公绿头鸭（Anas platyrhynchos，如上图）因其长而螺旋的生殖器闻名天下。

如今，科学家发现，它们还有其他一些值得炫耀的东西。将绿头鸭的精液与一种常见细菌——大肠杆菌混合在一起，研究人员注意到，这些鸭子的精液能够杀死细菌。

研究人员在4月12日的《生物学快报》网络版上报告说，那些喙更加华美的公鸭的精液具有最强的抗菌能力，所消灭的细菌是长着暗淡的喙的公鸭的3倍。

这些发现表明，母绿头鸭被色彩鲜艳的公鸭所吸引并非仅仅因为后者更加艳俗，还缘于它们在交配过程中仅会传播较少的细菌。

推荐原文出处：

Biol. Lett.  doi: 10.1098/rsbl.2011.0276

Sexual ornamentation reflects antibacterial activity of ejaculates in mallards

Melissah Rowe1,2,*, Gábor árpád Czirják3, Kevin J. McGraw1 and Mathieu Giraudeau1

Abstract

Bacteria present in ejaculates can impair sperm function and reduce male reproductive success. Thus, selection should favour the evolution of antimicrobial defences to limit the detrimental effects of sperm-associated bacteria. Additionally, current hypotheses suggest that ornamental traits may signal information about the infection status of an individual or the ability of an individual to resist bacterial-induced sperm damage. However, despite the evolutionary implications of ejaculate antimicrobials, and the putative importance of pathogens for the evolution of male ornamentation, tests of these hypotheses are lacking. We examined the antibacterial activity of semen from mallard ducks (Anas platyrhynchos) and tested whether the bactericidal capacity of semen was associated with bill coloration, a sexually selected trait. We show that mallard semen exhibits significant antibacterial activity, as measured by the in vitro capacity to kill Escherichia coli and Staphylococcus aureus. Furthermore, we demonstrate that males with more colourful bills have semen with superior bacterial-killing ability. These results suggest that females could use male phenotypic traits to avoid sexually transmitted pathogens and acquire partners whose sperm suffer less bacteria-induced damage.