LTREB: The Evolution of Alternative Strategies

Indiana State University, Terre Haute IN

Investigators

Abstract

The goal of this proposal is to help determine why individual variation (e.g. alternative strategies) is maintained in natural populations. In order to be maintained over the long-term, alternative strategies must have the same long-term success. If one strategy is better than the other, it will become fixed in the population and the poorer strategy will be lost over time. Both temporal and spatial factors can contribute to the success or failure of a particular strategy. Dr. Tuttle proposes to examine the maintenance of alternative strategies in the North American songbird, the white-throated sparrow (Zonotrichia albicollis). This species is unique because males and females can have either tan or white crown stripes. White birds behave differently than tan birds; they are more aggressive, sing more often, and are more promiscuous than tan birds. Tan birds are less aggressive, guard their females more, and spend more time caring for their young than white birds. Tan birds almost always mate with white birds and this unusual mating system ensures that both types always occur in the population. Dr. Tuttle proposes to test two hypotheses. One, that these two alternative strategies (white and tan) may be affected by different environmental and social "demands", and two, that each strategy does best under a different set of environmental conditions that might occur in space and time. For example during a year of limited resources and high predation, the more parental tan strategy may be more successful. However, during good years, the promiscuous white males may be more successful. Although these two strategies may have different success rates in the short term, long-term cycles may cause each strategy to have equal success over time thereby maintaining stability in the system. Long-term trends in previously collected data (13 years) and data to be collected over the next 5 years will allow testing for the effects of differential selection and environmental cycling. While pursuing the goals of this proposal, Dr. Tuttle will incorporate new technologies such as relational databases, GIS, and GPS. In addition, Dr. Tuttle proposes to develop web-based instructional materials based on the long-term data that will be obtained. Since empirical evidence is often lacking, factors maintaining variation in natural populations have long been debated. The white-throated sparrow system may prove to be a classic vertebrate example of how individual variation is maintained in nature. Study of this species will provide insight into similar mechanisms affecting diversity in other species, as well as how evolution proceeds in general.