Department of Entomology, University of Georgia, Athens, GA, USA.
Department of Biological Sciences, Mississippi State University, Mississippi State, MS, USA.
J Anim Ecol. 2020 Aug;89(8):1895-1905. doi: 10.1111/1365-2656.13238. Epub 2020 May 27.
Ecologically relevant symbioses are widespread in terrestrial arthropods but based on recent findings these specialized interactions are likely to be especially vulnerable to climate warming. Importantly, empirical data and climate models indicate that warming is occurring asynchronously, with night-time temperatures increasing faster than daytime temperatures. Daytime (DTW) and night-time warming (NTW) may impact ectothermic animals and their interactions differently as DTW results in greater daily temperature variation and moves organisms nearer to their thermal limits, while NTW avoids thermal limits and may relieve constraints of cooler night-time temperatures; a nuance that has largely been ignored in the literature. In laboratory experiments, we investigated how the timing of warming influences a widespread defensive mutualism involving the pea aphid Acyrthosiphon pisum, and its heritable symbiont, Hamiltonella defensa, which protects against an important natural enemy, the parasitic wasp Aphidius ervi. Three aphid sublines were experimentally created from single aphid genotype susceptible to A. ervi: one line infected with a highly protective H. defensa strain, one infected with a moderately protective strain and one without any facultative symbiont. We examined aphid fitness in the presence and absence of parasitoids and when exposed to an average 2.5°C increase occurring across three warming scenarios (night-time vs. daytime vs. uniform) relative to no-warming controls. An increase of 2.5°C, as predicted to occur by the IPCC before 2100, was sufficient to disable the aphid defensive mutualism regardless of the timing of warming; a surprising result given that the daily maxima for control and NTW scenarios were identical. We also found that warming negatively impacted (a) symbiont-mediated interactions between host and parasitoid more than symbiont-free ones; (b) species interactions (host-parasitoid) more than each participant independently and (c) aphids more than parasitoids even though higher trophic levels are generally predicted to be more affected by warming. Here we show that 2.5°C warming, regardless of timing, negatively impacted a common microbe-mediated defensive mutualism. While this was a laboratory-based study, results suggest that temperature increases predicted in the near-term may disrupt the many ecological symbioses present in terrestrial ecosystems.
生态相关共生关系在陆地节肢动物中广泛存在，但根据最近的发现，这些专门的相互作用可能特别容易受到气候变暖的影响。重要的是，实证数据和气候模型表明，变暖是异步发生的，夜间温度的上升速度快于白天温度。白天（DTW）和夜间升温（NTW）可能会以不同的方式影响变温动物及其相互作用，因为 DTW 导致更大的日温度变化，并使生物更接近其热极限，而 NTW 则避免了热极限，并可能缓解较冷的夜间温度的限制；这一细微差别在文献中基本上被忽略了。在实验室实验中，我们研究了升温时间如何影响广泛存在的防御共生关系，涉及豌豆蚜 Acyrthosiphon pisum 及其可遗传共生体 Hamiltonella defensa，后者可抵御重要的自然天敌，寄生蜂 Aphidius ervi。从对 A. ervi 敏感的单一蚜虫基因型中，我们实验性地创建了三个蚜虫亚系：一个系感染了高度保护性的 H. defensa 菌株，一个系感染了中度保护性菌株，一个系没有任何兼性共生体。我们在有无寄生蜂的情况下检查了蚜虫的适应性，并在相对于无升温对照的情况下，当暴露于三个升温情景（夜间 vs. 白天 vs. 均匀）中发生的平均 2.5°C 增加时检查了蚜虫的适应性。根据 IPCC 的预测，到 2100 年之前，这种 2.5°C 的升温足以使蚜虫防御共生关系失效，尽管对照和 NTW 情景的日最大值相同，但这是一个令人惊讶的结果。我们还发现，升温对（a）共生体介导的宿主与寄生蜂之间的相互作用的负面影响大于无共生体的相互作用；（b）物种相互作用（宿主-寄生蜂）大于每个参与者的相互作用，（c）蚜虫大于寄生蜂，尽管较高的营养级通常被预测更容易受到升温的影响。在这里，我们表明，无论时间如何，2.5°C 的升温都会对常见的微生物介导的防御共生关系产生负面影响。虽然这是一项基于实验室的研究，但结果表明，在不久的将来预测的温度升高可能会破坏陆地生态系统中存在的许多生态共生关系。
