Department of Biological Sciences, Macquarie University, Sydney, NSW, 2109, Australia.
Labex Corail & ISEA Université de la Nouvelle-Calédonie, BP R4, 98851, Nouméa cedex, New Caledonia.
Sci Rep. 2021 Oct 8;11(1):20026. doi: 10.1038/s41598-021-99113-2.
In snakes, divergence in head size between the sexes has been interpreted as an adaptation to intersexual niche divergence. By overcoming gape-limitation, a larger head enables snakes of one sex to ingest larger prey items. Under this hypothesis, we do not expect a species that consumes only tiny prey items to exhibit sex differences in relative head size, or to show empirical links between relative head size and fitness-relevant traits such as growth and fecundity. Our field studies on the sea snake Emydocephalus annulatus falsify these predictions. Although these snakes feed exclusively on fish eggs, the heads of female snakes are longer and wider than those of males at the same body length. Individuals with wider heads grew more rapidly, reproduced more often, and produced larger litters. Thus, head shape can affect fitness and can diverge between the sexes even without gape-limitation. Head size and shape may facilitate other aspects of feeding (such as the ability to scrape eggs off coral) and locomotion (hydrodynamics); and a smaller head may advantage the sex that is more mobile, and that obtains its prey in narrow crevices rather than in more exposed situations (i.e., males).
在蛇类中，两性之间头部大小的差异被解释为对两性生态位差异的适应。通过克服口裂限制，较大的头部使某个性别的蛇能够摄入更大的猎物。根据这一假设，我们不应期望一个只食用微小猎物的物种在相对头部大小上存在性别差异，或者在相对头部大小与与生长和繁殖力等与适应性相关的特征之间显示出经验联系。我们对环纹海蛇的实地研究推翻了这些预测。尽管这些蛇只以鱼卵为食，但在相同体长的情况下，雌性蛇的头部比雄性蛇的头部更长、更宽。头部更宽的个体生长得更快，繁殖得更频繁，并且产下的窝卵数更多。因此，头部形状可以影响适应性，即使没有口裂限制，也可以在两性之间产生差异。头部大小和形状可能有助于其他方面的进食（例如从珊瑚上刮取卵的能力）和运动（水动力）；较小的头部可能有利于更具活动性的性别，并且该性别在狭窄的缝隙中获得猎物，而不是在更暴露的环境中（即雄性）。
