EFFECTS OF A PREDATOR ON PREY METAMORPHOSIS - PLASTIC RESPONSES BY PREY OR SELECTIVE MORTALITY

Models for organisms with complex life cycles predict decreased size a t, and altered time to, metamorphosis for organisms experiencing great er mortality rate during the larval stages. We tested this prediction by exposing larvae of the tree hole mosquito, Aedes triseriatus, to pr edation by the mosquito Toxorhynchites rutilus in a series of five exp eriments. Populations both sympatric and allopatric to the predator we re tested, and meta-analysis was used to synthesize the results of all experiments, and to test for heterogeneity of effects of actual vs. p erceived predation (predator unable to kill prey). In the presence of this predator, A. triseriatus from both sympatric and allopatric popul ations had lower mass at pupation, as predicted. This effect was prese nt in both sexes, but was more pronounced in females. The presence of the predator also increased time to pupation for females (but not for males). Reduced size at pupation appears to result from decreased grow th rate in the presence of the predator, and we tested the hypothesis that this predator induced behavioral changes in A. triseriatus that l ead to reduced growth (e.g., reduced movement and foraging) Behavioral observations did not support the hypothesis of be- havioral change. M eta-analysis revealed significant heterogeneity of the effects of actu al predation vs. perceived predation on size at pupation, which decrea sed significantly only in response to actual predation. There was no s ignificant heterogeneity in the effect of actual predation vs. perceiv ed predation on time to pupation. These results suggest that effects o f this predator on metamorphosis of A. triseriatus may be products of either facultative responses to the predator or of selective mortality due to predation in experiments with actual predation. Sympatric and allopatric populations of A. triseriatus used in these experiments did not differ consistently in size at and time to pupation, nor in their developmental responses to T. rutilus. Although these results general ly support the predictions of existing models of complex life cycles, they suggest that the mechanisms producing these effects in this syste m may not be the same as the behavioral mechanisms producing similar e ffects in amphibian systems.