Kimberley A. Phillips

Primary motor cortex asymmetry is correlated with handedness in capuchin monkeys (Cebus apella).

Humans exhibit a population-wide tendency toward right-handedness, and structural asymmetries of the primary motor cortex are associated with hand preference. Reported are similar asymmetries correlated with hand preference in a New World monkey (Cebus apella) that does not display population-level handedness. Asymmetry of central sulcus depth is significantly different between left-handed and right-handed individuals as determined by a coordinated bimanual task. Left-handed individuals have a deeper central sulcus in the contralateral hemisphere; right-handed individuals have a more symmetrical central sulcus depth. Cerebral hemispheric specialization for hand preference is not uniquely human and may be more common among primates in general.

Tool use in wild capuchin monkeys (Cebus albifrons trinitatis)

White‐fronted capuchins were observed to use leaves as cups to retrieve water from tree cavities. On multiple occasions several individuals performed this behavior. Thus, these capuchins engage in habitual tool use, as defined by McGrews classificatory scheme of tool using behavior. Am. J. Primatol. 46:259–261, 1998.

Do dogs (Canis familiaris) show contagious yawning

We report an experimental investigation into whether domesticated dogs display contagious yawning. Fifteen dogs were shown video clips of (1) humans and (2) dogs displaying yawns and open-mouth expressions (not yawns) to investigate whether dogs showed contagious yawning to either of these social stimuli. Only one dog performed significantly more yawns during or shortly after viewing yawning videos than to the open-mouth videos, and most of these yawns occurred to the human videos. No dogs showed significantly more yawning to the open-mouth videos (human or dog). The percentage of dogs showing contagious yawning was less than chimpanzees and humans showing this behavior, and considerably less than a recently published report investigating this behavior in dogs (Joly-Mascheroni et al. in Biol Lett 4:446–448, 2008).

Survey of the gastrointestinal parasites of the primate community at Tambopata National Reserve, Peru

The main objective of this project was to provide baseline data on faecal parasites of groups of non-human primates from Tambopata Research Center, Tambopata National Reserve, Peru. All primate species found in this area were sampled: red howler monkeys Alouatta seniculus, night monkeys Aotus vociferans, spider monkeys Ateles bezlebuth chamek, brown titi monkeys Callicebus brunneus, white-fronted capuchins Cebus albifrons, brown capuchins Cebus apella, saddleback tamarins Saguinus fuscicollis and squirrel monkeys Saimiri sciureus. Individuals from four howler monkey troops, three brown titi monkey troops, two squirrel monkey troops and one troop each of night monkeys, spider monkeys, brown capuchins, white-fronted capuchins and saddleback tamarins were sampled. Faecal samples were collected from July to October 2002 from 86 individuals. A concentration test was used to analyse faecal samples. Results indicate the presence of various protozoans, Ancyclostoma sp., Ascaris sp., Strongyloides stercoralis, Trichuris trichiura, Prosthenorchis elegans and Schistosoma mansoni.

Corpus Callosum Morphology in Capuchin Monkeys Is Influenced by Sex and Handedness

Sex differences have been reported in both overall corpus callosum area and its regional subdivisions in humans. Some have suggested this reflects a unique adaptation in humans, as similar sex differences in corpus callosum morphology have not been reported in any other species of primate examined to date. Furthermore, an association between various measurements of corpus callosum morphology and handedness has been found in humans and chimpanzees. In the current study, we report measurements of corpus callosum cross-sectional area from midsagittal MR images collected in vivo from 14 adult capuchin monkeys, 9 of which were also characterized for hand preference on a coordinated bimanual task. Adult females were found to have a significantly larger corpus callosum: brain volume ratio, rostral body, posterior midbody, isthmus, and splenium than adult males. Left-handed individuals had a larger relative overall corpus callosum area than did right-handed individuals. Additionally, a significant sex and handedness interaction was found for anterior midbody, with right-handed males having a significantly smaller area than right-handed females. These results suggest that sex and handedness influences on corpus callosum morphology are not restricted to Homo sapiens.

Cortical Development in Brown Capuchin Monkeys: A Structural MRI Study

Relative to other primates, Cebus monkeys display unusually fast postnatal brain growth and motor skill development. The neonatal capuchin brain, at approximately 29-34 g, is a smaller proportion of the adult brain weight (c. 50%) than is the brain of other primates except humans and great apes. Here we describe, from a cross-sectional sample, brain development in 29 brown capuchin monkeys (Cebus apella) using high-resolution structural magnetic resonance images, focusing on growth patterns in total brain volume, cortical gray and white matter volume, frontal lobe gray and white matter volume, and corpus callosum area. Non-linear age-related changes in total brain volume, cortical white matter volume and frontal white matter volume were detected from birth - 5 years. Sex differences in corpus callosum:brain ratio were also found, with males having a 10% smaller corpus callosum:brain ratio than females regardless of age. Female corpus callosum:brain ratio showed significant age-related related changes, whereas males did not display any significant changes across age. Sex differences were also found in cortical gray and frontal lobe gray matter volumes, with males having larger volumes than females. These findings support the conclusion that capuchins undergo rapid neurological change during the first few years of life.

Cerebral petalias and their relationship to handedness in capuchin monkeys (Cebus apella)

Cerebral asymmetries are thought to be associated with increased hemispheric specialization of function. We investigated cerebral petalias, the protrusion of one cerebral hemisphere relative to the other, and their relationship to lateralized behavior in capuchin monkeys (Cebus apella). Magnetic resonance images of the brain and behavioral data on a coordinated bimanual task were obtained from 13 capuchins. While a significant population-level left-frontal petalia was found, this was not related to handedness. The role of the morphologically asymmetric frontal cortex in capuchins is unclear, but may reflect developmental gradients or directional selection for various behavioral functions, such as extractive foraging or social group complexity.

Applying GPS to the study of primate ecology: A useful tool?

Data on the spatiotemporal distribution of resources can be collected and plotted using GPS (global positioning system) and GIS (geographical information system) technologies. By combining such data with information on foraging and ranging behavior of nonhuman primates, one can analyze the influence of resource distribution on social organization and group cohesion. We investigated the abilities of a three‐channel GPS receiver to collect location data under varying canopy densities in both temperate and tropical forests. Eighty randomly selected points were sampled in a beech–maple forest in northeast Ohio, USA; 65 points also were sampled at several tropical forests in Costa Rica and Trinidad. At each point we attempted to obtain a GPS position fix; we also determined the speed of satellite acquisition and measured canopy density using a spherical densiometer. The ability to obtain a reading differed greatly between the two forest types (χ2 = 53.79, P < 0.001). Ninety‐seven percent of all attempts were successful in the temperate forest, whereas only a 34% acquisition rate was obtained in the tropical forests. Logistic regression showed that the probability of obtaining a reading in Neotropical forests was 75% but only when canopy cover was less than 20%. Thus, these minimal‐channel GPS units may be of limited utility for behavioral ecologists working in closed‐canopy Neotropical forests. Am. J. Primatol. 46:167–172, 1998.

Natural conceptual behavior in squirrel monkeys (saimiri sciureus): An experimental investigation

Natural conceptual discriminations have been tested in many different species, including pigeons and a variety of non-human primates. The ability of four male squirrel monkeys (Saimiri sciureus) to learn and use the natural concept ‘squirrel monkey’ was investigated in this study. After a training phase, subjects were presented with novel stimuli in transfer and test trials. All subjects performed at a rate significantly above chance on the first test trial (p<.001), indicating that squirrel monkeys can utilize natural concepts in the laboratory.

Sylvian fissure asymmetry in capuchin monkeys (Cebus apella)

Asymmetries of the sylvian fissure (SF) are believed to reflect an enlargement of the posterior temporal lobe, particularly a region that corresponds to part of Wernickes area in humans. In nonhuman primates the homologue to the region may be involved in the discrimination and processing of species-specific vocalisations. As capuchin monkeys are large brained, socially complex primates with a rich vocal repertoire, it was hypothesised that they would display asymmetry of the SF. We used high-resolution 3T MRI scans to investigate this asymmetry in 17 brown capuchin monkeys (Cebus apella; 9 males, 8 females). Results indicated a trend towards population-level leftward asymmetry in the lateral region of the SF. Post hoc analyses revealed significant sex differences in SF asymmetry, with females displaying a population-level leftward asymmetry of the lateral region of the SF. Age was a significant mediator of the effects of sex on asymmetry of the lateral region of the SF. These results provide evidence that capuchin monkeys display sex differences in the asymmetry of the SF and show developmental changes in hemispheric lateralisation.