Supplementary Material for: Pride Diaries: Sex, Brain Size and Sociality in the African Lion (Panthera leo) and Cougar (Puma concolor)

The purpose of this study was to examine if differences in social life histories correspond to intraspecific variation in total or regional brain volumes in the African lion (Panthera leo) and cougar (Puma concolor). African lions live in gregarious prides usually consisting of related adult females, their dependent offspring, and a coalition of immigrant males. Upon reaching maturity, male lions enter a nomadic and often, solitary phase in their lives, whereas females are mainly philopatric and highly social throughout their lives. In contrast, the social life history does not differ between male and female cougars; both are solitary. Three-dimensional virtual endocasts were created using computed tomography from the skulls of 14 adult African lions (8 male, 6 female) and 14 cougars (7 male, 7 female). Endocranial volume and basal skull length were highly correlated in African lions (r = 0.59, p < 0.05) and in cougars (r = 0.67, p < 0.01). Analyses of total endocranial volume relative to skull length revealed no sex differences in either African lions or cougars. However, relative anterior cerebrum volume comprised primarily of frontal cortex and surface area was significantly greater in female African lions than males, while relative posterior cerebrum volume and surface area was greater in males than females. These differences were specific to the neocortex and were not found in the solitary cougar, suggesting that social life history is linked to sex-specific neocortical patterns in these species. We further hypothesize that increased frontal cortical volume in female lions is related to the need for greater inhibitory control in the presence of a dominant male aggressor.

本研究旨在探究非洲狮（Panthera leo）与美洲狮（Puma concolor）的社会生活史差异，是否与其整体或区域脑体积的种内变异（intraspecific variation）存在关联。非洲狮群居生活，通常形成由亲缘成年雌性、其需依赖照料的幼崽，以及外来雄性联盟组成的狮群（prides）。雄性非洲狮性成熟后，会进入游牧且多为独居的生命阶段；而雌性则终生主要为留居型（philopatric），且始终保持高度社会化的生活模式。与之形成鲜明对比的是，美洲狮的雌雄个体间社会生活史并无差异，二者均为独居生活。研究人员借助计算机断层扫描（computed tomography）技术，对14头成年非洲狮（8雄、6雌）与14头美洲狮（7雄、7雌）的头骨进行扫描，构建了三维虚拟颅腔模型（three-dimensional virtual endocasts）。在两类物种中，颅腔体积（endocranial volume）与颅底长度均呈现显著相关性：非洲狮的相关系数r=0.59，p<0.05；美洲狮的相关系数r=0.67，p<0.01。针对基于头骨长度校正后的整体颅腔体积的分析显示，非洲狮与美洲狮均未出现性别差异。不过，主要由前额叶皮层（frontal cortex）构成的相对前脑体积及其表面积，在雌性非洲狮中显著高于雄性；而雄性个体的相对后脑体积与表面积则显著高于雌性。此类差异仅存在于新皮层（neocortex）中，在独居的美洲狮中并未观测到，这表明社会生活史与这两个物种种群的性别特异性新皮层模式存在关联。我们进一步提出假说：雌性非洲狮的前额叶皮层体积更大，或与其在遭遇优势雄性入侵者时需要更强的抑制控制能力相关。