Abstract
The Caspian Sea has been a highly dynamic environment throughout the Quaternary and witnessed major oscillations in lake level, which were associated with changes in salinity and habitat availability. Such environmental pressures are considered to drive strong phylogeographic structures in species by forcing populations into suitable refugia. However, little is actually known on the effect of lake-level fluctuations in the Caspian Sea on its aquatic biota. We compared the phylogeographic patterns of the aquatic Neritidae snail genus Theodoxus across the Pontocaspian region with refugial populations in southern Iran. Three gene fragments were used to determine relationships and divergence times between the sampled populations in both groups. A dated phylogeny and statistical haplotype networks were generated in conjunction with the analyses of molecular variance and calculations of isolation by distance using distance-based redundancy analyses. Extended Bayesian skyline plots were constructed to assess demographic history. Compared with the southern Iranian populations, we found little phylogeographic structure for the Pontocaspian Theodoxus group, with more recent diversification, homogeneity of haplotypes across the Pontocaspian region and a relatively stable demographic history since the Middle Pleistocene. Our results argue against a strong influence of Caspian Sea low stands on the population structure post the early Pleistocene, whereas high stands may have increased the dispersal possibilities and homogenization of haplotypes across the Pontocaspian region during this time. However, during the early Pleistocene, a more dramatic low stand in the Caspian Sea, around a million years ago, may have caused the reduction in Theodoxus diversity to a single lineage in the region. In addition, our results provide new insights into Theodoxus taxonomy and outlooks for regional conservation.
Highlights
The Caspian Sea is one of the largest and oldest lakes on the planet
We found some indication for an early catastrophic bottleneck reducing Theodoxus diversity to a single lineage in the Pontocaspian region during the early Pleistocene
In contrast with strong intraspecific phylogeographic structure and isolation by distance (IBD) observed in the southern Iranian Theodoxus, haplotypes belonging to the Pontocaspian group are shared among a variety of locations and IBD was either far weaker or not supported at all
Summary
The Caspian Sea is one of the largest and oldest lakes on the planet. Barring episodic overflow events, the Caspian Sea has been an isolated endorheic basin since at least the early Pliocene, around 5.3 million years ago (Ma) [1]. The Caspian Sea and its catchment cover an area of approximately 3 500 000 km2 [2,3] It is renowned for its dramatic historical lake-level fluctuations and salinity shifts, primarily as a consequence of glacial cycles during the Quaternary [1,4]. Temporary connections occurred between the Caspian Sea and other Pontocaspian basins (i.e. the Aral, Azov and Black seas [1]) during high stands. These changes are hypothesized to have had a major effect on the evolutionary history of its aquatic biota, such as the highly endemic gastropod fauna [5]. Such fluctuations make the Caspian Sea a suitable model system to study the effect of palaeo-environmental changes on the phylogeographic structure in long-lived lake biota
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
