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

2019 Scholars at Work Conference Program

Program for the 2019 Scholars at Work Conference at Minnesota State University, Mankato on March 29, 2019

Multiple Determinants of Whole and Regional Brain Volume among Terrestrial Carnivorans

Mammalian brain volumes vary considerably, even after controlling for body size. Although several hypotheses have been proposed to explain this variation, most research in mammals on the evolution of encephalization has focused on primates, leaving the generality of these explanations uncertain. Furthermore, much research still addresses only one hypothesis at a time, despite the demonstrated importance of considering multiple factors simultaneously. We used phylogenetic comparative methods to investigate simultaneously the importance of several factors previously hypothesized to be important in neural evolution among mammalian carnivores, including social complexity, forelimb use, home range size, diet, life history, phylogeny, and recent evolutionary changes in body size. We also tested hypotheses suggesting roles for these variables in determining the relative volume of four brain regions measured using computed tomography. Our data suggest that, in contrast to brain size in primates, carnivoran brain size may lag behind body size over evolutionary time. Moreover, carnivore species that primarily consume vertebrates have the largest brains. Although we found no support for a role of social complexity in overall encephalization, relative cerebrum volume correlated positively with sociality. Finally, our results support negative relationships among different brain regions after accounting for overall endocranial volume, suggesting that increased size of one brain regions is often accompanied by reduced size in other regions rather than overall brain expansion

The Procyonid Social Club: Comparison of Brain Volumes in the Coatimundi (Nasua nasua, N. narica), Kinkajou (Potos flavus), and Racoon (Procyon lotor)

The present study investigated whether increased relative brain size, including regional brain volumes, is related to differing behavioral specializations exhibited by three member species of the family Procyonidae. Procyonid species exhibit continuums of behaviors related to social and physical environmental complexities: the mostly solitary, semiarboreal and highly dexterous raccoons (Procyon lotor); the exclusively arboreal kinkajous (Potos flavus), which live either alone or in small polyandrous family groups, and the social, terrestrial coatimundi (Nasua nasua, N. narica). Computed tomographic (CT) scans of 45 adult skulls including 17 coatimundis (9 male, 8 female), 14 raccoons (7 male, 7 female), and 14 kinkajous (7 male, 7 female) were used to create three-dimensional virtual endocasts. Endocranial volume was positively correlated with two separate measures of body size: skull basal length (r = 0.78, p \u3c 0.01) and basicranial axis length (r = 0.45, p = 0.002). However, relative brain size (total endocranial volume as a function of body size) varied by species depending on which body size measurement (skull basal length or basicranial axis length) was used. Comparisons of relative regional brain volumes revealed that the anterior cerebrum volume consisting mainly of frontal cortex and surface area was significantly larger in the social coatimundi compared to kinkajous and raccoons. The dexterous raccoon had the largest relative posterior cerebrum volume, which includes the somatosensory cortex, in comparison to the other procyonid species studied. The exclusively arboreal kinkajou had the largest relative cerebellum and brain stem volume in comparison to the semi arboreal raccoon and the terrestrial coatimundi. Finally, intraspecific comparisons failed to reveal any sex differences, except in the social coatimundi. Female coatimundis possessed a larger relative frontal cortical volume than males. Social life histories differ in male and female coatimundis but not in either kinkajous or raccoons. This difference may reflect the differing social life histories experienced by females who reside in their natal bands, and forage and engage in antipredator behavior as a group, while males disperse upon reaching adulthood and are usually solitary thereafter. This analysis in the three procyonid species supports the comparative neurology principle that behavioral specializations correspond to an expansion of neural tissue involved in that function

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 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

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

PGLS regression outputs for all variables other than diet.

<p>Multiple regression output for the best model for each of the different response variables, not including effects of diet, because diet is categorical. Body SCI is the size change index for body mass or skull size. Brain SCI is the size change index for brain volume. Sociality is PC1 from the PCA of the variables describing social complexity. Home range is log home range size corrected for body size in the same way as brain volume. Forelimb use is our measure of forelimb dexterity. Finally, life history is PC1 from a PCA of the three life history variables we included in our analysis.</p