据美国《科学》杂志在线新闻报道，有很多方法能让对手和伴侣留下深刻印象，雄狮会长出浓密而巨大的鬃毛，孔雀会展示它们美丽的羽毛，雄鹿则会晃动头上粗大的鹿角。而非洲大羚羊的招数可谓更加巧妙——它们会像人类捏响指关节一样让膝盖发出“啪啪”的响声。研究人员在11月出版的《BMC生物学》杂志上报告了这一发现。这种声音在几百米之外都能听到，它取决于羚羊的大小和力气。羚羊个头越大，“啪啪”声也就越响——恐怕没有哪个家伙愿意和这样的对手过不去。（生物谷Bioon.com）
生物谷推荐原始出处：
BMC Biology，doi:10.1186/1741-7007-6-47，Jakob Bro-J?rgensen，Torben Dabelsteen
Knee-clicks and visual traits indicate fighting ability in eland antelopes: multiple messages and back-up signals
Jakob Bro-J?rgensen and Torben Dabelsteen
Background
Given costs of signalling, why do males often advertise their fighting ability to rivals using several signals rather than just one? Multiple signalling theories have developed largely in studies of sexual signals, and less is known about their applicability to intrasexual communication. We here investigate the evolutionary basis for the intricate agonistic signalling system in eland antelopes, paying particular attention to the evolutionary phenomenon of loud knee-clicking.
Results
A principal components analysis separated seven male traits into three groups. The dominant frequency of the knee-clicking sound honestly indicated body size, a main determinant of fighting ability. In contrast, the dewlap size increased with estimated age rather than body size, suggesting that, by magnifying the silhouette of older bulls disproportionately, the dewlap acts as an indicator of age-related traits such as fighting experience. Facemask darkness, frontal hairbrush size and body greyness aligned with a third underlying variable, presumed to be androgen-related aggression. A longitudinal study provided independent support of these findings.
Conclusion
The results show that the multiple agonistic signals in eland reflect three separate components of fighting ability: (1) body size, (2) age, and (3) presumably androgen-related aggression, which is reflected in three backup-signals. The study highlights how complex agonistic signalling systems can evolve through the simultaneous action of several selective forces, each of which favours multiple signals. Specifically, loud knee-clicking is discovered as an honest signal of body size, providing an exceptional example of the potential for non-vocal acoustic communication in mammals.
