Intergenerational plasticity alters competitive interactions in a zooplankton system

Background/Question/Methods

Ecological theory typically assumes that differences between species remain constant over the ecological time scales relevant for competition. However, species’ traits may change over a few generations due to phenotypic plasticity and maternal effects. Such rapid changes in species’ traits may have implications for the strength and type of species interactions in communities. For example, the zooplankton Daphnia magna can vary in size, predator defense and reproductive charactersitics, via plasticity and maternal effects. These effects are often ignored or controlled for when considering dynamics in zooplankton communities. We asked whether maternal effects (“intergenerational plasticity”) alter the outcome of competitive interactions, using microcosms of D. magna and the ostracod genus Cypris. We used monocultures and competitive trials to test whether populations of D. magna differ in their interactions with the ostracod species depending on their genetic background (adaptation to warm vs. cold temperatures) and whether maternal effects have been standardized or left intact.

Results/Conclusions

We developed 2 locally adapted populations of D. magna, one adapted to 17C, one adapted to 24C; these populations differed in a number of ecologically relevant traits. In a 24C environment, we grew both populations in monoculture and competition with the ostracod species. Concurrently, individuals from the two locally adapted populations were cultured in common garden conditions for several generations. These individuals were used to repeat the monoculture and competition microcosms. Our results suggest that trait differences between the two locally adapted populations included contributions from genetic differences and from maternal effects. The outcomes of competition between D. magna and the ostracod varied significantly depending on both the identity of the D. magna source population and whether maternal effects had been standardized. We used model fitting techniques to estimate competition coefficients across the different competition trials and found significant variation in competition intensity. These results suggest that ignoring changes in species’ traits that occur over short time scales may result in an incomplete understanding of community dynamics. This may be particular important for questions about range shifts and changing climates, invasion, and eco-evolutionary feedbacks.