequences produced an unresolved polytomy including samples from peninsular Italy, Balkans and Greece, and three main clades: southern France, Corsica-Sardinia and Portoscuso(SW Sardinia). Nuclear markers confirm these data, further highlighting a more significant divergence at the regional scale. The results obtained for the peri-Tyrrhenian area agree with major paleogeographic and paleoclimatic events that shaped the biodiversity of the local fauna. K. flavicollis biodiversity and its phylogeographic pattern are also evaluated in the light of the data available for the other native European termite taxon (genus Reticulitermes), in order to produce a more complete scenario of the Mediterranean. In the area comprised between southern France and Italy, the degree of diversity is similar; however, in the eastern area, while K. flavicollis is differentiated only at the population level, the genus Reticulitermes comprises at least six entities of specific and/or subspecific level. This discrepancy may be explained by taking into account the different evolutionary histories of the two taxa.