Division of Biological Sciences, University of Montana, Missoula, Montana, USA.
Department of Biology, University of Virginia, Charlottesville, Virginia, USA.
Mol Ecol. 2023 Aug;32(16):4482-4496. doi: 10.1111/mec.16772. Epub 2022 Nov 27.
Antagonistic coevolution between natural enemies can produce highly exaggerated traits, such as prey toxins and predator resistance. This reciprocal process of adaptation and counter-adaptation may also open doors to other evolutionary novelties not directly involved in the phenotypic interface of coevolution. We tested the hypothesis that predator-prey coevolution coincided with the evolution of conspicuous coloration on resistant predators that retain prey toxins. In western North America, common garter snakes (Thamnophis sirtalis) have evolved extreme resistance to tetrodotoxin (TTX) in the coevolutionary arms race with their deadly prey, Pacific newts (Taricha spp.). TTX-resistant snakes can retain large amounts of ingested TTX, which could serve as a deterrent against the snakes' own predators if TTX toxicity and resistance are coupled with a conspicuous warning signal. We evaluated whether arms race escalation covaries with bright red coloration in snake populations across the geographic mosaic of coevolution. Snake colour variation departs from the neutral expectations of population genetic structure and covaries with escalating clines of newt TTX and snake resistance at two coevolutionary hotspots. In the Pacific Northwest, bright red coloration fits an expected pattern of an aposematic warning to avian predators: TTX-resistant snakes that consume highly toxic newts also have relatively large, reddish-orange dorsal blotches. Snake coloration also seems to have evolved with the arms race in California, but overall patterns are less intuitively consistent with aposematism. These results suggest that interactions with additional trophic levels can generate novel traits as a cascading consequence of arms race coevolution across the geographic mosaic.
天敌之间的拮抗协同进化会产生高度夸张的特征，如猎物毒素和捕食者抗性。这种适应和反适应的相互过程也可能为其他与协同进化表型界面没有直接关系的进化新特性开辟道路。我们检验了这样一个假设，即捕食者-猎物协同进化与保留猎物毒素的抗性捕食者的显眼颜色进化同时发生。在北美西部，常见的束带蛇（Thamnophis sirtalis）在与致命猎物太平洋蝾螈（Taricha spp.）的协同进化军备竞赛中进化出了对河豚毒素（TTX）的极端抗性。TTX 抗性蛇可以保留大量摄入的 TTX，如果 TTX 毒性和抗性与显眼的警告信号相结合，那么 TTX 可能会对蛇类自身的捕食者起到威慑作用。我们评估了在协同进化地理镶嵌体中，蛇种群的军备竞赛升级是否与蛇的鲜艳红色有关。蛇的颜色变化偏离了种群遗传结构的中性预期，并与新蝾螈 TTX 和蛇抗性的升级梯度在两个协同进化热点上相关。在太平洋西北部，鲜艳的红色与鸟类捕食者的警戒性警告模式相吻合：消耗高毒性蝾螈的 TTX 抗性蛇也有相对较大的、橙红色的背部斑块。蛇的颜色似乎也随着加利福尼亚的军备竞赛而进化，但总体模式与警戒性不太一致。这些结果表明，与其他营养层次的相互作用可以作为地理镶嵌体中协同进化军备竞赛的级联后果产生新的特性。
