Testing adaptive plasticity: Are the effects of social density on offspring size consistent over multiple food regimes in Heterandria formosa

Background/Question/Methods

Adaptive plasticity has been documented in the least killifish, Heterandria formosa, by their ability to adjust the size of their offspring in response to conspecific density. In this study, we assigned females from a single river to one of four density treatments in order to determine the shape of the reaction norm. The responses of these females to the social densities were compared across three food regimes to conclude how consistent this plasticity remains given contextual differences. This project was designed to answer questions regarding the nature of adaptive plasticity and the reliability of phenotypic cues upon which evolution can be expected to act.

Results/Conclusions

We found that females responded plastically in response to social density in both the number of broods produced and the number of offspring per brood. Females reduced the number of offspring in response to high density treatments, but did not increase offspring size, as would be expected by previous work. We found no effect of food level on any of the measured responses. The results demonstrated by this project show how the immediate plastic response differs from those exhibited in long term studies on the same species.