The uniquely enlarged noses of male proboscis monkeys are prominent adornments, and a sexually selected male trait. A recent study showed significant correlations among nose, body, and testis sizes and clear associations between nose size and the number of females in a male’s harem. However, to date, the analyses of other common male traits, i.e., canines, are lacking. Whereas male nose size had a positive correlation with body size, we unexpectedly found a negative correlation between body and canine sizes. We explain this by an interaction between sexual and natural selection. Larger noses in males may interfere with the use of canines, thereby reducing their effectiveness as weapons. Additionally, longer canines are opposed by natural selection because the larger gape it imposes upon its bearer reduces foraging efficiency, particularly in folivores. This unique case of decoupling of body and canine size reveals that large canines carry an ecological cost.

雄性长鼻猴独特的大鼻子是突出的装饰品，也是性选择的雄性特征。最近的一项研究表明，鼻子、身体和睾丸大小之间存在显着相关性，并且鼻子大小与男性后宫中的女性数量之间存在明显关联。然而，迄今为止，缺乏对其他常见男性特征（即犬科动物）的分析。虽然雄性鼻子大小与体型呈正相关，但我们意外地发现体型和犬类大小之间呈负相关。我们通过性选择和自然选择之间的相互作用来解释这一点。雄性较大的鼻子可能会干扰犬类的使用，从而降低它们作为武器的有效性。此外，较长的犬齿会受到自然选择的反对，因为它对承载者施加的更大的张开会降低觅食效率，特别是在食叶动物中。这种身体和犬类大小脱钩的独特案例表明，大型犬类会带来生态成本。