Abiotic Conditions and Fitness in the Caribbean Termite, Nasutitermes acajutlae
I started this project when I was a visiting faculty member at the University of the Virgin Islands, on St. Thomas (1995-1996). One of my colleagues, Dr. Philip Rock, was very interested in lipid processing and had heard that termites were very fatty critters. Termites are abundant and accessible in the Caribbean because they build large arboreal colonies that hold up to 1 million individuals. Dr. Rock dissected some termites (Nasutitermes acajutlae) and discovered that they were infected by a larval acanthocephalan worm.
Larval acanthocephalans are famous for altering the appearance and behavior of their hosts to make the host more susceptible to predation by their next host. These changes clearly affect the evolutionary fitness of the infected animal because that animal gets eaten. Acanthocephalans had never before been documented in a social insect. We wondered whether our “acanth” altered the termites and, if so, what the ramifications would be for the colony as a whole. Were enough individual termites eaten to influence a nest of a million? We determined that both the color and behaviors of infected termites were modified (Fuller et al. 2003) and that these changes made them more susceptible to predation. In addition, colonies with high levels of infections had lower rates of reproduction and trail building than uninfected colonies (Fuller and Jeyasingh 2004).
I had been interested in how abiotic conditions interact with an animals’ ability to ward off parasites since I finished my dissertation on impacts of parasites on deer mice (Peromyscus maniculatus). I transferred this interest to N. acajutlae and began to ask how temperature and humidity, two factors that greatly influence many facets of termite life, might affect their immune system. I began working with Dr. Rebeca Rosengaus from Northeastern University and her Ph.D student, now Dr. Marielle Postava-Davignon. We discovered that temperature and, to a lesser degree, humidity influence both the immune system directly and the ability of the termites to survive an assault by a fungal pathogen (Fuller et al 2011).
Our current work is a continuation of this line of research. Some of the questions we are seeking to address are 1) is there a genetic component to susceptibility and immune function; 2) are long term changes in climate correlated with fitness of N. acajutlae colonies; 3) can we model termite growth rate to predict how climate change will affect this important tropical degrader?
Effects of Water Pollution on Immunity and Life History in Larval Dragon Flies
One of the key issues facing aquatic organisms is water pollution. Although much is known about the impact of pollutants on mortality, sublethal impacts received little attention until quite recently. We chose to examine impacts on the immune system because a decrease in the ability to produce an immune response can increase susceptibility to pathogens, affecting animals over the long term. We chose to work with larval dragonflies because they are typically in the water (and potentially exposed to pollutants) for several months to a year and they are relatively hardy, thus are unlikely to die at first exposure.
We first surveyed a number of ponds in our area to determine the organic and inorganic pollutants. We found a range of pollutants in both categories as well as numerous dragonfly species. We examined the immune system (phenoloxidase levels and encapsulation) in the most common species in the ponds and found a correlation between some persistent organic pollutants and low immunity. Use of these DDT derivatives has been discontinued; however, newer pesticides may also impact immunity in aquatic organisms.
We are currently examining the relationship between one of these pesticides (atrazine) and immunity. Coy St. Clair (MS student) conducted a long term bench-top experiment on both immunity and behavior; Ann Gilmore (MS student) extended the project to mesocosm environments. Her experimental design incorporated how a natural stressor (predator presence) interacts with the artificial stressor (atrazine) to impact dragonfly larvae.
Funding for our research has included grants from:
Committee on Institutional Studies and Research (MSU)
Howard Hughes Institute
Kentucky Academy of Science
Kentucky EPSCOR (NSF)
Kentucky Water Resources Research Institute (USGS)
National Science Foundation
Watershed Studies Institute (MSU)
Special Thanks to Drs. Fannin, Loganathan and Volp, MSU Chemistry Department.