Abstract
DNA sequence data from mitochondrial cytochrome-b (Cytb) and Y-linked structural maintenance of chromosomes (SmcY) genes were combined with 478 nuclear loci obtained from amplified fragment length polymorphisms (AFLP) to assess the extent of hybridization and genetic spatial structure of populations in two hybridizing species of ground squirrel (Ictidomys parvidens and Ictidomys tridecemlineatus). Based on AFLP analyses of 134 individuals from 28 populations, 10 populations were identified that possessed hybrid individuals. Overall estimates of FST values revealed strong support for population structure in the Cytb data set; however, analyses of the SmcY gene and the AFLP data indicated ongoing gene flow between species. Pairwise FST comparisons of populations were not significant for the SmcY gene; although they were significant for the Cytb gene, indicating that these populations were structured and that gene flow was minimal. Therefore, gene flow between I. parvidens and I. tridecemlineatus appeared to be restricted to populations that exhibited hybridization. In addition, the fragmented nature of the geographic landscape suggested limited gene flow between populations. As a result, the distributional pattern of interspersed parental and hybrid populations were compatible with a mosaic hybrid zone model. Because ground squirrels display female philopatry and male-biased dispersal, the ecology of these species is compatible with this hypothesis.
Highlights
Hybrid zones are the result of the interaction of genetically distinct groups that produce offspring of mixed ancestry (Barton and Hewitt 1985; Arntzen 1996; Abbott et al 2013)
Ecology and Evolution published by John Wiley & Sons Ltd
The second network contained individuals identified morphologically as I. parvidens, I. tridecemlineatus, and hybrids (Thompson et al, in press). These individuals were from populations with potential hybrids, as well as reference populations of I. tridecemlineatus
Summary
Hybrid zones are the result of the interaction of genetically distinct groups that produce offspring of mixed ancestry (Barton and Hewitt 1985; Arntzen 1996; Abbott et al 2013). Hybrid zones often provide a natural laboratory for addressing major evolutionary concepts (Hewitt 1988; Baker et al 1989; Harrison 1993). Studies of hybrid zones offer the opportunity to examine genetic control of speciation, mechanistic models of maintenance, premating and postmating isolation, direction of introgression, and other processes and patterns of hybridization a 2013 The Authors. Understanding the spatial structure of phenotypes and genotypes in a hybrid zone is essential to determine the underlying mechanisms responsible for hybridization (Cain et al 1999)
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