Robert T. Mason - US grants

This award supports visits over a three-year period by Dr. Robert T. Mason of Oregon State University to the University of Queens- land, Australia, to work with Dr. Joan Margaret Whittier on reproduction in the tropical colubrid brown tree snake, Boiga irregularis, which is native to Australia, New Guinea, and the Solomon Islands. During World War II, the snake was introduced onto Guam, where it clearly established itself as a serious threat to native fauna and to humans. This snake is responsible for the extinction of three species of native birds on Guam, and the serious declination in the populations of most, if not all, remaining small vertebrates on the island. B. irregularis is a prolific colonizer and it has now been found on several additional islands, including Hawaii. Little is known of the biology in general of these snakes. Of particular importance in terms of managing this emerging threat to Pacific island fauna is the investigation of the reproductive potential of female brown tree snakes in their natural range in Australia. Specifically, the investigators will (1) characterize histologically the cycle of egg and sperm production, and sperm storage; (2) determine by radioimmunoassay sex steroid hormone secretion in both sexes; and (3) investigate the chemical ecology of these animals by isolating and chemically characterizing potential sex attractant pheromones produced by females.

9357245 Mason This NSF Young Investigator award investigates the interrelationships among natural products chemistry, behavioral biology, reproductive physiology, and ecology. This research uses a comparative, interdisciplinary approach that combines and integrates the molecular, organismal, and ecological levels of analysis. It is conducted both in the laboratory and in the field to illustrate the adaptive functions of semiochemicals or pheromones. Field and laboratory studies are complementary, bridging the gap between natural products chemistry and behavioral ecology by incorporating laboratory-based analyses of the structure, manufacture, and delivery of semiochemicals with studies of the animals's physiological ecology and behavior in the field. Specifically, the research focuses on vertebrate sex pheromones. Using state-of-the-art chemical techniques such as gas chromatography/mass spectrometry and nuclear magnetic resonance spectroscopy, the principal investigator has isolated, identified, and synthesized the first pheromone in a reptile, the Canadian red- sided garter snake, Thamnophis sirtalis parietalis. These studies address the practical applications of this research. Currently rattlesnake repellent based on semiochemicals produced by other snakes is being developed. A second project is aimed at using pheromones to help control populations of the Guam brown tree snake, an introduced pest species that has destroyed most of the native bird populations on Guam and threatens the ecology of other Pacific Ocean islands, including Hawaii. ***

Chemical communication by pheromones is the predominant mode of information
transfer in most vertebrates. The female garter snake (Thamnophis sirtalis) sex
pheromone, a nonpolar, hydrophobic blend of saturated and monounsaturated methyl
ketones, is insoluble in aqueous solutions. This pheromone is detected by the
vomeronasal organ (VNO), which is specialized for the reception of nonvolatile
chemical cues, but the mechanism by which the pheromone gains access to the
aqueous environment of the organ is unknown. Preliminary data indicate that the
Harderian glands' (HG) secretions, which duct exclusively into the VNO in snakes,
contain solubilizing and/or pheromone-binding properties. For over 300 years, the
function of the cephalic HG has been the subject of speculation from numerous
sources. Certainly their relatively large size, their phylogenetic age, and persistent
conservation in almost all tetrapod groups as they emerged from an aqueous to an
air/land environment suggest that they probably play an important role in the
physiological adaptation to terrestrial life. This project will examine the role of the
HG as a mediator in providing access for the female sex pheromone to the VNO of male
garter snakes. Using radiolabeled garter snake sex pheromone, studies will be
conducted to determine the solubilizing effect of HG secretion on the female sex
pheromone and the potential of the HG secretion to possess pheromone-binding
proteins.
The effects of HG removal on courtship behavior and prey attack, both known to require
a functional VN system, will also be investigated, as will the effects of seasonal and
hormonal variation on the composition of the HG. The integrative research described
here will provide demonstrations of a novel mechanism by which nonpolar, hydrophobic
pheromone molecules reach the VNO, using a very well characterized system: the VN
system of garter snakes. If a pheromone-binding protein is involved, it will be the
first identified in a non-mammalian species. This research will provide a compelling
model for the examination of HG involvement in perireceptor events mediating VNO
function of other mammalian and non-mammalian vertebrates. In addition, this study
takes advantage of two unambiguous, quantifiable behaviors exhibited by a species in
its natural habitat that not only offers a robust model for insights into seasonal shifts
in reproductive behavior and feeding, but also proposes a physiological mechanism
mediating these seasonally regulated changes. This proposal involves an integrative,
multidisciplinary approach including field and lab studies that will yield significant
insights into the unifying principles of pheromonal communication common to many,
if not most, vertebrates. The broader impacts of this proposal include multidisciplinary
training in research and education through the mentoring of graduate students,
undergraduates and outreach to high school and grade school students.
Undergraduates are an integral part of the PI's laboratories, assisting in animal
husbandry, field work and behavior experiments. These undergraduates have been
co-authors on 23 published papers from the two laboratories. The PI's have a
long-term commitment to mentoring, with more than a dozen high school students
involved in minority training programs and Intel/Westinghouse competitions, and an
additional nine high school students having worked in an NSF-initiated Apprenticeships
in Science and Engineering program. These experiences, coupled with appropriate
course work, will provide a firm foundation for these scientists-in-training to
experience the joys and frustration of field and laboratory work.

Females of many species mate with multiple males in a breeding season. One explanation for this behavior is that it facilitates mate choice after copulation. Female choice that occurs after copulation is detectable because not all the female's mates have equal paternity; it is called cryptic female choice because the process is hidden. For example, females may transport sperm from particular males to storage sites near where fertilization occurs, which could result in paternity biased towards those males. Cryptic female choice can have profound effects on the strength and direction of sexual selection, the evolution of mating systems, and the coevolution of female and male reproductive traits that leads to speciation. However, the cryptic nature of postcopulatory female choice has made it extremely difficult to document. The PIs have developed a method to label live sperm with fluorescent particles so that the fate of the sperm can be observed in vivo. By observing both where sperm are stored and which sperm fertilize eggs, it will be possible to measure the extent of cryptic female choice. The work will be conducted with garter snakes and the methods are likely to be valuable for many species.

The PIs will develop and pilot an integrated inquiry-based lecture, field and laboratory unit appropriate for upper-level high school biology students. This program builds on a successful module that the PIs developed for middle-school students. The PIs also intend to sustain their commitment to undergraduate research opportunities by training at least two undergraduates in PCR, genotyping, and paternity analysis.