M. S. Meselson
Election Year: 1968
Primary Section: 26, Genetics
Secondary Section: 27, Evolutionary Biology
Membership Type: Member
Our objective is to discover why sexual reproduction and genetic recombination are maintained in evolution. Nearly all species of animals and plants reproduce sexually. A few species reproduce only asexually but, in most cases, do not persist long enough to allow the evolution of asexual genera, let alone families or higher taxa. A striking exception to this generalization is the Class Bdelloidea of the Phylum Rotifera. These small aquatic animals, comprising numerous genera and more than 350 species, appear to reproduce exclusively without sex. No male bdelloids or hermaphrodites have been observed, and bdelloid oogenesis occurs by mitosis. Nevertheless, a more rigorous test is required before one may accept the remarkable conclusion that sexual reproduction has been entirely absent in the evolution of the bdelloids. We are using DNA sequence analysis and chromosome mapping to test this supposition. These tests depend on the expectation that diploid organisms that lack sexual reproduction and all forms of germline genetic recombination will eventually accumulate high levels of heterozygosity and that such hyper-heterozygosity will exhibit a monophyletic distribution of inheritance throughout the Class. If bdelloid rotifers have indeed evolved without sexual reproduction and genetic recombination for millions of years, they represent a uniquely advantageous system for studying why sex exists. The next phase of our investigation will be to use the bdelloids to test specific hypotheses that seek to explain why sexual reproduction and genetic recombination are so nearly universal.