Growth, body condition and contest performance after early‐life food restriction in a long‐lived tropical fish

Abstract

Adverse conditions during early life can cause lasting body size deficits with effects on social and sexual competition, while an accelerated growth response can allow animals to catch up in body size but can be physiologically costly as well. How animals balance growth deficits and growth compensation is predicted to depend on the effects of each on lifetime fitness. We investigated the effects of experimental early‐life food restriction on growth, body condition, and adult contest competition in a cichlid fish ( Tropheus sp.). Their longevity and aseasonal breeding suggest that, with view on lifetime reproductive success, temporarily growth‐restricted Tropheus should rather invest extra time in reaching competitive body size than risk the potential costs of accelerated growth. However, size‐selective predation pressure by gape size‐limited piscivores may have favored the evolution of an accelerated growth response to early‐life delays. Experimentally food‐restricted fish temporarily reduced their growth rate compared to a control group, but maintained their body condition factor at the control level throughout the 80‐week study period. There was no evidence for an accelerated growth response following the treatment, as the food‐restricted fish never exceeded the size‐specific growth rates that were measured in the control group. Food‐restricted fish caught up with the body size of the control group several months after the end of the treatment period and were as likely as control fish to win size‐matched contests over territories. Regardless of feeding regime, there were sex‐specific differences in growth rates and in the trajectories of condition factors over time. Females grew more slowly than males but maintained their condition factors at a high level throughout the study period, whereas the males' condition factors declined over time. These differences may reflect sex‐specific contributions of condition and body size to adult fitness that are associated with female mouthbrooding and male competition for breeding territories.

Abstract

We investigated how long‐lived tropical cichlid fish ( Tropheus sp.) balance costly growth deficits and costly growth compensation after early‐life food stress. Monitoring body sizes, growth rates, and condition factors of juvenile fish during and after an experimental food restriction, as well as performance in contest competition later in life, we showed that the fish caught up by prolonged growth at normal size‐specific rates without suffering a deterioration of any of the fitness‐related traits that were monitored in this experiment. We detected sex‐specific differences in growth rates and condition factors, which likely reflect the sex‐specific contributions of condition and body size to adult fitness.