Fox Gerad A, Cooper Allen M, Hayes William K
Department of Earth and Biological Sciences, School of Medicine, Loma Linda University, Loma Linda, California, United States of America.
PLoS One. 2015 Mar 20;10(3):e0120392. doi: 10.1371/journal.pone.0120392. eCollection 2015.
Sexual differences in morphology, ranging from subtle to extravagant, occur commonly in many animal species. These differences can encompass overall body size (sexual size dimorphism, SSD) or the size and/or shape of specific body parts (sexual body component dimorphism, SBCD). Interacting forces of natural and sexual selection shape much of the expression of dimorphism we see, though non-adaptive processes may be involved. Differential scaling of individual features can result when selection favors either exaggerated (positive allometry) or reduced (negative allometry) size during growth. Studies of sexual dimorphism and character scaling rely on multivariate models that ideally use an unbiased reference character as an overall measure of body size. We explored several candidate reference characters in a cryptically dimorphic taxon, Hadrurus arizonensis. In this scorpion, essentially every body component among the 16 we examined could be interpreted as dimorphic, but identification of SSD and SBCD depended on which character was used as the reference (prosoma length, prosoma area, total length, principal component 1, or metasoma segment 1 width). Of these characters, discriminant function analysis suggested that metasoma segment 1 width was the most appropriate. The pattern of dimorphism in H. arizonensis mirrored that seen in other more obviously dimorphic scorpions, with static allometry trending towards isometry in most characters. Our findings are consistent with the conclusions of others that fecundity selection likely favors a larger prosoma in female scorpions, whereas sexual selection may favor other body parts being larger in males, especially the metasoma, pectines, and possibly the chela. For this scorpion and probably most other organisms, the choice of reference character profoundly affects interpretations of SSD, SBCD, and allometry. Thus, researchers need to broaden their consideration of an appropriate reference and exercise caution in interpreting findings. We highly recommend use of discriminant function analysis to identify the least-biased reference character.
形态学上的性别差异，从细微到显著，在许多动物物种中普遍存在。这些差异可能包括整体体型大小（两性体型差异，SSD）或特定身体部位的大小和/或形状（两性身体组成部分差异，SBCD）。自然选择和性选择的相互作用塑造了我们所看到的许多二态性表达，不过可能也涉及非适应性过程。当选择在生长过程中有利于夸张（正向异速生长）或缩小（负向异速生长）的大小时，个体特征的差异缩放就可能产生。对两性异形和性状缩放的研究依赖于多变量模型，理想情况下，这些模型使用无偏参考性状作为体型大小的总体衡量标准。我们在一个隐性二态分类群——亚利桑那肥尾蝎中探索了几个候选参考性状。在这种蝎子中，我们检查的16个身体组成部分中的几乎每一个都可以被解释为二态性的，但SSD和SBCD的识别取决于用作参考的性状（前体长度、前体面积、全长、主成分1或后体第1节宽度）。在这些性状中，判别函数分析表明后体第1节宽度是最合适的。亚利桑那肥尾蝎的二态性模式与其他更明显二态性的蝎子中所见的模式相似，大多数性状的静态异速生长趋向于等速生长。我们的研究结果与其他人的结论一致，即繁殖力选择可能有利于雌性蝎子拥有更大的前体，而性选择可能有利于雄性蝎子的其他身体部位更大，尤其是后体、栉板，可能还有螯。对于这种蝎子以及可能大多数其他生物来说，参考性状的选择深刻影响着对SSD、SBCD和异速生长的解释。因此，研究人员需要拓宽对合适参考的考虑范围，并在解释研究结果时谨慎行事。我们强烈建议使用判别函数分析来识别偏差最小的参考性状。
