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(2012)ThesisMorphological 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.
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(2016)ThesisThis research was about how life history traits were influenced by the nutrient components in the juvenile diet. The aim of this study was to provide more understanding about the function and the purpose of nutrients consumption. The first chapter addresses how essential and non-essential amino acids in the juvenile diet influence the juvenile performance and adult morphological traits. The second chapter addresses the effects of additional vitamin E in the protein-unrestricted juvenile diets on adult fitness and longevity. Both chapters had used Telostylinus angusticollis, neriid flies as the experimental organism. This was because this species is exceptionally plastic in adult morphology to its larval diet. The experimental larvae in the first chapter were raised in the nutrient-poor diet with the combination of extra essential amino acids, non-essential amino acids and sugar. The adult body size and relative head, antenna, wing and foreleg length were boosted by the presence of extra essential amino acids while the relative hind leg length was not affected, but the cost of such benefit was the decrease of larval viability. In contrast, the viability was significantly reduced to almost none by the non-essential amino acids. This may be caused by the large change in pH associated with the addition of non-essential amino acids. The development time was not affected by either essential or non-essential amino acids. The larvae in chapter two were raised in treatments with three levels (1, 3, 5μg/mL) of vitamin E and the presence of an additional amount of protein to the nutrient-poor base diet in the first experiment. The larvae in the second experiment were raised in treatments of the nutrient-poor base diet with the addition of 3μg/mL of vitamin E and the poor base diet as the control. The first experiment provided little evidence of a vitamin E by protein interaction. The second experiment showed that vitamin E itself had a positive effect on body size, but this effect was dependent to the sterilization of the larval environment. The presence of vitamin E in the juvenile diet decreased adult longevity and activity, especially in males. Nonetheless, it did not have any effects on juvenile development time, adult relative head length and adult relative antenna length. In conclusion, the effect of amino acids and the effect of vitamin E on life history traits were complex, indicating a need for further study.
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(2013)ThesisMy thesis aimed to investigate the influence of selection on an animal invading a novel habitat and how subsequent differences in natural selection, sexual selection and genetic drift might influence phenotypic variation among populations. The Pacific leaping blenny on Guam (Alticus arnoldorum) provided a novel opportunity to address these aims as it has made one of the most extreme ecological transitions possible, it is a fish that lives its entire adult life on land. Furthermore, the presence of multiple populations of this fish around the island allowed the investigation of how differences in selection pressures and gene flow might generate or limit phenotypic variation between populations that otherwise occupy the same broad habitat type (intertidal rocks on land). First, I examined the influence of natural selection in the form of predation on colonising a novel environment (here, a shift onto land). The colouration of male and female blennies from five populations was examined along with the colour of their respective backgrounds. I found the body colour of all populations closely resembled the habitat on land. A subsequent predation experiment confirmed that this background matching functioned to reduce predation and was therefore adaptive. These results suggested that closely resembling the colour of habitat backgrounds has probably aided the Pacific leaping blenny in successfully colonising land. Second, I examined the relative influence of natural selection (predation), sexual selection and gene flow on phenotypic variation among populations on land. Results suggested that variation in natural selection and sexual selection had a predictable influence on phenotypic expression: sexual selection has promoted the exaggeration of ornaments, while natural selection has reduced the conspicuousness of these features. Most notably, this population divergence in ornamentation has occurred despite high gene flow. Overall, my thesis demonstrates how adopting an integrative approach is essential for isolating the mechanisms leading to phenotypic divergence during the invasion of new environments, and how populations can subsequently diverge in response to variation in social factors and predation once colonisation has occurred.