BE/GenEn: A Biochemical, Genetic, and Genomic Investigation of the Evolution and Ecology of Sexual Reproduction

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Sexual reproduction is widespread among plants and animals, but its selective advantages are poorly understood. Genetic recombination produced by sexual reproduction strongly influences evolutionary rates, genome structure, and adaptation, however little is known about how genes and ecosystems interact to maintain sexual reproduction and determine its frequency. In many species, mutations or hybridization give rise to populations that reproduce asexually. However, most species and nearly all higher-order taxa maintain sexual reproduction, implying that the evolutionary loss of sex eventually leads to extinction. This paradox is particularly striking in species capable of both sexual and asexual reproduction. In these species the majority of reproduction is asexual but environmental cues trigger episodic sexual reproduction. Although sex can be readily lost in these species, both asexual and sexual reproduction are maintained over evolutionary time. Thus asexual/sexual species represent an especially powerful system in which to study the dynamic interaction of asexual and sexual reproduction, environment, and species evolution.Of central importance to understanding the dynamics of sex is the evolution and ecological role of the genes that determine the frequency and prevalence of sexual reproduction in populations. Ultimately, these genes influence genetic diversity, rates of adaptation and speciation, and levels of biocomplexity in ecosystems. Despite their importance, few of these genes have been identified in animals and their evolutionary dynamics remain largely unknown. The objective of the research is to isolate and characterize these genes in rotifers, one of the largest, most successful asexual/sexual groups, and to track the evolution and functional interaction of these genes with the genome and the environment in order to understand how genes and environment interact to regulate sexual reproduction and determine its frequency. The project will employ a combination of biochemical, genetic, and mathematical approaches, including protein purification and functional assays, gene library analysis, and the identification of regulatory pathways by comparing natural and laboratory populations that have lost the capacity to reproduce sexually. The first of three aims in this one-year exploratory project is to complete protein purification of the rotifer sex (i.e., mixis) inducing protein (MIP). The second is to obtain amino acid sequence on both the MIP and the rotifer mate recognition pheromone (MRP) so that we can deduce the nucleotide sequence of the genes. The third aim will be the isolation of the MRP and MIP genes by screening a cDNA genetic library made from a sexually reproducing population of rotifers. Ultimately, these measurements will elucidate the forces maintaining sexual reproduction in life cycles, the dynamics of loss of sexual reproduction in lab and natural populations, the underlying genetic mechanisms of such loss, and establish correlations with environmental variables that may influence these processes. Models will be developed to explain and predict the sex ratio, sex induction threshold, and identify environments where loss of sexual reproduction is expected.The project will provide interdisciplinary research training for a research technician and 2 undergraduates. A library of well characterized rotifer stocks will be maintained and samples distributed upon request. The project will expand a website (jbpc.mbl.edu/wheelbase) to provide a searchable database of genetic libraries, experimental results, and descriptions of techniques. These tools and resources will enable many researchers to incorporate rotifers into comparative genetic studies.