25 September
Katie Peichel
Fred Hutchinson Cancer Research Center
Sex, spines and videotape: genetics of reproductive isolation in sticklebacks
Abstract
The study of speciation has undergone a renaissance in the past few decades, yet relatively little is known about the genetic and molecular basis of traits that are important for the initial establishment of reproductive isolation between incipient species. Threespine sticklebacks (Gasterosteus aculeatus) are well suited for identifying the selective forces and genetic mechanisms that underlie the evolution of reproductive isolation between species. Throughout the range of this small teleost fish, there are multiple, independent pairs of recently diverged populations that share overlapping habitats, yet are reproductively isolated. In Japan, there is a unique stickleback species pair, consisting of the Pacific Ocean and Japan Sea forms. Geological evidence suggests that these two forms have likely diverged in allopatry within the past two million years, although the forms are currently found in sympatry along the coast of Hokkaido. Our genetic analysis of these sympatric populations is consistent with a divergence time of 1.5 million years, and further suggests that there is limited hybridization between the forms in regions of sympatry. We have shown that both prezygotic isolating barriers (behavioral and spatial isolation) and postzygotic isolating barriers (hybrid male sterility; extrinsic hybrid inviability) contribute to reproductive isolation between this recently diverged species pair. In the Japanese species pair, behavioral isolation results in part from striking differences in male mating behavior. In addition, hybrid male sterility is observed only in the male progeny of crosses between Japan Sea females and Pacific Ocean males, suggesting that there are genetic factors that are incompatible between the two populations. We have performed genetic linkage mapping of male behaviors and hybrid male sterility and identified regions of the genome with a relatively large effect on these traits. These traits are linked to the sex chromosomes, including a neo-sex chromosome system that we have identified in the sympatric Japanese stickleback population. This study is one of the few genetic analyses of reproductive isolation in a vertebrate system and will be an important comparison for genetic studies in other taxa, particularly for the identification of loci that are important in the initial stages of speciation. Finally, these genetic studies lay the groundwork for the ultimate identification of the genes and molecular changes that underlie reproductive isolation, which will provide insight into the selective forces that have acted on the genome to drive the formation of new species.
Bio
Dr. Peichel was an undergraduate at the University of California, Berkeley, and received a B.A. in Molecular and Cellular Biology in 1991. She received her Ph.D. in Molecular Biology in 1998 from Princeton University, where she worked with Tom Vogt on the genetic basis of mouse limb mutants. From 1998-2002, she did post-doctoral work with David Kingsley at Stanford University, where they developed a genetic linkage map and other genomic tools for threespine stickleback fish to study the genetic basis of morphological and behavioral evolution. In 2003, she moved to Seattle and is an Associate Member in the Human Biology division at the Fred Hutchinson Cancer Research Center.
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