University of Belgrade, Faculty of Biology, Studentski Trg 16, 11000, Belgrade, Serbia.
Zoology (Jena). 2021 Dec;149:125970. doi: 10.1016/j.zool.2021.125970. Epub 2021 Oct 5.
Covariation of multiple morphological traits and modularity have been widely studied in the field of evolutionary developmental biology. Subunits of a morphological structure can evolve separately from each other in a modular fashion. The aims of our study therefore were: i) to test the hypothesis of modularity in the dorsal part of the head capsule and the gnathochilarium separately during late postembryogenesis in the julidan millipede Megaphyllum unilineatum (C. L. Koch, 1838) using geometric morphometrics; and ii) to investigate the influence of allometry on overall morphological integration in the dorsal part of the head capsule and the gnathochilarium in the mentioned species. Individuals from different ontogenetic stadia (stadium VI - stadium XI) were included in the analyses. Significant influence of fluctuating asymmetry on the dorsal part of the head capsule shape was detected by Procrustes ANOVA. Regressions were significant for the symmetric component of both analysed morphological traits, while non-significant regression was detected for the asymmetric component of the head capsule's dorsal part. Hypotheses of modularity for the dorsal part of the head capsule and the gnathochilarium are rejected because our results indicate that a small proportion of alternate partitions has higher covariation between subsets of structure than between the hypothesized modules. Contrary to our expectations, results of the present study show that allometry does not increase the level of morphological integration in the dorsal part of the head capsule and the gnathochilarium in M. unilineatum. Based on the obtained results, we conclude that the dorsal part of the head capsule and the gnathochilarium are not composed of independent modules and that in the case of the capsule's dorsal part, developmental processes affect morphological integration in different ways at different levels of shape variation.
在进化发育生物学领域，形态特征的协同变化和模块性已经得到了广泛的研究。形态结构的亚单位可以以模块的方式彼此独立地进化。因此，我们的研究目的是：i）使用几何形态测量学分别测试在 Julidan 倍足纲动物 Megaphyllum unilineatum（C. L. Koch，1838）的头部背面和颚足板在后胚胎发生晚期的模块性假设；ii）研究在所述物种中，头部背面和颚足板的整体形态整合受同形性影响的情况。分析中包含了来自不同个体发育阶段（阶段 VI - 阶段 XI）的个体。Procrustes ANOVA 检测到形态不对称性对头部背面形状的显著影响。两个分析形态特征的对称成分的回归是显著的，而头部背面的不对称成分的回归是不显著的。头部背面和颚足板的模块性假设被拒绝，因为我们的结果表明，一小部分交替分区的子集之间的相关性高于假设的模块之间的相关性。与我们的预期相反，本研究的结果表明，同形性不会增加 M. unilineatum 头部背面和颚足板的形态整合水平。基于获得的结果，我们得出结论，头部背面和颚足板不是由独立的模块组成的，并且在头部背面的情况下，发育过程以不同的方式在不同的形状变化水平上影响形态整合。
