Strong nonlinear selection against fluctuating asymmetry in wild populations of a marine fish

Abstract

Theoretical links between fluctuating asymmetry (FA) and fitness have led many to use FA as a proxy for average fitness. However, studies examining whether asymmetry actually correlates with individual fitness in wild populations are relatively rare and often use simple measures of association (e.g., correlation coefficients). Consequently, the pattern of selection on asymmetry in the wild is seldom clear. We examined selection on FA of pectoral fin morphology in two wild populations of a marine fish (the kelp perch; Brachyistius frenatus). As expected, variance in signed FA in each initial sample was significantly greater than that found in the surviving population, indicating selection against FA. Our estimate of the fitness surface confirmed perfect symmetry as the phenotypic optimum and indicated strong, nonlinear selection against asymmetry. No difference in the form of selection was detected between populations. However, the level of FA in the initial samples varied among populations, leading to an overall difference in the level of selective mortality. Our results suggest that selection on asymmetry in wild populations may be strongly nonlinear, and indicate that the demographic costs of asymmetry may play a substantial role in the dynamics of populations.

Patterns of fluctuating asymmetry in the limbs of freshwater turtles: Are more functionally important limbs more symmetrical?

“…2005), and the fins of fish (Tocts et al. 2016). A final requirement is that selection be able to act differentially on the two limb sets.…”

“…With respect to vertebrate limbs, the pattern between FA and performance is well established, being observed in numerous taxa, ranging from lizards (Martín and López 2001) to horses (Manning and Ockenden 1994) to humans (Trivers et al 2013). Third, selection must act against fluctuating asymmetry; such evidence for selection against fluctuating asymmetry in natural populations exists for the wings of birds (Brown and Brown 1998), limbs of rodents (Galeotti et al 2005), and the fins of fish (Tocts et al 2016). A final requirement is that selection be able to act differentially on the two limb sets.…”

“…It has been demonstrated that developmental instability has a heritable basis on which selection is capable of acting to drive evolutionary changes in FA (Carter and Houle 2011). These findings, coupled with evidence of selection acting against FA in nature (Brown and Brown 1998;Galeotti et al 2005;Tocts et al 2016), suggest that natural selection could play a role in regulating FA.…”

Patterns of fluctuating asymmetry in the limbs of anurans

“…Moreover, while our analyses focused on only a single bone in the fore‐ and hindlimb, asymmetry in individual bones (Manning & Ockenden, ; Martín & López, ) have been correlated with locomotor performance. Third, selection must act against FA; such evidence for selection against FA in natural populations exists for the limbs of rodents (Galeotti, Sacchi, & Vicario, ) and the fins of fish (Tocts, Johnson, & Carter, ). To some extent, directional differences in limbs can reflect handedness; for example, the right forelimb bones of humans generally have larger dimensions (Auerbach & Ruff, ).…”

“…Third, selection must act against FA; such evidence for selection against FA in natural populations exists for the limbs of rodents (Galeotti, Sacchi, & Vicario, 2005) and the fins of fish (Tocts, Johnson, & Carter, 2016). To some extent, directional differences in limbs can reflect handedness; for example, the right forelimb bones of humans generally have larger dimensions (Auerbach & Ruff, 2006).…”