Throughout an animal’s life, species may occupy different environments and exhibit distinct life stages, known as ontogenetic shifts. The life histories of most sharks (class: Chondrichthyes) are characterized by these ontogenetic shifts, which can be defined by changes in habitat and diet as well as behavioral changes at the onset of sexual maturity. In addition, fishes experience indeterminate growth, whereby the brain and body grow throughout the organism’s life. Despite a presupposed lifelong neurogenesis in sharks, very little work has been done on ontogenetic changes in the brain, which may be informative about functional shifts in sensory and behavioral specializations. This study quantified changes in brain-body scaling and the scaling of six major brain regions (olfactory bulbs, telencephalon, diencephalon, optic tectum, cerebellum, and medulla oblongata) throughout ontogeny in the Atlantic sharpnose shark, Rhizoprio­nodon terraenovae. As documented in other fishes, brain size increased significantly with body mass throughout ontogeny in this species, with the steepest period of growth in early life. The telencephalon, diencephalon, optic tectum, and medulla oblongata scaled with negative allometry against the rest of the brain throughout ontogeny. However, notably, the olfactory bulbs and cerebellum scaled hyperallometrically to the rest of the brain, whereby these structures enlarged disproportionately as this species matured. Changes in the relative size of the olfactory bulbs throughout ontogeny may reflect an increased reliance on olfaction at later life history stages in R. terraenovae, while changes in the relative size of the cerebellum throughout ontogeny may be indicative of the ability to capture faster prey or an increase in migratory nature as this species moves to offshore habitats, associated with the onset of sexual maturity.
Brain Behav Evol

中文翻译：

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大西洋尖鼻鲨脑大小和脑组织的个体发生变化，Rhizoprinodon terraenovae

在动物的整个生命周期中，物种可能占据不同的环境并表现出不同的生命阶段，称为个体发生转变。大多数鲨鱼（类：软骨鱼类）的生活史以这些个体发生变化为特征，这可以通过栖息地和饮食的变化以及性成熟开始时的行为变化来定义。此外，鱼类经历了不确定的生长，大脑和身体在整个生物体的一生中都在生长。尽管预先假定鲨鱼的终生神经发生，但关于大脑个体发生变化的研究很少，这可能对感官和行为特化的功能变化提供信息。这项研究量化了脑体缩放和六个主要大脑区域（嗅球、端脑、间脑、视顶盖、小脑、Rhizoprionodon terraenovae。正如在其他鱼类中所记录的那样，在该物种的整个个体发育过程中，大脑大小随着体重显着增加，生命早期的增长最为陡峭。在整个个体发育过程中，端脑、间脑、视顶盖和延髓以负异速生长与大脑的其余部分进行缩放。然而，值得注意的是，嗅球和小脑与大脑的其余部分超异位生长，随着该物种的成熟，这些结构不成比例地扩大。整个个体发育过程中嗅球相对大小的变化可能反映了在R. terraenovae 的后期生活史阶段对嗅觉的依赖增加，而在整个个体发育过程中小脑相对大小的变化可能表明捕捉更快猎物的能力或随着该物种向近海栖息地迁移的能力增加，与性成熟的开始有关。
大脑行为进化