Eastman J T, Lannoo M J
Department of Biological Sciences, Ohio University, Athens 45701-2979.
J Morphol. 1995 Jan;223(1):47-83. doi: 10.1002/jmor.1052230107.
The Notothenioidei, a perciform suborder of 120 species, dominates the ichthyofauna of the Southern Ocean around Antarctica. Unlike most teleost groups, notothenioids have undergone a corresponding ecological and phyletic diversification and therefore provide an excellent opportunity to study the divergence of the nervous system in an unusual environment. Our goal is to evaluate notothenioid brain variation in light of this diversification. To provide a baseline morphology, we examine the gross morphology and histology of the brain of Trematomus bernacchii, a generalized member of the family Nototheniidae. We then examine the variation in brain gross anatomy (32 species) and histology (10 species) of other notothenioids. Our sample represents about 27% of the species in this group and includes species from each of the six families, as well as species representing diverse ecologies. For comparison we reference the well-studied brains of two species of temperate perciformes (Perca flavescens and Lepomis humilis). Our results show that, in general, notothenioid brains are more similar to the brains of temperate perciforms than to the unusual brains of cave-dwelling and deep-sea fishes. Interspecific variation in gross brain morphology is comparable to that in Old World cyprinids and is illustrated for 17 species. Variation is especially noteworthy in the ecologically and geographically diverse family Nototheniidae. Measurements indicate that sensory regions (olfactory bulbs, eminentia granularis, and crista cerebellaris) exhibit the most pronounced variation in relative surface area. Association areas, including the corpus cerebelli and the telencephalon, exhibit moderate variation in size, shape, and lobation patterns. Regulatory areas of the brain, including the saccus vasculosus and the subependyma of the third ventricle, are also variable. These regions are best developed in species living in the subfreezing water close to the continent. In some species the expanded ependymal lining forms ventricular sacs, not previously described in any other vertebrate. Three species, including two nototheniids (Eleginops maclovinus and Pleuragramma antarcticum) and the only artedidraconid in our sample, have distinctive brains. The unique brain morphology of Pleuragramma is probably related to a sensory (lateral line) specialization for feeding. Within the Nototheniidae, a phyletic effect on cerebellar morphology is evident in the Coriiceps group and in the Pleuragramminae. Neither phyletic position nor ecological factors (water temperature, position in the water column, dietary habits) alone fully explain the pattern of notothenioid brain diversification.
南极鱼亚目是鲈形目的一个亚目，有120个物种，在南极洲周围的南大洋鱼类区系中占主导地位。与大多数硬骨鱼群不同，南极鱼亚目经历了相应的生态和系统发育多样化，因此为研究在特殊环境中神经系统的分化提供了绝佳机会。我们的目标是根据这种多样化来评估南极鱼亚目的脑变异。为提供一个基线形态，我们研究了伯氏南极鱼（南极鱼科的一个广义成员）脑的大体形态和组织学。然后我们研究了其他南极鱼亚目动物脑的大体解剖结构（32个物种）和组织学（10个物种）的变异。我们的样本代表了该类群约27%的物种，包括六个科中的每个科的物种，以及代表不同生态类型的物种。为作比较，我们参考了两种温带鲈形目鱼类（黄斑鲈和钝吻太阳鱼）研究充分的脑。我们的结果表明，总体而言，南极鱼亚目的脑与温带鲈形目的脑比与穴居和深海鱼类不同寻常的脑更相似。脑大体形态的种间变异与东半球鲤科鱼类的变异相当，并以17个物种为例进行了说明。变异在生态和地理上多样的南极鱼科中尤为显著。测量表明，感觉区域（嗅球、颗粒隆起和小脑嵴）在相对表面积上表现出最明显的变异。联合区域，包括小脑体和端脑，在大小、形状和叶状模式上表现出适度变异。脑的调节区域，包括血管囊和第三脑室的室管膜下区，也存在变异。这些区域在生活在靠近大陆的亚冰点水域的物种中发育得最好。在一些物种中，扩大的室管膜内衬形成脑室囊，这在其他脊椎动物中未曾描述过。三个物种，包括两种南极鱼科鱼类（麦氏南美南极鱼和南极小带腭鱼）以及我们样本中唯一的阿氏龙䲢科鱼类，具有独特的脑。南极小带腭鱼独特的脑形态可能与觅食的一种感觉（侧线）特化有关。在南极鱼科中，小脑形态的系统发育效应在突吻南极鱼属组和小带腭鱼亚科中很明显。单独的系统发育位置和生态因素（水温、水柱中的位置、饮食习惯）都不能完全解释南极鱼亚目脑多样化的模式。
