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.

Major projects are:

1. Male nuptial color and female preference for male nuptial color.
Male sticklebacks normally acquire a bright red throat and belly in breeding season, and female sticklebacks prefer to mate with redder males. Nuptial color appears to be one of the strongest signals used by female sticklebacks for mate selection. However, there are several populations where the males acquire a black nuptial color, and in at least one of these populations the females have lost their preference for red males. We are analyzing crosses from several of these black populations to identify the genetic basis of male coloration, female color perception, and female color preference.

2. Male mating behaviors and aggression.
In addition to color, there are several other important signals used in the stickleback mating ritual. Male sticklebacks also perform a "zig-zag dance" to attract females to their nests. There is wide variation in this display behavior in natural stickleback populations. It is also important that males protect their breeding territory from other males, and male-male aggression is also observed during the breeding season. We are analyzing multiple crosses for male display and aggressive behaviors.

3. Sex determination and sex chromosome evolution.
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 that sex is determined by a single locus in threespine sticklebacks. This male determining locus appears to be on a evolving Y chromosome because recombination rates around this locus are specifically reduced in males and there is a very high rate of sequence divergence between the male and female chromosomes near this locus, yet there is no cytogenetic evidence for the presence of heteromorphic chromosomes in threepsine sticklebacks. However, there is a cytogenetically visible Y chromosome present in the closely related black-spotted stickleback (Gasterosteus wheatlandi). Ongoing work is focusing on the identification of the sex-determining gene in threespine sticklebacks, a detailed sequence analysis of the evolving Y chromosome region, and a comparison of the sex determination locus in closely related species of sticklebacks.