Talloen W, Van Dyck H, Lens L
Laboratory of Animal Ecology, Department of Biology, University of Antwerp, 2610 Wilrijk, Belgium.
Evolution. 2004 Feb;58(2):360-6. doi: 10.1111/j.0014-3820.2004.tb01651.x.
Evolutionary studies typically focus on adaptations to particular environmental conditions, thereby often ignoring the role of possible constraints. Here we focus on the case of variation in dorsal wing melanization in a satyrine butterfly Pararge aegeria. Because melanin is a complex polymer, its synthesis may be constrained if ambient conditions limit the resource budget. This hypothesis was tested by comparing melanization among butterflies that fed as larvae on host grasses experiencing different drought-stress treatments. Treatment differences were validated both at the level of the host plant (nitrogen, carbonate, and water content) and of the butterfly (life-history traits: survival, development time, and size at maturity). Melanization rate was measured as average gray value of the basal dorsal wing area. This area, close to the thorax, is known to be functionally significant for basking in order to thermoregulate. Individuals reared on drought-stressed host plants developed paler wings, and development of darker individuals was slower and less stable as estimated by their level of fluctuating asymmetry. These results provide evidence that melanin is indeed costly to synthesize, and that differences in environmental quality can induce phenotypic variation in wing melanization. Therefore, studies dealing with spatial and/or temporal patterns of variation in wing melanization should not focus on adaptive explanations alone, but rather on a cost-benefit balance under particular sets of environmental conditions.
进化研究通常聚焦于对特定环境条件的适应，因此常常忽略了可能存在的限制因素的作用。在此，我们聚焦于一种眼蝶科蝴蝶——绿眼蛱蝶（Pararge aegeria）翅背黑化的变异情况。由于黑色素是一种复杂的聚合物，如果环境条件限制了资源预算，其合成可能会受到限制。通过比较以经历不同干旱胁迫处理的寄主草为食的幼虫发育而成的蝴蝶之间的黑化情况，对这一假设进行了检验。在寄主植物层面（氮、碳酸盐和含水量）以及蝴蝶层面（生活史特征：存活率、发育时间和成熟时的大小）均验证了处理差异。黑化率通过翅背基部区域的平均灰度值来衡量。这个靠近胸部的区域，已知在为了体温调节而晒太阳时具有重要功能。在干旱胁迫的寄主植物上饲养的个体翅膀颜色较浅，而且根据其波动不对称程度估计，颜色较深个体的发育较慢且不太稳定。这些结果提供了证据，表明黑色素的合成确实成本高昂，并且环境质量的差异会导致翅背黑化的表型变异。因此，研究翅背黑化变异的空间和/或时间模式时，不应仅关注适应性解释，而应关注特定环境条件下的成本效益平衡。
