Publications by authors named "Robert T Mason"

As global temperatures continue to rise, understanding the impacts of warming environments has become increasingly important. Temperature is especially relevant for ectothermic organisms which depend upon consistent and predictable annual temperature cycles for reproduction and development. However, additional research is required in this area to elucidate the potential impacts of climate change on future generations.

View Article and Find Full Text PDF

Reptiles signal to conspecifics using lipids in their skin, primarily to enable mate tracking and assessment. The isolation of these lipids has utility in research focused on evolutionary patterns and mechanisms of chemical communication, in addition to understanding the waterproofing role of lipids in the evolution of terrestrial life. In an applied approach, such skin-based cues have potential use for wildlife managers dealing with invasive species.

View Article and Find Full Text PDF

Life-history strategies vary dramatically between the sexes, which may drive divergence in sex-specific senescence and mortality rates. Telomeres are tandem nucleotide repeats that protect the ends of chromosomes from erosion during cell division. Telomeres have been implicated in senescence and mortality because they tend to shorten with stress, growth and age.

View Article and Find Full Text PDF

Trematodes of the genus Alaria develop into an arrested stage, known as mesocercariae, within their amphibian second intermediate host. The mesocercariae are frequently transmitted to a non-obligate paratenic host before reaching a definitive host where further development and reproduction can occur. Snakes are common paratenic hosts for Alaria spp.

View Article and Find Full Text PDF

The non-sperm components of an ejaculate, such as copulatory plugs, can be essential to male reproductive success. But the costs of these ejaculate components are often considered trivial. In polyandrous species, males are predicted to increase energy allocation to the production of non-sperm components, but this allocation is often condition dependent and the energetic costs of their production have never been quantified.

View Article and Find Full Text PDF
Article Synopsis
  • Polyandry can lead to sexual conflict, particularly as males attempt to control female mating behavior through mechanisms like copulatory plugs and antiaphrodisiacs.
  • Male red-sided garter snakes use large copulatory plugs that potentially prevent remating and impact female receptivity, but the effectiveness can be influenced by the male's sperm supply.
  • Research indicates that females are more likely to remate after mating with sperm-less (vasectomized) males than intact males, suggesting that females assess sperm presence as a signal for seeking additional mating opportunities for fertility assurance.
View Article and Find Full Text PDF

Vertebrates communicate their sex to conspecifics through the use of sexually dimorphic signals, such as ornaments, behaviors and scents. Furthermore, the physiological connection between hormones and secondary sexual signal expression is key to understanding their dimorphism, seasonality and evolution. The red-sided garter snake (Thamnophis sirtalis parietalis) is the only reptile for which a described pheromone currently exists, and because garter snakes rely completely on the sexual attractiveness pheromone for species identification and mate choice, they constitute a unique model species for exploring the relationship between pheromones and the endocrine system.

View Article and Find Full Text PDF

Sexual conflict over mating can result in sex-specific morphologies and behaviours that allow each sex to exert control over the outcome of reproduction. Genital traits, in particular, are often directly involved in conflict interactions. Via genital manipulation, we experimentally investigated whether genital traits in red-sided garter snakes influence copulation duration and formation of a copulatory plug.

View Article and Find Full Text PDF

Vertebrates indicate their genetic sex to conspecifics using secondary sexual signals, and signal expression is often activated by sex hormones. Among vertebrate signaling modalities, the least is known about how hormones influence chemical signaling. Our study species, the red-sided garter snake (Thamnophis sirtalis parietalis), is a model vertebrate for studying hormonal control of chemical signals because males completely rely on the female sex pheromone to identify potential mates among thousands of individuals.

View Article and Find Full Text PDF

During the breeding season, female red-sided garter snakes (Thamnophis sirtalis parietalis) produce and express a sexual attractiveness pheromone that elicits male courtship behavior. Composed of a homologous series of saturated and monounsaturated methyl ketones, this pheromone is expressed in female skin lipids. Recent studies have shown that the sexual attractivity of unmated female garter snakes declines as the breeding season progresses.

View Article and Find Full Text PDF

During the breeding season, two distinct male phenotypes are exhibited by red-sided garter snakes (Thamnophis sirtalis parietalis), with courtship behavior being directed not only toward females, but also toward a sub-population of males called she-males. She-males are morphologically identical to other males except for a circulating androgen level three times that of normal males and their ability to produce a female-like pheromone. As in other vertebrates, limbic nuclei in the red-sided garter snake brain are involved in the control of sexual behaviors.

View Article and Find Full Text PDF
Article Synopsis
  • The study investigates how hormones like melatonin and corticosterone interact during stress in red-sided garter snakes.
  • Capture stress increased melatonin in the snakes, but additional corticosterone treatment did not replicate this effect and instead inhibited melatonin synthesis from its precursor.
  • The findings suggest that different phases of stress responses have distinct impacts on melatonin production, highlighting a complex relationship between hormonal signals and stress in these snakes.
View Article and Find Full Text PDF
Social behavior and pheromonal communication in reptiles.

J Comp Physiol A Neuroethol Sens Neural Behav Physiol

October 2010

The role of pheromones in orchestrating social behaviors in reptiles is reviewed. Although all reptile orders are examined, the vast majority of the literature has dealt only with squamates, primarily snakes and lizards. The literature is surprisingly large, but most studies have explored relatively few behaviors.

View Article and Find Full Text PDF

We investigated regional and seasonal variations in neural aromatase activity (AA), the enzyme that converts androgens into estrogens, to examine a possible indirect role of testosterone (T) in mediating spring reproductive behavior of red-sided garter snakes, a species exhibiting a dissociated reproductive pattern. Neural AA in male snakes varied significantly among brain regions. Additionally, there were significant interactions between brain region and season.

View Article and Find Full Text PDF

Low temperature dormancy is a necessary requirement of the annual cycle of most nonmigratory, temperate vertebrates. The red-sided garter snake, Thamnophis sirtalis parietalis, overwinters in communal dens during its prolonged winter dormancy (8 mo), and upon emergence, reproductive behavior of both sexes is maximal. Previous work on this species showed that male courtship behavior is maximally induced after simulated low temperature dormancy.

View Article and Find Full Text PDF

We investigated the mechanisms by which temperature induces seasonal reproductive behavior in red-sided garter snakes (Thamnophis sirtalis parietalis). Specifically, we addressed whether elevated temperatures during winter dormancy influence (1) diel melatonin and corticosterone rhythms; (2) sex steroid hormone and corticosterone profiles; and (3) the expression of reproductive behavior following emergence. Elevated hibernation temperatures (i.

View Article and Find Full Text PDF

Data addressing adrenocortical modulation across taxonomic groups are limited, especially with regard to how female reproductive condition influences the sensitivity of the hypothalamus-pituitary-adrenal axis. We investigated seasonal and reproductive variation in basal and stress-induced hormone profiles in a population of free-ranging timber rattlesnakes (Crotalus horridus) in north-central Pennsylvania during spring (i.e.

View Article and Find Full Text PDF

Transduction of environmental cues into endocrine signals that synchronize physiology and behavior with optimal environmental conditions is central to an animal's timekeeping system. Using a common garden approach, we investigated possible geographic variation in timekeeping systems by comparing 24-h melatonin and corticosterone rhythms and reproductive behavior among three populations of garter snakes with very different life histories: red-sided garter snakes (Thamnophis sirtalis parietalis) from Manitoba, Canada; red-spotted garter snakes (Thamnophis sirtalis concinnus) from western Oregon; and eastern garter snakes (Thamnophis sirtalis sirtalis) from southern Florida. Melatonin and corticosterone cycles differed significantly among the three snake populations in a majority of the sampling periods.

View Article and Find Full Text PDF

The body condition index is a common method for quantifying the energy reserves of individual animals. Because good body condition is necessary for reproduction in many species, body condition indices can indicate the potential reproductive output of a population. Body condition is related to glucocorticoid production, in that low body condition is correlated to high concentrations of corticosterone in reptiles.

View Article and Find Full Text PDF

Ring-necked snakes (Diadophis punctatus) are suspected of being venomous because their Duvernoy's gland secretions have high levels of phospholipase activity, which is characteristic of many viperid and elapid venoms, and because anecdotal reports of feeding behavior are consistent with the use of a venom. We tested the toxicity of northwestern ring-necked snake oral secretions to a natural prey species, northwestern garter snakes (Thamnophis ordinoides), by injecting 2-35 microl of oral secretions intraperitoneally. All doses were 100% lethal within 180 min.

View Article and Find Full Text PDF

Seasonal modulation of baseline glucocorticoid concentrations as well as the sensitivity of the hypothalamic-pituitary-adrenal (HPA) axis plays an important role in supporting critical life-history events such as seasonal reproduction and migration. Despite numerous studies on adrenocortical modulation, little is known about the exact timing of this seasonal modulation with respect to critical life-history stages. We tested the hypothesis that seasonal modulation of the HPA axis during the spring mating season in male red-sided garter snakes (Thamnophis sirtalis parietalis) is temporally linked to the mechanisms regulating dispersal.

View Article and Find Full Text PDF

The vomeronasal organ (VNO) is important for activating accessory olfactory pathways that are involved in sexually dimorphic mating behavior. The VNO of male garter snakes is critically important for detection of, and response to, female sex pheromones. In the present study, under voltage-clamp conditions, male snake VNO neurons were stimulated with female sexual attractiveness pheromone.

View Article and Find Full Text PDF

A trend for larger males to obtain a disproportionately high number of matings, as occurs in many animal populations, typically is attributed either to female choice or success in male-male rivalry; an alternative mechanism, that larger males are better able to coercively inseminate females, has received much less attention. For example, previous studies on garter snakes (Thamnophis sirtalis parietalis) at communal dens in Manitoba have shown that the mating benefit to larger body size in males is due to size-dependent advantages in male-male rivalry. However, this previous work ignored the possibility that larger males may obtain more matings because of male-female interactions.

View Article and Find Full Text PDF

Females of many species behave in ways that make it difficult for males to locate, court, and inseminate them. Two hypotheses have been advanced to explain such behavior: either a female thereby minimizes costs of harassment (sexual conflict model) or by playing "hard to get" she discourages inferior suitors (indirect mate choice model). Our studies of garter snakes (Thamnophis sirtalis parietalis) at a communal den in Manitoba support an interpretation of sexual conflict rather than indirect mate choice.

View Article and Find Full Text PDF