Chimpanzee feeding ecology and fallback food use in the montane forest of Nyungwe National Park,Rwanda

Almost all primates experience seasonal fluctuations in the availability of key food sources. However, the degree to which this fluctuation impacts foraging behavior varies considerably. Eastern chimpanzees (Pan troglodytes schweinfurthii) in Nyungwe National Park, Rwanda, live in a montane forest environment characterized by lower primary productivity and resource diversity than low‐elevation forests. Little is known about chimpanzee feeding ecology in montane forests, and research to date predominantly relies on indirect methods such as fecal analyses. This study is the first to use mostly observational data to examine how seasonal food availability impacts the feeding ecology of montane forest chimpanzees. We examine seasonal changes in chimpanzee diet and fallback foods (FBFs) using instantaneous scan samples and fecal analyses, supported by inspection of feeding remains. Chimpanzee fruit abundance peaked during the major dry season, with a consequent change in chimpanzee diet reflecting the abundance and diversity of key fruit species. Terrestrial herbaceous vegetation was consumed throughout the year and is defined as a “filler” FBF. In contrast to studies conducted in lower‐elevation chimpanzee sites, figs (especially Ficus lutea) were preferred resources, flowers were consumed at seasonally high rates and the proportion of non‐fig fruits in the diet were relatively low in the current study. These divergences likely result from the comparatively low environmental diversity and productivity in higher‐elevation environments.     

Use of novel objects to enhance environments of captive chimpanzees

A small group of chimpanzees was allowed to manipulate different quantities of novel objects in order to enhance their captive conditions. This procedure led to a general increase in the manipulation frequency by the apes. It decreased their inactivity and their self-grooming, and almost eliminated the abnormal behaviors displayed by one individual. The distribution of novel objects did not affect the total frequency of social interactions and did not increase the aggressivity of the animals, even though dominant individuals secured most of the objects when only a small number of them were available. Following their familiarization with the novel objects, the chimpanzees' manipulation frequency decreased whereas self-grooming and abnormal behaviors were increased. Suggestions are made on how to maximize the use of a limited bank of toys to occupy captive chimpanzees.     

The chimpanzee M blood-group antigen is a variant of the human M-N glycoproteins

Chimpanzee erythrocytes express strong M but weak, occasional N blood-group activity, as detected by anti-M and anti-N reagents. We have found that the M activity is carried by a major membrane glycoprotein that is similar but not identical to the human MM glycoprotein (glycophorin A). We have isolated and characterized this glycoprotein from erythrocyte membranes of four individual chimpanzees. The purified glycoproteins strongly inhibited agglutination of M cells by rabbit anti-human M sera and only weakly inhibited the agglutination of N cells by rabbit anti-human N sera. They also displayed medium-to-strong inhibitory activity against chimpanzee iso- and crossimmune antisera tested with chimpanzee erythrocytes of various V-A-B-D and W^c specificities, which are known as chimpanzee extensions of the human type M-N system and the Miltenberger counterpart, respectively. Each glycoprotein was cleaved with CNBr into three fragments, whose size, solubility, and composition were analogous to those obtained by similar treatment of the human M-N antigens. The amino-terminal fragment was found to be a glycooctapeptide whose amino acid composition and partial sequence indicated that it is an intermediate form of the human M and N glycooctapeptides. Its carbohydrate content comprised two threonine-linked saccharide units that, although similar in composition to the human threonine-linked units, were fewer in number than the three units found in the corresponding human glycooctapeptides. Structural similarities to the human antigens strongly suggest that the amino terminus bears the major antigenic determinants of the molecule, and the occurrence in this region of numerous, albeit rare, variants among humans and in chimpanzees indicates that the corresponding coding sequence of the structural gene is particularly susceptible to mutational events. We conclude that the chimpanzee M gene product is a variant of the human type and that the chimpanzee gene is an allele of the human polymorphic M-N locus.This research was supported by National Institutes of Health Grants GM 16389 and HL 19011 and March of Dimes Grant 1-661.     

Summation in chimpanzees (Pan troglodytes): Effects of amounts,number of wells,and finer ratios

Research conducted by Rumbaugh, Savage-Rumbaugh, and Hegel (1987) demonstrated that chimpanzees, presented with two pairs of quantities of chocolate chips, were capable of combining noncontiguous areas in order to choose the pair that contained the greater quantity. Further research (Rumbaugh, Savage-Rumbaugh, and Pate, 1988) showed that this ability is not based on the avoidance of the pair containing the smallest single amount or selection of the pair containing the largest single amount. In the experiments in the present sutdy, the influence of wells containing zero or one chocolate on summation and the consequences of eliminating the requirement to sum noncontiguous areas by interpersing trials in which only two (rather than four) food wells were investigated. It was found that summation of quantities occurred regardless whether food wells containing zero or one were present. Also, the chimpanzees performed significantly better on two-well trials than on four-well trials, thereby suggesting that they were not simply discounting the space between the wells on four-well trials but, instead, were employing a combinatorial process which we call summation.     

Fission-fusion social organization inAteles andPan

Recent research on the ecology and behavior of free-ranging spider monkeys (Ateles paniscus chamek) allows a more detailed comparison with the chimpanzee,Pan troglodytes, than has been possible previously. Despite their distant common ancestry, chimpanzees and spider monkeys share an unusual fission-fusion social system. In this paper, I compare subgroup size and composition, social unit structure, ranging behavior, patterns of philopatry and dispersal, and social relationships in the two taxa. It is proposed that spatial and temporal patchiness in food dispersion and abundance, resulting in a high-level of feeding competition between females within a group, has been the most important ecological selection pressure leading to the evolution of fission-fusion social organization in both species.     

A unique genomic sequence in the Wolf-Hirschhorn syndrome [WHS] region of humans is conserved in the great apes

The Wolf-Hirschhorn syndrome (WHS) is caused by a partial deletion in the short arm of chromosome 4 band 16.3 (4p16.3). A unique-sequence human DNA probe (39 kb) localized within this region has been used to search for sequence homology in the apes' equivalent chromosome 3 by FISH-technique. The WHS loci are conserved in higher primates at the expected position. Nevertheless, a control probe, which detects alphoid sequences of the pericentromeric region of humans, is diverged in chimpanzee, gorilla, and orangutan. The conservation of WHS loci and divergence of DNA alphoid sequences have further added to the controversy concerning human descent.     

Telomeric repeat [TTAGGG]n sequences of human chromosomes are conserved in chimpanzee (Pan troglodytes)

Summary Using a series of genetic parameters, attempts have been made for more than two decades to establish the close kinship of human (Homo sapiens) with chimpanzee (Pan troglodytes). Molecular and cytogenetic data presently suggest that the two species are closely related. The recent isolation of a human telomeric probe (P5097-B.5) has prompted us to cross hybridize it to chimpanzee chromosomes in order to explore convergence and/or divergence of the telomeric repeat sequences (TTAGGG)_n. On hybridization, the human probe bound to both ends (telomeres) of chimpanzee chromosomes, suggesting a concerted evolution of tandemly repeated short simple sequences (TTAGGG)_n. Even the terminal heterochromatin of chimpanzee chromosomes was found to be endowed with telomeric repeats, suggesting that evolution of heterochromatin and capping with tandemly repeated short sequences are highly complex phenomena.     

Hominization in the rainforest: The chimpanzee's piece of the puzzle

Many models of human evolution propose that key behavioral innovations were involved in the divergence of the human line from the ape line. An ecological reason, the shift from dense forests to a more open habitat, is suggested as the basis for these innovations. Primate models can be useful to our understanding of how environmental factors can affect such key behaviors. New results on forest chimpanzees demonstrate that for most patterns of behavior considered to favor a savanna model, the environmental influences are in opposition to the expectations. A new evaluation of the environmental influences on human evolution is required. We propose that either patterns of key human behaviors were inaccurately distinguished or that the hominization process started while the common ancestor of the chimpanzee and man was alive.     

Innovation in wild chimpanzees (Pan troglodytes)

Innovations of behavior have major implications for the concept of culture in animals. Innovation has rarefy been documented in wild animal populations. The chimpanzees of the Ta? National Park, C?te d’Ivoire, spontaneously included new patterns of behavior in their repertoire during our study. Some innovations were incorporated into a minority of the group members’ repertoire, whereas others, such as building day nests in trees and on the ground more frequently, became general behaviors. Similarly, new contexts for use of leaf- clipping behavior and novel ways of feeding on some leaves appeared and rapidly became part of the behavior of most group members. The environmental parameters were too stable to explain these new forms of behavior, as most of them took place within 1 month during the same dry season. In a similar way, leaf- grooming acquired a new function in Gombe chimpanzees. A process similar to social conventions could explain the emergence of these new functions for an existing behavior in a way rather similar to human “fashion. ” Three major characteristics of human culture — the absence of individual variations in the performance of the behavior, the general use of the behavior by group members, and the ability to modify the function of a behavior — characterize leaf-clipping in Ta? chimpanzees and leaf- grooming in Gombe chimpanzees.