School of Natural Sciences, Macquarie University, Sydney, NSW, 2109, Australia.
School of Life and Environmental Sciences, University of Sydney, Sydney, NSW, 2006, Australia.
Sci Rep. 2022 Mar 18;12(1):4680. doi: 10.1038/s41598-022-08639-6.
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 grey-banded. Consistent with the idea that mimicry may protect snakes from attack by large fish and sea eagles, behavioural studies have shown that smaller fish species in these bays flee from banded snakes but attack black individuals. As predicted by theory, mimetic (banded) morphs are less common than the cryptically-coloured melanic morph.
进化理论表明，只有在特定条件下，单一群体中才能维持多态性特征，例如负频率依赖选择或杂合优势。生活在新喀里多尼亚努美阿附近浅湾的无毒龟首海蛇（Emydocephalus annulatus）表现出三种颜色形态：黑色、黑白相间带纹的和中间（灰色带纹的）形态，随着年龄的增长而变暗。我们在连续 18 年的调查中记录了形态频率，发现属于每种形态的新兵（新生儿加移民）数量在该形态在种群中异常罕见的年份增加，而在该形态异常常见的年份减少。因此，形态频率是通过负频率依赖选择维持的。我们将这种情况解释为与生活在同一海湾、颜色从黑白相间带纹到灰色带纹变化的剧毒海蛇（Aipysurus、Hydrophis、Laticauda）的贝氏拟态，贝氏拟态可以保护蛇类免受大鱼和海鹰的攻击。与拟态可能保护蛇类免受攻击的观点一致，行为研究表明，这些海湾中的小鱼种会逃避带纹蛇类，但会攻击黑色个体。正如理论所预测的那样，拟态（带纹）形态比隐蔽色的黑素形态更为罕见。
