Department of Biology, Boston University, 5 Cummington Mall, Boston, MA 02215, USA.
Departamento de Ciencias Biológicas, Universidad de los Andes, Cra 1 No. 18A-70, 111711, Bogotá, Colombia.
J Exp Biol. 2022 Oct 15;225(20). doi: 10.1242/jeb.244533. Epub 2022 Oct 21.
Arboreal embryos of red-eyed treefrogs, Agalychnis callidryas, hatch prematurely in response to hypoxia when flooded and to mechanosensory cues in snake attacks, but hatching later improves tadpole survival. We studied ontogenetic changes in risk assessment and hatching performance of embryos in response to flooding and physical disturbance. We hypothesized that risk assessment decreases as hatchling survival improves and hatching performance increases as embryos develop. Because snakes eat faster than embryos asphyxiate, we hypothesized that embryos decide to hatch sooner and hatch faster in response to mechanosensory cues. We video-recorded individual embryos hatching in response to each cue type, then compared the incidence and timing of a series of events and behaviors from cue onset to complete hatching across ages and stimuli. Latency from cue to hatching decreased developmentally in both contexts and was shorter with mechanosensory cues, but the elements contributing to those changes differed. Hypoxia assessment involved position changes, which decreased developmentally along with assessment time. Mechanosensory cue assessment occurred more rapidly, without movement, and decreased with age. The first stages of hatching, membrane rupture and head emergence, were surprisingly age independent but faster with mechanosensory cues, congruent with greater effort under more immediate risk. In contrast, body emergence and compression showed ontogenetic improvement consistent with morphological constraints but no cue effect. Both appropriate timing and effective performance of hatching are necessary for continued development. Different stages of the process vary with development and environmental context, suggesting combinations of adaptive context- and stage-dependent behavior, cue-related constraints on information acquisition, and ontogenetic constraints on elements of performance.
红目树蟾的树栖胚胎在水淹时会因缺氧而过早孵化，在受到蛇类攻击时则会因机械感觉线索而孵化，但较晚的孵化会提高蝌蚪的存活率。我们研究了胚胎在应对水淹和物理干扰时的风险评估和孵化性能的发育变化。我们假设，随着幼体存活率的提高，风险评估会降低，随着胚胎的发育，孵化性能会提高。由于蛇类进食速度比胚胎窒息速度快，我们假设胚胎在受到机械感觉线索时会更早决定孵化，并更快地孵化。我们对个体胚胎在对每种线索类型进行孵化时进行了视频记录，然后比较了在不同年龄和刺激条件下，从线索开始到完全孵化的一系列事件和行为的发生和时间。在两种情况下，从线索到孵化的潜伏期都随发育而降低，且机械感觉线索的潜伏期更短，但导致这些变化的因素不同。缺氧评估涉及位置变化，这些变化随着评估时间的推移而逐渐减少。机械感觉线索评估发生得更快，没有运动，并且随年龄的增长而减少。孵化的最初阶段，膜破裂和头部出现，令人惊讶的是与年龄无关，但在机械感觉线索下更快，这与在更直接的风险下更大的努力相一致。相比之下，身体出现和压缩表现出与形态限制相一致的发育改善，但没有线索效应。适当的孵化时机和有效的孵化性能对于持续发育都是必要的。该过程的不同阶段因发育和环境背景而异，这表明了适应性的、依赖于环境和依赖于阶段的行为组合，信息获取的线索相关限制，以及表现要素的发育限制。
