Temporal patterns and processes of genetic differentiation of the Brachionus calyciflorus (Rotifera) complex in a subtropical shallow lake

Abstract

Sympatric distribution and temporal overlap of cryptic zooplankton species pose a challenge to the framework of the niche differentiation theory and the mechanisms underlying the coexistence of potentially strong competitors. In this study, we collected Brachionus calyciflorus Pallas monthly from Lake Tingtang over the course of 1 year and clonally cultured them in the laboratory. Finally, 204 clones were established, and their nuDNA ITS1 and mtCOI sequences were analyzed. The phylogenetic relationships and GMYC model analyses revealed that B. calyciflorus was a species complex composed of three cryptic species. Cryptic species BcI-W, and BcII-S and Bc-SW underwent a clear seasonal succession. However, BcII-S and Bc-SW overlapped in June and July, and all the three cryptic species coexisted in November. Different preferences to water temperature might contribute to the seasonal succession. More investment in sexual reproduction accelerated the disappearance of cryptic species from the water column during the seasonal succession process. Differential responses in rate of population growth of the two overlapping cryptic species to increasing food level might reduce the intensity of competition between them and promote their coexistence over time. Differences in population growth rate partially resulted in the different relative abundances of the two overlapping cryptic species.