Populations at risk of extinction due to climate change may be rescued by adaptive genetic evolution or phenotypic plasticity. Whether these processes can match the current rapid pace of environmental change remains an open question. Measuring local adaptation to climate among populations throughout a species’ range and the degree of phenotypic plasticity within populations is one way to assess the potential for evolutionary rescue. Here, we tested the life history and population growth response to temperature of Daphnia pulicaria populations native to alpine lakes in the Sierra Nevada (CA) that are arrayed along an elevational climate gradient and have been exposed to different predation (fish stocking) regimes (long-term selection). In addition, we measured the short-term response to selection by growing these same populations at two elevations in field mesocosms over two years. Then, D. pulicaria were collected from mesocosms to measure heritable and plastic life history variation in response to test temperatures in a common garden experiment. Using this approach we could partition the phenotypic response to selection over long (as determined by the lake of origin) and short (as determined by the temperature in the mesocosm experiment) time scales.
Results/Conclusions
In the life-history experiment, overall we observed plastic response in all traits, being increase in size at maturity, number of offspring and intrinsic growth rate, and decrease in age at maturity when clones were tested at warmer temperature compared to those tested at colder temperature. However, the level of plasticity was influenced by long- and short-term selection. Specifically, we found that age at maturity was only affected by temperature in the life-history experiment. Additionally, short-term selection by high temperatures increased plasticity of population intrinsic growth rate in response to temperature. Fecundity was higher in populations from fishless lakes, and size at maturity showed greater plasticity in populations from warm lakes but both were unaffected by short term selection. Multivariate life history variation was affected by long-term selection by elevation and predator presence, implying genetic variation among populations, but also by short-term selection, indicating that greater phenotypic plasticity evolved rapidly in response to recent exposure to high temperature. These results demonstrate that both genetic variation and phenotypic plasticity are important components of the life history to temperature in Daphnia, and that the plasticity in response to elevated temperature can evolve in response to selection over only a few generations.