Experimental alterations of morphological traits during development can reveal life history tactics and resource allocation patterns. I examined effects of amputation of a structure directly involved with mating compared to one that is less associated with fitness. I amputated one of the paired external copulatory organs (palps) of juvenile male black widow spiders Latrodectus hesperus), and compared changes in life history traits and fitness to males with amputated legs and controls. I show that palps are more likely to be regenerated than legs, smaller juveniles are more likely to regenerate, and mating success is adversely affected in all adults that suffered early amputation. The pre-existing relationship between juvenile size and development was a critical determinant of regeneration, however no life history costs of regeneration were evident. I conclude that plasticity in life history facilitates regeneration, and that this may mask trade-offs involved in compensatory effects at the population level.

Experimental alterations of morphological traits during development can reveal life history tactics and resource allocation patterns. I examined effects of amputation of a structure directly involved with mating compared to one that is less associated with fitness. I amputated one of the paired external copulatory organs (palps) of juvenile male black widow spiders Latrodectus hesperus), and compared changes in life history traits and fitness to males with amputated legs and controls. I show that palps are more likely to be regenerated than legs, smaller juveniles are more likely to regenerate, and mating success is adversely affected in all adults that suffered early amputation. The pre-existing relationship between juvenile size and development was a critical determinant of regeneration, however no life history costs of regeneration were evident. I conclude that plasticity in life history facilitates regeneration, and that this may mask trade-offs involved in compensatory effects at the population level.

The hypothalamic-pituitary-adrenal (HPA) axis, or stress axis, is a key physiological system that mediates the relationship of the organism with its environment. Because activation of the HPA axis mobilizes energy stores for immediate use, but sustained activation can have deleterious effects on survival, the HPA axis has been implicated in the tradeoff between reproduction and survival. In this thesis, I investigate whether there is an association between one life history trait, reproductive lifespan, and the functioning of the HPA axis as predicted by the “adaptive stress hypothesis”. The adaptive stress hypothesis predicts that species adopting life history strategies characterized by short lifespans and early reproduction should maximize the energy available for reproduction through high levels of circulating glucocorticoids caused by the dysregulation of the HPA axis in the breeding season, whereas those characterized by long lifespans and extended reproduction should maintain a functioning HPA axis with low levels of glucocorticoids throughout life. To test this hypothesis, I studied five species of ground squirrels that vary dramatically in male reproductive lifespan: arctic, Richardson’s, Columbian, thirteen-lined, and Franklin’s ground squirrels (Urocitellus parryii, U. richardsonii, U. columbianus, Ictidomys tridecemlineatus, and Poliocitellus franklinii). I used a stress profile to characterize the HPA axis of male ground squirrels immediately before and immediately after the breeding season. The stress profile included measures of plasma glucocorticoid concentrations, determinants of plasma glucocorticoid concentrations (corticosteroid binding globulin levels, adrenal sensitivity/capacity, negative feedback, and intrinsic restraint), and markers of the biological effects of glucocorticoids (energy mobilization, health, and immune function). Contrary to the adaptive stress hypothesis, I found no relationship between reproductive lifespan and postbreeding glucocorticoid levels. Species also varied significantly and unexpectedly in how determinants of glucocorticoid levels changed over the breeding season, and in how glucocorticoids levels translated into biological effects. I also observed unexpected patterns of individual variation within species. Thus, life history alone did not predict HPA axis functioning. My results suggest that the HPA axis is so flexible in its functioning, that we will need to adopt a much more detailed model of the HPA axis in order to fully understand the relationship between the HPA axis and life history variation.

Evolutionary transitions between marine and freshwater habitats are rare events that can have profound impacts on aquatic biodiversity. The main goal of my thesis is determining the processes involved in transitions between marine and freshwater biomes, and the resulting patterns of diversity using phylogenetic approaches. To test hypotheses regarding the geography, timing, frequency, and mechanisms regulating biome transitions I generated multi-locus time-calibrated molecular phylogenies for groups of fishes that include both exclusively marine and freshwater species. My analysis of anchovies demonstrated that Neotropical freshwater anchovies represent a monophyletic radiation with a single origin in South American freshwaters. I used a phylogeny of herring and allies (Clupeiformes) to investigate the evolution of diadromy, a migratory behavior in which individuals move between oceans and freshwater habitats for reproduction and feeding. These analyses do not support the hypothesis that differences in productivity between marine and freshwater explain the origins of diadromous lineages. Diadromy has been considered an evolutionary pathway for permanent biome transitions, however I found that diadromy almost never produces a fully marine or freshwater clade. Marine lineages often invade continental freshwaters during episodes of marine incursion. In South America, the rich diversity of marine derived fish lineages invaded during Eocene marine incursions from either the Pacific or the Caribbean, and Oligocene marine incursions from the Caribbean. I falsified the highly cited Miocene marine incursion hypothesis, but found that the Pebas Mega-Wetland catalyzed diversification in some marine derived lineages. Using diversification analyses, I investigated the evolutionary processes that have generated disparate patterns of diversity between continents and oceans. I found that freshwater silversides have higher speciation and extinction rates than marine silversides. Lineages accumulation plots suggest ecological limits are not regulating clade growth in either marine or freshwater biomes. Overall, biome conservatism is a widespread pattern among fishes, and this pattern is largely driven by competition in clades that are physiologically capable of biome transitions. Biome transitions are facilitated by rare paleogeographic events, such as marine incursions. Finally, a difference in net diversification rate is the macroevolutionary mechanism that best explains the difference in diversity between continents and oceans.

The hypothalamic-pituitary-adrenal (HPA) axis, or stress axis, is a key physiological system that mediates the relationship of the organism with its environment. Because activation of the HPA axis mobilizes energy stores for immediate use, but sustained activation can have deleterious effects on survival, the HPA axis has been implicated in the tradeoff between reproduction and survival. In this thesis, I investigate whether there is an association between one life history trait, reproductive lifespan, and the functioning of the HPA axis as predicted by the “adaptive stress hypothesis”. The adaptive stress hypothesis predicts that species adopting life history strategies characterized by short lifespans and early reproduction should maximize the energy available for reproduction through high levels of circulating glucocorticoids caused by the dysregulation of the HPA axis in the breeding season, whereas those characterized by long lifespans and extended reproduction should maintain a functioning HPA axis with low levels of glucocorticoids throughout life. To test this hypothesis, I studied five species of ground squirrels that vary dramatically in male reproductive lifespan: arctic, Richardson’s, Columbian, thirteen-lined, and Franklin’s ground squirrels (Urocitellus parryii, U. richardsonii, U. columbianus, Ictidomys tridecemlineatus, and Poliocitellus franklinii). I used a stress profile to characterize the HPA axis of male ground squirrels immediately before and immediately after the breeding season. The stress profile included measures of plasma glucocorticoid concentrations, determinants of plasma glucocorticoid concentrations (corticosteroid binding globulin levels, adrenal sensitivity/capacity, negative feedback, and intrinsic restraint), and markers of the biological effects of glucocorticoids (energy mobilization, health, and immune function). Contrary to the adaptive stress hypothesis, I found no relationship between reproductive lifespan and postbreeding glucocorticoid levels. Species also varied significantly and unexpectedly in how determinants of glucocorticoid levels changed over the breeding season, and in how glucocorticoids levels translated into biological effects. I also observed unexpected patterns of individual variation within species. Thus, life history alone did not predict HPA axis functioning. My results suggest that the HPA axis is so flexible in its functioning, that we will need to adopt a much more detailed model of the HPA axis in order to fully understand the relationship between the HPA axis and life history variation.

The snake genus Oligodon, known for its egg-eating feeding behaviour, is a taxonomically and systematically challenging group from South and Southeast Asia. This work provides the first phylogenetic hypothesis for the genus, and includes a checklist and key to the species. I use approximately 1900 base pairs of mitochondrial DNA sequence data to infer the relationships of these snakes, and I examine congruence between the molecular phylogeny and hemipenial characters. A hypothesis for the position of Oligodon within the Colubridae is also proposed. I discuss the implications of the phylogeny for previous taxonomic groupings, and consider the usefulness of the trees in analysis of behaviour and biogeography.

Evolutionary transitions between marine and freshwater habitats are rare events that can have profound impacts on aquatic biodiversity. The main goal of my thesis is determining the processes involved in transitions between marine and freshwater biomes, and the resulting patterns of diversity using phylogenetic approaches. To test hypotheses regarding the geography, timing, frequency, and mechanisms regulating biome transitions I generated multi-locus time-calibrated molecular phylogenies for groups of fishes that include both exclusively marine and freshwater species. My analysis of anchovies demonstrated that Neotropical freshwater anchovies represent a monophyletic radiation with a single origin in South American freshwaters. I used a phylogeny of herring and allies (Clupeiformes) to investigate the evolution of diadromy, a migratory behavior in which individuals move between oceans and freshwater habitats for reproduction and feeding. These analyses do not support the hypothesis that differences in productivity between marine and freshwater explain the origins of diadromous lineages. Diadromy has been considered an evolutionary pathway for permanent biome transitions, however I found that diadromy almost never produces a fully marine or freshwater clade. Marine lineages often invade continental freshwaters during episodes of marine incursion. In South America, the rich diversity of marine derived fish lineages invaded during Eocene marine incursions from either the Pacific or the Caribbean, and Oligocene marine incursions from the Caribbean. I falsified the highly cited Miocene marine incursion hypothesis, but found that the Pebas Mega-Wetland catalyzed diversification in some marine derived lineages. Using diversification analyses, I investigated the evolutionary processes that have generated disparate patterns of diversity between continents and oceans. I found that freshwater silversides have higher speciation and extinction rates than marine silversides. Lineages accumulation plots suggest ecological limits are not regulating clade growth in either marine or freshwater biomes. Overall, biome conservatism is a widespread pattern among fishes, and this pattern is largely driven by competition in clades that are physiologically capable of biome transitions. Biome transitions are facilitated by rare paleogeographic events, such as marine incursions. Finally, a difference in net diversification rate is the macroevolutionary mechanism that best explains the difference in diversity between continents and oceans.

The snake genus Oligodon, known for its egg-eating feeding behaviour, is a taxonomically and systematically challenging group from South and Southeast Asia. This work provides the first phylogenetic hypothesis for the genus, and includes a checklist and key to the species. I use approximately 1900 base pairs of mitochondrial DNA sequence data to infer the relationships of these snakes, and I examine congruence between the molecular phylogeny and hemipenial characters. A hypothesis for the position of Oligodon within the Colubridae is also proposed. I discuss the implications of the phylogeny for previous taxonomic groupings, and consider the usefulness of the trees in analysis of behaviour and biogeography.

Parkinson’s disease (PD) is a debilitating movement disorder associated with the death of dopaminergic nigrostriatal neurons. In addition to dopamine deficiency, abnormalities in glutamate and other receptors at striatal synapses have been reported. Synapse associated protein 97 (SAP97) is involved in regulation of glutamate receptor function. In the striatum of unilaterally-lesioned 6-OHDA rat model of PD, SAP97 levels are decreased in post synaptic density fraction, as well as in the whole striatum. I hypothesize that changes in striatal levels and subcellular distribution of SAP97 are responsible for abnormal neurotransmission in striatum and the motor symptoms of PD. GFP-tagged wild type SAP97 and SAP97 mutants were over-expressed in the striatum of 6-OHDA-lesioned rat model of PD. A single 6.5 mg/kg dose of L-DOPA eliminated parkinsonism in 6-OHDA-lesioned rats over-expressing SAP97-GFP, whereas, three 6.5 mg/kg doses of L-DOPA negated parkinsonism in 6-OHDA-lesioned rats over-expressing SAP97-GFP and SAP97∆1-65-GFP. The over-expression of SAP97∆1-65-GFP enhanced parkinsonism in 6-OHDA-lesioned rats and blocked the antiparkinsonian effect of L-DOPA.

Parkinson’s disease (PD) is a debilitating movement disorder associated with the death of dopaminergic nigrostriatal neurons. In addition to dopamine deficiency, abnormalities in glutamate and other receptors at striatal synapses have been reported. Synapse associated protein 97 (SAP97) is involved in regulation of glutamate receptor function. In the striatum of unilaterally-lesioned 6-OHDA rat model of PD, SAP97 levels are decreased in post synaptic density fraction, as well as in the whole striatum. I hypothesize that changes in striatal levels and subcellular distribution of SAP97 are responsible for abnormal neurotransmission in striatum and the motor symptoms of PD. GFP-tagged wild type SAP97 and SAP97 mutants were over-expressed in the striatum of 6-OHDA-lesioned rat model of PD. A single 6.5 mg/kg dose of L-DOPA eliminated parkinsonism in 6-OHDA-lesioned rats over-expressing SAP97-GFP, whereas, three 6.5 mg/kg doses of L-DOPA negated parkinsonism in 6-OHDA-lesioned rats over-expressing SAP97-GFP and SAP97∆1-65-GFP. The over-expression of SAP97∆1-65-GFP enhanced parkinsonism in 6-OHDA-lesioned rats and blocked the antiparkinsonian effect of L-DOPA.