Death‐feigning behaviours increase survival rate of littoral cladocerans under predation by odonate larvae

• Published in: Freshwater biology Vol. 66; no. 11; pp. 2030 - 2037
• Main Authors: Yamada, Sayumi, Urabe, Jotaro
• Format: Journal Article
• Language: English
• Published: Oxford Wiley Subscription Services, Inc 01-11-2021
• Subjects: Aquatic habitats; Behavior; Crustacea; Death; fresh waters; Interspecific relationships; Larvae; littoral; Littoral environments; Mortality; Predation; Predators; Prey; Risk taking; Survival; Swimming; zooplankton
• ISSN: 0046-5070; 1365-2427
• DOI: 10.1111/fwb.13808

Because littoral cladocerans are common prey for odonate larvae, they are ideal organisms to examine prey and predator interactions in aquatic habitats. Although death‐feigning behaviour observed in littoral cladocerans is viewed as a trait to reduce predation risk, no study has examined the effectiveness of death‐feigning at reducing mortality. We studied the effectiveness of death‐feigning behaviour by two littoral cladocerans, Chydorus sphaericus and Oxyurella tenuicaudis, against the odonate larvae of Sympetrum frequens.
We first examined how the odonate larvae detected the prey and found that the larvae consumed active cladocerans, even under dark conditions, but they did not consume anaesthetised cladocerans, indicating that the larvae detect the prey using mechanical cues such as vibrational currents created by the prey individuals.
We then observed behavioural events of odonate larvae and prey cladocerans using a video‐recording system to count the number of cladocerans that showed death‐feigning behaviours when odonate larvae attacked and those that were not consumed when they showed death‐feigning behaviours.
We observed a total of 1,099 behavioural events in prey–predator interactions. On average, the odonate larvae pursued 63% of the cladocerans encountered, attacked 89% of the cladocerans pursued, and successfully captured only 29% of the cladocerans with the first attack. Among the cladocerans that were not captured, 38% of the individuals continually swam, but 62% ceased to move and exhibited death‐feigning behaviours. The odonate larvae's capture rate for cladocerans exhibiting the death‐feigning behaviours fell significantly short of that for cladocerans that were continually swimming.
The experiments clearly showed that the littoral cladocerans' death‐feigning behaviour effectively decreased predation rate by odonate larvae. The results suggest that the death feigning serves as an adaptive behaviour to reduce mortality risk in littoral cladocerans under predation by such predators that can detect prey using mechanical cues such as those of vibrational currents.