The influence of adaptation to life at high-altitude on condition dependent sexual shape and size dimorphism in Drosophila melanogaster

Abstract

Sexual dimorphism is common despite factors such as inter-sex genetic correlations and sex-specific patterns of selection that might limit its evolution. Sexual dimorphism can be phenotypically plastic and condition dependent, that themselves may be targets of selection. However, it remains unclear how sexual dimorphism, its plasticity and condition dependence evolves, in particular during rapid adaptation to a new environment. Furthermore, the interplay between SSD and other forms of dimorphism, such as shape dimorphism co-evolves. Using Sub-Saharan populations of Drosophila melanogaster that vary for size and shape as a result of adaptation to high altitude environments, we examined sex specific patterns of developmental plasticity. We raised strains of Drosophila from low (Zambia) and high (Ethiopia) altitude populations varying for food quality or rearing temperature. We observed expected differences in wing size and shape due to population, sex and plasticity. While larval mass showed substantial evolved changes for sex specific condition dependence, effects on wing size and shape were modest. We examined shape-size allometric effects between groups. Allometric effects were generally similar across sexes, but differed substantially due to population of origin and plasticity. We discuss findings within the context of the evolution of plasticity for SSD, condition dependence and allometric relationships.