Cooley Nikita L, Emlen Douglas J, Woods H Arthur
Division of Biological Sciences, 32 Campus Drive HS104, University of Montana, Missoula, MT, 59812, USA.
Division of Biological Sciences, 32 Campus Drive HS104, University of Montana, Missoula, MT, 59812, USA.
J Therm Biol. 2016 Dec;62(Pt A):76-83. doi: 10.1016/j.jtherbio.2016.10.002. Epub 2016 Oct 17.
Do insect larvae ever self-heat significantly from their own metabolic activity and, if so, under what sets of environmental temperatures and across what ranges of body size? We examine these questions using larvae of the Japanese rhinoceros beetle (Trypoxylus dichotomus), chosen for their large size (>20g), simple body plan, and underground lifestyle. Using CO respirometry, we measured larval metabolic rates then converted measured rates of gas exchange into rates of heat production and developed a mathematical model to predict how much steady state body temperatures of underground insects would increase above ambient depending on body size. Collectively, our results suggest that large, extant larvae (20-30g body mass) can self-heat by at most 2°C, and under many common conditions (shallow depths, moister soils) would self-heat by less than 1°C. By extending the model to even larger (hypothetical) body sizes, we show that underground insects with masses >1kg could heat, in warm, dry soils, by 1.5-6°C or more. Additional experiments showed that larval critical thermal maxima (CT) were in excess of 43.5°C and that larvae could behaviorally thermoregulate on a thermal gradient bar. Together, these results suggest that large larvae living underground likely regulate their temperatures primarily using behavior; self-heating by metabolism likely contributes little to their heat budgets, at least in most common soil conditions.
昆虫幼虫会因其自身的代谢活动而显著自热吗？如果会，是在何种环境温度条件下，以及在多大的体型范围内呢？我们利用日本独角仙（双叉犀金龟）的幼虫来研究这些问题，选择它是因为其体型较大（>20克）、身体结构简单且为地下生活方式。通过二氧化碳呼吸测定法，我们测量了幼虫的代谢率，然后将测得的气体交换率转换为产热率，并建立了一个数学模型，以预测地下昆虫的稳态体温会比环境温度升高多少，这取决于体型大小。总体而言，我们的结果表明，现存的大型幼虫（体重20 - 30克）最多能自热2°C，并且在许多常见条件下（浅埋深度、较湿润的土壤）自热幅度会小于1°C。通过将模型扩展到更大（假设的）体型，我们发现体重>1千克的地下昆虫在温暖、干燥的土壤中可能会升温1.5 - 6°C或更多。额外的实验表明，幼虫的临界热最大值（CT）超过43.5°C，并且幼虫能够在热梯度条上进行行为性体温调节。这些结果共同表明，生活在地下的大型幼虫可能主要通过行为来调节体温；代谢产生的自热对它们的热量收支贡献可能很小，至少在大多数常见的土壤条件下是这样。
