||Environmental Research Lab., Gulf Breeze, FL. ;Virginia Polytechnic Inst. and State Univ., Blacksburg. Dept. of Biology. ;Brevard Mosquito Control District, Titusville, FL.;National Science Foundation, Washington, DC.
Recombination is unknown in natural populations of Rivulus marmoratus, a selfing hermaphrodite, and genetic variation is likely due to mutation alone. DNA fingerprinting with an array of microsatellite (e.g., (CT)sub 9) and minisatellite (e.g. the 33.15 core sequence) probes reveals very high clonal diversity within samples of 7 Floridian populations, 5 contain about as many clones as there are individuals. There are 42 clones among 58 individual surveyed (mean = 1.4 individuals/clone), a level of genetic diversity unprecedented among clonal animals. Moreover, all of the probes recognize the same clones even though, at high hybridization stringencies, there is little overlap in the fingerprint patterns they generate. This suggests that most sympatric clones differ by multiple and independent mutational steps. In one population studied in detail, the average number of mutational steps separating two clones is estimated at about 9-10, and may be substantially higher. The mutational discontinuities among sympatric clones make it unlikely that they evolved by the accumulation of neutral mutations in populations that are otherwise genetically uniform. The data argue that the mixing of unrelated individuals from different local populations occurs to an extent previously unappreciated and/or that divergence of clones is mediated by natural selection. In confirmed, the latter would be a serious challenge to current ideas on the predominant role of recombination in promoting the evolution of biological novelty.