Evaluating the Benefits and Trade-offs of Kleptopredation by the Prey-specialist Nudibranchs Cratena peregrina and Berghia stephanieae

Abstract

Dietary specialisation is a perilous feeding strategy, as the dependence of predators on their preferred prey increases their vulnerability to prey fluctuations and depletion. Conversely, dietary specialisation may increase the strain caused by voracious predators on their prey populations. In the current context of environmental change and anthropogenic disturbances, specialised predators may face trade-offs between the increased performance of feeding on a preferred resource and the increased vulnerability and risks associated with prey dependence. The mechanisms which enable these specialised predators and prey to coexist are still poorly understood. Kleptopredation, a feeding mechanism where nudibranchs preferentially consume prey with a freshly caught meal, suggests that more is yet to be understood about these specialised pairings. Following the recent discovery of kleptopredation, this thesis aims at describing the benefits and trade-offs of this feeding strategy for both the nudibranchs and their prey. Through an integrated succession of experiments, the use and impact of this feeding mechanism on the behaviour, functional response, physiology, and physiological energetics of Cratena peregrina and Berghia stephanieae was assessed. Feeding on prey which has just caught its own meal affects the foraging behaviour and may provide a protective advantage to C. peregrina and B. stephanieae predators, as the nematocyst discharges induced by cnidarian prey when touched by their predator may be reduced or inhibited in the hours following feeding. Fewer prey items are consumed by B. stephanieae when using kleptopredation, nonetheless contributed to increased growth rates, increased probability of oviposition and dry weight of egg-masses. Trade-offs may occur in the production of offspring, as kleptopredation decreases the number of embryos laid by B. stephanieae per clutch, although no substantial effects were detected on the total number of clutches produced. By using Kleptopredation, thus feeding on freshly fed prey, the energy intake of B. stephanieae is higher than when consuming prey with an empty gut. As a result, more energy is ingested and allocated towards somatic growth, but results on energy allocation to reproduction were less conclusive. Kleptopredation decreases the magnitude of the functional response of C. peregrina and B. stephanieae nudibranchs as the number of prey items consumed given prey density within a unit area is decreased. Therefore, beyond the physiological benefits provided to the predator, kleptopredation decreases the foraging pressure exercised by nudibranchs on their prey.

Date of Award	15 May 2023
Original language	English
Supervisor	Simon Cragg (Supervisor), Alex Ford (Supervisor) & Trevor John Willis (Supervisor)