Project description: Positive assortative mating occurs when individuals select mates who are more similar to themselves than expected by chance. A recent analysis of more than 1,000 case studies found that positive assortative mating is the rule rather than the exception within human and non-human animals. Positive assortative mating maintains genetic variation in populations, biases genetic mapping studies (e.g., to find disease-causing genes), and may drive the origin of new species. In light of the important genetic effects of assortative mating, it is surprising that little is known about its behavioral and evolutionary causes. The investigator will conduct experiments to test competing hypotheses as to why positive mating evolves. Specifically this study will (1) evaluate the frequency and strength of assortative mating within 20 populations of an important model organism (the threespine stickleback, Gasterosteus aculeatus), (2) identify the mate-choice behaviors that generate assortment, and (3) test whether assortment is favored by direct versus indirect selection, and/or disfavored by costs or barriers to signal transmission. Notably, this work provides the first field-based empirical test of the long-standing theory that disruptive natural selection favors positive assortative mating. This hypothesis, if true, would change our view about how new species arise.
Broader significance: The project will improve our understanding of the causes and incidence of assortative mating. By focusing attention on this form of non-random mating, the work will increase awareness of the high frequency of assortment and therefore the need to account for non-random mating in genetic and association mapping studies in both evolutionary biology and medicine. In addition, the project will pair scientists with high-school biology teachers and pre-service teachers-in-training. This will give K-12 science teachers practical experience in biological research, and foster communication between scientists and current and future teachers.
