Motychak Jeffrey E, Brodie Edmund D, Brodie Edmund D
Department of Biology, Utah State University, Logan, Utah, 84322-5305.
Department of Biology, Indiana University, Bloomington, Indiana, 47405.
Evolution. 1999 Oct;53(5):1528-1535. doi: 10.1111/j.1558-5646.1999.tb05416.x.
Coevolutionary interactions typically involve only a few specialized taxa. The factors that cause some taxa and not others to respond evolutionarily to selection by another species are poorly understood. Preadaptation may render some species predisposed for evolutionary response to new pressures, whereas a lack of genetic variation may limit the evolutionary potential of other taxa. We evaluate these factors in the predator-prey interaction between toxic newts (Taricha granulosa) and their resistant garter snake predators (Thamnophis sirtalis). Using a bioassay of resistance to tetrodotoxin (TTX), the primary toxin in the prey, we examined phenotypic evolution in the genus Thamnophis. Reconstruction of ancestral character states suggests that the entire genus Thamnophis, and possibly natricine snakes in general, has slightly elevated TTX resistance compared to other lineages of snakes. While this suggests that T. sirtalis is indeed predisposed to evolving TTX resistance, it also indicates that the potential exists in sympatric congeners not expressing elevated levels of TTX resistance. We also detected significant family level variation for TTX resistance in a species of Thamnophis that does not exhibit elaborated levels of the trait. This finding suggests that evolutionary response in other taxa is not limited by genetic variability. In this predator-prey system, species and population differences in resistance appear to be largely determined by variation in the selective environment rather than preadaptation or constraint.
协同进化的相互作用通常只涉及少数几个特化的分类群。导致一些分类群而非其他分类群对另一个物种的选择做出进化响应的因素，目前还了解得很少。预适应可能使一些物种倾向于对新压力做出进化响应，而缺乏遗传变异可能会限制其他分类群的进化潜力。我们在有毒蝾螈（粗皮渍螈）与其具有抗性的束带蛇捕食者（西部束带蛇）之间的捕食者 - 猎物相互作用中评估这些因素。通过对猎物中主要毒素河豚毒素（TTX）的抗性生物测定，我们研究了束带蛇属的表型进化。祖先性状状态的重建表明，与其他蛇类谱系相比，整个束带蛇属，可能一般来说游蛇科的蛇，对TTX的抗性略有提高。虽然这表明西部束带蛇确实倾向于进化出对TTX的抗性，但这也表明在同域分布的同类蛇中存在不表现出高TTX抗性水平的潜在可能性。我们还在一种未表现出该性状复杂水平的束带蛇物种中检测到了TTX抗性在家族水平上的显著差异。这一发现表明，其他分类群的进化响应不受遗传变异性的限制。在这个捕食者 - 猎物系统中，抗性的物种和种群差异似乎在很大程度上是由选择环境的变化决定的，而不是由预适应或限制因素决定的。
