Abstract
To examine the processes that maintain genetic diversity among closely related taxa, we investigated the dynamics of introgression across a contact zone between two lineages of California voles (Microtus californicus). We tested the prediction that introgression of nuclear loci would be greater than that for mitochondrial loci, assuming ongoing gene flow across the contact zone. We also predicted that genomic markers would show a mosaic pattern of differentiation across this zone, consistent with genomes that are semi‐permeable. Using mitochondrial cytochrome b sequences and genome‐wide loci developed via ddRAD‐seq, we analyzed genetic variation for 10 vole populations distributed along the central California coast; this transect included populations from within the distributions of both parental lineages as well as the putative contact zone. Our analyses revealed that (1) the two lineages examined are relatively young, having diverged ca. 8.5–54 kya, (2) voles from the contact zone in Santa Barbara County did not include F1 or early generation backcrossed individuals, and (3) there appeared to be little to no recurrent gene flow across the contact zone. Introgression patterns for mitochondrial and nuclear markers were not concordant; only mitochondrial markers revealed evidence of introgression, putatively due to historical hybridization. These differences in genetic signatures are intriguing given that the contact zone occurs in a region of continuous vole habitat, with no evidence of past or present physical barriers. Future studies that examine specific isolating mechanisms, such as microhabitat use and mate choice, will facilitate our understanding of how genetic boundaries are maintained in this system.
Highlights
| INTRODUCTIONCalifornia, we used both mitochondrial and genome-wide nuclear markers to test two sets of predictions regarding the nature of the putative contact zone
Understanding the processes that generate and maintain genetic differences among organisms is central to understanding the evolution of biodiversity (Seehausen et al, 2014; Vellend, 2005)
We investigated the occurrence of a putative contact zone between genetically distinct northern and southern lineages of M. californicus in the vicinity of Santa Barbara County, California (Conroy & Neuwald, 2008)
Summary
California, we used both mitochondrial and genome-wide nuclear markers to test two sets of predictions regarding the nature of the putative contact zone If this zone reflects speciation with gene flow (Feder, Egan, & Nosil, 2012; Nosil, 2008) associated with Bateson-Dobzhansky-Muller incompatibilities (Coyne & Orr, 2004c; Haldane, 1922), multiple generations of backcrossing of hybrids should be evident and genomic loci should show a mosaic pattern of differentiation across the contact zone consistent with semi- permeability of the diverging genomes; collectively, these features should result in a gradual transition between genomes (i.e., unimodal contact zone; Jiggins & Mallet, 2000). In addition to providing insights into the maintenance of genetic differences between northern and southern lineages of California voles, our analyses generate new insights regarding the processes operating in contact zones between closely related, presumably recently diverged lineages that are not associated with conspicuous geographic or environmental barriers
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.
