MacMillan Heath A, Ferguson Laura V, Nicolai Annegret, Donini Andrew, Staples James F, Sinclair Brent J
Department of Biology, University of Western Ontario, London, ON, Canada N6A 5B7
Department of Biology, University of Western Ontario, London, ON, Canada N6A 5B7.
J Exp Biol. 2015 Feb 1;218(Pt 3):423-32. doi: 10.1242/jeb.115790. Epub 2014 Dec 18.
Low temperature tolerance is the main predictor of variation in the global distribution and performance of insects, yet the molecular mechanisms underlying cold tolerance variation are poorly known, and it is unclear whether the mechanisms that improve cold tolerance within the lifetime of an individual insect are similar to those that underlie evolved differences among species. The accumulation of cold-induced injuries by hemimetabolous insects is associated with loss of Na(+) and K(+) homeostasis. Here we show that this model holds true for Drosophila; cold exposure increases haemolymph [K(+)] in D. melanogaster, and cold-acclimated flies maintain low haemolymph [Na(+)] and [K(+)], both at rest and during a cold exposure. This pattern holds across 24 species of the Drosophila phylogeny, where improvements in cold tolerance have been consistently paired with reductions in haemolymph [Na(+)] and [K(+)]. Cold-acclimated D. melanogaster have low activity of Na(+)/K(+)-ATPase, which may contribute to the maintenance of low haemolymph [Na(+)] and underlie improvements in cold tolerance. Modifications to ion balance are associated with both phenotypic plasticity within D. melanogaster and evolutionary differences in cold tolerance across the Drosophila phylogeny, which suggests that adaptation and acclimation of cold tolerance in insects may occur through similar mechanisms. Cold-tolerant flies maintain haemolymph osmolality despite low haemolymph [Na(+)] and [K(+)], possibly through modest accumulations of organic osmolytes. We propose that this could have served as an evolutionary route by which chill-susceptible insects developed more extreme cold tolerance strategies.
低温耐受性是昆虫全球分布和表现变化的主要预测指标，然而耐寒性变化背后的分子机制却鲜为人知，而且尚不清楚个体昆虫在其生命周期内提高耐寒性的机制是否与物种间进化差异背后的机制相似。半变态昆虫冷诱导损伤的积累与Na(+)和K(+)稳态的丧失有关。在这里，我们表明这个模型对果蝇也适用；冷暴露会增加黑腹果蝇血淋巴中的[K(+)]，而冷驯化的果蝇在静止和冷暴露期间都能维持较低的血淋巴[Na(+)]和[K(+)]。这种模式在果蝇系统发育的24个物种中都存在，耐寒性的提高一直与血淋巴[Na(+)]和[K(+)]的降低相关。冷驯化的黑腹果蝇Na(+)/K(+)-ATP酶活性较低，这可能有助于维持较低的血淋巴[Na(+)]，并成为耐寒性提高的基础。离子平衡的改变与黑腹果蝇的表型可塑性以及果蝇系统发育中耐寒性的进化差异都有关，这表明昆虫耐寒性的适应和驯化可能通过相似的机制发生。耐寒的果蝇尽管血淋巴[Na(+)]和[K(+)]较低，但仍能维持血淋巴渗透压，可能是通过适度积累有机渗透剂来实现的。我们认为，这可能是易受寒冷影响的昆虫发展出更极端耐寒策略的一条进化途径。
