Robert T. Mason

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Over a 2-yr period, we investigated the annual cycles of plasma testosterone and corticosterone and the relationships between these hormones and body condition in a wild population of male red-spotted garter snakes, Thamnophis sirtalis concinnus. In the 10 mo that were sampled, a peak in testosterone was observed in late summer during gametogenesis and(More)
Stress and reproduction are generally thought to work in opposition to one another. This is often manifested as reciprocal relationships between glucocorticoid stress hormones and sex steroid hormones. However, seasonal differences in how animals respond to stressors have been described in extreme environments. We tested the hypothesis that garter snakes,(More)
The majority of pheromones identified to date are insect pheromones, which are volatile in nature. Identification of nonvolatile pheromones have been relatively rare, especially in vertebrates. Male and female garter snakes use pheromones to mediate sexual behavior. The female sex attractiveness pheromone of the Canadian red-sided garter snake, Thamnophis(More)
In many diverse taxa, males of the same species often exhibit multiple mating strategies. One well-documented alternative male reproductive pattern is 'female mimicry', whereby males assume a female-like morphology or mimic female behaviour patterns. In some species males mimic both female morphology and behaviour. We report here female mimicry in a(More)
Plasma levels of progesterone (P), testosterone (T), estradiol (E2), and corticosterone (B) of female red-sided garter snakes were measured during the period of ovarian development. Differences in hormone levels were analyzed with respect to three factors: whether the female mated in the spring, ovarian condition, and time after emergence from hibernation.(More)
The red-sided garter snake, Thamnophis sirtalis parietalis is an ideal model for the study of chemical or pheromonal communication in vertebrates. Results of long-term field and laboratory investigations of the chemical ecology of these unusual animals is summarized. These studies include a description of the characterization of the female attractiveness(More)
Red-sided garter snakes (Thamnophis sirtalis parietalis) court and mate in spring, soon after they emerge from large communal overwintering dens in south-central Manitoba. Because of a massive bias in the operational sex ratio, every female attracts intense courtship from dozens to hundreds of males. We suggest that this courtship constitutes significant(More)
In the red-sided garter snake (Thamnophis sirtalis parietalis) adult females are larger than adult males; this difference is apparent within 3 wk of birth, a time coinciding with high circulating levels of androgens. To study the ontogeny and regulation of this sexual dimorphism, male neonates were either castrated, castrated and given Silastic capsules(More)
When choosing between two potential mates, a male may benefit by picking a larger (longer and/or more heavy-bodied) female because she is likely to produce more or larger offspring. Males of many species use visual cues to evaluate the sizes of their mates, but in some situations (at night or in a crowded mating swarm), vision may be useless. Potentially,(More)
Male leopard geckoes,Eublepharis macularius, rely on skin-derived semiochemicals to determine the sex of conspecifics. Males respond to other males with agonistic behavior while females elicit courtship behavior from males. While females were shedding, males responded to them with agonistic behavior. The same females were courted both before and after(More)