Museum and Institute of Zoology, Polish Academy of Sciences, Wilcza 64, 00-679, Warszawa, Poland.
Kanagawa Prefectural Museum of Natural History, 499 Iryuda, Odawara, Kanagawa, 250-0031, Japan.
Sci Rep. 2019 Mar 12;9(1):4184. doi: 10.1038/s41598-019-40956-1.
Morphological integration and modularity are important for understanding phenotypic evolution because they constrain variation subjected to selection and enable independent evolution of functional and developmental units. We report dental integration and modularity in representative otariid (Eumetopias jubatus, Callorhinus ursinus) and phocid (Phoca largha, Histriophoca fasciata) species of Pinnipedia. This is the first study of integration and modularity in a secondarily simplified dentition with simple occlusion. Integration was stronger in both otariid species than in either phocid species and related positively to dental occlusion and negatively to both modularity and tooth-size variability across all the species. The canines and third upper incisor were most strongly integrated, comprising a module that likely serves as occlusal guides for the postcanines. There was no or weak modularity among tooth classes. The reported integration is stronger than or similar to that in mammals with complex dentition and refined occlusion. We hypothesise that this strong integration is driven by dental occlusion, and that it is enabled by reduction of modularity that constrains overall integration in complex dentitions. We propose that modularity was reduced in pinnipeds during the transition to aquatic life in association with the origin of pierce-feeding and loss of mastication caused by underwater feeding.
形态整合和模块性对于理解表型进化很重要，因为它们限制了受选择影响的变异，并使功能和发育单元能够独立进化。我们报告了代表性鳍足类（真海豹属的 Eumetopias jubatus、港海豹属的 Callorhinus ursinus）和海豹类（环斑海豹属的 Phoca largha、髯海豹属的 Histriophoca fasciata）的牙齿整合和模块性。这是对具有简单咬合的次生简化齿系进行整合和模块性研究的首次报告。在两个真海豹物种中，整合度均强于任何一个海豹物种，并且与牙齿的咬合正相关，与所有物种的模块性和牙齿大小变异性负相关。犬齿和第三上切牙的整合度最强，构成了一个可能作为后牙咬合向导的模块。牙齿类之间没有或只有弱的模块性。报告的整合度强于或类似于具有复杂齿系和精细咬合的哺乳动物。我们假设这种强烈的整合是由牙齿的咬合驱动的，并且是由模块性的减少所允许的，这种减少限制了复杂齿系的整体整合。我们提出，在向水生生活过渡期间，模块化程度降低与刺穿式进食的起源以及水下进食导致的咀嚼丧失有关。
