Meeting Abstract
P1.178 Saturday, Jan. 4 15:30 Ear development and function in red-eyed treefrog embryos: a sensor for egg-predator cues? WARKENTIN, K. M.*; ADDIS, C. J.; COHEN, K. L.; Boston Univ.; Boston Univ.; Boston Univ. kwarken@bu.edu
Red-eyed treefrog, Agalychnis callidryas, embryos hatch rapidly and prematurely in predator attacks, cued by physical disturbance of eggs. Playback of vibrations recorded during snake attacks can induce hatching, but the mechanosensory system mediating the response is unknown. We have begun to assess a potential role for inner ears in predator-induced hatching. Mature frog ears receive inputs from sound, vibration, linear acceleration, and angular acceleration via eight sensory surfaces, but the ontogenetic onset of these functions is known in few species. In Gamboa, Panama, A. callidryas hatch as early as age 3 d in extreme hypoxia. They begin hatching in snake and wasp attacks at 4 d; escape success improves from 4–5 d and is ~80% thereafter. Undisturbed embryos typically hatch at 6–7 d. We histologically examined 3–8 d A. callidryas and found their ears developed from small otic vesicles to large, complex labyrinths during this period. Invagination of the otic vesicle, an early stage of horizontal canal formation, appeared at 4 d. In Xenopus this coincides with the first appearance of hair cells and onset of vestibuloocular reflexes (VOR), eye movements that compensate for head movements to stabilize the visual field and depend on otic sensory input. We tested the roll-induced VOR of A. callidryas to assess ear function. Some, but not all, 4-d embryos showed VOR and all older embryos tested showed strong reflexes, indicating otic sensory function. Thus, sensory information available to embryos must change during the period of hatching competence, and older embryos are likely better able to sense egg motion. The apparent ontogenetic coincidence of the onset of predator-induced hatching and otic mechanoreception suggests a role for developing ears in perception of predator cues.
