Abstract
Selection may favor greater investment into sexual ornaments when opportunities for future reproduction are limited, for example, under high adult mortality. However, predation, a key driver of mortality, typically selects against elaborate sexual ornaments. Here, we examine the evolution of sexual ornaments in killifishes, which have marked contrasts in life-history strategy among species and inhabit environments that differ in accessibility to aquatic predators. We first assessed if the size of sexual ornaments (unpaired fins) influenced swimming performance. Second, we investigated whether the evolution of larger ornamental fins is driven primarily by the pace of life-history (investment into current vs. future reproduction) or habitat type (a proxy for predation risk). We found that larger fins negatively affected swimming performance. Further, males from species inhabiting ephemeral habitats, with lower predation risk, had larger fins and greater sexual dimorphism in fin size, compared to males from more accessible permanent habitats. We show that enlarged ornamental fins, which impair locomotion, evolve more frequently in environments that are less accessible to predators, without clear associations to life-history strategy. Our results provide a rare link between the evolution of sexual ornaments, effects on locomotion performance, and natural selection on ornament size potentially through habitat differences in predation risk.
Highlights
Selection may favor greater investment into sexual ornaments when opportunities for future reproduction are limited, for example, under high adult mortality
FIN SIZE NEGATIVELY AFFECTED SWIMMING PERFORMANCE As predicted, we found that residual total fin area negatively affected swimming performance in killifishes
Sex, the pace of life-history, or their interactions affected swimming performance, we found that males overall had a lower turning performance, compared to females
Summary
Selection may favor greater investment into sexual ornaments when opportunities for future reproduction are limited, for example, under high adult mortality. The evolution of exaggerated or enlarged sexual ornaments could be more likely when adult mortality is high and the opportunity for future reproductive success is limited (Andersson 1982, 1994). Assessing the relative roles that predation risk and life-history strategy have on the occurrence of sexual ornaments may increase our understanding of the mechanisms that promote their evolution Making such an assessment requires a system where the pace of life-history—at least in part—is driven by mortality from sources other than predation. We use a system of freshwater fishes, the killifishes (Suborder: Aplocheiloidei), which appear to be ideally suited for making a comparative empirical assessment of the effects of the pace of life-history and predation risk on the evolution of ornamental sexual traits
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