Morphological Variation and Diversification in Australian Neriid Flies

Abstract

Morphological variation is a result of complex interactions between physiological constraints, selection pressures and ecological conditions. All of these factors are vital in the understanding of the evolution of morphological adaptations. In this thesis, I examine three aspects of the phenotypic plasticity and morphological variation in two species of neriid flies, Telostylinus angusticollis and Telostylinus lineolatus. Chapter one examines allometric constraints on the diversification of populations. Static allometry slope is generally thought to constrain adaptation and diversification. We examined the diversification of static allometry by manipulating larval nutrient concentration and comparing allometric slopes in sexual and non-sexual traits across populations. We found evidence of slope diversification within T. angusticollis and T. lineolatus in a sexual trait. Our results suggest the diversification of static allometry slope can be driven by sexual selection. Following this, chapter two discusses sexual selection and its impact on diversification in males and females. Using reaction norms for nutrient concentration in a range of sexual and non-sexual body shape components, we identify different patterns of morphological diversification between the sexes. In addition to this, the patterns of diversification seen in males suggest that sexual selection is acting upon male body shape as a whole, rather than specific morphological traits. We consider the ecological and selective forces contributing to the diversification of the sexes. Chapter three examines another aspect of larval ecology, group relatedness, and its benefits or disadvantages. We find that fly larvae gain an advantage from being housed with closely related individuals, and emerge larger as adults, congruent with the kin selection hypothesis. These three chapters outline some of the different factors contributing to morphological variation and highlight the importance and complexity of phenotypic plasticity.