Meeting Abstract
Agalychnis callidryas embryos hatch prematurely to escape predation, cued by physical disturbance in snake attacks. This response appears strongly mediated by otoconial organs in the developing vestibular system, but some mechanosensory-cued hatching (MCH) occurs before these sensors function. We tested if lateral line mechanoreceptors contribute to MCH by blocking neuromast function with gentamicin then exposing embryos to hatching cues at 3 developmental stages: just before and after the onset of vestibular function and closer to spontaneous hatching. To assess vestibular function, we measured the vestibulo-ocular reflex (VOR); it was unaffected by gentamicin. We confirmed lateral line blocking with DiAsp staining. We used egg-jiggling and vibration playbacks to test for MCH. Just prior to vestibular function, at age 4.2 d, gentamicin reduced the hatching response to jiggling from 22% to 1%, revealing a lateral line contribution to risk assessment. After vestibular function, MCH increased substantially. At 4.8 d, the lateral line still contributed, as gentamicin reduced hatching from 72% to 40%. By 5.4 d all jiggled embryos hatched, regardless of neuromast function, and their response to vibration playbacks (ca. 80%) was indistinguishable, suggesting redundancy of mechanosensory modalities. A. callidryas embryos clearly use lateral line mechanoreceptors, as well as otoconial organs, to sense mechanosensory risk cues, and their relative importance changes developmentally. The occurrence of MCH in a few embryos lacking both vestibular and lateral line function suggests cutaneous mechanoreceptors may also contribute to risk assessment. A. callidryas embryos appear to use all available sensors to assess mechanosensory risk cues for escape-hatching decisions.
