Abstract
In this study, genetic variation was assessed in Aphanius fasciatus and Aphanius iberus characterized by similar ecological traits but with very different distribution ranges in the Mediterranean area. Five populations of A. iberus and five of A. fasciatus were analysed using five polymorphic microsatellite loci and partial mitochondrial control region (D-loop) sequences. Congruent results were found with both nuclear and mitochondrial molecular markers. The results showed that similar levels of genetic divergence, based on mitochondrial control region sequences, are present among populations of A. iberus and among populations of A. fasciatus despite the very different geographic distance existing among the examined populations of the two species (low geographic distance in A. iberus and high in A. fasciatus). A possible explanation could be that the populations of A. iberus were isolated for a longer time than the populations of A. fasciatus supporting the hypothesis that the split in the lineage leading to A. iberus is older than the split in the lineage leading to A. fasciatus. The possibility that the wide circum-Mediterranean distribution of A. fasciatus ensures the high connectivity of its populations, preventing, in some cases, local differentiation, however, cannot be ruled out.
Highlights
The population structure of brackish water species has attracted considerable interest, because they often exhibit narrow habitat specificity, which in combination with geographic isolation of the different populations may lead to higher chances of evolutionary divergence among populations and speciation (e.g. Carvalho, 1993; Cognetti & Maltagliati, 2000; Bilton et al., 2002)
All examined loci were polymorphic in A. fasciatus except locus Af11, which was fixed in this species
Three Fis values remained significant after Bonferroni correction, which indicates their departure from HW equilibrium due to a strong heterozygote deficit (Table II, Fig. SI)
Summary
The population structure of brackish water species has attracted considerable interest, because they often exhibit narrow habitat specificity, which in combination with geographic isolation of the different populations may lead to higher chances of evolutionary divergence among populations and speciation (e.g. Carvalho, 1993; Cognetti & Maltagliati, 2000; Bilton et al., 2002). The population structure of brackish water species has attracted considerable interest, because they often exhibit narrow habitat specificity, which in combination with geographic isolation of the different populations may lead to higher chances of evolutionary divergence among populations and speciation Killifish (order Cyprinodontiformes) usually inhabit estuarine and salt marshes along the coastlines of the New and Old World, and some species have been used as model for understanding local and regional adaptation to variable environments Aphanius killifishes living in freshwater as well as in brackish water bodies along the Mediterranean coast have been considered a model system to study speciation phenomena Aphanius in the Mediterranean basin using mitochondrial (mt) DNA supported a predominantly vicariant-based speciation hypothesis with a major role played by the Messinian Salinity Crisis (Hrbek & Meyer, 2003). The two species belong to the western clade formed when the final closing of the Tehys Sea (approximately 20 MYA) separated the ancestral
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