The ‘good genes’ model of sexual selection predicts that sexual and natural selection should act concordantly. However sexual selection can favour alleles in males that are costly when expressed in daughters, placing the two in opposition. The relationship between natural and sexual selection depends on the nature of genetic variation for fitness. Laboratory adaptation may deplete sexually concordant fitness variation, overestimating sexually antagonistic variation and obscuring good genes. I investigated sire-offspring fitness correlations in Drosophila melanogaster populations expected to differ in their levels of sexually concordant fitness variation. In maladapted populations, successful sires produced fitter daughters than unsuccessful sires; this pattern was reversed in adapted populations. Several generations later, successful sires in both population types produced lower fitness daughters than unsuccessful sires, consistent with predictions. However, subsequent generations revealed no effect of sire status on daughter fitness, highlighting the difficulty in testing predictions on the evolutionary dynamics of fitness heritability.

Exposure to chronic hypoxia (CH) leads to ventilatory acclimatisation to hypoxia (VAH) which is a time-dependent increase in breathing. This study examined the role of the GABAA receptor in establishing VAH. Rats were exposed to CH or control (normoxic) conditions for 10 days during which the GABAA receptor antagonist, bicuculline, was infused systemically or directly into the nucleus of the solitary tract (NTS). Acute breathing trials were then performed to measure resting ventilation and ventilatory chemoreflexes. Systemic administration of bicuculline caused reductions in breathing during acute hypoxia and acute hypercapnia in the control but not the CH animals. Continuous infusion of bicuculline in to the NTS caused a reduction in the acute hypoxic ventilatory response in animals exposed to CH but not in the control animals. The results indicate that exposure to CH alters the GABAA-mediated regulation of acute ventilatory chemoreflexes both in the NTS and elsewhere in the brain.

The ‘good genes’ model of sexual selection predicts that sexual and natural selection should act concordantly. However sexual selection can favour alleles in males that are costly when expressed in daughters, placing the two in opposition. The relationship between natural and sexual selection depends on the nature of genetic variation for fitness. Laboratory adaptation may deplete sexually concordant fitness variation, overestimating sexually antagonistic variation and obscuring good genes. I investigated sire-offspring fitness correlations in Drosophila melanogaster populations expected to differ in their levels of sexually concordant fitness variation. In maladapted populations, successful sires produced fitter daughters than unsuccessful sires; this pattern was reversed in adapted populations. Several generations later, successful sires in both population types produced lower fitness daughters than unsuccessful sires, consistent with predictions. However, subsequent generations revealed no effect of sire status on daughter fitness, highlighting the difficulty in testing predictions on the evolutionary dynamics of fitness heritability.

Understanding the ecological and evolutionary processes responsible for shaping patterns of genetic variation in natural populations is a long-standing goal in molecular ecology. Although an extensive number of recent studies focus on patterns and processes throughout tropical rain forest ecosystems, substantially less effort has been placed on tropical dry forests (TDFs); a habitat known to harbour a large percentage of Earth’s diversity. In this thesis I use leaf-toed geckos of the genus Phyllodactylus to understand both the historical and contemporary processes influencing diversification throughout Mexico’s TDFs. In Chapter 2 I isolate and characterize microsatellite markers for the gecko P. tuberculosus. Chapter 3 uses these loci to conduct a landscape genetic analysis of the species near Alamos, Sonora. I find that the inclusion of landscape variables explains more genetic variance versus Euclidean distance alone. Chapter 4 examines the evolutionary history of the P. tuberculosus group throughout western Mexico. Results suggest that habitat and climate shifts during the Miocene and Pleistocene were important divers of diversification. Chapter 5 uses microsatellite and mtDNA markers to compare historical and contemporary demographic parameters in P. tuberculosus. I find evidence for low historical gene flow and high female philopatry, recent reductions in population sizes, and higher correlations between landscape and contemporary gene flow versus historical gene flow and mtDNA divergence. In Chapter 6 I examine the biogeographic and taxonomic consequences of the dynamic history of Baja California. My phylogenetic results provide evidence for a trans-peninsular seaway in the Isthmus of La Paz region and suggests that P. xanti nocticolus warrants species status. My results also suggest the possibility of a seaway near the Loreto area that needs to be evaluated further. By combining multiple molecular marker-types and analytical methods, this thesis adds to our understanding of diversification processes throughout the threatened Mexican TDF.

Unraveling the relationships between organisms and patterns of diversity is a central goal of evolutionary biology, pursuant to the aim of reconstructing the history of life. I constructed a hypothesis for species relationships in the shorebird suborder Scolopaci, and mapped onto this framework behavioural and life-history traits to infer their evolutionary history. Relationships were well-resolved and well-supported, although reliable resolution of certain nodes will require additional, independent sources of information. We estimated the Scolopaci ancestor to be monogamous, and care-giving through fledging, but ancestral breeding location and migration distance reconstructions were equivocal. Tests for correlations between parental care and other traits to explain extant species’ trait diversity show that, contrary to previous reports, evolution of Scolopaci diversity was a complex process that cannot be explained by individual character correlations. This study provides important insights into Scolopaci and shorebird evolutionary history, and the general practice of inferring past processes from phylogenetic hypotheses.

Mobility of the vertebral column is important for many ecological aspects of vertebrates, especially in the cervical series, which connects the head to the main body. Thus, fusion within the cervical series is hypothesized to have ecological and behavioural implications. Fused, anterior cervical vertebrae have evolved independently over 20 times in ecologically disparate amniotes, most commonly in pelagic, ricochetal, and fossorial taxa, suggesting an adaptive function for the ‘syncervical.’ Fusion may help increase out-force during head-lift digging or prevent anteroposteriorly shortened vertebrae from mechanically failing during locomotion, but no hypothesis for syncervical function has been tested. The syncervical of neoceratopsian dinosaurs is hypothesized to support large heads or aid in intraspecific combat. Tests of correlated character evolution within a ceratopsian phylogeny falsify these hypotheses, as the syncervical evolves before large heads and cranial weaponry. Alternative functional hypotheses may involve ancestral burrowing behaviour or unique feeding ecology in early neoceratopsians.

Understanding the ecological and evolutionary processes responsible for shaping patterns of genetic variation in natural populations is a long-standing goal in molecular ecology. Although an extensive number of recent studies focus on patterns and processes throughout tropical rain forest ecosystems, substantially less effort has been placed on tropical dry forests (TDFs); a habitat known to harbour a large percentage of Earth’s diversity. In this thesis I use leaf-toed geckos of the genus Phyllodactylus to understand both the historical and contemporary processes influencing diversification throughout Mexico’s TDFs. In Chapter 2 I isolate and characterize microsatellite markers for the gecko P. tuberculosus. Chapter 3 uses these loci to conduct a landscape genetic analysis of the species near Alamos, Sonora. I find that the inclusion of landscape variables explains more genetic variance versus Euclidean distance alone. Chapter 4 examines the evolutionary history of the P. tuberculosus group throughout western Mexico. Results suggest that habitat and climate shifts during the Miocene and Pleistocene were important divers of diversification. Chapter 5 uses microsatellite and mtDNA markers to compare historical and contemporary demographic parameters in P. tuberculosus. I find evidence for low historical gene flow and high female philopatry, recent reductions in population sizes, and higher correlations between landscape and contemporary gene flow versus historical gene flow and mtDNA divergence. In Chapter 6 I examine the biogeographic and taxonomic consequences of the dynamic history of Baja California. My phylogenetic results provide evidence for a trans-peninsular seaway in the Isthmus of La Paz region and suggests that P. xanti nocticolus warrants species status. My results also suggest the possibility of a seaway near the Loreto area that needs to be evaluated further. By combining multiple molecular marker-types and analytical methods, this thesis adds to our understanding of diversification processes throughout the threatened Mexican TDF.

Unraveling the relationships between organisms and patterns of diversity is a central goal of evolutionary biology, pursuant to the aim of reconstructing the history of life. I constructed a hypothesis for species relationships in the shorebird suborder Scolopaci, and mapped onto this framework behavioural and life-history traits to infer their evolutionary history. Relationships were well-resolved and well-supported, although reliable resolution of certain nodes will require additional, independent sources of information. We estimated the Scolopaci ancestor to be monogamous, and care-giving through fledging, but ancestral breeding location and migration distance reconstructions were equivocal. Tests for correlations between parental care and other traits to explain extant species’ trait diversity show that, contrary to previous reports, evolution of Scolopaci diversity was a complex process that cannot be explained by individual character correlations. This study provides important insights into Scolopaci and shorebird evolutionary history, and the general practice of inferring past processes from phylogenetic hypotheses.

Mobility of the vertebral column is important for many ecological aspects of vertebrates, especially in the cervical series, which connects the head to the main body. Thus, fusion within the cervical series is hypothesized to have ecological and behavioural implications. Fused, anterior cervical vertebrae have evolved independently over 20 times in ecologically disparate amniotes, most commonly in pelagic, ricochetal, and fossorial taxa, suggesting an adaptive function for the ‘syncervical.’ Fusion may help increase out-force during head-lift digging or prevent anteroposteriorly shortened vertebrae from mechanically failing during locomotion, but no hypothesis for syncervical function has been tested. The syncervical of neoceratopsian dinosaurs is hypothesized to support large heads or aid in intraspecific combat. Tests of correlated character evolution within a ceratopsian phylogeny falsify these hypotheses, as the syncervical evolves before large heads and cranial weaponry. Alternative functional hypotheses may involve ancestral burrowing behaviour or unique feeding ecology in early neoceratopsians.

Exposure to chronic hypoxia (CH) leads to ventilatory acclimatisation to hypoxia (VAH) which is a time-dependent increase in breathing. This study examined the role of the GABAA receptor in establishing VAH. Rats were exposed to CH or control (normoxic) conditions for 10 days during which the GABAA receptor antagonist, bicuculline, was infused systemically or directly into the nucleus of the solitary tract (NTS). Acute breathing trials were then performed to measure resting ventilation and ventilatory chemoreflexes. Systemic administration of bicuculline caused reductions in breathing during acute hypoxia and acute hypercapnia in the control but not the CH animals. Continuous infusion of bicuculline in to the NTS caused a reduction in the acute hypoxic ventilatory response in animals exposed to CH but not in the control animals. The results indicate that exposure to CH alters the GABAA-mediated regulation of acute ventilatory chemoreflexes both in the NTS and elsewhere in the brain.