Darwin pointed out that one potentially weak area in his theory of evolution by natural selection was the existence of complex traits, the components of which appear to be non-adaptive on their own. Gaining a better understanding the evolution of such traits at a quantitative level is still an important challenge. The proposed research will examine the genetic basis of moth sexual communication traits where a female produces a sex pheromone with a precise blend of a number of volatile compounds, and males are behaviorally responsive only to the blend of females of the same species. Mutant females that produce a novel blend and rare males with genes for responding to as yet non-existing blends appear to be selected against, so it is hard to understand how Darwinian selection could result in the thousands of diversified pheromones and moth species that we see today. Crosses between two moth species that utilize different pheromone blends will be used to identify the specific genes responsible for the differences between them in pheromone production and perception. As a next step, the controlling nucleotide changes will be determined and their fitness consequences measured.
We will use our work on moth pheromone diversification as a means to educate the public about evolutionary processes that can result in complex traits that seem to have intermediate forms that are selected against. In addition to its inherent value to the field of biology, the knowledge of sexual communication genes could lead to development of new ways to control moth pests.
Textbooks typically describe evolution as a process in which individuals with forms of genes causing the highest survival and reproduction become more common and other forms of those genes are lost from a population. Some traits such as the eye appear to involve a set of interacting genes in which each gene individually does not result in higher fitness. Some critics of evolution argue that the existance of such traits indicates that the traits came about by a process other than natural selection. Even without the challenge of critics, the issue of evolution of complex traits has been important to evoltuionary biologists. Our project aimed at dissecting the genetics of a minimally complex trait, that is one with a small number of genes that have evolved great diversity even though not expected to do so based on a simple textbook view of evolution. The trait we looked at was sexual communication in moths. This trait requires interaction of two separate systems, one in females and one in males. The females produce a very specific set of airborne chemicals that only males of the same species perceive as attractive. The expectation is that any mutant female with a different blend of chemicals would be less likely to attract a mate, and any mutant male that responds to a non-exisiting blend (or one of another species) would also be at a disadvantage. This should result in stasis --that is no evolution of a change in blends. However, there are over 100,000 moth species with very different blends and male responses. How this diversity could evolve has been the goal of our research. Our approach has been to find two species that aren't attracted to each other, but can be mated in the lab. With these two species, we conducted genetic crosses in the lab to isolate those genes that contribute to the different pheromones and male responses. Once we found the location of these genes we were able to recreate the genetic forces that would favor or inhibit evolution of diverse sexual signals and responses. In some cases we found selection that would inhibit diversification, but in other cases we found that interesting interactions among genes could result in evolution of diversification in these traits.
