Abstract
Genetic connectivity is expected to be lower in species with limited dispersal ability and a high degree of habitat specialization (intrinsic factors). Also, gene flow is predicted to be limited by habitat conditions such as physical barriers and geographic distance (extrinsic factors). We investigated the effects of distance, intervening pools, and rapids on gene flow in a species, the Tuxedo Darter (Etheostoma lemniscatum), a habitat specialist that is presumed to be dispersal‐limited. We predicted that the interplay between these intrinsic and extrinsic factors would limit dispersal and lead to genetic structure even at the small spatial scale of the species range (a 38.6 km river reach). The simple linear distribution of E. lemniscatum allowed for an ideal test of how these factors acted on gene flow and allowed us to test expectations (e.g., isolation‐by‐distance) of linearly distributed species. Using 20 microsatellites from 163 individuals collected from 18 habitat patches, we observed low levels of genetic structure that were related to geographic distance and rapids, though these factors were not barriers to gene flow. Pools separating habitat patches did not contribute to any observed genetic structure. Overall, E. lemniscatum maintains gene flow across its range and is comprised of a single population. Due to the linear distribution of the species, a stepping‐stone model of dispersal best explains the maintenance of gene flow across its small range. In general, our observation of higher‐than‐expected connectivity likely stems from an adaptation to disperse due to temporally unstable and patchy habitat.
Highlights
Understanding dispersal and gene flow is fundamental to many ecology, evolution, and conservation biology studies, as both contribute to population persistence through space and time
We expected E. lemniscatum would exhibit reduced gene flow as predicted of a habitat specialist, dispersal-limited species, especially given that its microhabitat is separated by long reaches of unsuitable habitat
We found that gene flow occurs at high levels up to 2.45 km and is well maintained up to 5.8 km, distances greater than the pool lengths separating most adjacent habitat patches
Summary
Understanding dispersal and gene flow is fundamental to many ecology, evolution, and conservation biology studies, as both contribute to population persistence through space and time. This endemic fish is found in only a 38.6 km reach of the mainstem Big South Fork River where its upstream range is constrained by a Class IV rapid, Angel Falls, that is thought to impede upstream movement (Davis & Cook, 2010), and its downstream range is limited due to inundation effects (e.g., sedimentation and reduced flow) from a reservoir created by Wolf Creek Dam in 1950 (Campbell, Risk, Andrews, Palmer-Bell, & MacGregor, 1990) This species is expected to show high levels of genetic structure, even at small spatial scales, since it is a habitat specialist with hypothesized limited dispersal ability (Centeno-Cuadros et al, 2011; Fluker, Kuhajda, & Harris, 2014). E. lemniscatum to help guide future conservation decisions, given that the species displays several intrinsic characteristics (habitat specialist, dispersal-limited, benthic larvae, and small native range) indicative of an elevated extinction risk and vulnerability to anthropogenic habitat fragmentation (Douglas et al, 2013; Warren et al, 2000)
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