A distance-performance trade-off in the phenotypic basis of dispersal

Abstract

Across taxa, individuals vary in how far they disperse, with most individuals staying close to their origin and fewer dispersing long distances. Costs associated with dispersal (e.g., energy, risk) are widely believed to trade off with benefits (e.g., reduced competition, increased reproductive success) to influence dispersal propensity. However, this framework has not been applied to understand variation in dispersal distance, which is instead generally attributed to extrinsic environmental factors. We alternatively hypothesized that variation in dispersal distances results from trade-offs associated with other aspects of locomotor performance. We tested this hypothesis in the stream salamander Gyrinophilus porphyriticus and found that salamanders that dispersed farther in the field had longer forelimbs but swam at slower velocities under experimental conditions. The reduced swimming performance of long-distance dispersers likely results from drag imposed by longer forelimbs. Longer forelimbs may facilitate moving longer distances, but the proximate costs associated with reduced swimming performance may help to explain the rarity of long-distance dispersal. The historical focus on environmental drivers of dispersal distances misses the importance of individual traits and associated trade-offs among traits affecting locomotion.

Keywords: dispersal distance; locomotion; plethodontid salamanders; trade‐off.

Figure 1

Gyrinophilus porphyriticus (photograph by Maddy Cochrane)

Figure 2

Dispersal distances of Gyrinophilus porphyriticus from three streams in the Hubbard Brook Watershed in central New Hampshire (inset map). Distances are from individuals recaptured between 2012 and 2015 (n = 575). Negative distances indicate downstream movements; positive distances indicate upstream movements. Data are binned in 4 m increments. Gray portions of the columns are individuals for which both morphological and performance data were collected (n = 50)

Figure 3

Correlations between size‐adjusted morphological variables (PC2 scores) and proportional size of each body element (e.g., log trunk length/log snout–vent length [SVL]) for Gyrinophilus porphyriticus individuals in the Hubbard Brook Watershed (n = 50). Letters in the top left of plots indicate corresponding measurements of (a) trunk length, (b) trunk width, (c) forelimb length, and (d) hindlimb length on salamanders. PC2 scores were from principal component analyses including each body measurement and SVL. The percentage of variation accounted for by these PC2s is indicated within each plot. Lines of best fit are plotted for each correlation to show trends

Figure 4

The relationship between sized‐adjusted forelimb length (PC2) and dispersal distance (left) and swimming velocity (right) in Gyrinophilus porphyriticus individuals that dispersed >4 m in the Hubbard Brook Watershed (n = 50). Dotted linear regression lines indicate significant associations (p < .05); gray bands indicate 95% confidence intervals. Size‐adjusted forelimb length is positively weighted by humerus length; therefore, individuals with longer forelimbs dispersed the farthest but swam at the lowest velocities