Comparative anatomy of the caudate nucleus in canids and felids: Associations with brain size, curvature, cross-sectional properties, and behavioral ecology

The evolutionary history of canids and felids is marked by a deep time separation that has uniquely shaped their behavior and phenotype toward refined predatory abilities. The caudate nucleus is a subcortical brain structure associated with both motor control and cognitive, emotional, and executive functions. We used a combination of three-dimensional imaging, allometric scaling, and structural analyses to compare the size and shape characteristics of the caudate nucleus. The sample consisted of MRI scan data obtained from six canid species (Canis lupus lupus, Canis latrans, Chrysocyon brachyurus, Lycaon pictus, Vulpes vulpes, Vulpes zerda), two canid subspecies (Canis lupus familiaris, Canis lupus dingo), as well as three felids (Panthera tigris, Panthera uncia, Felis silvestris catus). Results revealed marked conservation in the scaling and shape attributes of the caudate nucleus across species, with only slight deviations. We hypothesize that observed differences in caudate nucleus size and structure for the domestic canids are reflective of enhanced cognitive and emotional pathways that possibly emerged during domestication.

Neuropil Variation in the Prefrontal, Motor, and Visual Cortex of Six Felids

INTRODUCTION

Felids have evolved a specialized suite of morphological adaptations for obligate carnivory. Although the musculoskeletal anatomy of the Felidae has been studied extensively, the comparative neuroanatomy of felids is relatively unexplored. Little is known about how variation in the cerebral anatomy of felids relates to species-specific differences in sociality, hunting strategy, or activity patterns.

METHODS

We quantitatively analyzed neuropil variation in the prefrontal, primary motor, and primary visual cortices of six species of Felidae (Panthera leo, Panthera uncia, Panthera tigris, Panthera leopardus, Acinonyx jubatus, Felis sylvestris domesticus) to investigate relationships with brain size, neuronal cell parameters, and select behavioral and ecological factors. Neuropil is the dense, intricate network of axons, dendrites, and synapses in the brain, playing a critical role in information processing and communication between neurons.

RESULTS

There were significant species and regional differences in neuropil proportions, with African lion, cheetah, and tiger having more neuropil in all three cortical regions in comparison to the other species. Based on regression analyses, we find that the increased neuropil fraction in the prefrontal cortex supports social and behavioral flexibility, while in the primary motor cortex, this facilitates the neural activity needed for hunting movements. Greater neuropil fraction in the primary visual cortex may contribute to visual requirements associated with diel activity patterns.

CONCLUSION

These results provide a cross-species comparison of neuropil fraction variation in the Felidae, particularly the understudied Panthera, and provide evidence for convergence of the neuroanatomy of Panthera and cheetahs.

Muscular anatomy of the forelimb of tiger (Panthera tigris)

Dissection reports of large cats (family Felidae) have been published since the late 19th century. These reports generally describe the findings in words, show drawings of the dissection, and usually include some masses of muscles, but often neglect to provide muscle maps showing the precise location of bony origins and insertions. Although these early reports can be highly useful, the absence of visual depictions of muscle attachment sites makes it difficult to compare muscle origins and insertions in living taxa and especially to reconstruct muscle attachments in fossil taxa. Recently, more muscle maps have been published in the primary literature, but those for large cats are still limited. Here, we describe the muscular anatomy of the forelimb of the tiger (Panthera tigris), and compare muscle origins, insertions, and relative muscle masses to other felids to identify differences that may reflect functional adaptations. Our results reiterate the conservative nature of felid anatomy across body sizes and behavioral categories. We find that pantherines have relatively smaller shoulder muscle masses, and relatively larger muscles of the caudal brachium, pronators, and supinators than felines. The muscular anatomy of the tiger shows several modifications that may reflect an adaptation to terrestrial locomotion and a preference for large prey. These include in general a relatively large m. supraspinatus (shoulder flexion), an expanded origin for m. triceps brachii caput longum, and relatively large m. triceps brachii caput laterale (elbow extension), as well as relatively large mm. brachioradialis, abductor digiti I longus, and abductor digiti V. Muscle groups that are well developed in scansorial taxa are not well developed in the tiger, including muscles of the cranial compartment of the brachium and antebrachium, and m. anconeus. Overall, the musculature of the tiger strongly resembles that of the lion (Panthera leo), another large-bodied terrestrial large-prey specialist.

Brain gyrification in wild and domestic canids: Has domestication changed the gyrification index in domestic dogs?

Over the last 15 years, research on canid cognition has revealed that domestic dogs possess a surprising array of complex sociocognitive skills pointing to the possibility that the domestication process might have uniquely altered their brains; however, we know very little about how evolutionary processes (natural or artificial) might have modified underlying neural structure to support species-specific behaviors. Evaluating the degree of cortical folding (i.e., gyrification) within canids may prove useful, as this parameter is linked to functional variation of the cerebral cortex. Using quantitative magnetic resonance imaging to investigate the impact of domestication on the canine cortical surface, we compared the gyrification index (GI) in 19 carnivore species, including six wild canid and 13 domestic dog individuals. We also explored correlations between global and local GI with brain mass, cortical thickness, white and gray matter volume and surface area. Our results indicated that GI values for domestic dogs are largely consistent with what would be expected for a canid of their given brain mass, although more variable than that observed in wild canids. We also found that GI in canids is positively correlated with cortical surface area, cortical thickness and total cortical gray matter volumes. While we found no evidence of global differences in GI between domestic and wild canids, certain regional differences in gyrification were observed.