Meeting Abstract
Red-eyed treefrogs, Agalychnis callidryas, are among the best-studied examples of adaptive phenotypic plasticity in hatching timing. Embryos hatch early to escape many egg-stage threats, using cues in multiple sensory modalities. There are well-documented costs of early hatching, for the tadpole stage, and undisturbed embryos typically hatch later. Substantial development occurs between the earliest environmentally cued hatching and the point when most undisturbed embryos have hatched spontaneously (age 3.5–8 days under usual conditions in Gamboa, Panama). However, standard staging tables for anuran embryos (e.g. Gosner 1960) and their prior application to A. callidryas (Pyburn 1963) offer little resolution during this period. Stage 23, the last stage with bilateral external gills, stretches from 4 d until after hatching, whenever it occurs. Moreover, the traits differentiating the earliest hatching stages (Stage 22, tail fin circulation; Stage 23, operculum formed) are not the most visible morphological changes during this period. A more detailed system to describe and compare development is needed to facilitate integrative research on developmental changes in behavior, physiology, and performance, as well as environmental effects on development per se. I used periodic observations of egg clutches through development and time-lapse macro-photography to identify a sequential series of marker traits with greater developmental resolution. These include the formation and elongation of external gill branches, melanophore and iridophore development, changes in yolk sac venation, changes in eye structure and angle, beak keratinzation, and division of the yolk sac into gut coils. Using developmental markers to subdivide the plastic hatching period should facilitate the integration of research results across studies.
