Ontogeny and sex alter the effect of predation on body shape in a livebearing fish: Sexual dimorphism, parallelism, and costs of reproduction

Abstract

Predation can cause morphological divergence among populations, while ontogenyand sex often determine much of morphological diversity among individuals. Weused geometric morphometrics to characterize body shape in the livebearing fishBrachyrhaphis rhabdophora to test for interactions between these three major shapedeterminingfactors. We assessed shape variation between juveniles and adults ofboth sexes, and among adults for populations from high- and low-predation areas.Shape differed significantly between predation regimes for all juveniles regardlessof sex. As males grew and matured into adults, ontogenetic shape trajectorieswere parallel, thus maintaining shape differences in adult males between predationenvironments. However, shape of adult females between predation environmentsfollowed a different pattern. As females grew and matured, ontogenetic shape trajectoriesconverged so that shape differences were less pronounced between maturefemales in predator and nonpredator environments. Convergence in female bodyshape may indicate a trade-off between optimal shape for predator evasion versusshape required for the livebearing mode of reproduction. © 2012 The Authors.