Ecological genetics of the rotifer Brachionus plicatilis in Soda Lake,Nevada, USA

In an earlier study we found that the rotifer Brachionus plicatilis in Soda Lake, Nevada (USA) maintains extensive genetic variation for three isozymes. This variation was present both within and between different collections. No evidence was found that there was a seasonal succession of distinct electromorphs. In this paper we ask: is the genetic variation maintained by selective neutrality among electromorphs? Parthenogenetic females from ten clones representing seven different composite electromorphs were selected for life table analysis. Substantial main effects of genotype or interactions of genotype with experimental food quantities and temperatures, were found for the intrinsic rates of increase, net reproductive rates, and mean life spans of these clones. We conclude that these fitness differences permit us to reject the hypothesis that genetic variation is maintained because of selective neutrality among clones. Instead, it seems likely that directional selectional may be either too weak or of too brief a duration in Soda Lake for clonal exclusion to occur.