Multiple Pleistocene refugia and repeated phylogeographic breaks in the southern Caspian Sea region: Insights from the freshwater crab Potamon ibericum

Abstract

Aim: Phylogeographic studies on a number of Western Palaearctic taxa imply that the southern Caspian Sea region served as a refugium during the Last Glacial Maximum (LGM). Nevertheless, the LGM biogeography of the terrestrial and freshwater organisms in this region is poorly understood. By studying phylogeography of a species of freshwater crab, we unravel the location of probable local refugia and colonization patterns across this topographically complex landscape.Location: Southern Caspian Sea region.Taxon: The freshwater crab Potamon ibericum. Methods:We inferred the demographic history of Potamon ibericum using 163 mtDNA Cox1 sequences from 16 localities. For a subset of specimens, we amplified mtDNA 16S and four nuclear markers (28S, Histone3, Enolase, NaK) to confirm the phylogeographic structure. We tested Pleistocene expansion-contraction dynamics, using species distribution modelling (SDM) and assessed morphological variability by geometric-morphometric methods. Results: Mitochondrial markers revealed the existence of three parapatrically distributed lineages in the western, central and eastern parts of the region. The more conserved nuclear markers did not reflect this. The SDM revealed the fundamental niche expansion of P. ibericum along the southern Caspian Sea during the LGM, agreeing with results from the Cox1 data of demographic expansions. Despite strong morphological resemblance, geometric-morphometrics elucidated clinal carapace shape variation. Main Conclusions: Considering the Caspian Sea level fluctuations during the late Pleistocene, we hypothesize a scenario of demographic contraction during interglacial/warmer conditions, due to the Caspian Sea transgression and latitudinal range shift within the narrow distribution of the species between the southern Caspian Sea and northern slopes of the Alborz Mountains. During the glacial periods, the sea regressed and moist and warm conditions, characterizing glacial refugia, became prevalent in the region and caused isolated populations to expand. Our study confirms the deep transverse phylogeographic break, previously identified for Darevskia lizards in the region, and adds support to the presence of several LGM refugia in the southern Caspian Sea region.

Phylogeography of Potamon ibericum (Brachyura: Potamidae) identifies Quaternary glacial refugia within the Caucasus biodiversity hot spot

“…We used leg muscle tissue, preserved in absolute ethanol at −20°C, to extract genomic DNA, using a Puregene protocol (Gentra Systems, Minneapolis). Partial fragments of the cytochrome oxidase subunit I gene were amplified by polymerase chain reaction with primer pairs COL6 (Schubart, ) and COH10Po (Parvizi et al, ) following the procedures as described in Keikhosravi, Fratini, and Schubart (). The amplified products were sequenced by Macrogen (Seoul, South Korea).…”

“…The haplotype network was edited and visualized in tcsBU (dos Santos, Cabezas, Tavares, Xavier, & Branco, ). In order to identify the relationship of the obtained haplotypes from this study with the previously recognized evolutionary lineages of P. ibericum species complex (Jesse et al, ; Parvizi et al, ), we retrieved COI sequences from GenBank (accession numbers –; ; ; ; ) and reconstructed a phylogenetic tree with Bayesian Inference (BI) by using MrBayes 3.2.2 (Ronquist et al, ). We used HKY+I as best‐fitting model of nucleotide substitution (previously selected with Jmodeltest 2.1.4, Darriba, Taboada, Doallo, & Posada, ) and conducted the BI analysis with four Markov Chain Monte Carlo (MCMC) simulations that were run for 5 000 000 generations and parameters sampled from each chain every 5000th generation.…”

“…A recent phylogeographic study of P . ibericum inhabiting the drainages of Hyrcania elucidated three parapatrically distributed lineages, including western, central, and eastern Caspian lineages with substantial genetic diversity and strong population structure within each lineage (Parvizi et al, ). These findings showed that the Caspian Sea level fluctuations during glacial‐interglacial periods contributed to the cyclic expansion and contraction of populations from several independent local refugia in the southern Caspian Sea.…”

“…Potamon ibericum (Bieberstein, 1808) is a primary freshwater crab with a relatively wide range of distribution from river systems of the southern Caspian Sea to the Caucasus, through the river systems of the southern and western Black Sea, to the northern Aegean Sea in its western limit ( Figure 1a; Brandis, Storch, & Turkay, 2000). Potamid crabs have limited dispersal abilities and seawater, large dry terrestrial landscapes and mountain ranges can act as their dispersal barrier (Parvizi, Naderloo, Keikhosravi, Solhjouy-Fard, & Schubart, 2018;Shih, Zhou, Chen, Chien, & Ng, 2011;Yeo et al, 2008). They also lack pelagic larval dispersal, which intensifies their prolonged restriction to a freshwater system (Yeo et al, 2008) and consequently influences the spatial genetic pattern of their populations during colonization (Ibrahim, Nichols, & Hewitt, 1996).…”

“…They also lack pelagic larval dispersal, which intensifies their prolonged restriction to a freshwater system (Yeo et al, 2008) and consequently influences the spatial genetic pattern of their populations during colonization (Ibrahim, Nichols, & Hewitt, 1996). Previous studies on P. ibericum revealed the presence of at least seven separately evolving lineages within its total distribution (Jesse, Grudinski, Klaus, Streit, & Pfenninger, 2011;Parvizi et al, 2018). The eastern distribution of P. ibericum extends into two glacial refugia ( Figure 1a): Hyrcania, located along the southern (Tarkhnishvili, Gavashelishvili, & Mumladze, 2012).…”