Colour polymorphism in the sea snake Emydocephalus annulatus

Evolutionary theory suggests that polymorphic traits can be maintained within a single population only under specific conditions, such as negative frequency-dependent selection or heterozygote advantage. Non-venomous turtle-headed sea snakes (Emydocephalus annulatus) living in shallow bays near Noumea in New Caledonia exhibit three colour morphs: black, black-and-white banded, and an intermediate (grey-banded) morph that darkens with age. We recorded morph frequencies during 18 consecutive years of surveys, and found that the numbers of recruits (neonates plus immigrants) belonging to each morph increased in years when that morph was unusually rare in the population, and decreased when that morph was unusually common. Thus, morph frequencies are maintained by negative frequency-dependent selection. We interpret the situation as Batesian mimicry of highly venomous sea snakes (Aipysurus, Hydrophis, Laticauda) that occur in the same bays, and range in colour from black-and-white banded to ...

进化论指出，多态性状仅能在特定条件下于单一种群中得以维持，例如负频率依赖选择（negative frequency-dependent selection）或杂合子优势（heterozygote advantage）。栖息于新喀里多尼亚努美阿附近浅海湾的无毒龟头海蛇（Emydocephalus annulatus）具有三种体色形态：纯黑色、黑白环纹型，以及一种随年龄加深的中间型（灰环纹型）。我们通过连续18年的野外调查记录了各体色形态的频率，结果显示：当某一形态在种群中占比异常偏低时，该形态的新生个体（幼蛇+迁入个体）数量会随之上升；而当该形态在种群中占比异常偏高时，其新生个体数量则会下降。由此，体色形态的频率由负频率依赖选择维持。我们将这一现象解读为对同海湾内分布的剧毒海蛇（艾基海蛇属Aipysurus、海蜂属Hydrophis、扁尾海蛇属Laticauda）的贝茨拟态（Batesian mimicry），这类剧毒海蛇的体色从黑白环纹型至……