Two monoclonal antibodies (mAbs), 5A4 and 6D6, directed against cortisol, have been obtained; 6D6 is used in an assay kit for cortisol. The antibodies also recognize other, structurally related steroids present in the sample assayed. To improve the specificity of the assay, we aimed to minimize the recognition of non-cortisol steroids by the two anti-cortisol mAbs. Our strategy consisted in constructing an efficient expression vector in E. coli which produced the single-chain variable fragment (scFv) of the mAbs in the periplasmic space. We demonstrated that temperature and inducer concentration of the bacterial culture influenced dramatically the yield of active scFv. From the nucleotide sequence we constructed a three-dimensional model of the two variable fragments in order to understand why related steroids are, or are not recognized by the antibody. For both antibodies, we have identified chemical groups which are probably involved in the binding of the steroid haptens and the antibodies. The hydrophobic pocket formed by the antibody comprises two or three tryptophan residues which can interact with the steroid nucleus by stacking. The serine at position 35 of the heavy chain is buried in the back of the pocket and can form a hydrogen bond with the 20-keto group of the cortisol. The stacking interactions and the hydrogen bond orient the steroid in the pocket. This reactivity of the binding site is sustained by the analysis of the cross-reactions of related steroids with the mAbs.

Most methods of estimating chimpanzee population densities rely on nest counts. We tested the most frequently used techniques on a known chimpanzee community living in the rainforest of the Taï National Park, Côte d’Ivoire. The best density estimates are given by counts that assume groups of nests to be distributed randomly and that use the mean group size for homogenous habitat but the median for heterogenous habitats. Correction for real forest cover within the region should be made because chimpanzees make nests only in forested regions. This method gave the exact chimpanzee density for the Taï population, i.e. 1.7 nest builders/km2. For the nationwide survey, we first estimated the chimpanzee density for different types of habitat (e.g. intact primary forest: 1.64 chimpanzees/km2; degraded forests: 0.4 chimpanzees/km2; human encroached forests and mosaic habitats: 0.09 chimpanzees/km2). Second, we estimated the total forest cover of the country with satellite pictures. This gave an estimated chimpanzee population in Côte d’Ivoire of about 11,676 ± 1,168 individuals, which equals the number of spectators at a soccer game in an average European town. Sadly, only three National Parks may have chimpanzee populations large enough to be viable, whereas the rest are scattered and isolated small populations that are already threatened in their survival.

Nut cracking behaviour, once thought to be typical for most West African chimpanzees, is in reality restricted to a very small area within the evergreen forest perimeter. In Côte d'Ivoire, the N'Zo-Sassandra river is the eastern limit of its distribution. Neither the chimpanzee density, the density of nut-producing tree, anvils and hammers, nor the type of forest can explain this clear-cut limit. From two cases of chimpanzee populations less than 50 km apart on either side of the river we can conclude that this limit is most probably cultural. This result completes the image of cultural behaviour in wild chimpanzees having irregular and unpredictable distribution patterns similar to those of human culture.