Grupo de Herpetología, Eco-Fisiología & Etología, Department of Biology, Universidad del Tolima, Tolima, 730006299, Colombia; Programa Doctorado en Ciencias Biológicas, Pontificia Universidad Javeriana, Bogotá, 11001000, Colombia.
Department of Evolutionary Ecology, Estación Biológica de Doñana, CSIC, Sevilla, 41092, Spain.
J Therm Biol. 2023 May;114:103545. doi: 10.1016/j.jtherbio.2023.103545. Epub 2023 May 11.
Plasticity in the critical thermal maximum (CT) helps ectotherms survive in variable thermal conditions. Yet, little is known about the environmental mechanisms modulating its time course. We used the larvae of three neotropical anurans (Boana platanera, Engystomops pustulosus and Rhinella horribilis) to test whether the magnitude of temperature changes and the existence of fluctuations in the thermal environment affected both the amount of change in CT and its acclimation rate (i.e., its time course). For that, we transferred tadpoles from a pre-treatment temperature (23 °C, constant) to two different water temperatures: mean (28 °C) and hot (33 °C), crossed with constant and daily fluctuating thermal regimes, and recorded CT values, daily during six days. We modeled changes in CT as an asymptotic function of time, temperature, and the daily thermal fluctuation. The fitted function provided the asymptotic CT value (CT∞) and CT acclimation rate (k). Tadpoles achieved their CT∞ between one and three days. Transferring tadpoles to the hot treatment generated higher CT∞ at earlier times, inducing faster acclimation rates in tadpoles. In contrast, thermal fluctuations equally led to higher CT∞ values but tadpoles required longer times to achieve CT∞ (i.e., slower acclimation rates). These thermal treatments interacted differently with the studied species. In general, the thermal generalist Rhinella horribilis showed the most plastic acclimation rates whereas the ephemeral-pond breeder Engystomops pustulosus, more exposed to heat peaks during larval development, showed less plastic (i.e., canalized) acclimation rates. Further comparative studies of the time course of CT acclimation should help to disentangle the complex interplay between the thermal environment and species ecology, to understand how tadpoles acclimate to heat stress.
热极值的可塑性帮助变温动物在多变的热环境中生存。然而，对于调节其时间进程的环境机制，我们知之甚少。我们使用三种新热带蛙类（Boana platanera、Engystomops pustulosus 和 Rhinella horribilis）的幼虫来测试温度变化的幅度和热环境中波动的存在是否会影响 CT 的变化量及其驯化率（即时间进程）。为此，我们将蝌蚪从预处理温度（23°C，恒温）转移到两种不同的水温：平均（28°C）和热（33°C），同时经历恒温和每日波动的热环境，并记录六天内每天的 CT 值。我们将 CT 的变化建模为时间、温度和每日热波动的渐近函数。拟合函数提供了渐近 CT 值（CT∞）和 CT 驯化率（k）。蝌蚪在一到三天之间达到 CT∞。将蝌蚪转移到热处理中会在较早的时间产生更高的 CT∞，从而诱导蝌蚪更快的驯化率。相比之下，热波动同样导致更高的 CT∞值，但蝌蚪需要更长的时间才能达到 CT∞（即较慢的驯化率）。这些热处理与研究的物种以不同的方式相互作用。一般来说，热广食性 Rhinella horribilis 表现出最具可塑性的驯化率，而在幼虫发育过程中更易受到热峰影响的短暂池塘繁殖者 Engystomops pustulosus 表现出较少的可塑性（即 canalized）驯化率。对 CT 驯化时间进程的进一步比较研究应有助于厘清热环境和物种生态之间复杂的相互作用，以了解蝌蚪如何适应热应激。
