Does competition modify predator-induced phenotypic plasticity in three tadpole species?

Background/Question/Methods

Frogs may select breeding sites that maximize the survival of their offspring by avoiding sites with predators and competitors. For ephemeral pool-breeding species, it can be difficult for adults to assess the risks to their offspring because predators and competitors can colonize pools after oviposition has happened. Thus, some tadpoles have evolved plasticity in traits associated with avoiding predation and ameliorating the effects of competition. The aims of this study were to: 1) determine whether the tadpoles of 3 coexisting ephemeral pool breeding species (Fejervarya limnocharis, Microhyla fissipes, and Polypedates leucomystax) have plastic responses to predation and competition; 2) identify whether competition affects the plastic response to predation. For two weeks, I raised each tadpole species under 3 competition treatments (single species at low density, single species at high density and mixed species at high density), and 4 predator treatments (no predator, tilapia predator, odonate larva predator, and odonate plus tilapia). At the conclusion of two weeks, I measured growth, development, body pigmentation and morphology.

Results/Conclusions

There were significant effects of intraspecific competition on growth and development for all three species, however, the strengths of inter- and intraspecific competition were equal for F. limnocharis while interspecific competition was less severe than intraspecific competition for the other two species. Each species had a unique response to the predators with respect to growth and development. Both tilapia and odonates caused reduced growth and development in M. fissipes. F. limnocharis exhibited reduced growth and development after exposure to tilapia and increased growth and development after exposure odonates. P. leucomystax showed reduced growth and development after exposure to tilapia and no change in growth and development due to odonates. Competition only affected M. fissipes’ response to predation. M. fissipes exhibited unique pigmentation changes to tilapia and odonates, F. limnocharis changed pigment only in response to odonates, and P. leucomystax exhibited no changes in pigmentation.  Together these results suggest that although these three tadpole species coexist in the same ephemeral pools, they have evolved very different responses to predation. These unique responses are possibly due to the differences in each species’ susceptibility to predation and competition.