Evolution of Hermaphroditism in Nematodes

Rowan University School Of Osteopathic Medicine, Stratford NJ

Investigators

Abstract

In the past twenty years, the fields of Evolutionary and Developmental Biology have been revolutionized by the discovery of regulatory genes that are conserved in all animals. These discoveries established the universal nature of many aspects of development, but also revealed profound differences in the developmental machinery. Thus, two crucial questions today are: (1) what aspects of these regulatory pathways can change to create new traits during evolution, and (2) how does the structure of these pathways influence the process of evolution? Intellectual Merit: The best way to address these questions is by comparing regulatory pathways from closely related species. Sexual characteristics make ideal subjects, since they are among the most rapidly evolving traits, and of interest to many biologists. One of the most dramatic differences in sexual development occurs in the elegans group of nematodes, a clade within the genus Caenorhabditis that contains some species with self-fertile hermaphrodites, and others with normal females. Because C. elegans is a leading model for the study of sex-determination, a wealth of data exists that can aid in the study of mating systems in this group. Recent results suggest that hermaphroditism evolved independently in C. elegans and C. briggsae. To test this hypothesis, the regulation of hermaphroditism in these two species must be compared at the level of gene regulatory pathways. In addition, these regulatory pathways have to be compared with those operating in a closely related male/ female species. Aim #1. In a pilot screen for mutations that prevent hermaphrodite development in C. briggsae, Dr. Ellis found a single allele of the glf-1 gene. These mutants reproduce as a male/ female population, so glf-1 is required for XX animals to become self-fertile hermaphrodites. Mutations like this one provide the key to understanding hermaphrodite development in C. briggsae, and comparing it with C. elegans. Thus, he will continue this screen to saturation, to find additional alleles of glf-1, and alleles of other genes that control hermaphrodite development. He will backcross each mutation, assign recessive alleles to complementation groups, map each gene, and analyze double mutants to see where each gene acts in the regulatory pathway. Aim #2. The ancestor of these nematodes was probably a male/ female species. To learn how C. elegans and C. briggsae evolved self-fertile hermaphroditism, it is necessary to learn how sex-determination worked in this ancestor. Thus, this aim involves the genetic characterization of how tra-1, the key sex-determination gene in C. elegans, regulates germ cell fates in the male/ female species C. remanei. In addition, Dr. Ellis has produced XX C. remanei that make sperm and oocytes. Surprisingly, their sperm do not activate in vivo. He will study the requirements for sperm activation in these animals, to test the model that hermaphroditism required two steps to evolve: the production of XX sperm, and the activation of these sperm to allow self-fertilization. Broader Impacts: Recruiting minority students into the Biological Sciences, and providing them with the background and training needed to excel, are as important in South Jersey as in any part of the country. However, despite the existence of the Rutgers-Camden and Rowan campuses, there are few local opportunities to expose talented Undergraduates to cutting-edge research. This proposal describes an innovative Summer Research program for Undergraduates that should address this problem. It features an intensive week of full-time lectures and computer exercises designed to bring the students up to speed in Classical, Molecular and Population genetics, with examples that focus on the interplay between human medicine and basic research on model organisms. The next ten weeks are devoted to research projects in one of the basic science or medical laboratories at the UMDNJ. Finally, the experience closes with workshops on presenting scientific research, and talks by each of the students.