Meeting Abstract
The arboreal embryos of Agalychnis callidryas experience hypoxia when individual eggs or whole clutches fall into ponds. This can slow development or kill embryos too young to hatch, and induces premature hatching once embryos are able to hatch. Nonetheless, hatching early carries costs, and the extent to which flooding constrains metabolism must vary with egg surface-exposure and aquatic oxygen level. We measured oxygen just outside eggs flooded in clutches and singly. Oxygen depletion was faster and more severe when whole clutches were flooded. We examined responses of premature, hatching-competent embryos to a best-case flooding scenario, submerging fully-exposed individual eggs in normoxic water. Embryos began hatching within 20 min of flooding and nearly half hatched within a few hours, but many tolerated a 2–3 day period of submergence and moderate hypoxia before hatching. We continuously monitored behavior of individual embryos for 15 min in air and 75 min after flooding to examine their oxygen-sampling process and decision to delay hatching. At ages 3 and 4-d, movement rate increased over four-fold upon flooding, then returned to pre-flooding levels after about 30 min of submergence. In earlier work, submerging less-exposed eggs in hypoxic water, movement rates peaked at much higher levels and all embryos decided to hatch, on average after 15 min at 3-d and 7 min at 4-d. With moderate hypoxia, oxygen-sampling was less intense but longer, differences between ages were weaker, and many embryos decided not to hatch immediately. A. callidryas embryos appear to modulate oxygen-assessment and hatching decisions with flooding context, and ontogenetic changes in the response to flooding are context-dependent.
