Egg size and food abundance interactively affect juvenile growth and behaviour

Abstract

Summary 1.Comparative evidence from several animal taxa suggests that juveniles hatching from larger eggs have fitness benefits when growing up in a harsh environment, whereas under benign conditions egg size should be of less importance. However, the physiological and behavioural mechanisms responsible for these context-dependent fitness differences are as yet poorly understood. 2. We studied the interactions between the phenotype of developing offspring and their environment in the mouthbrooding cichlid Simochromis pleurospilus. We hand-raised young from large and small eggs, and measured their initial body size and burst swimming speed. Thereafter we raised half of each egg-size class on high and half on low food ration and followed their growth trajectories and behavioural development until the age of 12 weeks. 3. We found that larger eggs gave rise to larger young that had a higher burst swimming speed. Food ration greatly influenced long-term growth, while egg size predominantly affected fish size during the first 2 weeks of life. However, large egg size caused a size advantage of juveniles persisting throughout the experimental period. 4. Egg size and food ration interactively affected the hiding and foraging behaviour of young. In the low-food treatment, individuals from small eggs spent less time in shelter and showed a higher commitment to foraging than individuals from large eggs. In a natural setting, this should markedly increase predation risk of young originating from small eggs, particularly in poor environments. In contrast, when food was plentiful juveniles behaved similarly, irrespective of egg size. 5. Our results show that egg size affects juvenile growth trajectories and behaviour differently in different environments. While it is well-established that a large egg size raises offspring fitness particularly in harsh environments, our study suggests that this advantage arises through riskaverse behaviour being tightly linked to offspring size.

Juvenile exposure to predator cues induces a larger egg size in fish

“…We propose that the observed increase in egg mass and in total investment in response to juvenile predator cues is an adaptive maternal effect [41]. In E. cyanostictus, heavier eggs give rise to larger offspring, and in fish, larger offspring will need less time to grow out of the reach of gape-size limited predators [22] and/or can afford to expose themselves less to predation risk by reducing their foraging activity [24]. Thus, our results suggest that based on early experience, females expected offspring predation risk to be high and compensated for the reduced offspring survival chances by increasing their egg size.…”

“…(d) Hand-raising of the offspring generation After measuring, we hatched the clutches separately in a selfconstructed egg tumbler [24]. The eggs hatched after an average of 4-5 days.…”

“…This expectation is straightforward from the perspective of offspring: in fish, the major predators are gape-size limited, so larger juveniles may outgrow these predators faster [22]. Moreover, larger juveniles have a higher burst swim speed [23,24], which should raise their survival chances in predator encounters. Likewise, females are expected to benefit from an increased investment per egg and thus higher survival chances of individual offspring, as mouthbrooders produce large but relatively few eggs per life, which makes each offspring highly valuable.…”

Life-history plasticity in female threespine stickleback

“…Thus, there is often found to be a positive correlation between egg size and fry size or capability (Einum and Fleming, 2000a;Segers and Taborsky, 2011). Because even small differences early in life can lead to large variations in fry fitness (Anderson, 1988;Perez and Munch, 2010; JA Baker, unpublished data) plasticity should be a considerable advantage to females.…”

Variations in egg characteristics of ruffe Gymnocephalus cernua inhabiting brackish and freshwater environments

“…A general rule is that bigger eggs give rise to bigger offspring (Bagenal 1969;Einum and Fleming 2000;Bownds et al 2010), but there are some exceptions (Lagomarsino et al 1988). Larger offspring have many advantages over smaller conspecifics: They are more resistant to starvation because of larger yolk reserves (Rideout et al 2005), have greater swimming speed for catching prey and escaping predators (Ojanguren et al 1996;Segers and Taborsky 2011), take fewer behavioral risks (Segers and Taborsky 2011), have generally faster growth rates (Wallace and Aasjord 1984) and outgrow their gape-size-limited predators faster (Sogard 1997). Also, large offspring are better adapted to extreme environmental conditions (Alcaraz and Garcia-Berthou 2007;Riesch et al 2012) and have greater probability to live through their first winter (Braaten and Guy 2004;Hurst 2007).…”