A 12-year retrospective study of 172 deceased captive syngnathids (Hippcampus kuda, H. abdominalis, and Phyllopteryx teaniolatus) from the Toronto Zoo was performed. The most common cause of mortality was an ulcerative dermatitis, occurring mainly in H. kuda. The dermatitis often presented clinically as ‘red-tail’, or hyperaemia of the ventral aspect of the tail caudal to the vent, or as multifocal epidermal ulcerations occurring anywhere. Light microscopy often demonstrated filamentous bacteria associated with these lesions, and it was hypothesized that the filamentous bacteria were from the Flavobacteriaceae family. Bacteria cultured from ulcerative lesions and DNA extracted from ulcerated tissues were examined using universal bacterial 16S rRNA gene primers. A filamentous bacterial isolate and DNA sequences with high sequence identity to Cellulophaga fucicola were obtained from ulcerated tissues. Additionally, in situ hybridization using species-specific RNA probes labeled filamentous bacteria invading musculature at ulcerative skin lesions.

Understanding how anthropogenic activity impacts the health and viability of wildlife populations is one of the most important tasks of environmental biology. A key concern related to bi-products of human activity is the accumulation of environmental pollutants within aquatic environments. Pollutants such as endocrine disruptors and heavy metals have the potential to impact both human and wildlife populations in contaminated areas. While much research has focused on how these compounds impact natural selection processes, such as viability and reproduction, their effect on sexual selection processes is not as clear. The goal of this dissertation was to address how environmental contaminants impact sexual selection processes in a sex-role reversed pipefish and evaluate how these effects may impact long-term population viability. Here we show that short periods of exposure to environmentally relevant concentrations of a synthetic estrogen result in male pipefish with female-like secondary sexual traits. While these males are capable of reproduction, exposed males are discriminated against by females in mate choice tests. In natural populations, this type of discrimination could reduce male mating opportunities, potentially reducing their reproductive success. In an additional component of this dissertation, it was discovered that pipefish populations around Mobile Bay, specifically Weeks Bay, are currently being exposed to significantly elevated levels of mercury. These populations are genetically distinct from coastal populations but moderate levels of gene flow occur among sites, and gene flow between contaminated and non-contaminated population may be influencing how environmental contaminants are impacting genetic diversity and population viability. In the case of endocrine disruptors, migration between contaminated and non-contaminated sites may negatively impact population viability. Morphological traits induced with exposure to contaminants may be maintained for extended periods of time, therefore, the effect the exposed phenotype has on mating dynamics and sexual selection could be carried to non-contaminated sites if exposed individuals move to new populations. On the other hand, immigration of individuals from non-contaminated sites into contaminated areas may help maintain genetic diversity within exposed populations. In conclusion, the work presented in this dissertation shows that the presence of environmental toxins can significantly impact sexual selection processes, which in turn can have profound effects on the viability and future evolutionary trajectory of populations. Future work in this area should not only address how these toxins impact individual fitness, but should also address how population structure may be influencing the severity of these compounds on natural populations.

Brain size varies greatly among vertebrates. It has been proposed that the diversity of brain size is produced and maintained through a balance of adaptations to different types and levels of cognitive ability and constraints for adaptive evolution. Phylogenetic comparative studies have made major contributions to our understanding of brain size evolution. However, previous studies have nearly exclusively focused on mammalian and avian taxa and almost no attempts have been made to investigate brain size evolution in ectothermic vertebrates. In my thesis, I studied brain size evolution in two groups of fish with extreme diversity in ecology, morphology and life history, Cichlidae and Syngnathidae. Using phylogenetic comparative methods, I investigated four key questions in vertebrate brain size evolution; cognitive adaptation, sexual selection, phenotypic integration and energetic constraints. I have demonstrated i) that phenotypic integration can link functionally unrelated traits, and this may constrain independent evolution of each part involved or promote concerted evolution of an integrated whole, ii) that brain-body static allometry constrains the direction of brain size evolution, even though the static-allometry showed ability to evolve, allowing evolution of relative brain size under allometric constraints, iii) that the energetic constraints of development and maintenance of brain tissue is an important factor in forming the diversity in brain size in cichlids and syngnathids, both at macroevolutionary and microevolutionary time scales, and iv) that adaptation for feeding and female mating competition may have played key roles in the adaptive evolution of brain size in pipefishes and seahorses. To conclude, my thesis shows the strong benefit of using fish as a model system to study brain size evolution with a phylogenetic comparative framework.

The aim of this study was to investigate the composition of an acoustic scattering layer in the North Sea that is particularly strong at 38 kHz. A full definition of the biological composition of the layer, along with its acoustic properties, would allow for it to be confidently removed from data collected during acoustic fish surveys, where it presents a potential source of bias. The layer, traditionally and informally referred to as consisting of zooplankton, appears similar to others observed internationally. The methodology utilised in this study consisted of biological and acoustic sampling, followed by application of forward and inverse acoustic modelling techniques. Acoustic data was collected at 38, 120 and 200 kHz in July 2003, with the addition of 18 kHz in July 2004. Net samples were collected in layers of relatively strong 38 kHz acoustic scattering using a U-tow vehicle (2003) and a MIKT net (2004). Acoustic data were scrutinised to determine actual backscattering, expressed as mean volume backscattering strength (MVBS) (dB). This observed MVBS (MVBSobs) was compared with backscattering predicted by applying the forward problem solution (MVBSpred) to sampled animal densities in order to determine whether those animals were responsible for the enhanced 38 kHz scattering. In most instances, MVBSobs > MVBSpred, more pronounced at 38 kHz. It was found that MVBSpred approached MVBSobs more closely with MIKT than with U-tow samples, but that the 38 kHz mismatch was present in both. Inversion of candidate acoustic models predicted gas-bearing scatterers, which are strong at 38 kHz, as most likely to be responsible for this. Potential sources of inconsistencies between MVBSpred and MVBSobs were identified. The presented forward and inverse solutions infer that although the layer often contains large numbers of common zooplankton types, such as copepods and euphausiids, these are not the dominant acoustic scatterer at 38 kHz. Rather, there remains an unidentified, probably gas-bearing scatterer that contributes significantly to observed scattering levels at this frequency. This study identifies and considerably narrows the list of candidates that are most likely to be responsible for enhanced 38 kHz scattering in the North Sea layer, and recommendations are made for potential future studies.

<p>A central goal of evolutionary biology is to understand the processes responsible for morphological, genetic and behavioural differentiation between sexes and among geographically distinct populations. Perhaps the most significant processes are genetic drift, natural selection, phenotypic plasticity and sexual selection. The main aim of this thesis was to investigate differentiation among individuals and populations of the sex-role reversed pipefish (<i>Syngnathus typhle</i>) and, consequently, determine which processes may be responsible for emerging patterns. This unique species is characterised by males predominately choosing amongst displaying females.</p><p>In this thesis I revealed, on a microgeographic scale, morphological differentiation without genetic divergence among populations. Interestingly, females differed in size whereas the males did not. For females in this sex-role reversed species, the costs of expressing a plastic phenotype may be outweighed by the potential gains from greater survivorship, higher fecundity or increased mating success. Thus, females gain the ability to make themselves as conspicuous and attractive to males as possible in the specific environment they are living. Moreover, behavioural experiments, which focussed on describing “personalities”, reproductive investment strategies, and mate-sampling tactics, also indicated that males as well as females had the behavioural plasticity required to adjust to the environment in which they live. To this end, using video playbacks as experimental stimuli may be especially rewarding in this species.</p><p>Overall, the studies in this thesis acknowledge the ability of species to fine-tune their phenotype to maximise fitness and, therefore, highlight the importance of considering patterns of differentiation in an environment-specific context. </p>

Understanding the processes that govern mating behaviors is a fundamental goal of evolutionary biology and behavioral ecology. Population-level patterns of mate acquisition and offspring production, otherwise known as the genetic mating system, play a central role in the sexual selection on morphological and behavioral traits and may facilitate speciation. The central hypothesis of this research is that variation in environmental conditions, such as temperature, turbidity, and habitat, and demographic influences such as population density, sex ratios and temporal availability of mates, may limit mating and reproductive success in a predictive manner. Therefore the goal of this dissertation is to examine the contributions of geographic and temporal variation on the plasticity of the genetic mating system in two species of pipefish. The first study examined whether meaningful variation in the genetic mating system exists between two natural populations of the dusky pipefish, Syngnathus floridae. Results of this investigation provide evidence that the genetic mating system differs among different geographic locations. The second study considered the relative contributions of environmental conditions and population demographics on differences in the genetic mating system of dusky pipefish from five natural populations. The results of this investigation show strong trends for demographic and environmental factors to strongly influence the genetic mating system between populations. The third study considered how variation in the number of available mates predicts the outcome of sexual selection during the course of a breeding season in the broad-nosed pipefish, Sygnathus typhle. The results of this study indicate a strong influence of the operational sex ratio on the genetic mating system. In addition to these studies, a study was conducted to investigate whether phylogeographic relationships may be responsible for geographic variation in the genetic mating system of the dusky pipefish of pipefish. Mitochondrial DNA analysis does not substantiate subspecies designations for this species and microsatellite analysis show a clear pattern of isolation by distance. Taken together, these studies significantly enhance the understanding of how mating systems are organized over broad environmental gradients and temporal/spatial scales and to the evolution of sexual selection on the whole.

A central goal of evolutionary biology is to understand the processes responsible for morphological, genetic and behavioural differentiation between sexes and among geographically distinct populations. Perhaps the most significant processes are genetic drift, natural selection, phenotypic plasticity and sexual selection. The main aim of this thesis was to investigate differentiation among individuals and populations of the sex-role reversed pipefish (Syngnathus typhle) and, consequently, determine which processes may be responsible for emerging patterns. This unique species is characterised by males predominately choosing amongst displaying females. In this thesis I revealed, on a microgeographic scale, morphological differentiation without genetic divergence among populations. Interestingly, females differed in size whereas the males did not. For females in this sex-role reversed species, the costs of expressing a plastic phenotype may be outweighed by the potential gains from greater survivorship, higher fecundity or increased mating success. Thus, females gain the ability to make themselves as conspicuous and attractive to males as possible in the specific environment they are living. Moreover, behavioural experiments, which focussed on describing “personalities”, reproductive investment strategies, and mate-sampling tactics, also indicated that males as well as females had the behavioural plasticity required to adjust to the environment in which they live. To this end, using video playbacks as experimental stimuli may be especially rewarding in this species. Overall, the studies in this thesis acknowledge the ability of species to fine-tune their phenotype to maximise fitness and, therefore, highlight the importance of considering patterns of differentiation in an environment-specific context.

Understanding the processes that govern mating behaviors is a fundamental goal of evolutionary biology and behavioral ecology. Population-level patterns of mate acquisition and offspring production, otherwise known as the genetic mating system, play a central role in the sexual selection on morphological and behavioral traits and may facilitate speciation. The central hypothesis of this research is that variation in environmental conditions, such as temperature, turbidity, and habitat, and demographic influences such as population density, sex ratios and temporal availability of mates, may limit mating and reproductive success in a predictive manner. Therefore the goal of this dissertation is to examine the contributions of geographic and temporal variation on the plasticity of the genetic mating system in two species of pipefish. The first study examined whether meaningful variation in the genetic mating system exists between two natural populations of the dusky pipefish, Syngnathus floridae. Results of this investigation provide evidence that the genetic mating system differs among different geographic locations. The second study considered the relative contributions of environmental conditions and population demographics on differences in the genetic mating system of dusky pipefish from five natural populations. The results of this investigation show strong trends for demographic and environmental factors to strongly influence the genetic mating system between populations. The third study considered how variation in the number of available mates predicts the outcome of sexual selection during the course of a breeding season in the broad-nosed pipefish, Sygnathus typhle. The results of this study indicate a strong influence of the operational sex ratio on the genetic mating system. In addition to these studies, a study was conducted to investigate whether phylogeographic relationships may be responsible for geographic variation in the genetic mating system of the dusky pipefish of pipefish. Mitochondrial DNA analysis does not substantiate subspecies designations for this species and microsatellite analysis show a clear pattern of isolation by distance. Taken together, these studies significantly enhance the understanding of how mating systems are organized over broad environmental gradients and temporal/spatial scales and to the evolution of sexual selection on the whole.

The sex-role reversal and male pregnancy found in syngnathids are highly unusual traits in vertebrates. Reproductive hormones likely influence development and regulation of these traits. However, very few studies have examined the underlying hormonal mechanisms that mediate female competitive behavior and male pregnancy. New methodologies and better husbandry practices have made such studies more feasible in recent years. Research on a relatively small number of species has suggested that androgens are likely regulators of spermatogenesis and the development of the male brood pouch prior to pregnancy. Androgens are also potential candidates for mediating sex-role reversed behavior in female syngnathids. The goal of this dissertation was to examine the role of androgens in the male reproductive cycle and female intrasexual competitive behavior in the sex-role reversed Gulf pipefish, Syngnathus scovelli. From review of the literature, I developed a model for the hormonal regulation of the male reproductive cycle in seahorses. I predicted that androgens would be low during the early stages of pregnancy and increase during the end of pregnancy as males go through another cycle of spermatogenesis in preparation for the next mating event. My study of 11-ketotestosterone and testis mass across the reproductive cycle in male S. scovelli supported this model. I also conducted several studies on the role of androgens in female competitive behavior. I determined that treatment with 11-ketotestosterone the evening prior to an intrasexual interaction resulted in an increase in competitive behavior in large over small test females. Conversely, treatment with 11-ketotestosterone one hour prior to an intrasexual interaction resulted in a decrease in competitive behavior in large over small females when stimulus female behavior was controlled. A comparative study of competitive and courtship behavior in S. scovelli and the closely related S. floridae suggested that sexual selection has affected competitive and courtship behavior in both males and females of these species. The diversity of reproductive patterns exhibited by syngnathids suggests that they will provide a unique opportunity to assess how hormonal regulation of reproductive behavior and function has evolved within this lineage.