School of Biological Sciences, University of Auckland, Auckland, New Zealand.
PLoS One. 2013 Nov 27;8(11):e82467. doi: 10.1371/journal.pone.0082467. eCollection 2013.
Sexual selection has driven the evolution of exaggerated traits among diverse animal taxa. The production of exaggerated traits can come at a cost to other traits through trade-offs when resources allocated to trait development are limited. Alternatively some traits can be selected for in parallel to support or compensate for the cost of bearing the exaggerated trait. Male giraffe weevils (Lasiorhynchus barbicornis) display an extremely elongated rostrum used as a weapon during contests for mates. Here we characterise the scaling relationship between rostrum and body size and show that males have a steep positive allometry, but that the slope is non-linear due to a relative reduction in rostrum length for the largest males, suggesting a limitation in resource allocation or a diminishing requirement for large males to invest increasingly into larger rostra. We also measured testes, wings, antennae, fore- and hind-tibia size and found no evidence of a trade-off between these traits and rostrum length when comparing phenotypic correlations. However, the relative length of wings, antennae, fore- and hind-tibia all increased with relative rostrum length suggesting these traits may be under correlational selection. Increased investment in wing and leg length is therefore likely to compensate for the costs of flying with, and wielding the exaggerated rostrum of larger male giraffe weevils. These results provide a first step in identifying the potential for trait compensation and trades-offs, but are phenotypic correlations only and should be interpreted with care in the absence of breeding experiments.
性选择驱动了不同动物类群中夸张特征的进化。当用于特征发育的资源有限时，产生夸张特征可能会通过权衡而对其他特征造成代价。或者，某些特征可以被选择并行发展，以支持或补偿承受夸张特征的代价。雄性长颈鹿象鼻虫（Lasiorhynchus barbicornis）展示出极度伸长的口吻，用于在争夺配偶的竞争中作为武器。在这里，我们描述了口吻和体型之间的比例关系，并表明雄性具有陡峭的正异速生长，但由于最大雄性的口吻长度相对减少，斜率是非线性的，这表明资源分配有限，或者大型雄性投入越来越多的资源来增大口吻的需求减少。我们还测量了睾丸、翅膀、触角、前和后胫骨的大小，在比较表型相关性时，没有发现这些特征与口吻长度之间存在权衡的证据。然而，翅膀、触角、前和后胫骨的相对长度都随着相对口吻长度的增加而增加，这表明这些特征可能受到相关选择的影响。因此，增加翅膀和腿部长度的投资可能会补偿较大雄性长颈鹿象鼻虫飞行和挥舞夸张口吻的成本。这些结果为识别特征补偿和权衡的潜力提供了第一步，但仅是表型相关性，在没有繁殖实验的情况下应谨慎解释。
