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Investigations of host-associated differentiation of parasitoids have largely focused on the degree of molecular genetic differentiation, but a true test of species status must examine the mating patterns of differentiated populations to determine if they can interbreed in the wild and produce viable offspring. We examined possible mechanisms of isolation between two genetically distinct host-plant complex races of the braconid, Cotesia congregata, originating from hosts on tobacco and catalpa. We compared male responses to female pheromones, elements of male acoustic courtship signals, and breeding success between the two races. Males responded to pheromones from both sources and male courtship signals showed only subtle differences, suggesting that factors other than courtship behavior may be involved in isolation of the two races. However, nearly 90% of females from one hybrid cross failed to produce offspring, leading to post-zygotic isolation. Development time, emerged brood size, and sex ratios between the races also differed.

O preá Cavia aperea é tido como um dos representantes atuais da espécie ancestral a partir da qual se originou a cobaia Cavia porcellus por meio de um processo de domesticação iniciado há cerca de 6000 anos. A comparação entre estas espécies constitui um modelo interessante para o estudo dos efeitos comportamentais da domesticação, além de ter implicações para a compreensão da taxonomia destas espécies. Nosso objetivo foi descrever e comparar o comportamento de corte em cobaias e preás em pares intraespecíficos e verificar, através de pareamentos interespecíficos, eventuais barreiras reprodutivas provenientes da domesticação. Pares intra e interespecíficos foram submetidos a dois experimentos, um a curto prazo em ambiente de sala-teste e outro a longo prazo em ambiente semi-natural, nos quais registrou-se os episódios de interação e as categorias comportamentais exibidas na interação entre os sujeitos. Encontrou-se diferenças significativas entre os pares intra e interespecíficos (taxa e duração da interação), assim como entre cobaias e preás (cobaias interagiram, cortejaram-se e exploraram-se mais do que preás, estes se mostraram mais ativos e exploradores do meio). As diferenças revelam possíveis efeitos do processo de domesticação. Os pares interespecíficos também diferiram significativamente entre si, de forma assimétrica: enquanto machos preás cortejaram fêmeas cobaias e copularam com estas (menos, contudo, do que no caso das fêmeas coespecíficas), machos cobaias praticamente não cortejaram fêmeas preás provavelmente por causa dos altos níveis de agressão destas. Nossos resultados demonstram a existência de barreiras comportamentais entre as duas espécies, devidas provavelmente à domesticação, capazes de gerar um isolamento reprodutivo parcial. / The wild cavy (Cavia aperea) is considered as one of the current exemplars of an ancestor species which through domestication processes starting six thousands years ago originated Cavia porcellus, the guinea pig. A formal comparison between the two species (Cavia aperea and Cavia porcellus), constitutes not only an interesting model for an investigation of the effects of domestication on behaviour, but also it may contribute to a taxonomic understanding of the two species. The aim of the study was to describe and compare the courtship behaviour exhibited by wild cavies and guinea pigs within intraspecific couples. In addition, arranging interspecific couples, we aimed to verify possible reproductive barriers which could be a consequence of the domestication processes. Intraspecific and interspecific couples took part in two experiments: the first was a short term experiment undertaken in a non-natural testing environment; the second was long term and conducted in a semi-natural environment. Interactive episodes were observed and a range of behavioural categories demonstrated by the individuals during interactions were registered. Significant differences were found between intra and interspecific couples (frequency and duration of the interactions) as well as between wild cavies and guinea pigs. Whilst the latter interacted and explored themselves more as well as showing more courtship behaviour, the former instead were more active towards exploring their environment. These differences suggest possible effects of the domestication processes. Furthermore, there were also significant asymmetrical differences among the interspecific couples themselves: whilst male wild cavy showed courtship behaviour towards the female guinea pigs and even mated with them. However, less than when compared to their behaviour towards female wild cavies. Male guinea pigs mostly did not court female wild cavies; this was mainly attributed to the female wild cavies showing high levels of aggression. The results account for the existence of behavioural barriers between the two species, which are probably due to the domestication process and can well generate partial reproductive isolation.

O preá Cavia aperea é tido como um dos representantes atuais da espécie ancestral a partir da qual se originou a cobaia Cavia porcellus por meio de um processo de domesticação iniciado há cerca de 6000 anos. A comparação entre estas espécies constitui um modelo interessante para o estudo dos efeitos comportamentais da domesticação, além de ter implicações para a compreensão da taxonomia destas espécies. Nosso objetivo foi descrever e comparar o comportamento de corte em cobaias e preás em pares intraespecíficos e verificar, através de pareamentos interespecíficos, eventuais barreiras reprodutivas provenientes da domesticação. Pares intra e interespecíficos foram submetidos a dois experimentos, um a curto prazo em ambiente de sala-teste e outro a longo prazo em ambiente semi-natural, nos quais registrou-se os episódios de interação e as categorias comportamentais exibidas na interação entre os sujeitos. Encontrou-se diferenças significativas entre os pares intra e interespecíficos (taxa e duração da interação), assim como entre cobaias e preás (cobaias interagiram, cortejaram-se e exploraram-se mais do que preás, estes se mostraram mais ativos e exploradores do meio). As diferenças revelam possíveis efeitos do processo de domesticação. Os pares interespecíficos também diferiram significativamente entre si, de forma assimétrica: enquanto machos preás cortejaram fêmeas cobaias e copularam com estas (menos, contudo, do que no caso das fêmeas coespecíficas), machos cobaias praticamente não cortejaram fêmeas preás provavelmente por causa dos altos níveis de agressão destas. Nossos resultados demonstram a existência de barreiras comportamentais entre as duas espécies, devidas provavelmente à domesticação, capazes de gerar um isolamento reprodutivo parcial. / The wild cavy (Cavia aperea) is considered as one of the current exemplars of an ancestor species which through domestication processes starting six thousands years ago originated Cavia porcellus, the guinea pig. A formal comparison between the two species (Cavia aperea and Cavia porcellus), constitutes not only an interesting model for an investigation of the effects of domestication on behaviour, but also it may contribute to a taxonomic understanding of the two species. The aim of the study was to describe and compare the courtship behaviour exhibited by wild cavies and guinea pigs within intraspecific couples. In addition, arranging interspecific couples, we aimed to verify possible reproductive barriers which could be a consequence of the domestication processes. Intraspecific and interspecific couples took part in two experiments: the first was a short term experiment undertaken in a non-natural testing environment; the second was long term and conducted in a semi-natural environment. Interactive episodes were observed and a range of behavioural categories demonstrated by the individuals during interactions were registered. Significant differences were found between intra and interspecific couples (frequency and duration of the interactions) as well as between wild cavies and guinea pigs. Whilst the latter interacted and explored themselves more as well as showing more courtship behaviour, the former instead were more active towards exploring their environment. These differences suggest possible effects of the domestication processes. Furthermore, there were also significant asymmetrical differences among the interspecific couples themselves: whilst male wild cavy showed courtship behaviour towards the female guinea pigs and even mated with them. However, less than when compared to their behaviour towards female wild cavies. Male guinea pigs mostly did not court female wild cavies; this was mainly attributed to the female wild cavies showing high levels of aggression. The results account for the existence of behavioural barriers between the two species, which are probably due to the domestication process and can well generate partial reproductive isolation.

Graduation date: 2006 / Most vertebrates exhibit seasonality in many life history traits. Such seasonal rhythms are temporally organized via the transduction of environmental cues (e.g., photoperiod, temperature) into appropriate endocrine signals. However, among ectothermic vertebrates that undergo continuous winter dormancy, temperature is the only environmental cue available for synchronizing seasonal rhythms. Most intriguing is that in species where reproduction occurs immediately following spring emergence, the associated changes in neurophysiology and behavior that accompany reproduction likely occur during winter dormancy. The purpose of this dissertation research was to explore the mechanisms by which temperature cues affect the chronobiology and seasonal reproduction of red-sided garter snakes (Thamnophis sirtalis parietalis). Because of their roles in circadian organization and energy balance, melatonin and corticosterone are likely hormonal components of these time-keeping systems. I first characterized the interactions between melatonin and corticosterone to better understand the hormonal mechanisms facilitating temperature-induced reproduction. Melatonin and corticosterone additively inhibit reproductive behavior during the spring mating season. Experimental manipulations with a serotonin receptor antagonist suggest the mechanism underlying these effects involves a serotonin-regulated system. Although melatonin does not influence corticosterone responses to capture stress, capture stress significantly increases melatonin concentrations. To investigate the functional significance of these interactions in regulating temperature-induced reproduction, I measured body temperatures of snakes as well as circadian melatonin and corticosterone cycles during winter dormancy and spring emergence using a combination of field and laboratory experiments. Surprisingly, an increase in body temperature is not necessary for emergence from winter dormancy. Rather, critically low temperatures may serve as a zeitgeber entraining an endogenous circannual cycle that regulates emergence. Decreased environmental temperatures, in the absence of changing photoperiod cues, modulate circadian melatonin and corticosterone rhythms during hibernation. Such temperature-induced changes in hormone rhythms may facilitate seasonal reproductive behavior following spring emergence. Furthermore, a phase-shift in corticosterone rhythms during the mating season may regulate the seasonal transition between reproductive and non-reproductive states in red-sided garter snakes. Such studies investigating the environmental and hormonal mechanisms underlying time-keeping systems may provide valuable insight into the potential impact of environmental perturbations (e.g., climate change) on seasonal rhythms in physiology and behavior.