Edward Grey Institute, Department of Zoology, University of Oxford, Oxford, UK.
J Evol Biol. 2011 Oct;24(10):2118-38. doi: 10.1111/j.1420-9101.2011.02345.x. Epub 2011 Jun 27.
The evolution of sexually monomorphic (i.e. mutual) ornamentation has attracted growing attention as a 'blind-spot' in evolutionary biology. The popular consensus is that female ornaments are subject to the same modes of sexual selection as males: intrasexual competition and mate choice. However, it remains unclear how these forces interact within and between sexes, or whether they fully capture selection on female traits. One possibility is that the 'armament-ornament' model - which proposes that traits used primarily in male-male contests are also co-opted by females as indicators of male quality - can be extended to explain signal evolution in both sexes. We examine this idea by testing the function of acoustic signals in two species of duetting antbirds. Behavioural observations and playback experiments suggest that male and female songs function primarily as armaments in competitive interactions. Removal experiments reveal that song is also a classic ornament used by unpaired males and females to advertise for mates. These results indicate that 'armament-ornament' processes may operate in reciprocal format, potentially explaining widespread mutual ornamentation in species with elevated intrasexual competition for resources. In addition, given that songs mediate competition between species outside the breeding season, our findings suggest that processes shaping monomorphic ornaments extend beyond the traditional definitions of sexual selection and are best understood in the broader framework of social selection.
性单态（即相互）装饰的进化作为进化生物学中的一个“盲点”，引起了越来越多的关注。人们普遍认为，雌性装饰物受到与雄性相同的性选择模式的影响：同性竞争和配偶选择。然而，这些力量如何在性别内部和性别之间相互作用，或者它们是否完全捕捉到对雌性特征的选择，仍不清楚。一种可能性是，“武器-装饰”模型——该模型提出，主要用于雄性间竞争的特征也被雌性用作雄性质量的指标——可以扩展到解释两性信号的进化。我们通过测试两种合唱蚁鸟的声学信号来检验这个想法。行为观察和回放实验表明，雄性和雌性的歌声主要在竞争互动中作为武器发挥作用。去除实验表明，歌声也是未配对的雄性和雌性用来求偶的经典装饰物。这些结果表明，“武器-装饰”过程可能以相互的方式运作，这可能解释了具有资源同性竞争加剧的物种中广泛存在的相互装饰。此外，鉴于歌曲在繁殖季节之外调节物种间的竞争，我们的研究结果表明，塑造单态装饰物的过程超出了性选择的传统定义，最好在更广泛的社会选择框架中理解。
