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Abstract：
Reciprocal adaptation is the hallmark of arms race coevolution. Local coadaptation between natural enemies should generate a geographic mosaic pattern where both species have roughly matched abilities across their shared range. However, mosaic variation in ecologically relevant traits can also arise from processes unrelated to reciprocal selection, such as population structure or local environmental conditions. We tested whether these alternative processes can account for trait variation in the geographic mosaic of arms race coevolution between resistant garter snakes (Thamnophis sirtalis) and toxic newts (Taricha granulosa). We found that predator resistance and prey toxin levels are functionally matched in co-occurring populations, suggesting that mosaic variation in the armaments of both species results from the local pressures of reciprocal selection. By the same token, phenotypic and genetic variation in snake resistance deviates from neutral expectations of population genetic differentiation, showing a clear signature of adaptation to local toxin levels in newts. Contrastingly, newt toxin levels are best predicted by genetic differentiation among newt populations, and to a lesser extent, by the local environment and snake resistance. Exaggerated armaments suggest that coevolution occurs in certain hotspots, but prey population structure seems to be of particular influence on local phenotypic variation in both species throughout the geographic mosaic. Our results imply that processes other than reciprocal selection, like historical biogeography and environmental pressures, represent an important source of variation in the geographic mosaic of coevolution. Such a pattern supports the role of \"trait remixing\" in the geographic mosaic theory, the process by which non-adaptive forces dictate spatial variation in the interactions among species.
摘要：
相互适应是军备竞赛共同进化的标志。天敌之间的局部共适应应产生地理马赛克模式，其中两个物种在其共享范围内具有大致匹配的能力。然而,生态相关性状的马赛克变异也可能来自与互惠选择无关的过程，例如人口结构或当地环境条件。我们测试了这些替代过程是否可以解释抗性吊袜带蛇（Thamnophissirtalis）和有毒new（Tarichagranulosa）之间军备竞赛共同进化的地理马赛克中的性状差异。我们发现，在共同发生的种群中，捕食者的抗性和猎物的毒素水平在功能上是匹配的，这表明两种物种武器的马赛克变异是由相互选择的局部压力引起的。出于同样的原因,抗蛇的表型和遗传变异偏离了种群遗传分化的中性预期，显示出适应new局部毒素水平的明显特征。相反，new毒素水平最好通过new种群之间的遗传分化来预测，在较小程度上，受当地环境和蛇的抵抗。夸张的军备表明，共同进化发生在某些热点地区，但是在整个地理马赛克中，猎物的种群结构似乎对两个物种的局部表型变异都有特别的影响。我们的结果表明，除了互惠选择之外，比如历史生物地理学和环境压力，代表了共同进化的地理镶嵌变化的重要来源。这种模式支持地理马赛克理论中“特征混合”的作用，非适应能力决定物种间相互作用空间变化的过程。
