蜣螂后胸叉骨的几何形态学分析及其适应进化研究

Geometric morphometrics evaluation and adaptive evolution study of scarabaeine metendosternites

【目的】甲虫的后胸叉骨是基部位于后足基节关节处,端部游离在胸腔内的几丁质构成的内骨骼。后胸叉骨作为胸腹部运动肌肉的联结点,在甲虫运动过程中扮演了重要角色,同时也承载了分类和系统发育信息。蜣螂根据其习性可分为滚粪球和直接掘洞两类行为类型。通过传统的比较形态学方法,我们无法得知滚粪球或直接掘洞的行为对后胸叉骨形态的影响。本研究旨在利用定量的几何形态学方法探究蜣螂后胸叉骨形态对不同行为选择压力的响应关系。【方法】对76种蜣螂后胸叉骨的形态多样性进行二维几何形态学定量评估;利用显微CT和计算机三维重建方法,对直接掘洞类蜣螂和滚粪球类蜣螂的代表种西班牙粪蜣螂Copris hispanus和忠诚泽蜣螂Kheper devotus的后胸叉骨进行三维重建,用于比较两者的三维形态差异。【结果】经过几何形态学分析可知,两类蜣螂后胸叉骨背面观和侧面观的马氏距离和普氏距离的p值均低于0.0001,表明两类蜣螂的后胸叉骨的形态存在显著性差异;通过对C.hispanus和K.devotus后胸叉骨3D模型的比较发现,两类蜣螂后胸叉骨的最大区别在于后胸叉骨的端半部(叉臂和中突)。前者的叉臂细长,中突面积大,背立脊呈窄条状且不发达;后者的叉臂宽扁,叉臂基半部十分宽大,中突面积小,背立脊呈鳍状且十分发达。【结论】滚粪球或直接掘洞的行为会对蜣螂后胸叉骨的形态有显著性影响,蜣螂后胸叉骨形态与滚粪球和直接掘洞两种行为的选择压力显著相关,这与后胸叉骨所附着的胸部肌肉参与相关运动关系密切。本研究为探索昆虫形态与功能关系提供了一个有益范例。

【Aim】The metendosternite of beetle is a kind of endoskeleton that is made of chitin. The base of metendosternite is located on hind coxae with free end in the thorax. As the junction point of muscles in chest movement,metendosternite not only plays an important role in the movement of beetles,but also loads the information of classification and system development. According to the habits,dung beetles have two behavior types： tunnelling and rolling. We can not understand the influences of the two behavior types on the morphology of metendosternites through traditional comparative morphology. This study aims to use quantitative geometric morphology method to explore the relationship between behavior type and the response of metendosternites of dung beetles to selective pressure. 【Methods 】 The morphological diversity of 76 species of dung beetles was quantitatively analyzed by two-dimension geometry morphology quantitative analysis. The 3D model of the two representative species of the dung beetles,Copris hispanus and Kheper devotus,was reconstructed using Micro CT and the three-dimension reconstruction,and the morphological differences of the metendosternites between both were compared.【Results】The p-values of the Mahalanobis distance and Procrustes distance of metendosternite of the two representative species were all less than 0. 0001 through the geometric morphology analysis,indicating that the two dung beetles have significant differences in morphology of the metendosternites. The largest differences are the front section of metendosternites（ furcal arm and median process） through the comparison of the 3D model of the two dung beetles. The furcal arms（ F. A.） of C. hispanus are long and thin,the median process（ M. P.） is wide,and the dorsal longitudinal flange（ D. L. F.） is narrow and underdeveloped. The furcal arms of K. devotus are flat and broad,the basal parts of the furcal arms are very wide,the median process is small,and the dorsal longitudinal flange is very derdeveloped and looks like a fins. 【Conclusion】The behavior type of tunnelling or rolling has a significant impact on the morphology of the metendosternites of dung beetles. The morphology of metendosternites has significant correlation with selective pressure of the two behavior types,and this morphology has a close relation with the movement of the muscles that adhere to the metendosternites involved in. This study provides a good example to explore the relationship between morphology and function in insects.