Effects of hatching age on development and hatchling morphology in the red-eyed tree frog, Agalychnis callidryas

Abstract

The red-eyed treefrog, Agalychnis callidryas, lays eggs on leaves overhanging ponds. Tadpoles hatch and enter the water at different ages, and late-hatched tadpoles survive aquatic predators better than do early-hatched tadpoles. Here I assess developmental consequences of hatching age through: (1) a morphological study of embryos and tadpoles through the plastic hatching period; (2) a behavioural assay for an effect of hatching age on feeding; and (3) a field experiment testing the effect of hatching age on growth to metamorphosis. Substantial development of feeding, digestive, respiratory and locomotor structures occurs in embryos over the plastic hatching period. Hatchling morphology thus varies with age, with consequences for behaviour and predation risk. Hatched tadpoles develop faster than embryos, and early-hatched tadpoles feed before late-hatched tadpoles. After all tadpoles have hatched, the effect of hatching age on size decreases. I found no evidence for an effect of hatching age on size at metamorphosis and only weak evidence for an effect on larval period. Hatching age affects the sequence of developmental change: early-hatched tadpoles lose external gills while otherwise more developed embryos maintain them. Plasticity in external gill resorption may be adaptive given differences in the respiratory environments of embryos and tadpoles. Early-hatched tadpoles also diverge from embryos in shape, growing relatively smaller tails. The study of functional morphology and developmental plasticity will contribute to understanding hatching as an ontogenetic niche shift.