Weisbecker Vera, Blomberg Simon, Goldizen Anne W, Brown Meredeth, Fisher Diana
School of Biological Sciences, University of Queensland, St. Lucia, Qld., Australia.
Brain Behav Evol. 2015;85(2):125-35. doi: 10.1159/000377666. Epub 2015 May 7.
Evolutionary increases in mammalian brain size relative to body size are energetically costly but are also thought to confer selective advantages by permitting the evolution of cognitively complex behaviors. However, many suggested associations between brain size and specific behaviors - particularly related to social complexity - are possibly confounded by the reproductive diversity of placental mammals, whose brain size evolution is the most frequently studied. Based on a phylogenetic generalized least squares analysis of a data set on the reproductively homogenous clade of marsupials, we provide the first quantitative comparison of two hypotheses based on energetic constraints (maternal investment and seasonality) with two hypotheses that posit behavioral selection on relative brain size (social complexity and environmental interactions). We show that the two behavioral hypotheses have far less support than the constraint hypotheses. The only unambiguous associates of brain size are the constraint variables of litter size and seasonality. We also found no association between brain size and specific behavioral complexity categories within kangaroos, dasyurids, and possums. The largest-brained marsupials after phylogenetic correction are from low-seasonality New Guinea, supporting the notion that low seasonality represents greater nutrition safety for brain maintenance. Alternatively, low seasonality might improve the maternal support of offspring brain growth. The lack of behavioral brain size associates, found here and elsewhere, supports the general 'cognitive buffer hypothesis' as the best explanatory framework of mammalian brain size evolution. However, it is possible that brain size alone simply does not provide sufficient resolution on the question of how brain morphology and cognitive capacities coevolve.
相对于身体大小而言，哺乳动物大脑尺寸的进化在能量方面代价高昂，但人们也认为，通过允许认知复杂行为的进化，这种进化能带来选择优势。然而，许多关于大脑尺寸与特定行为（特别是与社会复杂性相关的行为）之间的关联，可能因胎盘哺乳动物的生殖多样性而混淆，胎盘哺乳动物的大脑尺寸进化是研究最为频繁的。基于对有袋类动物生殖同质分支数据集的系统发育广义最小二乘法分析，我们首次对基于能量限制（母体投资和季节性）的两种假设与基于相对大脑尺寸行为选择（社会复杂性和环境相互作用）的两种假设进行了定量比较。我们发现，这两种行为假设所获得的支持远少于限制假设。大脑尺寸唯一明确的关联因素是产仔数和季节性这些限制变量。我们还发现，在袋鼠、袋鼬和负鼠中，大脑尺寸与特定行为复杂性类别之间没有关联。经过系统发育校正后，大脑最大的有袋类动物来自季节性较低的新几内亚，这支持了低季节性代表大脑维持营养更安全的观点。或者，低季节性可能会改善母体对后代大脑生长的支持。此处及其他地方发现的大脑尺寸与行为之间缺乏关联，支持了“认知缓冲假说”作为哺乳动物大脑尺寸进化的最佳解释框架这一观点。然而，仅大脑尺寸本身可能根本无法就大脑形态与认知能力如何共同进化这一问题提供足够的解析度。
