Meeting Abstract
Arboreal embryos of Agalychnis callidryas hatch prematurely to escape from both egg predators and hypoxic conditions, which kill eggs too young to hatch. To assess the developmental timing of response onset and potential limiting mechanisms, we tested embryo hatching-responses in developmental series of 11 sibships. Every 3 h, we tested 2 eggs per clutch by submerging them in hypoxic water or manually stimulating them with a simulated attack cue. Immediately after trials, we decapsulated unhatched embryos and photographed animals to assess development. To examine the potential role of otic mechanoreception in hatching for attack-cued individuals, we measured the roll-induced vestibulo-ocular reflex (VOR), in which eyes roll counter to body roll based on vestibular sensory input. We used confocal fluorescence microscopy with phalloidin staining to assess ear development across the onset of attack-cued hatching and of VOR. Across sibships, hatching responses to hypoxia began on average at 84 h, 8 h before attack-cued hatching. Also response consistency increased more rapidly and onset timing showed less variation across clutches, compared with responses to attack cues. Hatching ability is clearly not the sole constraint on the developmental onset of escape-hatching responses to attacks. The onset of hatching in response to attack cues coincided with the onset of VOR. Based on initial confocal images, stereociliary bundles start to appear in simple otic capsules shortly before the onset of VOR and attack-cued hatching, and there is substantial ear development across the onset of the hatching response. Ontogenetic coincidence of the appearance of inner ear mechanosensors, VOR, and hatching in response to simulated attack supports a role for developing ears in the perception of predator cues.
