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

Abstract

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.

Insights on the Existence of Ancient Glacial Refugee in the Northern Black/Azov Sea Lowland, with the Description of the First Stygobiotic Microcrustacean Species of the Genus Niphargus Schiödte, 1849 from the Mouth of the Don River

“…Formation of the northwestern foothills of the Great Caucasian Ridge and salinization of the Azov Sea basin during the last 1.0-1.5 Mya probably led to the formation of a rather isolated Azov-Prikubanskaya Lowland and its specific fauna. [100,101], also representing the recent speciation [54]. Formation of the northwestern foothills of the Great Caucasian Ridge and salinization of the Azov Sea basin during the last 1.0-1.5 Mya probably led to the formation of a rather isolated Azov-Prikubanskaya Lowland and its specific fauna.…”

“…Low diversity in these areas can also be explained by the influence of ancient periods of cooling and glaciation, especially the significant influence of the cold climate in Pleistocene [94,95]. Tya) [100,101], also representing the recent speciation [54]. Formation of the northwestern foothills of the Great Caucasian Ridge and salinization of the Azov Sea basin during the last 1.0-1.5 Mya probably led to the formation of a rather isolated Azov-Prikubanskaya Lowland and its specific fauna.…”

“…The formation of the Carpathian arc-shaped mountain belt led to the final division of Paratethys into two parts in the Late Miocene (about 11.63-5.333 Mya)-the Central Paratethys (Pannon Lake, or Pannonian Basin) and the Eastern Paratethys (Dacian, Euxine and Caspian basins) [64,65,98,99]. Later, the Messinian crisis (5.96-5.33 Mya), fluctuations in the level/salinity of the separated abovementioned basins of the Eastern Paratethys during the Pliocene (5.333-2.58 Mya), divided ancestral genetic lineages into various refugees, where they survived during the Pleistocene periods of cooling/glaciation (2.58 Mya-11.7 Tya)[100,101], also representing the recent speciation[54]. Formation of the northwestern foothills of the Great Caucasian Ridge and salinization of the Azov Sea basin during the last 1.0-1.5 Mya probably led to the formation of a rather isolated Azov-Prikubanskaya Lowland and its specific fauna.…”