School of Biomedical Sciences, The University of Queensland, Brisbane, Queensland, QLD 4072, Australia.
Queensland Brain Institute, The University of Queensland, Brisbane, Queensland, QLD 4072, Australia.
Proc Natl Acad Sci U S A. 2023 Aug 8;120(32):e2306516120. doi: 10.1073/pnas.2306516120. Epub 2023 Jul 31.
The thylacine, or Tasmanian tiger, is the largest of modern-day carnivorous marsupials and was hunted to extinction by European settlers in Australia. Its physical resemblance to eutherian wolves is a striking example of evolutionary convergence to similar ecological niches. However, whether the neuroanatomical organization of the thylacine brain resembles that of canids and how it compares with other mammals remain unknown due to the scarcity of available samples. Here, we gained access to a century-old hematoxylin-stained histological series of a thylacine brain, digitalized it at high resolution, and compared its forebrain cellular architecture with 34 extant species of monotremes, marsupials, and eutherians. Phylogenetically informed comparisons of cortical folding, regional volumes, and cell sizes and densities across cortical areas and layers provide evidence against brain convergences with canids, instead demonstrating features typical of marsupials, and more specifically Dasyuridae, along with traits that scale similarly with brain size across mammals. Enlarged olfactory, limbic, and neocortical areas suggest a small-prey predator and/or scavenging lifestyle, similar to extant quolls and Tasmanian devils. These findings are consistent with a nonuniformity of trait convergences, with brain traits clustering more with phylogeny and head/body traits with lifestyle. By making this resource publicly available as rapid web-accessible, hierarchically organized, multiresolution images for perpetuity, we anticipate that additional comparative insights might arise from detailed studies of the thylacine brain and encourage researchers and curators to share, annotate, and preserve understudied material of outstanding biological relevance.
袋狼，又称塔斯马尼亚虎，是现代最大的肉食有袋动物，曾被澳大利亚的欧洲殖民者捕杀至灭绝。它在身体结构上与真兽类狼相似，这是趋同进化到相似生态位的一个显著例子。然而，由于可用样本稀缺，袋狼大脑的神经解剖结构是否与犬科动物相似，以及它与其他哺乳动物的比较情况仍然未知。在这里，我们获得了一个世纪前袋狼大脑的苏木精染色组织学系列的数字化资料，以高分辨率对其进行数字化处理，并将其前脑细胞结构与 34 种现存的单孔目动物、有袋目动物和真兽类动物进行了比较。基于系统发育的皮质折叠、区域体积以及皮质区域和层的细胞大小和密度的比较，为大脑与犬科动物没有趋同提供了证据，而是证明了其具有有袋目动物的特征，更具体地说，具有袋鼬科的特征，以及与哺乳动物大脑大小相似的缩放特征。嗅觉、边缘和新皮质区域的增大表明，袋狼可能是一种以小型猎物为食的捕食者和/或食腐动物，与现存的袋鼬和袋獾相似。这些发现与特征趋同的非一致性一致，大脑特征与系统发育聚类更紧密，而头部/身体特征与生活方式聚类更紧密。通过将这个资源作为快速网络可访问的、分层组织的、多分辨率的图像永久公开，我们期望对袋狼大脑的详细研究能够产生更多的比较见解，并鼓励研究人员和策展人分享、注释和保存具有突出生物学相关性的未被充分研究的材料。
