Meeting Abstract

P3.23  Thursday, Jan. 6  The mechanism of rapid, plastic hatching in red-eyed treefrogs, Agalychnis callidryas COHEN, K.L.*; SEID, M.A.; ROUBEN, C.M.; WARKENTIN, K.M.; Boston University; Smithsonain Tropical Research Institute; Boston University; Boston University, Smithsonian Tropical Research Institute kcohen@bu.edu

Red-eyed treefrog embryos can hatch within seconds of attack, and as much as 30% prematurely, to escape from egg-eating snakes. The described mechanism of amphibian hatching involves gradual digestion of the vitelline membrane by proteolytic hatching enzymes secreted from hatching gland cells (HGCs) on the surface of the head. The two phyllomedusine frogs examined to date, A. callidryas and Phyllomedusa trinitatis, lack head-surface HGCs. We used high-speed video to analyze the hatching process of A. callidryas and observed two distinct stages: membrane rupture and exit. Membrane rupture, evidenced by localized leaking of perivitelline fluid, always occurred near the mouth and could occur without physical contact between embryo and rupture site. Rupture was often preceded by mouth-gaping; we therefore hypothesize that embryos release hatching enzymes from their mouths. Following rupture, embryos used vigorous swimming movements to exit the egg capsule through the initial opening. An antibody for tyrosine hydroxylase (TH) serves as a marker for HGCs in Xenopus laevis embryos. Initial work with the TH antibody in hatching-competent A. callidryas shows positive staining localized to a region of the posterior roof of the buccal cavity where mucus secretory cells are known to occur in older tadpoles. Histological investigation confirms the presence of mucus secretory cells in this area in hatching-competent embryos. We hypothesize that these cells may initially produce hatching enzymes before serving another function at later developmental stages, and that hatching enzyme release is under behavioral control.