Background High altitude insects are an ecologically specialized group and possess a suite of adaptions which allow persistence in the inhospitable conditions often associated with mountain tops. Changes in body coloration and reductions or increases in body size are thought to be examples of such adaptions. Melanic individuals, or individuals containing high levels of eumelanin, possess several traits which increase resistance to ultraviolet radiation and desiccation, while aiding thermoregulation. Trait variation is often observed in dung beetles and is associated with dimorphism and sexual selection. In this study, we identified trait changes which occur across an altitudinal gradient by measuring morphological color and body size traits in a montane insect. Methods Using standard digital photography and Image J, we examined individuals of Afromontane dung beetle Onthophagus proteus. Individuals were classified according to sex and color morph to identify intrasexual variance. Nine morphometric traits were measured per beetle to identify patterns of morphology across discrete 500 m altitude segments. Results The results of this study provide one of the first descriptions of trait changes associated with elevation in an African dung beetle. We suggest that color polymorphism in Onthophagus proteus might be at least partly driven by environmental factors as there is significantly increased melanism with increasing elevation and significant differences in color hues between altitude bands. We also suggest changes in horn length are density dependent, as we observed an increase in cephalic horn length at high elevations where O. proteus is the most abundant species.

中文翻译：

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粪甲虫 Onthophagus proteus 沿海拔梯度的表型可塑性证据

背景高海拔昆虫是一个生态特化的群体，具有一系列适应能力，可以在通常与山顶相关的恶劣条件下持续存在。身体颜色的变化和体型的缩小或增加被认为是这种适应的例子。黑色个体，或含有高水平真黑色素的个体，具有增加对紫外线辐射和干燥的抵抗力，同时有助于体温调节的几个特征。在粪甲虫中经常观察到性状变异，并且与二态性和性选择有关。在这项研究中，我们通过测量山地昆虫的形态颜色和体型特征，确定了在海拔梯度上发生的性状变化。方法 使用标准数码摄影和 Image J，我们检查了 Afromontane 粪甲虫 Onthophagus proteus 的个体。根据性别和颜色变形对个体进行分类，以识别性内差异。每只甲虫测量了九种形态特征，以识别离散的 500 m 海拔段的形态模式。结果 本研究的结果首次描述了与非洲粪甲虫海拔高度相关的性状变化。我们认为 Onthophagus proteus 的颜色多态性可能至少部分是由环境因素驱动的，因为随着海拔的增加，黑色素显着增加，并且海拔带之间的色调存在显着差异。我们还建议角长度的变化取决于密度，因为我们观察到在高海拔地区头角长度增加，其中 O.