Search

Colonizing populations at the leading edge of range expansion are expected to have a reduced genetic diversity and strong genetic structure caused by genetic drift and allele surfing. Until now, few studies have found the genetic signatures of allele surfing in expanding wild populations. Using mtDNA markers, we studied the genetic structure of the population of midday gerbils (Meriones meridianus) expanding their range to the west in Kalmykia (southern Russia) following the new cycle of desertification, re-colonizing areas abandoned in the mid-2010s. In the colonizing population, we found a reduced genetic diversity, the redistribution of haplotype frequencies—in particular, in favor of variants rare in the core population—and strong genetic structure combined with strong differentiation from the core population—patterns suggestive of allele surfing on the wave of expansion. In terms of genetic diversity and spatial structuration, the western edge population sampled in 2008 before its collapse in 2017 occupies the intermediate position between the current colonizing and core population. This suggests that reduced genetic diversity and increased genetic differentiation are general features of marginal populations, enhanced by the founder and allele-surfing effects at the leading edges of expanding ranges.

In Russia, Myotis nattereri was considered as a monotypic species, of which its range is divided into two parts.. One of them is the northern fragment consisting of Central Russia and the Urals, while the southern part of its range includes the Caucasus and Crimea. On the basis of morphological and molecular-genetic data, the taxonomic status of its Caucasian forms is discussed. In the Eastern Caucasus (Republic of Dagestan, Russia), we caught Myotis animals related to the group of «Myotis nattereri» species, similar to specimens of the West Asian Myotis cf. tschuliensis on the basis of skull size measurements. A comparison analysis showed that, outwardly, M. cf. tschuliensis 2 individuals are highly similar to specimens from Central Russia. However, these animals have some differences in the ear structure, os penis, attachment of the posterior edge of the wing membrane to the foot, and in the ratio of cilia lengths to bristles on the free edge of the tail membrane. The more reliable differences between M. cf. tschuliensis 2 animals and M. nattereri s.str. specimens were revealed on the basis of craniometric studies, but the complete confirmation of the species' independence of Caucasian specimens was obtained using the analysis of mtDNA sequences. According to phylogenetic constructions, Dagestan specimens designated by us as M. cf. tschuliensis 2, formed a well separated sister line in relation to the clade of Caucasian forms: M. schaubi and M. cf. tschuliensis 1 (p-distance: 7.4–7.0%). There are no reliable morphological differences between M. cf. tschuliensis 2 and M. cf. tschuliensis 1. Prior to genetic studies of M. tschuliensis specimens, we suggest using an open nomenclature for the East Caucasian form. If specimens designated as M. cf. tschuliensis 1, originated from the Near East, are genetically identical to the M. cf. tschuliensis specimens from its type location in Turkmenistan, then Dagestan bats designated as M. cf. tschuliensis 2 should be considered as a new, undescribed species.

The utility of DNA Barcoding for species identification and discovery has catalyzed a concerted effort to build the global reference library; however, many animal groups of economical or conservational importance remain poorly represented. This study aims to contribute DNA barcode records for all ground squirrel species (Xerinae, Sciuridae, Rodentia) inhabiting Eurasia and to test efficiency of this approach for species discrimination. Cytochrome c oxidase subunit 1 (COI) gene sequences were obtained for 97 individuals representing 16 ground squirrel species of which 12 were correctly identified. Taxonomic allocation of some specimens within four species was complicated by geographically restricted mtDNA introgression. Exclusion of individuals with introgressed mtDNA allowed reaching a 91.6% identification success rate. Significant COI divergence (3.5-4.4%) was observed within the most widespread ground squirrel species (Spermophilus erythrogenys, S. pygmaeus, S. suslicus, Urocitellus undulatus), suggesting the presence of cryptic species. A single putative NUMT (nuclear mitochondrial pseudogene) sequence was recovered during molecular analysis; mitochondrial COI from this sample was amplified following re-extraction of DNA. Our data show high discrimination ability of 100 bp COI fragments for Eurasian ground squirrels (84.3%) with no incorrect assessments, underscoring the potential utility of the existing reference librariy for the development of diagnostic 'mini-barcodes'.