The genetics of reproductive isolation and speciation in north Atlantic sea urchins

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The origin of new species remains the central and most elusive question in evolutionary biology. In marine environments, the problem of genetic divergence and speciation is especially complex, because the barriers to genetic exchange that are generally essential for allowing divergence to occur are far more subtle than in terrestrial systems. Both divergent selection along ecological boundaries, and the evolution of gamete incompatibilities to prevent hybridization (i.e., reinforcement) are expected to play key roles in the process of speciation in the sea, but exactly how these forces counteract the homogenizing effects of gene flow has long been debated. My research uses exciting advances in next generation sequencing techniques to investigate species divergence at the level of the genome. I focus on a contact zone between two species of broadcast spawning sea urchins in the northwest Atlantic, where populations overlap and hybridization frequently occurs. Hybrid zones are ideal “natural laboratories” for examining the role of selection in the process of speciation, because the fate of individuals with mixed ancestry can be traced as they move and from one ecological setting to another. Using both laboratory and field studies my students and I (i) will determine how many different genes are involved in the evolution of reproductive isolation across the hybrid zone, (ii) assess the role of adaptation to different habitats as a mechanism of reproductive isolation, and (iii) better understand the role of reinforcement at gamete recognition molecules that may have evolved to prevent hybridization from occurring. The experiments outlined in this proposal will extend our knowledge of the factors driving reproductive isolation at the population level, and contribute to a general understanding of the relative importance that the opposing forces of diversifying selection, gene flow and genetic drift play in the process of speciation.