Abstract
Many organisms are primarily constrained to the channels of the upstream terminus of river networks with limited capacities for both in‐stream and overland dispersal. Dispersal is believed to contribute to gene flow and the demographic stability of headwater populations. While assumed, the importance of overland dispersal to gene flow is largely unexplored in headwater salamanders. Six microsatellite markers were used to assess patterns of genetic population structure for a headwater salamander, Desmognathus fuscus. Tissue samples were collected using a nested hierarchical study design, which specifically addressed the contribution of overland movements to the genetic connectivity of headwater populations. Genetic divergence was significant among all populations (Fst = 0.027–0.405) and at all hierarchical spatial scales. However, lower degrees of genetic population structure were observed among proximal streams that shared no downstream hydrologic connections. Mantel tests indicated a significant relationship between genetic divergence and overland distance, suggesting that D. fuscus populations conform to an isolation‐by‐distance model of gene flow. Estimated dispersal among headwater streams was limited, with an average of less than one effective migrant per generation moving between paired headwater streams. These results indicate that regional patterns of genetic population structure are influenced by overland dispersal and suggest the importance of terrestrial movements in maintaining population connectivity among D. fuscus populations.
Highlights
Dispersal plays a key role in determining the population dynamics and genetic structure of organisms with patchy distributions
Hierarchical measures of genetic differentiation indicated greater genetic population structuring among streams within watersheds (Fst 1⁄4 0.091), than among paired watersheds (Fst 1⁄4 0.027; Table 1)
We provide evidence of overland dispersal and its contribution to gene flow among D. fuscus populations associated with headwater stream channels
Summary
Dispersal plays a key role in determining the population dynamics and genetic structure of organisms with patchy distributions. The capacity of an organism to disperse is driven largely by its ability to move between habitat patches across a landscape matrix characterized by suboptimal habitat (Turner et al 1995). There may be risks to individual fitness associated with moving across the landscape, such as death or injury, energy costs, or the possibility of settling in a habitat patch that was less suitable than the source (Bonte et al 2012). Dispersal provides an opportunity to colonize unoccupied habitat patches (Fagan 2002), it may stabilize or destabilize populations depending on the rate of dispersal among populations (Brown and Kodric-Brown 1977, Labonne et al 2008, Grant et al 2010).
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