Sexual Dimorphism and Speciation on Two Ecological Coins: Patterns From Nature and Theoretical Predictions

Abstract

Adaptive divergence of phenotypes, such as sexual dimorphism or adaptive speciation, can result from disruptive selection via competition for limited resources. Theory indicates that speciation and sexual dimorphism can result from identical ecological conditions, but co-occurrence is unlikely because whichever evolves first should dissipate the disruptive selection necessary to drive evolution of the other. Here, we consider ecological conditions in which disruptive selection can act along multiple ecological axes. Speciation in lake populations of threespine sticklebacks (Gasterosteus aculeatus) has been attributed to disruptive selection due to competition for resources. Head shape in sticklebacks is thought to reflect adaptation to different resource acquisition strategies. We measure sexual dimorphism and species variation in head shape and body size in stickleback populations in two lakes in British Columbia, Canada. We find that sexual dimorphism in head shape is greater than interspecific differences. Using a numerical simulation model that contains two axes of ecological variation, we show that speciation and sexual dimorphism can readily co-occur when the effects of loci underlying sexually dimorphic traits are orthogonal to those underlying sexually selected traits. K E Y W O R D S :Adaptive radiation, adaptive splitting, disruptive selection, ecological dimorphism, stickleback species pair.

Independent evolution of the sexes promotes amphibian diversification

“…Although formal development of the ideas presented here may inform the validity of this assumption, we see this as a largely empirical issue that may depend on the shape of the adaptive landscape on which a particular lineage is evolving. Theory suggests that sexual divergence can occur jointly with lineage divergence under some conditions of multivariate ecological opportunity [37]. Further, the ubiquity of sexually antagonistic selection in the wild [39] supports the assumption that sex-specific adaptive zones are commonplace.…”

“…A key assumption of the ecological theory of sexual dimorphism is that points in phenotype space that represent a natural selection peak in population mean fitness of one sex would, for example, also maximize mean fitness for the other sex of another species. Yet recent empirical evidence from lizards [2], stickleback [37] and stick insects [38] demonstrates that large regions of ecologically relevant morphospace in adaptive radiations of all scales can be sex-specific. In other words, ecological opportunity is sex-specific.…”

Ontogenetic variations and feeding habits of a Neotropical annual fish from southern Brazil

“…Feeding differences between males and females are more evident in species with marked sexual dimorphism in size and are a widely observed phenomenon in animals (Shine, 1989). Also, sexual morphological differences could cause a lower feeding overlap and lower intraespecific competition in some species (Rueffer et al, 2006;Cooper et al, 2011). However, in our study, the intersexual size differences was not sufficient to result in diet differenciation, as observed by Shibatta & Rocha (2001) for Simpsonichthys boitonei Carvalho, 1959 (by frequency and volume), Contente & Stefanoni (2010) for Atlantirivulus santensis (Köhler, 1906) (by volume and abundance), and Gonçalves et al (2011) for Cynopoecilus melanotaenia (Regan, 1912) (by frequency).…”

Competition, virulence, host body mass and the diversification of macro-parasites

“…Such a situation where the same ecological conditions can result in the evolutionary divergence of alternative traits have already rsif.royalsocietypublishing.org J. R. Soc. Interface 11: 20131108 been identified, for example, for sexual dimorphism and head shape/body size [114,115]. In such cases, coevolution between alternative traits is unlikely because whichever evolves first dissipates the disruptive selection necessary to drive evolution of the other [114].…”