Székely T, Reynolds J D, Figuerola J
Centre for Behavioural Biology, School of Biological Sciences, University of Bristol, United Kingdom.
Evolution. 2000 Aug;54(4):1404-13. doi: 10.1111/j.0014-3820.2000.tb00572.x.
Charadrii (shorebirds, gulls, and alcids) have an unusual diversity in their sexual size dimorphism, ranging from monomorphism to either male-biased or female-biased dimorphism. We use comparative analyses to investigate whether this variation relates to sexual selection through competition for mates or natural selection through different use of resources by males and females. As predicted by sexual selection theory, we found that in taxa with socially polygynous mating systems, males were relatively larger than females compared with less polygynous species. Furthermore, evolution toward socially polyandrous mating systems was correlated with decreases in relative male size. These patterns depend on the kinds of courtship displays performed by males. In taxa with acrobatic flight displays, males are relatively smaller than in taxa in which courtship involves simple flights or displays from the ground. This result remains significant when the relationship with mating system is controlled statistically, thereby explaining the enigma of why males are often smaller than females in socially monogamous species. We did not find evidence that evolutionary changes in sexual dimorphism relate to niche division on the breeding grounds. In particular, biparental species did not have greater dimorphism in bill lengths than uniparental species, contrary to the hypothesis that selection for ecological divergence on the breeding grounds has been important as a general explanation for patterns of bill dimorphism. Taken together, these results strongly suggest that sexual selection has had a major influence on sexual size dimorphism in Charadrii, whereas divergence in the use of feeding resources while breeding was not supported by our analyses.
鸻形目鸟类（滨鸟、海鸥和海雀）在两性体型差异方面具有不同寻常的多样性，范围从单态性到雄性偏向或雌性偏向的二态性。我们使用比较分析来研究这种变异是否与通过争夺配偶的性选择或雄性和雌性对资源的不同利用的自然选择有关。正如性选择理论所预测的，我们发现，在具有社会多配偶交配系统的分类群中，与多配偶性较低的物种相比，雄性相对比雌性更大。此外，向社会一妻多夫交配系统的进化与雄性相对体型的减小相关。这些模式取决于雄性所进行的求偶展示类型。在具有杂技飞行展示的分类群中，雄性相对比求偶涉及简单飞行或地面展示的分类群中的雄性更小。当与交配系统的关系进行统计控制时，这一结果仍然显著，从而解释了在社会一夫一妻制物种中雄性为何往往比雌性小的谜团。我们没有发现证据表明两性异形的进化变化与繁殖地的生态位划分有关。特别是，双亲育雏的物种在喙长上的二态性并不比单亲育雏的物种更大，这与认为繁殖地生态分化选择作为喙二态性模式的一般解释很重要的假设相反。综上所述，这些结果有力地表明，性选择对鸻形目鸟类的两性体型差异产生了重大影响，而我们的分析不支持繁殖期间觅食资源利用的差异。
