Developmental changes in vibration sensing and vibration-cued hatching decisions in red–eyed treefrogs
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Abstract
Arboreal embryos of red-eyed treefrogs, Agalychnis callidryas, hatch prematurely to escape from egg predators, cued by vibrations in attacks. Young embryos modulate hatching based on multiple, non-redundant frequency and temporal properties of vibration cues, reducing the chance of false alarms that unnecessarily expose hatchlings to risk in the water. We used a variety of techniques, including vibration playbacks, to test two hypotheses concerning why hatching responses increase developmentally. First, we tested the hypothesis that sensory development improves cue detection. In ch.1, we assessed the role of vestibular mechanoreception in A. callidryas embryos. We found ontogenetic congruence of vestibular system function and MCH, suggesting that the developing ear plays a role in egg-motion sensing. In ch.2, we tested if lateral line mechanoreceptors contribute to MCH by blocking neuromast function with gentamicin then exposing embryos to vibration cues across ontogeny. We found that the lateral line mediates the earliest onset of MCH, and MCH continues to increase with increasing numbers of neuromasts. Second, we tested the hypothesis that, once sensory capabilities have developed, embryos are able to consider the cues available to them and weigh their costs and benefits in order to make an informed, optimal decision to hatch. Ch.3 explored the ways in which embryo responses could be contextually modulated in complex ways. We showed that second-order temporal pattern elements such as prefixes and long gaps could be threatening in certain contexts and not in others, suggesting that embryos practice a very impressive, highly functioning decision-making process that incorporates multiple vibration properties to distinguish between threatening and non-threatening stimuli. Development had a drastic effect on this decision process because hatchlings face aquatic predators in ponds. Since older and bigger hatchlings were less likely to be killed by this new suite of predators, the costs of false alarms decreased as embryos approach spontaneous hatching and they should decide to hatch more readily compared to their younger and smaller counterparts. In ch.4, we showed that older embryos selectively accept more false alarms in response to ambiguous cues, providing evidence for ontogenetic adaptation in information use for escape-hatching decisions. Overall, this research will help us understand how animals facing different risk trade-offs use information to make crucial behavioral decisions.
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Attribution-NonCommercial-NoDerivatives 4.0 International