Genotype x Environment Interaction and the Evolution of Sexually Selected Traits
The presence of genetic variation for male sexual traits such as mating signals remains a major problem in evolutionary biology. Female choice often favors exaggerated mating signals and is thereby expected to reduce genetic variation greatly, yet recent surveys indicate that substantial variation remains in many species. This problem has been addressed in an acoustic pyralid moth, the lesser wax moth (Achroia grisella), in which males broadcast an ultrasonic mating song attractive to females up to several meters distant. Playback experiments show that female lesser wax moths prefer male songs that are distinguished by several key features, and breeding experiments demonstrate substantial genetic variance, and heritability, for these song features. Additional breeding experiments and tests with inbred lines indicate that genetic tradeoffs between life history characters and male song attractiveness are not responsible for maintaining this variance. That is, attractive singers are larger, do not take longer to attain that size, survive longer, and spend more time singing on nightly and lifetime bases. On the other hand, environmental variation over space and time, combined with interactions between genotypes and the environment, may contribute to the genetic variance observed for male song attractiveness: Certain lines exhibit superior attractiveness when developing under a favorable environmental regime but show marked declines under stress, while other lines exhibit only modest performance in favorable environments but show little reduction in stress; that is, no one genetic variant exhibits the superior performance in all environments. However, these findings have thus far been restricted to observations of highly inbred or artificially selected laboratory populations, and the actual significance of environmental variation and genotype x environment interaction for maintaining genetic variance in natural populations is unknown. In this project researchers will extend the aforementioned studies in an important way by determining whether: (1) the range of responses to environmental gradients; and (2) the environmental variation that actually occur in the field are likely to maintain the levels of genetic variance observed for male song attractiveness. In particular, they will determine whether the level of genetic variance reflects the amount of environmental variation a population has experienced, and whether genetic variants that exhibit maximum attractiveness in both favorable and stressful environments occur. The two co-Principal Investigators will also determine whether variation in female preference for male signals, and the response of the female preference trait to environmental variation, contribute to genetic variance for male song attractiveness. This possibility will be augmented via a parallel molecular genetic (quantitative trait locus, QTL) analysis of inbred lines in which they will examine the covariance between genes that influence male song and female preference traits. Overall, the project emphasizes the complex interplay between genes and the environment that can shape animal behavior. The focus on GEI will help direct the attention of biologists toward more realistic studies of mating behavior and away from tendencies toward 'typological' thinking with regard to signals and preferences. The QTL analysis will represent one of the first applications of this powerful genetic tool for investigating the genetic bases of intra-specific differences in traits responsible for mate choice. In addition, the project will involve undergraduate and graduate students and postdoctoral scientists who will be trained in the study of acoustic communication and evolutionary genetics. Students attending the N.S.F. Research Experiences for Undergraduates (REU) program offered during the summer by the Department of Ecology and Evolutionary Biology at the University of Kansas will do independent studies related to the proposed research. Moths from the various lines will be made available for laboratories in various undergraduate biology classes.
