據(jù)美國《科學(xué)》雜志在線新聞報(bào)道,，有很多方法能讓對手和伴侶留下深刻印象，雄獅會長出濃密而巨大的鬃毛,，孔雀會展示它們美麗的羽毛,，雄鹿則會晃動頭上粗大的鹿角。而非洲大羚羊的招數(shù)可謂更加巧妙——它們會像人類捏響指關(guān)節(jié)一樣讓膝蓋發(fā)出“啪啪”的響聲,。研究人員在11月出版的《BMC生物學(xué)》雜志上報(bào)告了這一發(fā)現(xiàn),。這種聲音在幾百米之外都能聽到，它取決于羚羊的大小和力氣,。羚羊個(gè)頭越大,，“啪啪”聲也就越響——恐怕沒有哪個(gè)家伙愿意和這樣的對手過不去。（生物谷Bioon.com）
生物谷推薦原始出處：
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.
