Limnetica 38

Cyclically parthenogenetic rotifers are facultative sexual aquatic microinvertebrates that live in continental and coastal waters and attracted the scientific interest of Professor M. R. Miracle. Some of her early studies anticipated the use of these rotifers as model organisms to test hypotheses in population and evolutionary ecology. This short review is aimed to stress the research she initiated at the University of Valencia. With this aim in mind, we enumerate and comment on (1) the biological and ecological features of rotifers that make them remarkable model organisms and (2) the research fields influenced by rotifer population biology. Among the latter, we selected some topics in order to illustrate how rotifer studies have contributed to our knowledge: phenotypic plasticity, competition and coexistence among cryptic species, the evolution of sex and complex life cycles, and aging. We deeply review studies on rotifer ecological genetics and evolutionary ecology with an emphasis on population studies conducted in eastern Spain and fostered by Professor Miracle. We conclude that rotifer populations harbor high local genetic diversity, with the occurrence of clonal selection during the planktonic growing season. Moreover, studies show that they have high population differentiation, which holds signatures of historical events (e.g., glacial refugia and posterior range expansion). Additionally, differential local adaptation occurs even among neighboring populations. Two remarkable conclusions are that (1) population differentiation in rotifers is most likely due to persistent founder effects rather than to “isolation by adaptation” and (2) rotifer populations can differentially adapt to the levels of environmental uncertainty in their respective localities. This occurs by adjusting the timing of sex and initiating sex and diapausing egg production earlier when populations inhabit localities with higher uncertainty. Related to environmental uncertainty but also to other environmental features (novel environments where recombination is needed to fuel natural selection, nutrient availability, etc.), experimental evolution studies have found that laboratory populations evolve quickly, allowing them to become easily adapted to new conditions. We suggest that rotifers should be used in the close future to address additional central hypotheses in evolutionary ecology as a result of the feasibility of experimental evolution and resurrection ecology on one hand and “omics” tools on the other hand. As specific topics for future research, we highlight the evolution of sex, speciation, eco-evolutionary dynamics and the regulation of complex life cycles in relation to environmental cues.