Meeting Abstract
Red-eyed treefrogs, Agalychnis callidryas, lay eggs on leaves over ponds. Older, more developed hatchlings survive better with aquatic predators, but embryos hatch early to escape from threats to eggs, including risk of suffocation in flooded clutches. The danger in flooding varies with water oxygenation and egg surface exposure. We assessed embryo decisions and developmental consequences in a best-case flooding scenario, submerging individual eggs in air-saturated water. We used a split-clutch design to compare development rates of embryos in eggs in air and water and tadpoles in water, starting at age 4 d when most embryos hatch in <1 h from flooded clutches. We used closed-system respirometry of eggs in air and water, and tadpoles, to compare metabolic rates across environments and oxygen levels at which eggs in water hatched, and tadpoles became oxygen-limited. Few submerged embryos hatched immediately (13% within 12 h of submergence); most hatched after siblings in air. Hatched tadpoles developed fastest and submerged embryos slowest. Hatchlings from submerged eggs were smaller than earlier-hatched sibs from eggs in air. In air-saturated water, metabolic rates of newly hatched tadpoles were higher than those of submerged eggs. Embryos hatched at oxygen levels near those that limited metabolism in newly hatched tadpoles, and metabolic rates tended to show a small increase just after hatching. Embryos submerged individually do not necessarily die, but suffer metabolic and developmental costs, even in well-oxygenated water. They appear to balance the severity of costs against benefits of being more developed at hatching. Submergence of terrestrial eggs may accelerate or retard hatching timing, with varying effects on development rate and hatching stage depending on embryo decisions.
