By performing a comparative analysis and using phylogenetic relationships of the Cervidaefamily this study aimed to address whether or not sexual selection may play a role in the extinctionof species by making species more vulnerable to extinction. The role of sexual selection in makingspecies more vulnerable to extinction is largely unexplored, and several factors such as ecologicaland life history traits may increase the risk of extinction.In all species of the family Cervidae (Gilbert et al. 2006, Geist 1998,Groves and Grubb2011,Meijaardand Groves2004,Price et al. 2005, Goss 1983) sexually selected characters plays amain role in determining species status and thus potentially their probability of extinction. In thisstudy the intensity of sexual selection (measured as sexual size dimorphism, antler size and matingsystem) and the rate of extinction (IUCN classification and anthropogenic effect) were counted asfactors to determine the role of sexual selection intensity in both species-rich and species-poorclades.By using the programme MESQUITE and phylogenetic trees, the results show an associationbetween species with larger body size and dimorphism, living in open habitats and having largerantler size expanded to more than three tines; such species are mostly non-territorial and formharems during the rutting season. The small species are territorial, live in closed habitats, aremonomorphic and have small antler size limited to two tines or less. Moreover species that aremore subjected to habitat degradation and anthropogenic effects tend to become smaller in size.Extinction risk for the species-rich clades with small sized, territorial and small antler sizedspecies is lower than for those consisting of species with larger antler size, larger body size, livingin open habitats and using harems as mating system.To sum up, the intensity of sexual selection in larger species in deer family put them in risk ofextinction; but on the other site, small species are more adapted to the environment by choosingdifferent strategy in mating system, and reducing antler and body size thus diminishing theextinction risk.

Sexual selection is pervasive in nature and plays an important role in the evolution of biological diversity both within and among sexual species. However, while we have a good understanding of how competition for reproductive opportunities and mate choice can drive the evolution of exaggerated secondary sexual traits, much less is known about how sexual selection interacts with other forms of natural selection and the consequences such interactions may have for adaptation to novel environments, the purging of deleterious mutations, and population divergence/speciation. In my thesis, I carried out a series of experiments with the fruit fly Drosophila melanogaster to test hypotheses regarding the operation of sexual selection and to broaden our understanding of how sexual selection may influence adaptation and diversification. Theory suggests that natural and sexual selection may align to promote adaptation and the purging of deleterious mutations, although the harm imposed by sexual conflict may counter this. In two separate experiments, I find no evidence that sexual selection promotes adaptation to a novel environment and, rather than aligning with natural selection, I find that the effects of sexual conflict may cause sexual selection to hamper the purging of deleterious mutations. With respect to diversification, sexual conflict has been suggested to be an important, non-ecological driver of population divergence. However, the traits involved in sexual conflict may also affect nonsexual fitness and natural selection may therefore act to constrain diversification. Using an evolution experiment, I demonstrate ecologically-dependent parallel evolution of traits involved in sexual conflict, providing evidence for ecology’s importance in divergence via sexual conflict. Overall, my work has shed light on the interaction of natural and sexual selection and the consequences this may have beyond the evolution of exaggerated sexual displays and armaments.

Guppies exhibit color based sexual dimorphism and females generally prefer the most colorful males. It has also recently been found that guppies possess a large opsin repertoire. As opsins are the receptors responsible for color vision, this ten gene repertoire might have contributed to the evolution of extravagant male coloration in this species. My study starts by characterizing the opsin repertoire of Jenynsia onca, a noncolorful relative of the guppy belonging to the family Anablepidae (sister group to Poeciliidae, of which the guppy is a member). A PCR based survey indicated that J. onca had a very similar opsin repertoire to the guppy; J. onca had nine genes including orthologs of all but one of the guppy opsins. To gain further insight into the origin of the guppy repertoire, a bioinformatics based survey of ray-finned fish opsins was undertaken. This revealed that large opsin repertoires are common in ray-finned fish and are the product of gene duplication events, spanning the age of the taxon Teleostei. Given that the large opsin repertoire of the guppy did not appear to be perfectly correlated with the evolution of color based sexual selection in this lineage, I turned to investigating the expression of this opsin repertoire. In situ hybridization was used to characterize the pattern of opsin expression across the surface of the retina of adult male and female guppies. In situ hybridization demonstrated that most opsin genes had distinct expression profiles. These expression patterns also indicated that sensitivity and discrimination in the dorsal retina might differ from the ventral retina; the ventral retina appears to be tuned to middle-wavelength light (green), while the dorsal retina is predicted to have exceptional wavelength discriminatory ability and broad spectral sensitivity. This expression data was then used to evaluate models of sexual selection in the context of the predicted visual capacity of the guppy. / Graduate

This thesis examines the existence of colour preferences in butterflies. Two polymorphic species - the Mocker Swallowtail (Papilio dardanus) and the Silver-Washed Fritillary (Argynnis paphia) are used as study species. Both the basis of colour preferences in mate choice and flower choice during feeding, and the implications of the preferences for the evolution of the species and morphs are investigated. In the Silver Washed Fritillary a non-genetically determined preference exists for highly saturated orange coloration in both mate and flower choice. This is shown not to be due to a bias for orange in colour reception through the use of electroretinograms, measuring the electrical output of the retina when exposed to light of varying wavelengths. It has not been possible, however, to rule out the possibility that the preference for the most common, orange, female morph is learnt. The flower colour preferences of the Mocker Swallowtail are investigated, and it is demonstrated that individuals show an initial preference for blue flowers, and also learn rapidly to feed off flowers of other colours that prove profitable. Their decision to try flowers of other colours is shown to be influenced by the behaviour of other individuals. In previous mate choice experiments, experienced males of the species have been shown to have a preference for the most common, black and white, morph. The colours of the morphs and the spectral sensitivities of the butterflies are analysed quantitatively. The initial and subsequent preferences of naive males are investigated in behavioural experiments, and a possible influence of learning on their subsequent choices is discovered. No influence of female choice is found. This information is then used to create a mathematical model of the population structure, for which it is also necessary to determine the relative payabilities of the model and mimic, and the mating frequency of wild males. The model demonstrates how the observed population structures might arise through evolutionary time. Measurements of the morphology of males and females of Papilio dardanus, and one of its putative models, Danaus chrysippus, shows that in Papilio dardanus females the centre of gravity is positioned significantly further back than in males and in Danaus chrysippus. This positioning far from the wing base has already been shown to handicap an individual escaping from a predator due to decreased acrobatic ability. It has also already been shown that mimetic species tend to have centres of mass positioned further back than non-mimetic species, and hence it is possible that the position of a centre of mass of a butterfly (and its effect on agility) may be a factor in the evolution of mimicry in a species or (where females carry a large egg load) in females of a species only.

Variation in condition can result from environmental heterogeneity or genetic variation affecting resource acquisition and processing ability. Although condition should be positively correlated with the fitness of both males and females, the strength of selection on condition may differ between the sexes due to differences in reproductive variance. Sexual selection on male condition has been proposed to reduce mutation load, but only if selection is greater on males than females. To investigate the strength of selection on condition, the quality of the larval environment was used to manipulate the condition of Drosophila melanogaster. Additionally, selection was measured when the availability of key resources for females (live yeast) and males (access to females) were altered. Overall, selection was found to be stronger on males than females. However, selection on males weakened under a female-biased sex ratio, whereas selection on females was not significantly affected by the abundance of live yeast.

Sexual differences are dramatic and widespread across taxa. However, a common genome between males and females should hinder phenotypic divergence. In this thesis I have used experimental, genomic, and theoretical approaches to study processes that can facilitate and maintain differences between males and females. I studied two mechanisms for the evolution of sexual dimorphism - condition-dependence and gene duplication. If sex-specific traits are costly, then individuals should only express such traits when they possess enough resources to do so. I experimentally manipulated adult condition and found that the sex-biased gene expression depends on condition. Second, duplication events can permit different gene copies to adopt sex-specific expression. I showed that half of all duplicate families have paralogs with different sex-biased expression patterns between members. I investigated how current sexual dimorphism may support novel dimorphism. With regards gene duplication, I found that related duplicates did not always have different expression patterns. However, duplicating a pre-existing sex-biased gene effectively increases organismal sexual dimorphism overall. From a theoretical perspective, I investigated how sexually dimorphic recombination rates allow novel sexually antagonistic variation to invade. Male and female recombination rates separately affect invasion probabilities of new alleles. Finally, I examined the assumption that a common genetic architecture impedes the evolution of sexual dimorphism. First, I conducted a literature review to test whether additive genetic variances in shared traits were different between the sexes. There were few significant statistical differences. However, extreme male-biased variances were more common than extreme female-biased variances. Sexual dimorphism is expected to evolve easily in such traits. Second, I compared these results to findings from the multivariate literature. In contrast to single trait studies, almost all multivariate studies of sexual dimorphism have found variance differences, both in magnitude and orientation, between males and females. Overall, this thesis concludes that sexual dimorphism can evolve by processes that generate novel sexual dimorphism or that take advantage of pre-existing dimorphism. Furthermore, a common genome is not necessarily a strong barrier if genetic variances differ between the sexes. It will be an exciting challenge to understand how mutation and selection work together to allow organisms differ in their ability evolve sexual dimorphism.

Variation in condition can result from environmental heterogeneity or genetic variation affecting resource acquisition and processing ability. Although condition should be positively correlated with the fitness of both males and females, the strength of selection on condition may differ between the sexes due to differences in reproductive variance. Sexual selection on male condition has been proposed to reduce mutation load, but only if selection is greater on males than females. To investigate the strength of selection on condition, the quality of the larval environment was used to manipulate the condition of Drosophila melanogaster. Additionally, selection was measured when the availability of key resources for females (live yeast) and males (access to females) were altered. Overall, selection was found to be stronger on males than females. However, selection on males weakened under a female-biased sex ratio, whereas selection on females was not significantly affected by the abundance of live yeast.

This thesis investigates the evolution of two secondary sexual characters in birds, large male body size and exaggerated male tail length. To determine whether the elaboration of these two characters is associated with two correlates of sexual selection intensity, mating system and parental care, I collected and examined morphological information for 1,990 species and natural history data for 745 species. Comparative studies should account for the problem of related species sharing similarities through common descent, so here I investigate associations with contrast scores that measure the variation radiating from unique ancestral nodes in a phylogeny. I show that greater polygyny correlates strongly with increasing male size but only slightly with longer male tail length, and that lesser paternal care correlates strongly with both traits. These results indicate that the evolution of increased male body size and exaggerated male tail length in birds is substantially influenced by the intensity of sexual selection.

This study explores the morphology and electrical behavior of breeding weakly electric fish. Wave-type electric fish communicate by means of a continuous oscillatory electric signal produced by an electric organ. The electric organ discharges at frequencies which are sexually dimorphic in many species of electric fish. This dimorphism is thought to be attributed to female mate choice, although to date, there is no evidence for mate choice or intrasexual competition to have driven the evolution of this signaling dimorphism in wave-type electric fish. Here, I have tracked changes in body shape and electric organ discharge (EOD) frequency of A. leptorhynchus throughout a breeding conditioning period. I find that only females alter the shape of their bodies, presumably to account for increasing egg mass, during the breeding conditioning period. Throughout this period, both females and males do not alter their EOD frequencies significantly. Gravid females were used in an unforced preference test, where they were presented with two live, male A. leptorhynchus. Female preference was indicated by a passage of the female into one of the two male compartments. I find that females show a preference for higher EOD frequency males, while no preference is shown for longer, heavier or larger-amplitude males. Further investigations are needed to dissociate the role of EOD frequency from potentially correlated male traits, such as rate and type of modulations of EOD frequency. The finding of this study that female A. leptorhynchus prefer males of higher EOD frequency establishes wave-type weakly electric fish as a promising model system for the study of the evolution and the sensory mechanisms of female choice.

The difference in evolutionary interests of males and females can select for traits that favour an individual??s fitness at the expense of their mate??s lifetime fitness. Despite the widespread occurrence of this sexual conflict over reproductive interactions, however, research to date has largely focused on the fitness costs imposed on females by manipulative males. Empirical evidence is particularly sparse for how mating can also be costly for males, the genetic structure of traits involved in reproductive interactions, and how sexual conflict can modify sexual selection in general. My aim was to explore the broader evolutionary consequence of sexual conflict and male-female interactions. In the nuptial-feeding Australian ground cricket, Pteronemobius sp., I used an experimental evolution approach to explore how diet and sexual conflict interact to determine the costs of mating. In the Australian black field cricket, Teleogryllus commodus, I used molecular and quantitative genetic approaches to characterise the fitness consequences and genetic basis of spermatophore attachment, a trait at the centre of inter-locus sexual conflict, and then related this to both condition and male attractiveness. Finally, in T. commodus, I quantified how sexual conflict alters the sexual selection acting on male sexual traits and how this in turn shapes genetic architecture and the persistence of additive genetic variance. My results demonstrate the complex nature of reproductive interactions between males and females. Importantly, I show that diet can mediate the expression of sexual conflict in a mating system and shape the evolution of male life-span. I also show that reproductive interactions influence the fitness benefits that both male and females obtain from mating in ways that are not predicted by current theory and that much of the potential for such traits to co-evolve is via a common genetic association with condition. Finally, I demonstrate that sexual conflict can profoundly modify the process and outcome of sexual selection, thereby influencing how additive genetic variation is maintained in a suite of male sexual traits. These results highlight the need for a greater integration of sexual conflict and sexual selection theory as the evolutionary potential and significance of sexual conflict may currently be underestimated.