Johan René Michaux

Mitochondrial phylogeography of the Woodmouse ( Apodemus sylvaticus ) in the Western Palearctic region

We sequenced 965 base pairs of the mitochondrial DNA cytochrome b from 102 woodmice (Apodemus sylvaticus) collected from 40 European localities. The aims of the study were to answer the following questions. (i) Did the Mediterranean peninsulas play a role as refuge for woodmice? (ii) Is genetic variability of A. sylvaticus higher in the Mediterranean region compared with northern Europe? (iii) Are the patterns of the postglacial colonization of Europe by woodmice similar to those presently recognized for other European species? The results provide a clear picture of the impact of the Quaternary glaciations on the genetic and geographical structure of the woodmouse. Our analyses indicate a higher genetic variability of woodmice in the Mediterranean peninsulas compared to northern Europe, suggesting a role of the former as refuge regions for this small mammal. An original pattern of postglacial colonization is proposed where the Iberian and southern France refuge populations colonized almost all European regions. The Sicilian population appears to be very differentiated and highly variable. This emphasizes the importance of this island as a ‘hot spot’ for the intraspecific genetic diversity of the woodmouse. Finally, woodmice in North Africa originated from southwestern Europe, most probably as a result of a recent anthropogenic introduction.

Phylogeography of a Nematode (Heligmosomoides polygyrus) in the Western Palearctic region : Persistence of Northern cryptic populations during ice ages?

This study establishes the continental phylogeographical pattern of a European nematode, Heligmosomoides polygyrus (Dujardin, 1845; Heligmosomoidea). We sequenced 687 base pairs of the mitochondrial DNA (mtDNA) cyt b gene for 136 individuals collected in 22 localities. The results revealed that H. polygyrus populations are separated into five major units corresponding to the Italian, northern European (Denmark and Ireland), Iberian, western European, and Balkan populations. Different subclades were also observed within the first two groups. Based on the rate of molecular evolution of H. polygyrus cyt b gene‐estimated to 3.5%–3.7% divergence per million years (Myr) in a previous study – the isolation time of the five clades was estimated between 2.5 ± 0.24 and 1.5 ± 0.23 million years ago. Moreover, H. polygyrus presents a higher genetic variability in the Mediterranean peninsulas as compared to northwestern Europe, highlighting the role of these regions as refuge areas. Like its specific host, the wood mouse Apodemus sylvaticus, H. polygyrus’ pattern of postglacial recolonization of northwestern Europe was initiated from Iberian populations, while Italian and Balkan populations did not expand to the north. The results also suggest the existence of forested and temperate refuges in the southern British Isles during the Quaternary. Finally, the genetic diversity as well as the level of genetic divergence between the lineages of H. polygyrus are compared to those observed in other vertebrate and invertebrate phylogeographical studies: the existence of highly differentiated lineages in H. polygyrus (5%−10% of genetic divergence) highlights that the effects of Pleistocene climate changes on free‐living organisms are also reflected in their obligate parasites.

Evolutionary journey of the retroviral restriction gene Fv1

Significance We have charted the evolution of the capsid-binding retroviral restriction factor Fv1 through murid evolution, extending its age to ∼45 million years. Functionality can be found outside of the genus Mus, and shared signatures of positive selection are visible across species. Modeling suggests that maintenance for these extended periods can only be parsimoniously explained by repeated selection events—waves of retroviral infection throughout murid evolution. Our results complement and extend findings with TRIM5α and suggest that conserved features of retroviral capsid lattice assemblies may be common targets in convergent evolution of intrinsic defenses to retroviral infection. Functional constraints on capsid structure may prevent effective escape of host factors and result in cyclical coevolution, which is visible in the evolution of Fv1. Both exogenous and endogenous retroviruses have long been studied in mice, and some of the earliest mouse studies focused on the heritability of genetic factors influencing permissivity and resistance to infection. The prototypic retroviral restriction factor, Fv1, is now understood to exhibit a degree of control across multiple retroviral genera and is highly diverse within Mus. To better understand the age and evolutionary history of Fv1, a comprehensive survey of the Muroidea was conducted, allowing the progenitor integration to be dated to ∼45 million years. Intact coding potential is visible beyond Mus, and sequence analysis reveals strong signatures of positive selection also within field mice, Apodemus. Fv1’s survival for such a period implies a recurring and shifting retroviral burden imparting the necessary selective pressures—an influence likely also common to analogous factors. Regions of Fv1 adapt cooperatively, highlighting its preference for repeated structures and suggesting that this functionally constrained aspect of the retroviral capsid lattice presents a common target in the evolution of intrinsic immunity.