Rummel A D, Sheehy E T, Schachner E R, Hedrick B P
Department of BioSciences, Rice University, Houston, TX 77005, USA.
Department of Ecology and Evolutionary Biology, Tulane University, New Orleans, LA 70118, USA.
Integr Org Biol. 2024 Jan 22;6(1):obae002. doi: 10.1093/iob/obae002. eCollection 2024.
Geometric morphometrics has had a profound impact on our understanding of morphological evolution. However, factors such as sample size and the views and elements selected for two-dimensional geometric morphometric (2DGM) analyses, which are often dictated by specimen availability and time rather than study design, may affect the outcomes of those analyses. Leveraging large intraspecific sample sizes ( > 70) for two bat species, and , we evaluate the impact of sample size on calculations of mean shape, shape variance, and centroid size. Additionally, we assessed the concordance of multiple skull 2D views with one another and characterized morphological variation in skull shape in and , as well as a closely related species, . Given that is a morphologically cryptic species with , we assessed whether differences in skull shape and in 2DGM approach would allow species discrimination. We found that reducing sample size impacted mean shape and increased shape variance, that shape differences were not consistent across views or skull elements, and that trends shown by the views and elements were not all strongly associated with one another. Further, we found that and were statistically different in shape using 2DGM in all views and elements. These results underscore the importance of selecting appropriate sample sizes, 2D views, and elements based on the hypothesis being tested. While there is likely not a generalizable sample size or 2D view that can be employed given the wide variety of research questions and systems evaluated using 2DGM, a generalizable solution to issues with 2DGM presented here is to run preliminary analyses using multiple views, elements, and sample sizes, thus ensuring robust conclusions.
几何形态测量学对我们理解形态演化产生了深远影响。然而，诸如样本大小以及为二维几何形态测量（2DGM）分析所选的视图和元素等因素，往往由标本可用性和时间而非研究设计决定，可能会影响这些分析的结果。利用两种蝙蝠物种（大足鼠耳蝠和普氏蹄蝠）的大量种内样本（>70），我们评估了样本大小对平均形状、形状方差和质心大小计算的影响。此外，我们评估了多个颅骨二维视图之间的一致性，并描述了大足鼠耳蝠和普氏蹄蝠以及一个近缘物种（中华鼠耳蝠）颅骨形状的形态变异。鉴于大足鼠耳蝠是一种形态隐秘的物种，与普氏蹄蝠相似，我们评估了颅骨形状差异和二维几何形态测量方法是否能实现物种区分。我们发现，减少样本大小会影响平均形状并增加形状方差，形状差异在不同视图或颅骨元素之间并不一致，且各视图和元素所显示的趋势并非都紧密相关。此外，我们发现使用二维几何形态测量法在所有视图和元素上，大足鼠耳蝠和普氏蹄蝠在形状上存在统计学差异。这些结果强调了根据所测试的假设选择合适的样本大小、二维视图和元素的重要性。鉴于使用二维几何形态测量法评估的研究问题和系统种类繁多，可能不存在可普遍适用的样本大小或二维视图，但此处针对二维几何形态测量法问题提出的一个普遍适用的解决方案是使用多个视图、元素和样本大小进行初步分析，从而确保得出可靠的结论。
