Powell Brian J, Leal Manuel
Duke University, Durham, N.C., USA.
Brain Behav Evol. 2012;80(3):170-80. doi: 10.1159/000341161. Epub 2012 Aug 17.
Patterns of brain evolution have been widely studied across vertebrates, with the bulk of studies using mammals and/or birds as model systems. Within these groups, species occupying different habitats have been shown to have divergent neuroanatomy, particularly with regard to differences in the relative size of different brain structures, correlated with differences in habitat complexity. We examined the pattern of allometric scaling across the telencephalon, dorsal cortex, dorsomedial cortex, medial cortex, dorsal ventricular ridge, medulla and cerebellum in six species of Puerto Rican Anolis lizards, which are grouped in three distinct ecomorphs (i.e. ecological types) according to interspecific differences in preferred habitat type. The differences in habitat preferences are accompanied by morphological and behavioral adaptations for effective use of each habitat type. Our results challenge this trend and demonstrate a lack of convergence in the relative size of different brain structures between species belonging to the same ecomorph type. Overall brain volume explained between 92.5 and 99.8% of the variance in the volume of each of the brain regions measured and 93.8 and 98.5% of the variance in the volume of each component measured within the telencephalon. This pattern of brain allometry is consistent with concerted brain evolution. However, in the case of the cerebellum, interspecific differences in volume exhibit a trend in accordance with mosaic brain evolution. This suggests that both concerted and mosaic brain evolution have shaped the anole brain, with the former playing a dominant role. Concerted brain evolution is the primary mechanism shaping the brain in mammals and cartilaginous fishes, and its presence in Anolis lizards provides additional evidence supporting the hypothesis that concerted brain evolution might result from a conserved pattern of brain development common to all vertebrates. More generally, our findings highlight the necessity of further studies of brain evolution in reptiles as they can provide valuable insights into the mechanisms underlying vertebrate brain evolution.
大脑进化模式在脊椎动物中得到了广泛研究，大部分研究以哺乳动物和/或鸟类作为模型系统。在这些类群中，已表明占据不同栖息地的物种具有不同的神经解剖结构，特别是在不同脑结构的相对大小差异方面，这与栖息地复杂性的差异相关。我们研究了六种波多黎各安乐蜥的端脑、背侧皮质、背内侧皮质、内侧皮质、背侧室嵴、髓质和小脑的异速生长模式，这些安乐蜥根据偏好栖息地类型的种间差异被分为三种不同的生态形态（即生态类型）。栖息地偏好的差异伴随着形态和行为上的适应，以有效利用每种栖息地类型。我们的结果挑战了这一趋势，并表明属于同一生态形态类型的物种之间，不同脑结构的相对大小缺乏趋同性。总体脑容量解释了所测量的每个脑区体积变异的92.5%至99.8%，以及端脑内所测量的每个组成部分体积变异的93.8%至98.5%。这种脑异速生长模式与协同脑进化一致。然而，在小脑的情况下，种间体积差异呈现出符合镶嵌脑进化的趋势。这表明协同和镶嵌脑进化都塑造了安乐蜥的大脑，前者起主导作用。协同脑进化是塑造哺乳动物和软骨鱼类大脑的主要机制，它在安乐蜥中的存在为协同脑进化可能源于所有脊椎动物共有的保守脑发育模式这一假说提供了额外证据。更普遍地说，我们的发现强调了进一步研究爬行动物脑进化的必要性，因为它们可以为脊椎动物脑进化的潜在机制提供有价值的见解。
