Metamorphic plasticity: an aquatic predator affects timing of and morphology at emergence of red-eyed treefrogs

GÓMEZ, VALERIA I.; WARKENTIN, KAREN M.

Gramado RS

Congreso; 7mo Congresso Brasileiro de Herpetologia; 2015

Sociedad Brasilera de Herpetologia

During metamorphosis, anurans can face high predation risk because their transitional morphology compromises locomotor performance. By moving to land metamorphs escape from aquatic predators, but they may encounter new terrestrial predators. The timing of emergence determines how the risky period of metamorphic climax is partitioned between environments with different predators. We hypothesized that metamorphs would accelerate emergence in response to an aquatic predator, entering the terrestrial habitat earlier in development. At the Smithsonian Tropical Research Institute, in Gamboa, Panama, we tested this hypothesis with red-eyed treefrogs, Agalychnis callidryas, and giant water bugs, Belostoma cf. porteri. Tadpoles hatched from 20 egg masses were reared in groups of 25 in 400-L plastic mesocosms. At Gosner stage 41?42, just before forelimb emergence, groups of 5 tadpoles were moved to 20 new mesocosms, half of which contained a caged belostomatid that was fed tadpoles to provide risk cues. Mesocosms were checked every 15 min through the evening to record when each A. callidryas emerged from the water and immediately photograph it for morphological measurements (SVL, tail length, forelimb length and hindlimb length). To assess emergence timing and morphology we used generalized linear mixed models (GLMM, function lmer in R v. 3.1.1) with an underlying Gaussian distribution. We used data from individuals with tank included as random effect. We estimated p-values of predictors by likelihood ratio tests of nested models. Metamorphs emerged from the experimental mesocosms after 2?5 days. We found that A. callidryas emerged earlier in the evening from mesocosms with predators, and later from those without predators (6?8 pm vs. 9?11 pm, X2 = 3.750, p = < 0.0001). We found no difference in SVL (X2 = 0.762, p = 0.449) or forelimb length (X2 = 0.435, p = 0.665) of metamorphs emerging from tanks with or without predators. However, metamorphs left water with Belostoma with significantly shorter hindlimbs, compared to those leaving predator-free water (X2 = 2.538, p = 0.013), and with marginally longer tails (X2 = 1.943, p = 0.056). A. callidryas? vulnerability to Belostoma increases greatly with forelimb emergence; therefore, reducing the portion of metamorphosis spent in the water with this predator would improve survival. However, this inducible defense may carry a cost, as large tails and small hindlimbs can reduce the ability to escape from predators on land.