Temporal Distribution Patterns of Cryptic <i>Brachionus calyciflorus</i> (Rotifera) Species in Relation to Biogeographical Gradient Associated with Latitude

Sympatric distribution and temporal overlap of cryptic zooplankton species pose a challenge to the framework of the niche differentiation theory and the mechanisms allowing competitor coexistence. We applied the methods of phylogenetic analysis, DNA taxonomy, and statistical analysis to study the temporal distribution patterns of the cryptic <i>B. calyciflorus</i> species, an excellent model, in three lakes, and to explore the putative mechanisms for their seasonal succession and temporal overlap. The results showed that in the warm-temperate Lake Yunlong, <i>B</i>. <i>fernandoi</i> and <i>B</i>. <i>calyciflorus</i> s.s. underwent a seasonal succession, which was largely attributed to their differential adaptation to water temperature. In the subtropical Lake Jinghu, <i>B</i>. <i>fernandoi</i>, <i>B</i>. <i>calyciflorus</i> s.s., and <i>B. dorcas</i> exhibited both seasonal succession and temporal overlap. Seasonal successions were largely attributed to their differential adaptation to temperature, and temporal overlap resulted from their differential responses to algal food concentration. In the tropical Lake Jinniu, <i>B</i>. <i>calyciflorus</i> s.s. persisted throughout the year and overlapped with <i>B. dorcas</i> for 5 months. The temporal overlap resulted from their differential responses to copepod predation. These results indicated that the temporal distribution pattern of the cryptic <i>B. calyciforus</i> species and the mechanism that allows competitor coexistence vary with different climate zones.