Storfer Andrew, Cross Jonra, Rush Victor, Caruso Joseph
Center for Ecology, Evolution and Behavior and T. H. Morgan School of Biological Sciences, University of Kentucky, Lexington, Kentucky, 40506-0225.
Evolution. 1999 Jun;53(3):889-898. doi: 10.1111/j.1558-5646.1999.tb05383.x.
Predation is an important selective force that influences animal color patterns. Some larval populations of the streamside salamander, Ambystoma barbouri, inhabit streams with fish predators. Other larval salamanders are found in shallow, ephemeral streams that are predator-free. Quantitative melanophore cell counts and estimates of percent body area pigmented indicated that larval coloration is strongly correlated with stream type. Larvae that coexist with fish tend to be lighter than larvae from streams that are Ashless and ephemeral. Two approaches demonstrated that lightly pigmented salamander larvae better match the common background in relatively permanent streams and are less conspicuous to fish than dark larvae. First, using a model based on the spectral sensitivity of the fish and reflectance properties of salamanders and natural stream backgrounds, we showed that light larvae are three times more cryptic than dark larvae on rocks. Second, lighter larvae had higher survival than darker salamanders on rocks in a predator- choice experiment. It is not clear why larvae in ephemeral streams are darker. Larvae in ephemeral streams should be active to feed and develop rapidly and reach sufficient size to metamorphose before seasonal drying. Several hypotheses may explain why larvae tend to be darker in ephemeral streams, such as increased thermoregulatory ability, better screening of ultraviolet radiation (in these shallower streams), or better background matching to terrestrial predators. Among populations where salamander larvae coexist with fish, there are differences in relative crypsis. Larvae from populations with fish and relatively high gene flow from ephemeral populations (where larvae are dark) tend to be darker (with more melanophores) and more conspicuous to predators than those from more genetically isolated populations, where larvae are lighter and more cryptic. These differences illustrate the role of gene flow as a constraint to adaptive evolution.
捕食是影响动物体色模式的一种重要选择力量。溪边蝾螈（Ambystoma barbouri）的一些幼虫种群栖息在有鱼类捕食者的溪流中。其他蝾螈幼虫则出现在没有捕食者的浅而短暂的溪流中。对黑素细胞数量的定量计数以及对身体色素沉着面积百分比的估计表明，幼虫的体色与溪流类型密切相关。与鱼类共存的幼虫往往比来自无鱼且短暂的溪流中的幼虫颜色更浅。两种方法表明，色素沉着较浅的蝾螈幼虫在相对永久性的溪流中更能与常见背景相匹配，并且比深色幼虫对鱼类来说更不显眼。首先，基于鱼类的光谱敏感性以及蝾螈和自然溪流背景的反射特性建立模型，我们发现浅色幼虫在岩石上的隐蔽性是深色幼虫的三倍。其次，在捕食者选择实验中，浅色幼虫在岩石上的存活率高于深色蝾螈。目前尚不清楚为什么短暂溪流中的幼虫颜色更深。短暂溪流中的幼虫应该活跃地觅食和快速发育，在季节性干涸之前达到足够的大小以完成变态。有几个假设可以解释为什么短暂溪流中的幼虫往往颜色更深，比如体温调节能力增强、更好地屏蔽紫外线（在这些较浅的溪流中），或者更好地与陆地捕食者的背景相匹配。在蝾螈幼虫与鱼类共存的种群中，相对隐蔽性存在差异。来自有鱼类且与短暂种群（幼虫颜色深）基因流动相对较高的种群的幼虫往往颜色更深（黑素细胞更多），对捕食者来说比来自基因隔离程度更高的种群的幼虫更显眼，后者的幼虫颜色更浅且更隐蔽。这些差异说明了基因流动作为适应性进化的一种限制因素所起的作用。
