It was reported over 65 years ago that chimpanzees, like humans, vary in taste sensitivity to the bitter compound phenylthiocarbamide (PTC). This was suggested to be the result of a shared balanced polymorphism, defining the first, and now classic, example of the effects of balancing selection in great apes. In humans, variable PTC sensitivity is largely controlled by the segregation of two common alleles at the TAS2R38 locus, which encode receptor variants with different ligand affinities. Here we show that PTC taste sensitivity in chimpanzees is also controlled by two common alleles of TAS2R38; however, neither of these alleles is shared with humans. Instead, a mutation of the initiation codon results in the use of an alternative downstream start codon and production of a truncated receptor variant that fails to respond to PTC in vitro. Association testing of PTC sensitivity in a cohort of captive chimpanzees confirmed that chimpanzee TAS2R38 genotype accurately predicts taster status in vivo. Therefore, although Fisher et al.'s observations were accurate, their explanation was wrong. Humans and chimpanzees share variable taste sensitivity to bitter compounds mediated by PTC receptor variants, but the molecular basis of this variation has arisen twice, independently, in the two species.

This study investigated the effects of habitat on the diet, population density, and social structure of a small-bodied folivore, Hapalemur griseus. Three groups of H. griseus were followed at two study sites (Tala and Vato) within Ranomafana National Park in southeastern Madagascar. These two sites differed in degree of habitat disturbance, forest composition, and forest structure, as determined by botanical plots (50 x 10 m) which were monitored twice monthly in the home ranges of three study groups (group T, n = 4; group V1, n = 4; group V2, n = 2). Tala has experienced more habitat disturbance compared to Vato, and this appeared to influence population density and group size. The H. griseus that inhabit Tala occur at much higher densities and in larger social groups than the H. griseus at Vato. These results may be attributable to: 1) a greater number of potential food sources, 2) a more dense resource base, and/or 3) higher-quality resources at Tala for this folivore. In general, dietary diversity for all groups was low, and groups exploited similar plant species. However, within this small range of food sources, each study group specialized in food sources found in the highest abundance within their home range. This resulted in dietary differences between groups within sites, as well as differences between sites. Introduced tree species such as Chinese guava (Psidium cattleyanum) may have greatly impacted the diet and social structure of those groups at Tala, whose home ranges included this food source. In contrast, Vato group 1 ingested more new and mature leaves of Ficus spp., and Vato group 2 primarily ate spider bamboo (Nastus elongatus). In conclusion, it seems that microhabitat differences, which may be related to habitat disturbance and/or other factors such as topography, influenced the food species ingested by H. griseus. Overall habitat quality, which is likely also affected by habitat disturbance, influenced general diet, population density, and group size.

Although some conservationists accept that not all species can be saved, we illustrate the difficulty in deciding which species are dispensable. In this article, we examine the possibility that the integrity of a forest relies on its entire faunal assemblage. In Madagascar, one faunal group, the lemurs, accounts for the greatest biomass and species richness among frugivores. For example, 7 of the 13 sympatric lemur species in Madagascar's eastern rainforests consume primarily fruit. Because of this, we suggest that some tree species may rely heavily on particular lemur taxa for both seed dispersal and germination. In Ranomafana National Park, the diets for four of the day-active lemur frugivores have been documented during annual cycles over a 5-year period. We predicted that, although the fruit of some plant taxa would be exploited by multiple lemur species, the fruit of others would be eaten by one lemur species alone. Analyses reveal that while lemurs overlap in a number of fruit taxa exploited, 46% (16/35) of families and 56% (29/52) of genera are eaten exclusively by one lemur species. We, therefore, predict local changes in forest composition and structure if certain of these lemur species are eliminated from a forest owing to hunting, disease, or habitat disturbance. We also suggest that this result may be of global significance because carbon sequestration by the tropical forests in Madagascar may be reduced as a result of this predicted change in forest composition.

Dietary data are used to categorize species diets, but these categorizations do not take into account the mutability of food resources in time or space, the level of interspecific competition in various communities as these resources change, nor the dietary flexibility of species. In this study, we assess the diets of three sympatric species, Eulemur rufifrons, Propithecus edwardsi, and Varecia variegata, in the Vatoharanana site in Ranomafana National Park, Madagascar. We determine dietary diversity, overlap, and interannual variation with data collected from 2001-2003. We then compare results on food preference and time feeding with data collected on each species in the late 1980s and early 1990s to determine whether these findings are consistent over the long-term. We found little inter-annual variation in the proportion of time spent eating particular plant parts for each of the lemur species during the three study years (2001-2003), and between the earlier and current study. Food items were not always consumed based solely on availability. Dietary diversity was lower in the two frugivorous species (Varecia and Eulemur) compared with the folivorous species (Propithecus), and V. variegata and E. rufifrons were more likely to focus their feeding time on one particular genus and plant part in each year. The study species used different strategies to deal with food, particularly fruit, shortages such as a plastic social structure (V. variegata), habitat shifting (E. rufifrons), and dietary switching (P. edwardsi). Although there was low dietary overlap between the study species, they depended on a small number of shared fruits in each of the study years (Chrysophyllum, Syzygium, Ocotea, Plagioscyphus), which may indicate some potential for interspecific competition. Because these lemur species, like all primates, lead relatively long lives (avg. >30 years) and have slow rates of aging, longitudinal studies are needed test hypotheses reliant on basic dietary information.