Big Cat Coalitions: A Comparative Analysis of Regional Brain Volumes in Felidae

Broad-based species comparisons across mammalian orders suggest a number of factors that might influence the evolution of large brains. However, the relationship between these factors and total and regional brain size remains unclear. This study investigated the relationship between relative brain size and regional brain volumes and sociality in 13 felid species in hopes of revealing relationships that are not detected in more inclusive comparative studies. In addition, a more detailed analysis was conducted of 4 focal species: lions (Panthera leo), leopards (Panthera pardus), cougars (Puma concolor), and cheetahs (Acinonyx jubatus). These species differ markedly in sociality and behavioral flexibility, factors hypothesized to contribute to increased relative brain size and/or frontal cortex size. Lions are the only truly social species, living in prides. Although cheetahs are largely solitary, males often form small groups. Both leopards and cougars are solitary. Of the four species, leopards exhibit the most behavioral flexibility, readily adapting to changing circumstances. Regional brain volumes were analyzed using computed tomography (CT). Skulls (n=75) were scanned to create three-dimensional virtual endocasts, and regional brain volumes were measured using either sulcal or bony landmarks obtained from the endocasts or skulls. Phylogenetic least squares (PGLS) regression analyses found that sociality does not correspond with larger relative brain size in these species. However, the sociality/solitary variable significantly predicted anterior cerebrum (AC) volume, a region that includes frontal cortex. This latter finding is despite the fact that the two social species in our sample, lions and cheetahs, possess the largest and smallest relative AC volumes, respectively. Additionally, an ANOVA comparing regional brain volumes in 4 focal species revealed that lions and leopards, while not significantly different from one another, have relatively larger AC volumes than are found in cheetahs or cougars. Further, female lions possess a significantly larger AC volume than conspecific males; female lion values were also larger than those of the other three species (regardless of sex). These results may reflect greater complexity in a female lion’s social world, but additional studies are necessary. These data suggest that within family comparisons may reveal variations not easily detected by broad comparative analyses

Sex and the Frontal Cortex: A Developmental CT Study in the Spotted Hyena

The purpose of this study was to examine developmental and individual variation in total endocranial volume and regional brain volumes, including the anterior cerebrum, posterior cerebrum and cerebellum/brain stem, in the spotted hyena (Crocuta crocuta). The spotted hyena is a highly gregarious animal noted for living in large, hierarchically organized groups. The social lives of male and female spotted hyenas do not differ until after puberty, when males disperse from the natal group, while females remain philopatric. Here we sought to determine whether the divergent life histories of male and female spotted hyenas are linked to differences in brain size or organization. Three-dimensional virtual endocasts were created using computed tomography from 46 spotted hyenas skulls (23 females, 22 males, 1 unknown sex) ranging in age from 1 day to 18 years. Brain volume and skull length were highly correlated (r = 0.91), and both reached asymptotic values by 34 months of age. Analyses of total endocranial volume (relative to skull length) and cerebellum/brain stem volume (relative to total endocranial volume) revealed no sex differences. However, relative anterior cerebrum volume, comprised mainly of frontal cortex, was significantly greater in adult males than adult females, and relative posterior cerebrum volume was greater in adult females than adult males. We hypothesize that the demands of neural processing underlying enhanced social cognition required for successful male transfer between matriarchical social groups at dispersal may be greater than cognitive demands on philopatric females

Phylogenetic autocorrelation as measured using Moran’s I, which ranges between

<p>−<b>1 and 1.</b> Black circles indicate statistically significant autocorrelation at α≤0.05, and grey circles indicate measures that are not significant at α≤0.05.</p

Carnivore phylogeny, demonstration of size-change indices, and relative endocranial volumes by family.

<p>a) Carnivore phylogeny with Pagel’s arbitrary branch lengths. Filled circles represent the hypothetical ancestors or nodes at which the ancestral traits were estimated. Heavy lines link each extant species to the ancestral node that was subtracted from the value for the extant species to obtain size change indices (SCIs). b) Demonstration of how SCIs were calculated. Most recent estimated ancestral size values (ASV) were subtracted from the associated value for extant species size (ESV), and the difference is equal to the SCI. c) Box-and-whisker plot displaying degree of variation in relative brain size within each family. Relative MCOEV is indicated by a white box and relative SCOEV by a grey box. Boxes indicate interquartile range, and whiskers spread to the furthest points outside the interquartile range, but within 1.5 times the interquartile range from the median.</p

Phylogenetic autocorrelation among brain measures.

<p>Degree of phylogenetic autocorrelation in relative brain volume measures using Blomberg’s k. K is the degree of phylogenetic signal, Z is the position in the Z distribution estimated from a tip rearrangement test using 100,000 iterations, and p is the p-value estimated from the tip rearrangement test.</p

Box plot showing relationship between diet and relative endocranial volume.

<p>Boxes indicate interquartile ranges, and whiskers spread to the furthest points outside the interquartile range, but within 1.5 times the interquartile range from the median.</p

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 \u3c 0.05) and in cougars (r = 0.67, p \u3c 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