Risk-induced hatching timing shows low heritability and evolves independently of spontaneous hatching in red-eyed treefrogs.

Plasticity in the timing of transitions between stages of complex life cycles allows organisms to adjust their growth and development to local environmental conditions. Genetic variation in such plasticity is common, but the evolution of context-dependent transition timing may be constrained by information reliability, lag-time and developmental constraints. We studied the genetic architecture of hatching plasticity in embryos of the red-eyed treefrog (Agalychnis callidryas) in response to simulated predator attacks using a series of paternal and maternal half-sibs from a captive breeding colony of wild-collected animals. We compared the developmental timing of induced early hatching across sibships and estimated cross-environment genetic correlations between induced and spontaneous hatching traits. Additive genetic variance for induced early hatching was very low, indicating a constraint on the short-term evolution of earlier hatching timing. This constraint is likely related to the maturation of the hatching mechanism. The most plastic genotypes produced the most extreme spontaneous hatching phenotypes, indicating that developmental range, per se, is not constrained. Cross-environment genetic correlation in hatching timing was negligible, so the evolution of spontaneous hatching in this species has not depended on the evolution of risk-induced hatching and vice versa.