Eco-geographical diversification of bitter taste receptor genes (TAS2Rs) among subspecies of chimpanzees (Pan troglodytes).

Chimpanzees (Pan troglodytes) have region-specific difference in dietary repertoires from East to West across tropical Africa. Such differences may result from different genetic backgrounds in addition to cultural variations. We analyzed the sequences of all bitter taste receptor genes (cTAS2Rs) in a total of 59 chimpanzees, including 4 putative subspecies. We identified genetic variations including single-nucleotide variations (SNVs), insertions and deletions (indels), gene-conversion variations, and copy-number variations (CNVs) in cTAS2Rs. Approximately two-thirds of all cTAS2R haplotypes in the amino acid sequence were unique to each subspecies. We analyzed the evolutionary backgrounds of natural selection behind such diversification. Our previous study concluded that diversification of cTAS2Rs in western chimpanzees (P. t. verus) may have resulted from balancing selection. In contrast, the present study found that purifying selection dominates as the evolutionary form of diversification of the so-called human cluster of cTAS2Rs in eastern chimpanzees (P. t. schweinfurthii) and that the other cTAS2Rs were under no obvious selection as a whole. Such marked diversification of cTAS2Rs with different evolutionary backgrounds among subspecies of chimpanzees probably reflects their subspecies-specific dietary repertoires.

Energetic costs of territorial boundary patrols by wild chimpanzees.

Chimpanzees are well known for their territorial behavior. Males who belong to the same community routinely patrol their territories, occasionally making deep incursions into those of their neighbors. Male chimpanzees may obtain several fitness benefits by participating in territorial boundary patrols, but patrolling is also likely to involve fitness costs. Patrollers risk injury or even death, and patrols may be energetically costly and may involve opportunity costs. Although territorial patrols have been reported at all long-term chimpanzee study sites, quantitative data on their energetic costs have not previously been available. I evaluated the energy costs of patrolling for male chimpanzees at Ngogo, Kibale National Park, Uganda during 14 months of observation. In 29 patrols and matched control periods, I recorded the distances covered and time spent traveling and feeding by chimpanzees. I found that male chimpanzees covered longer distances, spent more time traveling, and spent less time feeding during patrols than during control periods. These results support the hypothesis that chimpanzees incur energetic costs while patrolling and suggest that ecological factors may constrain the ability of chimpanzees to patrol.

Intraspecies variation in BMR does not affect estimates of early hominin total daily energy expenditure.

We conducted a meta-analysis of 45 studies reporting basal metabolic rate (BMR) data for Homo sapiens and Pan troglodytes to determine the effects of sex, age, and latitude (a proxy for climate, in humans only). BMR was normalized for body size using fat-free mass in humans and body mass in chimpanzees. We found no effect of sex in either species and no age effect in chimpanzees. In humans, juveniles differed significantly from adults (ANCOVA: P < 0.001), and senescent adults differed significantly from adults younger than 50 years (P < 0.001). Europeans differed significantly from tropical populations (P < 0.001). On the basis of these observations, we derived new equations describing the relationship between BMR and body size, and used them to predict total daily energy expenditure (TEE) in four early hominin species. Our predictions concur with previous TEE estimates (i.e. Leonard and Robertson: Am J Phys Anthropol 102 (1997) 265-281), and support the conclusion that TEE increased greatly with H. erectus. Our results show that intraspecific variation in BMR does not affect TEE estimates for interspecific comparisons. Comparisons of more closely related groups such as humans and Neandertals, however, may benefit from consideration of this variation.