Research Training Program

Mark Jordan
Luther College
Decorah, Iowa

Thomas Fritts, Ph.D.
Supervising Scientist
Department of Vertebrate Zoology
Division of Reptiles and Amphibians

"My participation in the RTP clearly helped me get into a competitive graduate school."

Determination of Sex and its Relation to the Biology of the Brown Tree Snake (Boiga irregularis)

This project involved the determination of sex and its relation to the biology of the Brown Tree Snake. Nearly 500 specimens collected form Guam since 1984 are held at the museum. Most of the snakes were previously unsexed. The snakes were sexed through dissection. Before sexing exclusively by dissection, x-ray analysis and scale counting were attempted in sex determination. Supplementary to the use of dissection was the use of histology for positive identification of reproductive organs.

The accumulated data was used to look at some population aspects of the snake. It was hypothesized that skewed male sex ratios and sexual dimorphism existed in the population. By comparing ratios and sizes of snakes over time and by various location it could be determined whether these characteristics were a result of ecological stress or simply part of the life history of the snake. It was determined that skewed male sex ratios did not exist in the populations that were examined. However, larger sample sizes would have allowed a better representation of the actual ratios in the population.

It appeared as if sexual dimorphism in terms of weight exists in current populations. This is more evident in recent (1990) than in the past (1988). This suggests that the dimorphism is a result of an ecological stress. Females tend to weigh less possibly because of the use of fat stores in egg development or the reduction of the ability to prey. Again a larger sample would have probably shown stronger relationships than the results that discovered in this project.

This research was supported by a grant from the James Smithson Society.