Spatial and temporal patterns of species replacement in the Middle Pleistocene: а case study of Мicrotus nivaloides Major, 1902 and morphologically related species of the Northern Black Sea and Azov areas

Abstract

AbstractThe Middle Pleistocene replacement of the extinct Microtus nivaloides with its likely descendant field vole (M. agrestis Linnaeus, 1761) shows regional differences suggesting the climatic control of the process. Our aim was to test this hypothesis. We studied samples of M. nivaloides and morphologically related species, both recent and extinct, from the Northern Black Sea and Azov areas by means of geometric morphometry. There were measured pairwise Euclidian distances between each fossil specimen and centroids of the extant groups, and between centroids of all studied groups. When the studied samples were arranged in stratigraphic order, the decrease in these distances indicated the nearest approach to (i.e. the appearance of) M. agrestis within the considered area. Our results show that it was an expansion rather than a continuation of previous evolutionary trends. M. agrestis, the species of wet habitats, came to the Northern Black Sea area from the west during the warm and humid Holsteinian interglacial (MIS 11). The species was not widespread within the area and allopatrically coexisted with M. nivaloides. Besides, Holsteinian warming enhanced migration of other mesophilic vole species from adjacent areas. Our approach may be expanded to other extinct species with overlapping ranges of variation.