Addressing Prey Selection And Predator Fitness: Ingestion By, And Growth Of Ochromonas danica On Multiple Bacterial Prey

Abstract

Nanoflagellates provide an important link in aquatic food webs by consuming bacterial biomass and subsequently providing nutrients to higher trophic levels by becoming prey themselves and regenerating nutrients consumed in excess of metabolic needs. Nanoflagellate predation has typically been addressed by examining one or two aspects of a seemingly complex prey identification process, and rarely has the subsequent fitness of the predator been quantified. In this work we examine how bacterial prey size, growth state, growth rate, nutritional composition, and phylogenetic class effect ingestion rate by, and growth rate of, the mixotrophic flagellate Ochromonas danica. A phylogenetically diverse group of fifteen bacterial species were offered to O. dancia in single prey feeding experiments. Bacterial cells were harvested from batch cultures grown in R2A broth under identical environmental conditions. O. danica was harvested from a chemostat culture prior to each feeding experiment to ensure physiologically similar predatory cells. Four different bacterial mortality curves were observed from the feeding experiments, indicating differential recognition by O. danica of different prey. Ingestion rates were affected more by prey growth state and prey class than by any other metric. Growth rate of the predator was affected by prey nutritional quality (carbon:element), prey growth rate, and prey class. Results suggest that Ochromonas dancia is a relatively indiscriminant consumer of bacterial prey but subsequent growth rates vary substantially for different types of prey. We conclude that O. danica may adjust ingestion rates to meet its nutritional demands, though it is largely unable to discriminate among prey prior to phagosome formation.