Schmidt Alejandro Raúl, Gariboldi María Constanza, Cortasa Santiago Andrés, Proietto Sofía, Corso María Clara, Inserra Pablo Ignacio Felipe, Jaime Vanina Soledad, Halperin Julia, Vitullo Alfredo Daniel, Dorfman Verónica Berta
Centro de Estudios Biomédicos Básicos, Aplicados y Desarrollo (CEBBAD), Universidad Maimónides, Buenos Aires, Argentina.
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina.
Brain Behav Evol. 2020;95(6):318-329. doi: 10.1159/000515638. Epub 2021 Apr 28.
Depending on the presence or absence of sulci and convolutions, the brains of mammals are classified as gyrencephalic or lissencephalic. We analyzed the encephalic anatomy of the hystricomorph rodent Lagostomus maximus in comparison with other evolutionarily related species. The encephalization quotient (EQ), gyrencephaly index (GI), and minimum cortical thickness (MCT) were calculated for the plains vizcacha as well as for other myomorph and hystricomorph rodents. The vizcacha showed a gyrencephalic brain with a sagittal longitudinal fissure that divides both hemispheres, and 3 pairs of sulci with bilateral symmetry; that is, lateral-rostral, intraparietal, and transverse sulci. The EQ had one of the lowest values among Hystricomorpha, while GI was one of the highest. Besides, the MCT was close to the mean value for the suborder. The comparison of EQ, GI, and MCT values between hystricomorph and myomorph species allowed the detection of significant variations. Both EQ and GI showed a significant increase in Hystricomorpha compared to Myomorpha, whereas a Pearson's analysis between EQ and GI depicted an inverse correlation pattern for Hystricomorpha. Furthermore, the ratio between MCT and GI also showed a negative correlation for Hystricomorpha and Myomorpha. Our phylogenetic analyses showed that Hystricomorpha and Myomorpha do not differ in their allometric patterning between the brain and body mass, GI and brain mass, and MCT and GI. In conclusion, gyrencephalic neuroanatomy in the vizcacha could have developed from the balance between the brain size, the presence of invaginations, and the cortical thickness, which resulted in a mixed encephalization strategy for the species. Gyrencephaly in the vizcacha, as well as in other Hystricomorpha, advocates in favor of the proposal that in the more recently evolved Myomorpha lissencephaly would have arisen from a phenotype reversal process.
根据脑沟和脑回的有无，哺乳动物的大脑可分为脑回脑和光滑脑。我们分析了豚鼠型啮齿动物大毛丝鼠的脑部解剖结构，并与其他进化相关物种进行了比较。计算了草原毛丝鼠以及其他鼠型亚目和豚鼠型亚目啮齿动物的脑化商（EQ）、脑回指数（GI）和最小皮质厚度（MCT）。毛丝鼠表现出脑回脑，有一条将两个半球分开的矢状纵裂，以及3对双侧对称的脑沟；即外侧吻侧沟、顶内沟和横沟。EQ在豚鼠型亚目中是最低值之一，而GI是最高值之一。此外，MCT接近该亚目的平均值。比较豚鼠型亚目和鼠型亚目物种的EQ、GI和MCT值，可以发现显著差异。与鼠型亚目相比，豚鼠型亚目的EQ和GI均显著增加，而豚鼠型亚目的EQ和GI之间的皮尔逊分析显示出负相关模式。此外，MCT与GI的比值在豚鼠型亚目和鼠型亚目中也呈负相关。我们的系统发育分析表明，豚鼠型亚目和鼠型亚目在脑与体重、GI与脑重以及MCT与GI之间的异速生长模式上没有差异。总之，毛丝鼠的脑回神经解剖结构可能是由脑大小、脑沟的存在和皮质厚度之间的平衡发展而来的，这导致了该物种的混合脑化策略。毛丝鼠以及其他豚鼠型亚目的脑回支持了这样一种观点，即在最近进化的鼠型亚目中，光滑脑可能是由表型逆转过程产生的。
