By training I am a behavioral ecologist, but in recent
years I’ve become more of a physiological ecologist and a behavioral neuroendocrinologist. I work with fish and birds in laboratory and field settings, respectively.
One of my current projects focuses on the physiological mechanisms and reproductive consequences of extreme aggressive behavior. For this research, my students and I study fighting fish (Betta splendens), which are ideal subjects because some strains have been selectively bred for sport fighting. I have recently published two research articles on this subject with four Amherst students as co-authors. One was based on senior honors theses conducted by Caleb Murphy ’04 and Leslie Curren ’05 and focused on the importance of male aggression in attracting or deterring potential mates. We found that, while females were attracted to males that performed intense aggressive displays, extreme male aggression disrupted the spawning process, such that the nests of more aggressive males had fewer fertilized eggs in them than the nests of less aggressive males. In the second article, co-authored by Meredith McNitt ’06 and Erin O’Hare ’06, we investigated the neural mechanism underlying aggression in this species. We demonstrated in a series of experiments that the characteristic aggressive behavior shown by Betta splendens is mediated, at least in part, by the binding of the neurotransmitter serotonin (5-HT) to one of its receptors, the 5-HT1A receptor subtype. Greater activity of serotonin in the synapses between neurons in fish brains results in decreased aggression, much as it results in a heightened sense of well-being in humans. We are currently investigating the possibility that additional serotonin receptor subtypes, such as 5-HT3, are involved in the expression of aggression in this species. Future plans related to this project include investigating the roles of other neurotransmitters, such as dopamine and norepinephrine, in modulating aggressive behavior in fish.
The second project is on the effects of endocrine disrupting chemicals on fish behavior, physiology, and reproductive success. Hundreds of industrial and agricultural chemicals are known to disrupt the endocrine system of animals by mimicking or interfering with the transport and binding of hormones, particularly sex steroids such as androgens and estrogens. As a result, endocrine disrupting chemicals can cause reproductive dysfunction, alter sexual differentiation, reduce the capacity of the immune system, and impair cognition. My students and I have focused primarily on a class of endocrine disruptors called phytoestrogens, which are compounds that naturally occur in plants but can mimic estrogens in animals. Phytoestrogens are released into the environment in places where plant material is concentrated and processed, such as agricultural fields, sewage treatment plants, and wood pulp mills. Such exposure is believed to have an estrogenic effect on animals, particularly aquatic species downstream from such sources of pollution. In work that I started at Providence College (funded by a grant from the National Institutes of Health), my students and I found that phytoestrogens disrupt development of amphibian eggs. I continued this line of research at Amherst College with Alison Rodriguez ’06, and we found that exposure to low levels of phytoestrogens affects normal territorial and nesting behavior in male Betta splendens. Since then, several students (Meredith McNitt ’06, Julian Damashek ’09, David Westwood ’09, and Natalie Ferraiolo ’09) and I have documented changes in testes size, deficits in sperm quality, decreased levels of testosterone and other hormones, and altered neurotransmitter activity in the brains of male fighting fish. I have recently been awarded a three-year research grant from the National Science Foundation to continue our studies of phytoestrogens’ effects on fish, and Karina Zaveri ’08 is currently conducting her senior thesis research in this area. My ultimate goal is to understand how the health of natural fish populations is affected by phytoestrogen contamination from human sources.
My third project is on the allocation of carotenoid pigments in fish. Most examples of red, orange, and yellow coloration in animals are the result of carotenoid pigments. Carotenoids are also antioxidants, which are important in supporting the immune system. Most animals obtain carotenoids through their diet because they cannot produce their own. If an animal is unable to ingest sufficient quantities of carotenoids, it must allocate existing carotenoids to either coloration or immune function. Therefore, if carotenoids are limited in the environment, an animal cannot be both colorful and healthy. My students and I are interested in how a fish’s initial coloration affects its carotenoid allocation strategy. In our first study, co-authored with Dan Ardia (Franklin & Marshall College) we administered supplemental dietary carotenoids (or a control diet) to male Betta splendens whose body color varied along a gradient from blue to red. We found that red fish allocated supplemental carotenoids to coloration, and thus increased in redness (measured with a spectrometer) over the experimental period. On the other hand, blue fish allocated their supplemental carotenoids to immunity, as they were able to mount a greater generalized immune response, which we measured using a technique validated in my laboratory. We are currently testing the generality of this phenomenon using Midas cichlids (Amphilophus citrinellum) from Nicaragua. These fish occur in two distinct color types, one black and gray and the other gold. Susan Lin ’08 is investigating whether there are differences in carotenoid allocation patterns between the two types.
The fourth project - led by Dan Ardia, a team of dedicated field assistants, and myself - focuses on the tradeoffs that female birds make between incubating their eggs and self-maintenance. In the Amherst College Wildlife Sanctuary, we set up a grid of more than 150 nest boxes, approximately half of which attract nesting tree swallows. To determine how incubation effort affects self-maintenance, we used battery-powered devices to warm or cool boxes to make it easier or more difficult, respectively, for females to keep their eggs warm. One paper from this study has been published in Behavioral Ecology, and several others are currently in preparation. This study was part of the honors theses of Jessamyn Conell-Price ’06, Elise Chad ‘07E, and Jonathan Perez ’07, and they will be co-authors on several future publications. We intend to continue monitoring the survival and reproductive success of females and their former nestlings whose nests were heated and cooled in order to determine the long-term consequences of changes in incubation temperature.
In the news
Follow these links to some popular media
articles that cite my work on endocrine
disruption of animal behavior, social
effects on aggression, and
avian brood parasitism.