Morphological Plasticity in Four Larval Anurans Distributed along an Environmental Gradient

Abstract

We investigated morphological plasticity to the presence of predators in the tadpoles of four ranid frog species distributed along a pond hydroperiod gradient in southeast Michigan. We first reared all four species (Wood Frog, Rana sylvatica; Leopard Frog R. pipiens; Green Frog, R. clamitans; and Bullfrog, R. catesbeiana) under identical laboratory conditions in the presence and absence of caged larval dragonflies (Anax spp.). We then reared wood frog and leopard frog in outdoor mesocosms to examine the predator-induced responses during ontogeny. Finally, we reared leopard frog with predators fed either leopard frog or wood frog larvae to determine whether prey responses depended upon predators consuming conspecific prey. All four ranids exhibited some degree of morphological change in the presence of Anax; these differences were species specific and fairly robust to different experimental conditions. The responses over ontogeny indicated that the changes were direct responses to the predator’s presence and not an indirect result of the predator slowing anuran growth or development. Finally, larval leopard frog responded similarly to predators feeding on conspecifics and congenerics. Taken together, these results suggest that morphological responses to predators may be relatively common in larval anurans. Further, because many of the responses are known to be adaptive antipredator strategies, predator-induced morphological plasticity has important evolutionary and ecological implications.