A wide range of environmental and physiological factors influence the type and extent of sexual dimorphism found in animals. Influential factors include variable climate, competition for resources and mates, mate choice, and parental investment. In addition, some investigators attribute differences in body size to physiological factors influenced by genetic and environmental variation. Since Darwin's time researchers studying the evolution of animal life-history have discussed the interactions that exist between this wide array of influences on sexual dimorphism in the context of natural selection. Much attention has been paid to the interrelationships of parental size, offspring size and number of offspring per reproductive bout. Spatial and temporal variation among these parameters have been investigated. However, these relationships have not been adequately examined while accounting for differences in offspring gender. In order to characterize the nature and extent of sexual size dimorphism found in adult red-spotted garter snakes, 108 adult females producing 782 female offspring and 790 male offspring were utilized to examine the relationships of the number and size of offspring, clutch mass and maternal size. The second facet of our investigation involved the hormonal manipulation of growth over the first year of post-natal life. To gain an understanding of which endogenous hormones may influence growth in this species we constructed a hormone profile of estradiol and testosterone from birth to 15 weeks of age. We experimentally tested the effects of exogenous hormone as well as the removal of endogenous hormone on growth with the use of estrogen and androgen antagonists. We have found that the extent of sexual size dimorphism observed in adult red-spotted garter snakes is not present at birth. The relative number of males or females born varies differentially with maternal size and age such that larger, older females produce predominately more male offspring. There are no differences in endogenous levels of testosterone and estradiol from birth though 15 weeks and at 36 weeks of age between the sexes. However, these sex steroids do differentially affect the growth of males and females. Finally, we suggest that while all of these factors contribute to sexual size dimorphism in this species, embryonic and environmental influences need to be explored. / Graduation date: 1999

Graduation date: 1994

Pheromones are chemical cues produced by organisms that affect the behavior and/or physiology of conspecifics. The orchestration of reproductive behaviors in many animals depends on the expression of sex pheromones. In insects, intraspecific variation in sex pheromone expression is commonly observed and often influences social interactions between individuals. To what extent similar variation is present in vertebrate sex pheromone systems is not well understood. This thesis investigated the occurrence and significance of phenotypic variation in the sexual attractiveness pheromone of the red-sided garter snake, Thamnophis sirtalis parietalis. Composed of a homologous series of saturated and unsaturated methyl ketones sequestered in the skin lipids of females, this pheromone elicits male courtship behaviors during the breeding season. Variation in the expression of the sexual attractiveness pheromone was examined at three levels: seasonal, individual and populational. Seasonal variation in pheromone expression was examined with respect to trailing behavior. In field experiments, males followed female trails during the breeding season but not during the non-breeding season. Skin lipid analysis revealed marked differences in pheromone composition between the two seasons, suggesting a role for this pheromone in regulating male trailing behavior. Individual variation in pheromone expression was examined with respect to mate choice. In arena trials, males displayed a courtship preference for larger females and continued to demonstrate this preference when visual, tactile, and behavioral cues from the females were removed through the use of skin lipid extracts. Analysis of pheromone profiles from individual females showed size-specific variation in composition, demonstrating that this pheromone can function as a reliable indicator of female size. Finally, populational variation in pheromone expression was examined with respect to sexual isolation among hibernacula. In arena and trailing experiments, males preferred to court and trail resident (same den) females over non-resident (distant den) females. Chemical analysis showed significant inter-den variation in pheromone composition, suggesting that this pheromone represents the cue that males use to identify females from their own population. In summary, these studies demonstrate that significant variation exists in the female sexual attractiveness pheromone of the red-sided garter snake and suggest that this variation has functional significance for this species. / Graduation date: 2002

Canada is the second highest producer of hydroelectric energy in the world. Nearly 50 of the hydroelectric reservoirs in the country have a capacity larger than 1 billion m3. Despite the great number and extent of hydropower developments in Canada and around the world, relatively little is known about how dams and their operations influence terrestrial and semi-aquatic wildlife. Reservoirs at northern latitudes are characterized by large fluctuations in water level, which create modified shorelines called drawdown zones. To evaluate the impact of these disturbances on amphibians and reptiles, I conducted visual encounter surveys at two sites in the drawdown zone of Kinbasket Reservoir, near Valemount, B.C. From April to August of 2010 and 2011, I documented the habitat use, reproductive phenology, and body condition of two amphibian species (Anaxyrus boreas and Rana luteiventris) as well as the growth, movements, diet, and distribution of one species of garter snake (Thamnophis sirtalis). At two sites in the drawdown zone, A. boreas and R. luteiventris were present for the duration of the summer and utilized several ponds for reproduction. The presence and abundance of Rana luteiventris eggs were generally associated with ponds that had higher mean temperatures, higher mean pH, and the presence of fish. In 2010, there was sufficient time for amphibian breeding and metamorphosis to occur before the reservoir inundated the drawdown zone, but low precipitation levels in that year led to desiccation of many breeding ponds. In 2011, high rainfall and snowmelt led to early inundation of breeding ponds, and thousands of tadpoles were presumably swept into the reservoir. Gravid Thamnophis sirtalis were found at just one of two sites in the drawdown zone, but both sites were frequented by foraging individuals of this species. Anaxyrus boreas appears to be the primary prey of T. sirtalis in the drawdown zone. An improved understanding of how the amphibians and reptiles at Kinbasket Reservoir have persisted in this highly disturbed environment may be vital to their conservation — the activation of a new generating unit at Mica Dam in 2014 will alter the pattern and timing of reservoir inundation for the first time since it was constructed 40 years previously. / Graduate

Projet de recherche réalisé avec Bernard Angers comme directeur de maîtrise, Denis Réale en tant que co-directeur et grâce à la collaboration active d'Emmanuel Milot. / La région métropolitaine de Montréal est formée de nombreuses îles à la jonction du fleuve Saint-Laurent et de la rivière des Outaouais, isolant ainsi les populations insulaires en fonction de distances respectives ainsi que des courants. Ce système offre un contexte idéal pour évaluer l’effet de la perte d’habitat liée à la pression d'urbanisation dans un paysage métropolitain insulaire ou en situation d’archipel. La présente étude a pour objectif de comparer l’effet de la perte d’habitat sur la diversité génétique de deux serpents très distincts, Storeria dekayi et Thamnophis sirtalis. Des analyses réalisées à l’aide de marqueurs microsatellites révèlent une plus importante structure génétique entre les populations de S. dekayi (FST=0,19) qu’entre celles de T. sirtalis (FST=0,07) dans la région montréalaise. Chez les deux espèces étudiées, la majorité des populations des habitats réduits présente une richesse allélique moyenne comparable à celle observée dans les habitats plus vastes. Néanmoins, certaines populations présentent des réponses différentes, dont des traces de goulots d’étranglement, une perte de richesse allélique ou encore une importante modification des fréquences alléliques. Au niveau régional, les résultats présentent une importante perte de diversité génétique chez les couleuvres se trouvant sur le continent alors que les populations insulaires de la région montréalaise constituent désormais un réservoir de diversité génétique. Les résultats observés auprès des populations insulaires démontrent que les effets de la perte d’habitat peuvent s’avérer très spécifiques à chaque situation et que la détection de traces génétiques d’un tel phénomène peut nécessiter un contexte logistique très particulier. Un nombre croissant de publications reportent une absence de signature génétique suite à la perte d’habitat chez des oiseaux et des mammifères. Il s’agit de la première étude témoignant de ce phénomène chez les reptiles. Une note est fournie en annexe à l’intention des gestionnaires au sujet de la conservation de la couleuvre brune, S. dekayi. / The Montreal metropolitan community includes numerous islands located at the confluence of the Saint-Lawrence and Ottawa Rivers. In such a fragmented landscape, dispersal of animals is limited by the distance between islands as well as the currents. This system offers an ideal context for the study of the effects of habitat loss on the genetic diversity of animal populations located on islands or archipelagos. This study seeks to assess the effects of habitat area by comparing the organization of genetic diversity of two highly distinct snake species, Storeria dekayi and Thamnophis sirtalis. Analysis realized with microsatellite markers reveals a much stronger genetic organisation in S. dekayi (FST=0.19) than in T. sirtalis (FST=0.07) in the Montreal area. For both studied species, most populations found in reduced habitats showed similar genetic diversity to what was observed in larger habitats. Nevertheless, some populations showed different responses to the loss of habitat, including traces of genetic bottlenecks, a loss in mean allelic richness or an important alteration of their allelic frequencies. This study also reveals an important loss of genetic diversity in the continental snake populations. At the regional scale, the results reveal an important loss of genetic diversity in the continental snake populations and that the insular populations of the Montreal area now constitute a reservoir of the remnant genetic diversity. Moreover, this study not only demonstrates that the genetic response to habitat loss can be very case-specific, but also that to detect traces of such a phenomenon can require a very particular framework. A growing number of publications based on birds and mammals have reported the absence of a genetic signature following a habitat loss. This is the first study to report this phenomenon in reptiles. A note intended for managers is provided about the conservation of the Dekay’s brown snake, S. dekayi.