Guevara-Molina Estefany Caroline, Gomes Fernando Ribeiro, Warkentin Karen M
Department of Physiology, Institute of Biosciences, Laboratory of Behavior and Evolutionary Physiology, University of São Paulo, São Paulo 05508-900, Brazil.
Department of Biology, Boston University, Boston, MA 02215, USA.
Integr Org Biol. 2022 Sep 28;4(1):obac041. doi: 10.1093/iob/obac041. eCollection 2022.
Climate change is increasing both environmental temperatures and droughts. Many ectotherms respond behaviorally to heat, thereby avoiding damage from extreme temperatures. Within species, thermal tolerance varies with factors such as hydration as well as ontogenetic stage. Many tropical anurans lay terrestrial eggs, relying on environmental moisture for embryonic development. These eggs are vulnerable to dehydration, and embryos of some species can hatch prematurely to escape from drying eggs. Warmer temperatures can accelerate development and thus hatching, but excess heat can kill embryos. Thus, we hypothesize that embryos may show a behavioral thermal tolerance limit, hatching prematurely to avoid potentially lethal warming. If so, because warming and drying are often associated, we hypothesize this limit, measurable as a voluntary thermal maximum, may depend on hydration. We manipulated the hydration of the terrestrial eggs of , in intact clutches and egg-groups isolated from clutch jelly, then warmed them to assess if embryos hatch early as a behavioral response to high temperatures and whether their thermal tolerance varies with hydration or surrounding structure. We discovered that heating induces hatching; these embryos show a behavioral escape-hatching response that enables them to avoid potentially lethal warming. Hydrated eggs and clutches lost more water and warmed more slowly than dehydrated ones, indicating that hydration buffers embryos from environmental warming via evaporative cooling. Embryos in hydrated clutches tolerated greater warming before hatching and suffered higher mortality, suggesting their behavioral Thermal Safety Margin is small. In contrast, lower thermal tolerance protected dry embryos, and those isolated from clutch jelly, from lethal warming. Heat-induced hatching offers a convenient behavioral assay for the thermal tolerance of terrestrial anuran embryos and the interactive effects of warming and dehydration at an early life stage. This work expands the set of threats against which embryos use hatching in self-defense, creating new opportunities for comparative studies of thermal tolerance as well as integrative studies of self-defense mechanisms at the egg stage.
气候变化正在使环境温度升高，干旱加剧。许多变温动物会通过行为来应对高温，从而避免极端温度造成的损害。在物种内部，热耐受性会因水合作用以及个体发育阶段等因素而有所不同。许多热带蛙类产陆栖卵，胚胎发育依赖环境湿度。这些卵易脱水，一些物种的胚胎会过早孵化以逃离干燥的卵。温度升高会加速发育从而导致孵化，但过热会杀死胚胎。因此，我们推测胚胎可能存在行为热耐受性极限，会过早孵化以避免潜在的致命升温。如果是这样，由于变暖和干燥往往同时出现，我们推测这个可作为自愿热最大值来衡量的极限可能取决于水合作用。我们对完整卵块以及从卵块凝胶中分离出的卵组中的蛙类陆栖卵的水合作用进行了操控，然后对其进行加热，以评估胚胎是否会因高温而提前孵化，以及它们的热耐受性是否会随水合作用或周围结构而变化。我们发现加热会诱导孵化；这些胚胎表现出一种行为性逃避孵化反应，使它们能够避免潜在的致命升温。与脱水的卵和卵块相比，水合的卵和卵块失水更多，升温更慢，这表明水合作用通过蒸发冷却为胚胎缓冲了环境变暖的影响。水合卵块中的胚胎在孵化前能耐受更高的温度，但死亡率也更高，这表明它们的行为热安全边际较小。相比之下，较低的热耐受性保护了干燥的胚胎以及从卵块凝胶中分离出的胚胎免受致命升温的影响。热诱导孵化提供了一种方便的行为检测方法，可用于研究陆栖蛙类胚胎的热耐受性以及早期生命阶段变暖和脱水的交互作用。这项工作扩展了胚胎用于自我防御性孵化所应对的威胁范围，为热耐受性的比较研究以及卵阶段自我防御机制的综合研究创造了新机会。
