Direct and correlated responses to artificial selection on foraging in Drosophila Artificial selection on foraging behaviour

Natural selection favours animals that forage more efficiently, such as those finding food faster, choosing better patches or increasing their rate of energy gain. Indeed, foraging behaviour has an effect on fitness, with better foragers producing more offspring. However, the evolution of foraging behaviour and its consequences on reproductive success has usually been tested in one generation only and the quantitative effects on fitness are not always measured. Here we artificially selected Drosophila melanogaster adults for their ability to find food quickly in a simple maze and measured the effect of this selection on their fitness. We tested two treatments, with four selected and two control independent replicates: i) selected flies, which were the fastest to find a food source inside a maze, and ii) control flies, which were randomly selected regarding their location in the maze. Fitness was calculated measuring fecundity and offspring survivorship. Our results show that after five generations, flies selected for better foraging found food two times faster than control flies. Additionally, selected flies had higher fitness than control flies, mainly because of greater fecundity in females during the first generation. These results show that foraging behaviour has a strong response to selection in few generations and that selection on foraging ability can have a correlated positive effect on fitness, nevertheless, this response is diluted over generations possibly due to the negative effect associated with the selection process.Significant statementNatural selection favours animals that forage more efficiently, such as those finding food faster. However, most of the literature measuring the relationship between foraging efficiency and fitness usually only measures the effects in the first generation. In an experiment, we artificially selected Drosophila adult flies that found food faster in a simple maze and we also measured the fecundity and offspring survivorships in selected and non-selected flies. After five generations, the selected flies found food 2.46 times faster than their F1 (founding population) and the control flies that were not selected. Fecundity was higher for selected flies only in the first generation, correlation that was lost as the generations passed. These results show that foraging behaviour has a strong response to selection in a few generations and that the possible correlated positive effects on fitness are diluted over generations.

Automated summary

Natural selection favors animals that forage more efficiently, such as those that find food faster. However, most studies on foraging behavior and its effects on fitness only measure the effects in the first generation. In this experiment, we artificially selected Drosophila flies that found food faster in a simple maze and measured their fecundity and offspring survivorship. After five generations, the selected flies found food 2.46 times faster than the control flies. Fecundity was higher in the selected flies only in the first generation, and this correlation decreased over generations. These results show that foraging behavior has a strong response to selection in a few generations, but the correlated positive effects on fitness weaken over time.