DNA-based evidence for post-glacial colonisation of Niphargus (Malacostraca: Amphipoda: Niphargidae) in formerly glaciated northern Germany

The pattern of postglacial re-colonization of Europe and the present population structure are known for various plant and animal species. The reed beetle Macroplea mutica (Fabricius, 1792) has characteristics that should influence both aspects in a peculiar way and therefore complement the currently known scenarios: It is fully aquatic but cannot swim or fly. Samples from 25 European populations of M. mutica and five specimens from China were investigated using amplified fragment length polymorphism (AFLP, 251 loci). Assessment of error rates associated with this method showed that the data set contains a strong population genetic signal. As hypothesized pronounced population differentiation and signs of inbreeding were found. Italian populations are clearly differentiated from northern populations (and from each other), which underlines the role of the Alps as a major barrier. Specimens from Lake Balaton (Hungary) show some affiliation with the populations in the Baltic Sea, which are all relatively similar. Populations from the eastern part of Northern Germany are similar to the Baltic populations, while those from the western part are allied to the British populations. The hypothesis is that the recolonization of Europe was from both the Southeast and a western refugium in the area of present-day southern England or Ireland, which resulted in a suture zone in Northern Germany. The effect of passive dispersal by drift attached to host plant material (especially in the Baltic Sea) and by zoochory (migrating waterfowl) is discussed.

Carabid Beetles: Ecology and Evolution

There is mounting evidence that some European temperate species did not respond to the last (Weichselian) glaciation by simply shifting their distributions to the Mediterranean region but also survived at higher latitudes previously considered inhospitable. However, it remains to be determined to what extent such high-latitude glacial refugia contributed to post-glacial colonization of Europe. The bank vole Myodes glareolus apparently survived in a high-latitude glacial refugium in the Carpathian Mountains. Here, we used 144 new mitochondrial DNA sequences (largely obtained from museum skins), together with relevant previous data, to investigate whether the phylogeography of bank voles currently living in deglaciated areas north of the Carpathians reflects colonization from this or other refugia. Phylogenetic reconstruction resolved the newly identified haplotypes into three major clades. The majority of voles sampled in Poland carried haplotypes of the Carpathian clade, previously only known from the Carpathians and their immediate vicinity. Voles from eastern Poland and northern Germany carried haplotypes of the Eastern clade, also found in eastern Europe and Siberia, and six voles from scattered localities carried haplotypes of the Western clade, which has a west European distribution. Therefore, the results suggest the contribution of multiple glacial refugia. However, the occurrence of the Carpathian clade over a large area north of the Carpathians up to the Baltic Sea coast indicates a particular importance of the Carpathian refugium. Thus, a substantial involvement of a high-latitude refugium in the post-glacial colonization of Europe by bank voles is inferred. Likely as the consequence of the high-latitude survival, the Carpathian clade lacks evidence of the severe demographic bottleneck during the Last Glacial Maximum that is observed in the Eastern clade. The contact zone between the expanding populations of the Carpathian and Eastern clades coincides with subdivisions in other species and may represent a new post-glacial suture zone.

Stochastic effects from demographic processes and selection are expected to shape the distribution of genetic variation in spatially heterogeneous environments. As the amount of genetic variation is central for long-term persistence of populations, understanding how these processes affect variation over large-scale geographical gradients is pivotal. We investigated the distribution of neutral and putatively adaptive genetic variation, and reconstructed demographic history in the moor frog (Rana arvalis) using 136 individuals from 15 populations along a 1,700-km latitudinal gradient from northern Germany to northern Sweden. Using double digest restriction-site associated DNA sequencing we obtained 27,590 single nucleotide polymorphisms (SNPs), and identified differentiation outliers and SNPs associated with growing season length. The populations grouped into a southern and a northern cluster, representing two phylogeographical lineages from different post-glacial colonization routes. Hybrid index estimation and demographic model selection showed strong support for a southern and northern lineage and evidence of gene flow between regions located on each side of a contact zone. However, patterns of past gene flow over the contact zone differed between neutral and putatively adaptive SNPs. While neutral nucleotide diversity was higher along the southern than the northern part of the gradient, nucleotide diversity in differentiation outliers showed the opposite pattern, suggesting differences in the relative strength of selection and drift along the gradient. Variation associated with growing season length decreased with latitude along the southern part of the gradient, but not along the northern part where variation was lower, suggesting stronger climate-mediated selection in the north. Outlier SNPs included loci involved in immunity and developmental processes.