Behavioral flexibility in prey selection by bacterivorous nanoflagellates

We used laboratory experiments to study the effects of changing food abundance on the selective feeding of two heterotrophic nanoflagellates on particles of similar size but differing nutritional quality (latex beads and fluorescently stained bacteria). Both Bodo saltans and Spumella so. exhibited similar shifts in selectivity with changes in food concentration Flagellates that were cultured under food-limiting conditions showed a modest but significant preference for beads when both particles were offered simultaneously. However, both flagellates exhibited strong discrimination against the inert beads within 30-60 min after the addition of a satiating concentration of live bacteria, As bacterial abundance declined over 24 h, discrimination against the inert beads gradually relaxed. The observed pattern of concentration-dependent selectivity is in agreement with the predictions of optimal diet model