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Maintenance of a narrow hybrid zone between native and introduced red foxes (Vulpes vulpes) despite conspecificity and high dispersal capabilities

Preckler-Quisquater, Sophie1; Quinn, Cate B.2; Sacks, Benjamin N.1

Research facility: University of California, Davis
Published Jun 05, 2024 on Dryad. https://doi.org/10.5061/dryad.tx95x6b50

Data files

Jun 05, 2024 version files 1.25 MB

Abstract

Human-facilitated introductions of nonnative populations can lead to secondary contact between previously allopatric lineages, resulting in either homogenization of the lineages or stable hybrid zones that are maintained by pre-zygotic (e.g., behavioral) or post-zygotic (e.g., reduced hybrid fitness) reproductive barriers. We investigated patterns of gene flow between the native Sacramento Valley red fox (Vulpes vulpes patwin) and an introduced conspecific population of captive-bred (fur-farm) origin in California’s Central Valley. Considering their recent divergence (i.e., ~50 kya), we hypothesized that pre-zygotic mechanisms primarily impede gene flow, rather than post-zygotic barriers. Additionally, some genes originating in nonnative foxes may confer higher fitness in the currently human-dominated landscape resulting in selective introgression into the native population. Genetic analysis of 682 red foxes (255 native, 427 nonnative) at both mitochondrial (cytB + Dloop) and nuclear loci (~19,000 SNPs) revealed significantly narrower cline widths than expected under a simulated model of unrestricted gene flow, consistent with the existence of pre- or post-zygotic reproductive barriers. We identified several loci with reduced introgression linked to behavioral divergence in captive bred foxes, which supports pre-zygotic mechanisms as a putative driver of the narrow hybrid zone. Additionally, several loci with elevated gene flow from the nonnative into the native population, were near genes associated with adaptation to human dominated landscapes.  Overall, this study contributes to our understanding of hybrid zone dynamics in vertebrates, particularly in the context of species introductions and landscape changes, underscoring the importance of considering multiple mechanisms that may be at play in maintaining lineages at both the species and subspecies level.