Can natural selection maintain long-distance dispersal? Insight from a stream salamander system

Abstract

Dispersal distributions are often characterized by many individuals that stay close to their origin and large variation in the distances moved by those that leave. This variation in dispersal distance can strongly influence demographic, ecological, and evolutionary processes. However, a lack of data on the fitness and phenotype of individual dispersers has impeded research on the role of natural selection in maintaining variation in dispersal distance. Six years of spatially explicit capture-mark-recapture data showed that survival increased with dispersal distance in the stream salamander Gyrinophilus porphyriticus. To understand the evolutionary implications of this fitness response, we tested whether variation in dispersal distance has a phenotypic basis. We used photographs of marked individuals to measure head, trunk, and leg morphology. We then tested whether dispersal distances over the six-year study period were predicted by these traits. Dispersal distance was significantly related to leg morphology: individuals with relatively long forelimbs and short hindlimbs dispersed the farthest. These results support the hypothesis that positive fitness consequences maintain phenotypes enabling long-distance dispersal. More broadly, they suggest that natural selection can promote variation in dispersal distance and associated phenotypes, offering an alternative to the view that dispersal distance is driven by stochastic or landscape-specific mechanisms.

Does dispersal influence the strength of intraspecific competition in a stream salamander?

“…Individuals of higher body condition are more likely to disperse upstream and contribute to population stability at upstream sites, suggesting that spatial sorting along streams may influence the strength and spatial structure of intraspecific competition (Lowe, ; Lowe, Likens & Cosentino, ). Individuals dispersing the farthest also have relatively long forelimbs and short hindlimbs in comparison with non‐dispersing individuals (Lowe & McPeek, ), and survival probability increases with dispersal distance, reinforcing the process of spatial sorting. In the same system, patterns of evolutionary divergence along streams were consistent with a reduction in upstream dispersal and gene flow with stream slope (Lowe et al ., , ; Lowe & McPeek, ).…”

“…Individuals dispersing the farthest also have relatively long forelimbs and short hindlimbs in comparison with non‐dispersing individuals (Lowe & McPeek, ), and survival probability increases with dispersal distance, reinforcing the process of spatial sorting. In the same system, patterns of evolutionary divergence along streams were consistent with a reduction in upstream dispersal and gene flow with stream slope (Lowe et al ., , ; Lowe & McPeek, ). Specifically, genetic distance increases with slope between downstream and upstream sampling sites separated by 1 km (Lowe et al ., , ), suggesting that intraspecific evolutionary divergence could also influence the strength and spatial structure of intraspecific competition.…”

Selecting for invasive tendencies: the evolution of morphological, physiological, and movement behaviour traits associated with dispersal

“…This relationship could be explained mechanistically by longer legs allowing an increased stride length, in turn allowing the animal to move a greater distance with each step taken, therefore also achieving a greater speed (Zollikofer 1994). A long-term study of stream salamanders (Gyrinophilus porphyriticus) found that individuals with long forelimbs relative to their hindlimbs dispersed greater distance, indicating that locomotor morphology has a major role in long-distance dispersal and fitness (Lowe & McPeek 2012). Evolutionary mechanisms can select for individuals that have phenotypic traits that allow them to move farther, which may indicate the presence of a dispersal phenotype (e.g.…”

“…Natural selection is the conventional mechanism for evolutionary change, whereby individuals that have traits better suited to their local environment will have a fitness advantage (Darwin 1859). Both of these evolutionary mechanisms are prevalent in shaping traits that are associated with accelerating range expansion in invasive species, including birds (Berthouly-Salazar et al 2012), toads (Shine et al 2011;Lindström et al 2013), fishes (Rehage & Sih 2004;Myles-Gonzalez et al 2015), salamanders (Lowe & McPeek 2012;Davenport & Lowe 2016), mites (Van Petegem et al 2015;2016a), and insects (Piiroinen et al 2011;Laparie et al 2013). Understanding trait evolution is a pre-condition for elucidating factors that contribute to shifts in the distributions of invasive species; such shifts have potentially dire consequences for the ecology of native species and the conservation of natural environments (Colautti & Lau 2015).…”

“…In invasive cane toads (Rhinella marina), dispersive individuals at the edge of their range that had a stronger propensity to move had longer bodies and greater endurance (Llewelyn et al 2010), and relatively longer legs (Phillips et al 2006). Functional locomotor morphology, such as leg length, wing shape, or supporting muscle architecture for limbs tends to relate positively with different movement characteristics and also has consequences for energy expenditure (Roff & Fairbairn 1991;Choi et al 2003;Ducatez et al 2012;Lowe & McPeek 2012).…”