P3.5 Friday, Jan. 6 Egg clutch dehydration induces early hatching in red-eyed treefrogs SALICA, M. J.*; VONESH, J. R.; WARKENTIN, K. M.; Universidad Nacional de Tucumán, Argentina; Virginia Commonwealth University, Richmond; Boston University, MA email@example.com
Hydration is essential for embryonic development. Dehydration is a particular risk for terrestrial amphibian embryos in gelatinous eggs. Red-eyed treefrogs, Agalychnis callidryas, lay eggs on plants over water. Maternally provided water allows shaded eggs in humid sites to develop to hatching without rainfall, but unshaded eggs and those in less humid sites can die from dehydration. A. callidryas is known to hatch early in response to several egg-stage risks, including predators, a pathogen and flooding. We experimentally tested how egg clutch dehydration affects their timing of hatching. We collected clutches from a pond in Gamboa, Panama, and randomly allocated them to wet or dry treatments at age 1 day. Wet clutches were heavily sprayed with aged tap water multiple times daily. Dry clutches were unsprayed, or minimally sprayed in some cases where eggs were dying from dehydration. Egg diameter increased initially in all clutches, as water moved from egg jelly to the perivitelline space. Then treatments diverged, so that dry eggs were smaller than wet eggs by the onset of hatching competence, at 4 days. Overall clutch thickness, including eggs plus jelly, was also less in dry than in wet clutches at 4 days. Embryos hatched earlier from dry clutches than from wet clutches, accelerating hatching by ~11%. Their hatching pattern was similar to that of fungus-infected clutches which, like healthy undisturbed clutches, hatch gradually over a period of days. For many species of amphibians that lay eggs above water, an early transition to the aquatic larval habitat could be an effective defense of embryos against the risk of mortality from egg dehydration.