Wormington Jillian D, Luttbeg Barney
Department of Integrative Biology, Oklahoma State University.
J Morphol. 2017 Dec;278(12):1619-1627. doi: 10.1002/jmor.20736. Epub 2017 Jul 29.
Contests between same-sex opponents over resources necessary for reproduction, as well interactions used to discern mate quality, often involve exaggerated traits wherein large individuals have disproportionately larger traits. This positive allometric scaling of weapons or signals facilitates communication during social interactions by accentuating body size differences between individuals. Typically, males carry these exaggerated traits, as males must compete over limited female gametes. However, in Nicrophorus beetles both males and females engage in physical contests over the vertebrate carcasses they need to provision and raise offspring. Male and female Nicrophorus beetles have extended clypeal membranes directly above their mandibles, which could serve as signals. We investigated the scaling relationships between clypeal membrane size and shape and body size for five species of North American burying beetle to determine whether clypeal membranes contain exaggerated body size information. We found that clypeal membranes for both sexes of all species scaled positively with body size (slope > 1). Three of the five species also displayed sexual dimorphism in aspects of clypeal membrane size and shape allometry despite lack of dimorphism in body size. In two dimorphic species, small male clypeal membranes were statistically indistinguishable from the female form. We conclude that colored clypeal membranes in Nicrophorus beetles do contain exaggerated body size information. Observed patterns of dimorphism suggest that males sometimes experience stronger selection on marking size and shape, which might be explained by life history differences among species.
同性对手之间围绕繁殖所需资源展开的竞争，以及用于辨别配偶质量的互动，通常涉及夸张的特征，即体型较大的个体具有不成比例的更大特征。武器或信号的这种正向异速生长缩放通过突出个体之间的体型差异，便于社交互动中的交流。通常情况下，雄性具有这些夸张的特征，因为雄性必须争夺有限的雌配子。然而，在埋葬虫中，雄性和雌性都会为了养育后代所需的脊椎动物尸体而进行身体对抗。雄性和雌性埋葬虫在下颚上方都有延伸的唇基膜，这可能起到信号的作用。我们研究了五种北美埋葬虫的唇基膜大小和形状与体型之间的缩放关系，以确定唇基膜是否包含夸张的体型信息。我们发现，所有物种的两性唇基膜大小都与体型呈正相关（斜率>1）。尽管体型没有二态性，但五个物种中有三个在唇基膜大小和形状的异速生长方面也表现出性二态性。在两个二态性物种中，小体型雄性的唇基膜在统计学上与雌性形态没有区别。我们得出结论，埋葬虫中带颜色的唇基膜确实包含夸张的体型信息。观察到的二态性模式表明，雄性有时在标记大小和形状方面受到更强的选择，这可能由物种间的生活史差异来解释。
