Amphibian metamorphosis is a dramatic larvae-to-adult transformation regulated by temporal changes in thyroid hormones (TH) as well as interactions with other hormone systems. This developmental process is extremely responsive to changes in environmental conditions and susceptible to aquatic contaminants that interfere with hormone-dependent processes. While many of these endocrine disrupting compounds (EDCs) have been studied for their estrogenic effects on reproduction, the plasticity of amphibian metamorphosis provides a unique model for examining the thyroid-mediated effects of developmental exposure to estrogenic EDCs. The first objective of this thesis was to assess the toxicological response and developmental effects of estrogenic EDCs during the larval life-stages of amphibian development. After establishing baseline toxicity data for the test species, Rana pipiens, a developmental exposure was conducted to determine the estrogen-sensitivity of distinct periods during metamorphosis. Stage-specific exposures altered tadpole growth parameters and resulted in lasting effects such as delayed metamorphosis and female-biased sex ratios. Therefore, the second objective was to identify potential mechanisms by which xenoestrogens alter TH-dependent metamorphosis using a targeted gene expression approach. Development of multiplex and simplex real-time PCR assays and subsequent analysis established that thyroid- and estrogen-responsive transcripts in the tadpole brain are differentially regulated by exogenous TH and upon exposure to an estrogenic EDC. A short-term "challenge" assay confirmed that estrogenic exposure suppresses and in some cases blocks the ability of TH to induce the expression of target genes involved in mediating tissue-specific TH sensitivity during metamorphosis. The results of this research (1) provide evidence of cross-regulation between thyroid and estrogen-regulated genes during amphibian development and (2) indicate that developmental exposure to estrogenic EDCs may affect normal TH-responsiveness necessary for proper timing of metamorphosis.

acase@tulane.edu

acase@tulane.edu

acase@tulane.edu

acase@tulane.edu

No description available.

No description available.

Spider venoms are complex mixtures of chemicals whose primary function is to immobilize prey. The chemical composition of venoms and the role of venoms in prey immobilization vary widely among spiders. Yet, little is known about patterns of venom diversity and evolutionary processes that influence venom diversification. I used a comparative approach to (1) investigate phenotypic and evolutionary plasticity in whole venom chemical composition by comparing venoms among taxa that differ in time since divergence; and (2) determine whether evolutionary changes in venom are predictable based on changes in behavior or ecology. Non-genetic variation in venoms of a funnel-web spider, Agelenopsis aperta, was investigated by determining the effect on adult venom expression that results from rearing broodmates on different diets. This analysis provided no evidence of an effect of rearing diet on the chemical composition of adult venoms. Variation within species in venoms among sexes and populations was investigated in two spider groups. Tegenaria agrestis, a species suspected of interpopulational differences in venom pharmacology, had limited differences in venom composition and potency between same-sex individuals from isolated populations. However, within populations, sexes differed in concentrations of shared components, and female venoms were more potent on insects. Similarly, venom sexual dimorphism was detected in species of Tetragnatha. Male venoms had large concentrations of high molecular weight proteins that were absent in females. The dimorphism in Tetragnatha is likely not a function of sexual niche differences. Finally, ecological and behavioral correlates of differences in venom chemistry among clades of spiders that differ in feeding behavior were investigated in Hawaiian Tetragnatha. Associated with loss of web-use in prey capture in a lineage of this genus, was a reduction in the concentration of low molecular weight components, and an increase in the concentration of components between 35 and 80 kDa. Coincident with this change was an increase in the taxonomic range of prey and a decrease in the rate of onset of paralysis in prey after bites. However, there were no detectable differences in the role of venom in prey immobilization, and the general physiological effects of bites on prey.

I evaluated the effects of simulated noise from low-flying jet aircraft on the behavior and physiology of 6 captive desert mule deer (Odocoileus hemionus crooki) and 5 captive mountain sheep (Ovis canadensis mexicana). I measured heart rate, body temperature, ambient temperature, and behavior related to the number of overflights/day, and decibel levels (dB) animals were exposed to (range = 92-112). I recorded heart rate and body temperatures from transmitters implanted into the body cavity of animals. Ambient temperature was recorded in the pens and behavior was described from visual observations. I compared heart rates during simulated overflights by jet aircraft (N = 112/season) of sheep and deer to data collected prior to and following treatments. I documented differences between heart rates, species, dB levels, and number of overflights/day within and between seasons. All animals became habituated to aircraft noise. Although heart rates increased during overflights, they returned to the resting heart rate in ≤ 2 minutes.

I sampled populations of Yellow-eyed Junco from six mountain ranges in southeastern Arizona to test hypotheses about morphological variation in the species. Morphometric variables were obtained from measurements in the field, and from photographic images of the head, wing, and tail. Statistical analyses revealed significant seasonal differences in values of bill-length variables, and sexual dimorphism in wing and tail characters, but not in bill characters. Statistically significant geographic discrimination among samples was found only for bill characters. Mahalanobis' distance values from subsets of bill and tailspot variables correlate most significantly with geographic distances between habitats measured along an arc of higher elevation in the region. These correlations, the lack of significant geographic discrimination for wing and tail characters, and the many extralimital records for the species imply that Yellow-eyed Juncos move between isolated populations, and that this movement tends to follow higher elevations in the region.