Cetaceans of the Black Sea: where did they survive glacial?

Abstract

11Three species of cetaceans, Phocoena phocoena, Delphinus delphis and Tursiops truncatus 12 ponticus are found in the Black Sea. The Black Sea populations of all three species show 13 morpho-ecological peculiarities that leaded to their subspecific status: P. p. relicta (PPR), D. 14 d. ponticus (DDP), and T. t. ponticus (TTP). It is not clear how long-lasting was their 15 isolation from the core conspecific populations that ensured the development of adaptive 16 features of PPR, DDP, and TTP. The analysis of mitochondrial haplotypes of PPR suggests 17 that the split time of the at least maternal lineage of the Black Sea population of harbour 18 porpoise lasted for over 100 ky (i.e. they should survive at least the latest glacial maximum 19within the Black Sea). However, the analysis of multiple microsatellite genotypes leaded 20 some authors to suggest that the isolation is much less long, since middle Holocene. We re-21 analysed published mitochondrial sequences of all three Black Sea cetaceans along with 22 several tens of sequences obtained from the stranded cetaceans. Our analyses suggest that 23 Black Sea populations of all three cetacean species have an important input of populations 24 that survived the last (and maybe earlier) glacial maxima within the Black Sea, most likely in 25 its south-eastern fragment, which did not freeze in winter time even during the glacial peaks. 26This analysis is supported by both molecular clock approach and simple population 27 modelling based on the assumption on the effective population size range. Different from the 28 PPR, whose Black Sea population is currently fully isolated, there is a limited migration 29 between the Black Sea and Atlantic populations of T. truncatus and D. delphis, through the 30 Mediterranean "bridge" population. However, the migration rates are not sufficient to 31 overweight differential selection between the Black Sea and Mediterranean populations, and 32 the local morpho-ecological specifics is successfully maintained. 33 34 35 65 the Atlantic and Black Sea populations of harbour porpoise suggests their separation at least 66 for 175 kyr (Tolley & Rosel, 2006; Viaud-Martínez et al., 2007). However, Fontaine et al. 67 4 (2010, 2012, 2014) disputed this dating, using the Bayesian model of divergence, based on 68 ten microsatellite loci analysis, as an argument. 69 The inference of Fontain et al. (2012; 2014) is however based on an assumption about strong 70 selection underlining the evolution of mitochondrial genome, and the authors acknowledge 71 this complication in the interpretation of the time of divergence between the Black Sea and 72 the Atlantic population of harbor porpoises. Besides, the Model for Interdisciplinary 73 Research on Climate (MIROC) (Braconnot et al., 2007) that was shown to be more realistic 74 than the other palaeoclimatic models (Tarkhnishvili et al., 2012) suggests positive winter 75 temperature at least at the south-eastern Black Sea Coast, which excludes complete freezing 76 of the Black Sea surface and does n...