Dr. Catherine Peichel

What is the genetic basis of morphological and behavioral variation between species? How do these differences lead to the formation of new species? In order to address these questions experimentally, we have developed the threespine stickleback (Gasterosteus aculeatus) as a new genetic system. Threespine sticklebacks have evolved an incredible diversity of morphologies and behaviors in freshwater populations in the last 10,000 years, and we have the ability to cross virtually any two diverse populations of sticklebacks using artificial fertilization in the lab. Therefore, they are an ideal system to determine the number of genetic changes that control morphological and behavioral differences between species, to map the location of these changes, and to ultimately find the DNA sequence changes responsible for evolutionary modifications in vertebrates. In my postdoctoral work with David Kingsley, we developed the first genetic linkage map for the threespine stickleback and have shown that we can use this map to define chromosomal regions underlying many variable skeletal traits in the stickleback.

One area of intensive study in threespine sticklebacks is reproductive behavior and mate choice. Reproductive isolation is seen between natural stickleback populations due to differences in male morphologies and behavior, and corresponding changes in female preferences for these male traits. Research in my laboratory uses a forward genetic approach of genome-wide linkage mapping to identify the genes controlling variable morphologies and behaviors related to reproduction and mate choice. By identifying genes that control these traits, we hope to define the molecular pathways underlying speciation.

Although reproductive isolation between threespine stickleback populations is mostly due to pre-zygotic barriers such as behavioral differences, post-zygotic isolation does exist between species of sticklebacks in the Gasterosteidae family. One potential source of this post-zygotic isolation is differences in the sex chromosomes of these species. We have found a diversity of sex chromosome systems within the stickleback family. One of these neo-sex chromosome systems is found in one population of threespine sticklebacks and harbors loci important for behavioral isolation between sympatric stickleback populations. These data suggest that sex chromosome turnover might play an important role in stickleback speciation. Ongoing work is focusing on the identification of the sex-determining gene in threespine sticklebacks, a detailed sequence analysis of the threespine stickleback Y chromosome region, and uncovering the evolutionary forces that have led to the diversity of sex chromosome systems found in sticklebacks.