Evolutionary genetics of speciation

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My research is at the leading edge of efforts to understand the genetic basis for speciation. My students and I study the population genetics of genes that encode proteins mediating reproductive compatibility among members of the same species and reproductive isolation between different species. The research focuses on sea stars with simple mate selection based on a small number of genes expressed on the surfaces of sperm and eggs. Theory and experiments show that sperm competition among males and sexual conflict between males and females over risks associated with fertilization can cause populations to evolve different combinations of male and female traits such as sperm and egg proteins, leading to population differences in gamete compatibility, reproductive isolation, and speciation. The short-term research objectives are to test these predictions for multiple gamete recognition gene systems and multiple sea star species, and relate the pattern of selection on gamete recognition genes to the function of those gene products in sperm-egg compatibility at fertilization. The long-term goal of the research is to understand at the molecular level how selection causes speciation. This proposed research builds on our recent success in: (1) identifying cases of old population isolation (where early stages of speciation are most easily detected) within several sea star species; (2) demonstrating evolutionary divergence between populations of one Canadian species (the bat star, Patiria miniata) caused by selection for amino acid differences in the sperm acrosomal protein bindin and the egg coat bindin receptor OBi1; and (3) developing expertise and infrastructure for new high-throughput next-generation sequencing of many fertilization genes expressed in sperm and eggs. Our new studies extend this work to genes acting at different times during fertilization; to populations at different stages in the speciation process; and to species with different mating system traits (and intensities of sexual conflict). The use of high-throughput transcriptomics is a key innovation that allows us to overcome significant limitations on previous work that used traditional PCR and sequencing methods. The results of this new research will for the first time give a comprehensive view at the molecular level of how selection on fertilization genes can shape the evolution of reproductive isolation and the formation of new species. Our recent discovery of coevolution between bindin and OBi1 in sea star populations led to interest in a comparable system of sperm- and egg-expressed genes in mammalian fertilization. Following on previous studies of the ZP3 protein in the egg coat and the ZP3R receptor in the sperm head of mice and humans, we used data from the 1000 Genomes Project (a database of human genetic variation) to show evidence for selection at one site in each gene, leading to non-random combinations of specific alleles between the two genes that are shared among all human populations. This strong linkage between ZP3 and ZP3R is probably caused by selection during mating that favours the fertilization of eggs with some female ZP3 genotypes by sperm with matching male ZP3R genotypes. Conversely, ZP3/ZP3R mismatching could be a source of human infertility. I propose to follow up this recent discovery with studies of clinical human populations in IVF treatment to test the hypothesis that some ZP3/ZP3R genotype combinations are overrepresented among infertile families due to male-female genotype mismatches.