Bdelloid rotifers are common fresh-water invertebrates comprising 4 families, numerous genera and hundreds of species. Neither males nor meiosis are known within the Class. Although remarkable, this does not exclude rare or unrecognized forms of genetic exchange. A more rigorous test is therefor required. The proposed investigation depends on the expectation that a diploid line that lost sexual reproduction and genetic recombination far back in its evolution will accumulate a much higher level of silent-site heterozygosity than a sexually reproducing line. For a given gene, heterozygosity will be measured by comparing the nucleotide sequences of its two homologues cloned from the DNA of a rotifer population grown from a single egg. Such tests will be done with a number of different genes and different bdelloid families and genera. Bdelloid DNA will also be examined for mobile genetic elements, in order to test the possible association between sexual reproduction and the load of insertion mutations. For comparison, heterozygosity and mobile elements will also be investigated in monogononts, a class of rotifers in which sexual reproduction and meiosis are known. %%% The usual and accepted view is that without sex and recombination, evolution and adaptive success is not possible. That hypothesis, however, has been impossible to test. The availability of Bdelloid rotifers and recombinant DNA technology have changed that and this work may make it possible to find a more definitive answer to a fundamental question in genetics.
