Substratum selection and feeding responses influence the demography of the sessile rotifer Cupelopagis vorax (Collothecacea: Atrochidae)

Abstract

Larvae of the sessile rotifer Cupelopagis vorax swim using their ciliated corona, but do not feed. Once they attach to a substratum and metamorphose into adults, they are predatory on protozoans and micrometazoans. Here we present information on ingestion time, feeding behaviour and food preference of C. vorax using protozoans and non-sessile rotifers as prey. We also tested effects of physical, chemical and biological stimuli on settlement of C. vorax larvae and, using life table experiments, determined their survivorship and fecundity on three, free-floating macrophytes. Ingestion time was shortest on prey species smaller than 100 µm. Capture/attack ratio was low for Brachionus calyciflorus, but high for Lecane inermis and Peranema sp. The ingestion/capture ratio was lowest for Oxytricha sp. and highest for Euchlanis lyra and Squatinella lamellaris. Species that swim slowly and close to the surface of hydrophytes (E. lyra, Lepadella patella, L. inermis, Peranema sp., Philodina sp. and S. lamellaris) had lower ingestion time, higher encounter/attack ratio, and were the preferred prey in selectivity experiments. Larval settlement was higher on macrophyte leaves of Ceratophyllum demersum, Lemna valdiviana and Wolffiella sp., but lower on Azolla filiculoides and Wolffia columbiana. Coverslips coated with dried extracts of macrophytes showed lower rates of larval settlement compared to live macrophytes, as well as coverslips that had been allowed to develop natural biofilms or were physically roughened. Contrary to what might be expected from the settling tests, life-table experiments showed that W. columbiana enhanced survivorship (mean lifespan and life expectancy) and rate of population increase, while animals attached to Wolffiella sp. had lower values for life history characteristics. This study adds to our understanding of the impact of Cupelopagis predation on protozoans and rotifers and the importance of substratum selection on larval settlement, adult survival, and reproductive potential after larval settlement.