Department of Biological Sciences, California State University San Marcos, 333 S Twin Oaks Valley Rd, San Marcos, CA, USA.
J Therm Biol. 2019 Dec;86:102434. doi: 10.1016/j.jtherbio.2019.102434. Epub 2019 Oct 10.
Temperature is a primary factor affecting species' ability to thrive in a particular ecological niche, but thermal conditions have changed dramatically in recent decades. Fishes shift their thermal tolerance range with a maximum and minimum temperature correlated to their recent thermal acclimation history, and species can show a reduced temperature quotient (Q) following chronic thermal acclimation. Neon tetra (Paracheirodon innesi) and Black Neon tetra (Hyphessobrycon herbertaxelrodi) are popular hobbyist aquarium fishes, and both species are examples of freshwater teleosts native to South American river systems that are potentially affected by changing thermal conditions. We acclimated these species to three different constant temperatures (26 °C, 29 °C, and 31 °C) for 15.4 ± 2.1 days, then measured acute critical thermal maxima (CTMax) and acute oxygen consumption rate (Ṁo) at each acclimation temperature. We also estimated chronic lethal thermal maximum (CLT) for both species following a 2-week acclimation to 30.4 °C. Mean CTMax of both species were found to increase with acclimation temperature from 38.5 to 39.6 °C for Neon tetra and from 39.5 to 41.0 °C for Black Neon tetra, gaining 0.24 (Neon tetra) or 0.29 °C (Black Neon tetra) of tolerance per 1 °C of acclimation. However, Black Neon tetra demonstrated consistently higher CTMax (1.0-1.4 °C). CLT was lower for Neon tetra (33.5 °C), compared to Black Neon tetra (35.9 °C). Mean Ṁo were statistically similar across acclimation temperatures within species; Q between 26-31 °C were 1.92 and 1.22 for Neon and Black Neon tetra, respectively. Neon and Black Neon tetras physiologically acclimated to changing thermal demands, and although they demonstrate robust CTMax responses, CLT responses indicated both species are unable to survive temperatures 4-5 °C above current average natural values. The demonstrated metabolic plasticity and CTMax values provide a moderate cushion for both species to combat changing temperatures due to climate change, but CLT values suggest vulnerability to projected climate trends.
温度是影响物种在特定生态位中生存能力的主要因素，但近几十年来，热条件发生了巨大变化。鱼类会根据最近的热驯化历史调整其热耐受范围，最大和最小温度与热驯化历史相关，物种在慢性热驯化后可能会表现出较低的温度商（Q）。霓虹脂鲤（Paracheirodon innesi）和黑霓虹脂鲤（Hyphessobrycon herbertaxelrodi）是受欢迎的水族馆鱼类，这两个物种都是原产于南美洲河流系统的淡水硬骨鱼的例子，可能会受到热条件变化的影响。我们将这些物种在三个不同的恒温（26°C、29°C 和 31°C）下驯化 15.4±2.1 天，然后在每个驯化温度下测量急性临界热最大值（CTMax）和急性耗氧量（Ṁo）。我们还在将两种鱼驯化到 30.4°C 两周后，估计了它们的慢性致死热最大值（CLT）。两种鱼的平均 CTMax 都随着驯化温度从 38.5°C 增加到 39.6°C，霓虹脂鲤增加了 0.24°C（霓虹脂鲤）或 0.29°C（黑霓虹脂鲤），每 1°C 的驯化温度增加了 0.24°C（霓虹脂鲤）或 0.29°C（黑霓虹脂鲤）。然而，黑霓虹脂鲤的 CTMax 一直较高（1.0-1.4°C）。 Neon tetra 的 CLT（33.5°C）低于 Black Neon tetra（35.9°C）。在同一物种内，平均 Ṁo 在驯化温度之间没有统计学差异；Neon 和 Black Neon tetra 在 26-31°C 之间的 Q 值分别为 1.92 和 1.22。霓虹脂鲤和黑霓虹脂鲤在生理上适应了不断变化的热需求，尽管它们表现出了强大的 CTMax 反应，但 CLT 反应表明，这两个物种都无法在比当前自然平均值高 4-5°C 的温度下生存。所表现出的代谢可塑性和 CTMax 值为这两个物种提供了一个适度的缓冲，以应对由于气候变化导致的温度变化，但 CLT 值表明它们容易受到预期的气候趋势的影响。
