Speciation processes in two co-distributed freshwater turtle complexes in a hotspot of genetic diversity (Emys orbicularis complex; Mauremys caspica, M. rivulata)
Final Report Abstract
Chelonians are capable of extensive hybridization even between very distantly related taxa. Thus, the questions arise how distinct species evolved and how they maintain their genetic integrity. For gaining insights in these issues, we selected two freshwater turtle groups (Emys orbicularis complex and Mauremys caspica, M. rivulata) with similar distributions and habitats, but representing distinct stages in the speciation process. We studied for each group genetic differentiation and gene flow across secondary contact zones. Using broad and dense geographic sampling, we applied an array of mitochondrial and nuclear genomic markers (cyt b gene, microsatellite loci, nuclear genes) to unravel horizontal gene flow. Besides the unexpected finding of massive gene flow across the Aegean Sea for one species (M. rivulata), our results unveiled that there are few general patterns for genetic differentiation, introgression and gene flow, suggesting that genetic differentiation leading to speciation follows in chelonians largely idiosyncratic pathways. Only mountain chains serve generally as genetic divides, while sea straits and the open sea can have this function or not, with rivers acting often as dispersal corridors. Even within the same group, hybridization and gene flow may differ across the distribution range, with regions with little hybridization and others with more or less complete amalgamation of taxa as evinced by the unexpected discovery of a hybrid swarm of Mauremys in a remote region (southern Levant). This hybrid swarm occurs far away from any extant contact zone and underlines also that historic processes and range shifts have to be taken into account and that range-wide sampling should be mandatory for hybridization studies. Our findings in M. rivulata further show that phylogeographic structuring, and most likely genomic diversity of a species, may be massively impacted by introgressed genes from another taxon since the negligible, but discernible, phylogeographic structuring in this species can be attributed to introgressed alleles from M. caspica. European pond turtles (Emys orbicularis, E. trinacris) show like M. caspica pronounced phylogeographic structuring. We found in E. trinacris, endemic to Sicily, much stronger population structuring than in subspecies of E. orbicularis. This is likely related to the fact that E. trinacris was largely stationary during the Pleistocene glacials on Sicily, whereas the ranges of the continental subspecies of E. orbicularis repeatedly contracted and expanded with glacial cycles. Our population genetic results also contribute to conservation planning. Conservation strategies for freshwater turtles often include translocation of animals, and our data can help selecting genetically fitting individuals. For M. rivulata in Croatia and several populations of E. orbicularis in the northern part of the range (Baltic countries), we could show that genetically mismatching animals were selected for large-scale translocations. Our data will help in future avoiding such unintended erosion of genetic diversity.
Publications
- (2013): Conservation genetics and phylogeography of the poorly known Middle Eastern terrapin Mauremys caspica (Testudines: Geoemydidae). Organisms, Diversity & Evolution, 13: 77-85
Vamberger, M., Stuckas, H., Ayaz, D., Graciá, E., Aloufi, A.A., Els, J., Mazanaeva, L.F., Kami, H.G. & U. Fritz
(See online at https://doi.org/10.1007/s13127-012-0102-6) - (2014): Massive transoceanic gene flow in a freshwater turtle (Testudines: Geoemydidae: Mauremys rivulata). Zoologica Scripta, 43: 313-322
Vamberger, M., Stuckas, H., Ayaz, D., Lymberakis, P., Široký, P. & U. Fritz
(See online at https://doi.org/10.1111/zsc.12055) - (2014): Where are you from, stranger? The enigmatic biogeography of North African pond turtles (Emys orbicularis). Organisms, Diversity & Evolution, 14: 295-306
Stuckas, H., Velo-Antón, G., Fahd, S., Kalboussi, M., Rouag, R., Arculeo, M., Marrone, F., Sacco, F., Vamberger, M. & U. Fritz
(See online at https://doi.org/10.1007/s13127-014-0168-4) - (2015): Differences in gene flow in a twofold secondary contact zone of pond turtles in southern Italy (Testudines: Emydidae: Emys orbicularis galloitalica, E. o. hellenica, E. trinacris). Zoologica Scripta, 44: 233-239
Vamberger, M., Stuckas, H., Sacco, F., D’Angelo, S., Arculeo, M., Cheylan, M., Corti, C., Lo Valvo, M., Marrone, F., Wink, M. & U. Fritz
(See online at https://doi.org/10.1111/zsc.12102) - (2016): Unexpected hybridization patterns in Near Eastern terrapins (Mauremys caspica, M. rivulata) indicate ancient gene flow across the Fertile Crescent. Zoologica Scripta
Vamberger, M., Stuckas, H., Vargas-Ramírez, M. Kehlmaier, C., Ayaz, D., Aloufi, A.A., Lymberakis, P., Široký, P. & U. Fritz
(See online at https://doi.org/10.1111/zsc.12227) - (2017): Hybridisation between turtle subspecies: a case study with the European pond turtle (Emys orbicularis). Conservation Genetics, 18: 287-296
Raemy, M., Fritz, U., Cheylan, M. & S. Ursenbacher
(See online at https://doi.org/10.1007/s10592-016-0901-y)
