It is postulated that melanism in ectotherms is adaptive by enhancing thermoregulation, subsequent resource acquisition, and growth. Such effects may differ between the sexes as a result of the differential costs of self-maintenance and reproduction, but empirical support for the sex-specific consequences of melanism remains inconsistent. We studied the effects of melanism on body size and sex ratio in a population of the European grass snake (Natrix natrix) in SE Poland and also carried out a systematic review of the literature on the consequences of melanism in terrestrial snakes. Melanistic grass snakes of both sexes appeared to be smaller than the typical phenotype, which indicates higher predation pressure and minimal thermal benefits for black individuals. A female-biased sex ratio was observed in the typical phenotype, but not in melanistic snakes, suggesting that the costs for females and/or benefits for males are higher in melanistic individuals. In conjunction with earlier studies, our data indicate that the consequences of melanism may be related to the reproductive mode of species. In viviparous species, melanism tends to improve growth and/or body size and is more frequent in females, whereas the opposite holds for oviparous snakes. Further studies on melanism should examine a wider array of species with different reproductive strategies and traits beyond the usual thermal benefits.

中文翻译：

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蛇的黑色素，体型和性别比-草蛇（Natrix natrix）和合成的新数据。

据推测，在等温线中的黑素病通过增强温度调节，随后的资源获取和生长而具有适应性。由于自我维持和生殖成本的差异，男女之间的这种影响可能有所不同，但对黑素病针对性别的特定后果的经验支持仍然不一致。我们研究了黑变病对欧洲草蛇（Natrix natrix）种群的大小和性别比的影响）在波兰东南部（SE Poland），并且对黑化病对陆地蛇的后果进行了文献综述。雌雄同体的黑色草蛇似乎比典型的表型要小，这表明捕食压力更高，对黑人个体的热效益却最小。在典型的表型中观察到女性偏向的性别比，而在黑色的蛇中则没有，这表明黑色素体个体中女性的成本和/或男性的收益较高。结合早期研究，我们的数据表明，忧郁症的后果可能与物种的繁殖方式有关。在胎生动物中，黑色素症倾向于改善生长和/或体型，并且在雌性中更为常见，而卵生蛇则相反。