Depth-selection behavior and longevity in Daphnia: an evolutionary test for the predation-avoidance hypothesis

Abstract

The classic evolutionary theory of senescence predicts that long lifespan evolves under low risk of extrinsic mortality. As lakes present planktonic animals with vertical gradients of mortality risk associated with fish predation, we expected the individual lifespan of Daphnia of the ''hypolymnetic'' clones to be longer than that of ''epilimnetic'' Daphnia. In order to test this prediction, we performed a laboratory study on 14 clones from the D. longispina species complex, taken during the daytime either from epilimnion or hypolimnion of three mesotrophic lakes. ''Epilimnetic'' Daphnia started reproduction earlier, aged faster, and lived shorter than their ''hypolimnetic'' conspecifics. Our results indirectly support the predation-avoidance hypothesis as the ultimate explanation for depth-selection behavior in Daphnia.

Phenotypic plasticity of senescence inDaphniaunder predation impact: no ageing acceleration when the perceived risk decreases with age

“…The survival cost of the reduction is negligible, because the risk of dying of extrinsic causes increases with gradually increasing size anyway (hence also with age). The short lifespan under such a risk is reported by both comparative studies of populations from habitats of different predation risk [59,60], as well as seen in phenotypic responses upon direct exposure to simulated predation [37,61] (both genetic and phenotypic effects discussed by Pietrzak et al [33]).…”

Behavioural and physiological mechanisms behind extreme longevity in Daphnia

“…This is also in part a consequence of fish predation pressure acting as a strong selective force under which probability of surviving to subsequent reproductive period is low, and thus Daphnia follow the r strategy, maximizing fitness by investing in early reproduction (Threlkeld, 1979;Boersma et al, 1998;Pijanowska et al, 2006;Dawidowicz et al, 2010). In deep oligotrophic habitats with no oxygen deficits, where fish predation pressure is reduced or absent, released from the selective pressure on early reproduction, Daphnia can maximize fitness by applying different strategies, including those involving the delay of the onset of reproduction and lengthening the lifespan (Dawidowicz et al, 2012). This is possible at the concurrent permanence and stability of the habitat, which favour the evolution of longevity (Pianka, 1970;Grime, 1977).…”