Effects of duration of the planktonic phase on rotifer genetic diversity

Abstract

In a homogeneous aquatic environment, clonal diversity in cyclical parthe- nogens should decrease with time while the population is active in the water column due to directional clonal selection. On the contrary, if planktonic populations experi- ence a heterogeneous environment the loss of clonal diversity with time could be neu- tralised. We tested the importance of these contrasting processes using ten rotifer pop- ulations belonging to four species from the Brachionus plicatilis species complex from four different ponds, and differing in their duration of the planktonic phase. Genotypic diversity and heterozygosity estimates were obtained using allozyme data. We found a negative correlation between genotypic diversity and the duration of the planktonic phase, indicating that our populations experience a homogeneous environment, and that directional clonal selection shapes the genetic structure of rotifer populations and has long-term consequences when this effect is repeated for several years. However, diversity fluctuations observed within a season suggests that the duration of the plank- tonic phase by itself is insufficient to explain the temporal dynamics of genetic divers- ity in cyclical parthenogenetic rotifers, and that there may be other factors acting on the genotypic diversity levels at a short-time scale.