Water Fleas and Global Warming

Van Doorslaer et al. (2009) tested for genetic adaptation to an increase in temperature in the water flea (Daphnia magna), which is a keystone species in many freshwater ecosystems, by performing a three-month-long thermal selection experiment under laboratory conditions followed by the quantification of microevolutionary responses to temperature for various life-history traits. More specifically, from mud samples taken from a lake in the United Kingdom, they collected 3600 dormant water flea eggs that they hatched at two different temperatures -- 20°C (the mean summer temperature of the water fleas' native habitat) and 24°C (representative of the degree of warming predicted by the IPCC for the coming 100 years) -- after which they grew the hatchlings to adulthood at the intermediate incubation temperature of 22°C and subsequently tested them in a common garden life table experiment.

Van Doorslaer et al. report that the initial populations "showed a significant plastic response to test temperature in all studied life-history traits," and that "compared to 20°C, performance at 24°C was higher," which "fast response," as they describe it, "suggests the capacity for genetic adjustment to temperature changes within a single growing season."

The five researchers say their findings imply that "in natural D. magna populations, sufficient genetic variation is present in the dormant egg bank to support rapid genetic adaptation in response to climate change," and that "these findings corroborate earlier results obtained in a mesocosm selection experiment using a littoral cladoceran species, S. vetulus (Van doorslaer et al., 2007)," both of which findings add to the findings of still other studies "unambiguously demonstrating microevolutionary responses to climate-mediated selection within a short ecological relevant, time frame (Gienapp et al., 2008)."

Additional References
Gienapp, P., Teplitsky, C., Alho, J.S., Mills, J.A. and Merila, J. 2008. Climate change and evolution: disentangling environmental and genetic responses. Molecular Ecology 17: 167-178.

Van Doorslaer, W., Stoks, R., Jeppesen, E. and De Meester, L. 2007. Adaptive microevolutionary responses to simulated global warming in Simocephalus vetulus: a mesocosm study. Global Change Biology 13: 878-886.