Influence of behavioral plasticity and foraging strategy on starvation tolerance of planktonic copepods

Abstract

Starvation is considered a major cause of non-predatory mortality in zooplankton. Planktonic copepods display behavioral plasticity and small-scale behaviors associated with different foraging strategies that can affect starvation tolerance. However, little is still known about the influence of behavior on starvation tolerance in zooplankton. Here, we experimentally investigated behavioral changes and survival of planktonic copepods (adults and nauplii) with different foraging strategies under prolonged starvation. The behavioral response to starvation varied depending on the foraging strategy. The strict ambusher Oithona nana showed a low and, almost constant, motile activity (relocation jumps, <4% of the time) whereas the feeding-current feeder Temora longicornis swam for most of the time (~100%) without reducing their activity under prolonged starvation. The switching-behavior feeder Acartia tonsa move actively in the presence of food but had a low motile activity in absence of food (~12%) and decreased its motile activity during starvation (from ~12% to 3%). The observed behavioral responses to the absence of food can be broadly classified in terms of motility as: (i) “sit-and-wait” strategy for copepods with low motile activity under starvation (mostly relocation jumps) and (ii) “searching” strategy for copepods with high motility activity (swimming/cruising) under starvation. Median survival time in absence of food increased with increasing copepod body weight and it was ~1.75 fold lower in active feeders (“searching” strategy under starvation) than in ambush and switching-behavior feeders (“sit-and-wait” strategy under starvation). Thus, copepods with foraging strategies linked to a low motility (ambush feeders) and/or with behavioral plasticity to reduce motility in absence of food (switching -behavior feeders) would cope better with resource limitation/fluctuation than some active feeders. We demonstrate that behavioral plasticity and motile activity associated with foraging strategy significantly influences starvation tolerance in planktonic copepods. These results help to quantify the main trade-offs (gain vs costs) of the main zooplankton foraging strategies and emphasize that behavior is a key trait to understand the distribution of planktonic copepods in marine environments depending on trophic conditions.