Enhanced anti‐predator defence in the presence of food stress in the water flea Daphnia magna

Abstract

Summary1. Many prey organisms show adaptive trait shifts in response to predation. These responses are often studied under benign conditions, yet energy stress may be expected to interfere with optimal shifts in trait values. 2. We exposed the water flea Daphnia magna to fish predation and food stress and quantified both life history responses as well as physiological responses (metabolic rate, stress proteins, energy storage and immune function) to explore the architecture of defence strategies in the face of the combined stressors and the occurrence of trade-offs associated with energy constraints. 3. All traits studied showed either an overall or clone-dependent response to food stress. The chronic response to predation risk was less strong for the measured physiological traits than for life history traits, and stronger under food stress than under benign conditions for age at maturity, intrinsic population growth rate and offspring performance (measured as juvenile growth). Immune function (measured as phenoloxidase activity) was lower under predation risk but only at high food, probably because minimum levels were maintained at low food. 4. Overall, food stress induced stronger adaptive predator-induced responses, whereas more energy was invested in reproduction under benign conditions at the cost of being less defended. Our results suggest that food stress may increase the capacity to cope with predation risk and underscore the importance of integrating responses to different stressors and traits, and show how responses towards one stressor can have consequences for the susceptibility to other stressors.

Stress by poor food quality and exposure to humic substances: Daphnia magna responds with oxidative stress, lifespan extension, but reduced offspring numbers

“…As a chaperon, Hsp60 is a more general stress response parameter and indicates that, upon exposure to HuminFeed Ò , the chaperon function particularly refolding of degenerated proteins is required. In D. magna, Hsp60 has the function of the, in most other organisms, more prevalent Hsp70 (Pijanowska & Kloc, 2004;Pauwels et al 2005Pauwels et al , 2007Pauwels et al , 2009. With degenerated primers, we identified for the first time a partial mRNA sequence for hsp60 in D. magna, an alignment with known hsp60 genes is shown in Supplement Fig.…”

“…Interestingly, xenobiotic exposure interacted synergistically with parasites, whereas predation threat showed antagonistic interactions with both parasites and pesticide exposure. Pauwels et al (2009) showed that food stress increase the capacity to cope with predation risk by inducing stronger adaptive predator-induced responses, whereas under optimal conditions more energy was invested in reproduction at the cost of being less defended. All these articles indicate that there is no clear picture emerging whether or not multiple simultaneous exposures act synergistically or antagonistically.…”

“…Yet to approach environmental realism, one has to take into account that organisms are often simultaneously exposed to more than one stressor; and if the multiplicity of stressors is addressed, the question arises, whether these stressors act synergistically or antagonistically and by which potential modes of action. Only few articles address the simultaneous exposure of Daphnia to more than one natural stressor (Folt et al, 1999;Coors & De Meester, 2008;Pauwels et al, 2009). Folt et al (1999), for instance, modeled the effects of thermal stress, cyanotoxin exposure, and low food on reproduction and survival of Daphnia.…”

Threat or treat: the role of fish exudates in the growth and life history of Daphnia

“…While the majority of investigations on the morphological (Wiackowski and Szkarlat 1996), life history (Walls et al 1991), growth rate (Weetman and Atkinson 2002) and behavioral adjustments (Hays et al 2001) of Daphnia show weaker reactions to kairomones at low food levels, some have not confirmed a synergistic effect (Doksaeter and Vijverberg 2001), and a few observed enhanced anti-predator defenses (Reede and Ringelberg 1995, Weber 2001, Pauwels et al 2010). In our study, the effect of kairomones alone appeared to be weaker at low than at high algal food concentration.…”

Inbreeding and adaptive plasticity: an experimental analysis on predator‐induced responses in the water flea Daphnia

“…Fish predation risk is also a stress factor (Pauwels et al. 2005, 2010) and is a suitable stressor to quantify adaptive phenotypic plasticity as we have good predictions on what the adaptive phenotypic plasticity responses to visual predators are (e.g., smaller size at maturity and increased energy allocation to reproduction; Dodson 1989; De Meester and Cousyn 1997; Spaak and Boersma 1997; Weber and Declerck 1997;Boersma et al. 1998; Tollrian and Harvell 1999; Bourdeau et al.…”