Metabolic acceleration and the evolution of human brain size and life history.

Humans are distinguished from the other living apes in having larger brains and an unusual life history that combines high reproductive output with slow childhood growth and exceptional longevity. This suite of derived traits suggests major changes in energy expenditure and allocation in the human lineage, but direct measures of human and ape metabolism are needed to compare evolved energy strategies among hominoids. Here we used doubly labelled water measurements of total energy expenditure (TEE; kcal day(-1)) in humans, chimpanzees, bonobos, gorillas and orangutans to test the hypothesis that the human lineage has experienced an acceleration in metabolic rate, providing energy for larger brains and faster reproduction without sacrificing maintenance and longevity. In multivariate regressions including body size and physical activity, human TEE exceeded that of chimpanzees and bonobos, gorillas and orangutans by approximately 400, 635 and 820 kcal day(-1), respectively, readily accommodating the cost of humans' greater brain size and reproductive output. Much of the increase in TEE is attributable to humans' greater basal metabolic rate (kcal day(-1)), indicating increased organ metabolic activity. Humans also had the greatest body fat percentage. An increased metabolic rate, along with changes in energy allocation, was crucial in the evolution of human brain size and life history.

Species-specific patterns in fecal glucocorticoid and androgen levels in zoo-living orangutans (Pongo spp.).

In contrast to most primate species, including the other great apes, orangutans maintain a fission-fusion social system in the wild without being part of a stable community. In zoos, however, they are kept in permanent groups, usually consisting of one adult male and several females. In zoo orangutans, we predict higher levels of glucocorticoids and androgens in the Bornean species compared to its congener from Sumatra, due to the much more solitary lifestyle of Bornean orangutans and the apparent higher frequency of male aggression directed towards females in this species in the wild. To compare hormone levels of the two orangutan species, we validated a fecal glucocorticoid and a fecal androgen assay. Subsequently, fecal samples from a total of 73 female and 38 male orangutans housed in 29 European zoos were analyzed to investigate the effect of species, social group size, age and (for female glucocorticoid levels) reproductive state and the presence of adult males on fecal hormone metabolite concentrations. The results of linear mixed effect models indicate that both male and female Bornean orangutans show a steeper increase in glucocorticoid levels with increasing group size than Sumatran orangutans. We therefore conclude that Sumatran zoo orangutans are better able to adjust to social housing conditions than their Bornean congeners. In addition, our analyses reveal higher glucocorticoid levels in lactating females of both species compared to non-lactating and juvenile females. Concerning androgen levels in males, our analyses revealed significantly higher concentrations in Bornean than Sumatran orangutans. These differences in both glucocorticoid and androgen output between the two species of orangutan are presumably linked to ecological and behavioral differences and could possibly be attributed to phenotypic plasticity. However, given that we found interspecific differences in hormone excretion in captivity, where both species live under very similar conditions, we conclude that this variation has a genetic basis.

Life history: the energy-efficient orangutan.

A study of orangutans' daily energy expenditure confirmed exceptionally slow metabolism. It suggests they evolved a lifestyle designed to minimize energy use. If so, shifting to a higher energy-use strategy may help explain how humans evolved.

Metabolic adaptation for low energy throughput in orangutans.

Energy is the fundamental currency of life--needed for growth, repair, and reproduction--but little is known about the metabolic physiology and evolved energy use strategies of the great apes, our closest evolutionary relatives. Here we report daily energy use in free-living orangutans (Pongo spp.) and test whether observed differences in energy expenditure among orangutans, humans, and other mammals reflect known differences in life history. Using the doubly labeled water method, we measured daily energy expenditure (kCal/d) in orangutans living in a large indoor/outdoor habitat at the Great Ape Trust. Despite activity levels similar to orangutans in the wild, Great Ape Trust orangutans used less energy, relative to body mass, than nearly any eutherian mammal ever measured, including sedentary humans. Such an extremely low rate of energy use has not been observed previously in primates, but is consistent with the slow growth and low rate of reproduction in orangutans, and may be an evolutionary response to severe food shortages in their native Southeast Asian rainforests. These results hold important implications for the management of orangutan populations in captivity and in the wild, and underscore the flexibility and interdependence of physiological, behavioral, and life history strategies in the evolution of apes and humans.

Macaque CYP2C76 encodes cytochrome P450 enzyme not orthologous to any human isozymes.

Cynomolgus monkey is used in the study of drug metabolism and toxicity due to its evolutionary closeness to human as compared with other non-human primate species. However, it has become certain that drug metabolism in monkeys is different than in humans. Such species differences have not been fully investigated at a molecular level largely due to the scarcity of information on drug-metabolizing enzyme genes. In cynomolgus monkey, we have identified cDNAs for 21 kinds of cytochromes P450 (CYPs), among which CYP2C76 does not correspond to any human CYP isozymes and is partly responsible for the difference in pitavastatin metabolism between cynomolgus monkey and human. In cynomolgus monkey CYP2C76, we identified numerous genetic variants including a null genotype. Heterozygotes for this null genotype are expected to be poor metabolizers in CYP2C76-mediated drug metabolism. To provide new clues to CYP2C76 function, here, we have taken advantage of sequence information that has been recently deposited to public databases to assess the presence of CYP2C76 orthologs in primate species. In this assessment, we found the CYP2C76 cDNA sequence in rhesus monkey, and a gene sequence highly homologous to cynomolgus monkey CYP2C76 in the marmoset and orangutan genomes, raising the possibility that CYP2C76 could also play a role in these primate species. This review paper gives an overview of CYP2C76 from isolation to molecular characterization, and its implication in drug metabolism.