Evolutionary change in metabolic rate of Daphnia pulicaria following invasion by the predator Bythotrephes longimanus

Metabolic rate is a trait that may evolve in response to the direct and
indirect effects of predator-induced mortality. Predators may indirectly
alter selection by lowering prey densities and increasing resource
availability or by intensifying resource limitation through changes in
prey behaviour (e.g. use of less productive areas). In the current study
we quantify evolution of metabolic rate in the zooplankton Daphnia
pulicaria following an invasive event by the predator Bythotrephes
longimanus in Lake Mendota, Wisconsin, US. This invasion has been shown to
dramatically impact D. pulicaria, causing a ~60% decline in their
biomass. Using a resurrection ecology approach, we compared the metabolic
rate of D. pulicaria clones originating from prior to the Bythotrephes
invasion with that of clones having evolved in the presence of
Bythotrephes. We observed a 7.4% reduction in metabolic rate among
post-invasive clones compared to pre-invasive clones, and discuss the
potential roles of direct and indirect selection in driving this change.