Eco-Evolutionary Dynamics of the Predatory Rotifer Asplanchna brightwellii

The rotifer Asplanchna brightwellii is a predator of freshwater zooplankton that produces diet-dependent morphotypes (a trophic polyphenism). Although interest in A. brightwellii has grown due to its potential as a model system, little is known about the ecology of this species and the plankton communities which it inhabits. In this study, we seek to identify the biotic and abiotic factors underlying the population and community dynamics of A. brightwellii in a freshwater pond in eastern North Carolina, USA. Samples were collected over a period of nine months, during which biotic (zooplankton diversity, prey abundance, and phytoplankton biovolume) and abiotic (temperature, water quality, and precipitation) variables were quantified. A. brightwellii was present in samples collected in June, July, and November 2024. All collected specimens were alpha-morphs, and no evidence of polyphenism was found over the sampling period. Our results suggest that abiotic variables (primarily phosphate concentration) predict A. brightwellii presence in this system, whereas biotic variables (including phytoplankton and prey zooplankton abundance) predict A. brightwellii population density. The species’ diet consisted of small rotifers and cladocerans, and diet composition and prey selectivity varied through time. These findings provide insight into A. brightwellii’s natural history, and they serve as a basis for future research into the dynamics of this ecosystem and the adaptive value of a trophic polyphenism.