Polymorphism of visual pigment genes in the muriqui (Primates, Atelidae).

Colour vision varies within the family Atelidae (Primates, Platyrrhini), which consists of four genera with the following cladistic relationship: {Alouatta[Ateles (Lagothrix and Brachyteles)]}. Spider monkeys (Ateles) and woolly monkeys (Lagothrix) are characteristic of platyrrhine monkeys in possessing a colour vision polymorphism. The polymorphism results from allelic variation of the single-locus middle-to-long wavelength (M/L) cone opsin gene on the X-chromosome. The presence in the population of alleles coding for different M/L photopigments results in a variety of colour vision phenotypes. Such a polymorphism is absent in howling monkeys (Alouatta), which, alone among platyrrhines, acquired uniform trichromatic vision similar to that of Old World monkeys, apes, and humans through opsin gene duplication. Dietary and morphological similarities between howling monkeys and muriquis (Brachyteles) raise the possibility that the two genera share a similar form of colour vision, uniform trichromacy. Yet parsimony predicts that the colour vision of Brachyteles will resemble the polymorphism present in Lagothrix and Ateles. Here we test this assumption. We obtained DNA from the blood or faeces of 18 muriquis and sequenced exons 3 and 5 of the M/L opsin gene. Our results affirm the existence of a single M/L cone opsin gene in the genus Brachyteles. We detected three alleles with predicted lambdamax values of 530, 550, and 562 nm. Two females were heterozygous and are thus predicted to have different types of M/L cone pigment. We discuss the implication of this result towards understanding the evolutionary ecology of trichromatic vision.

Ecological importance of trichromatic vision to primates.

Trichromatic colour vision, characterized by three retinal photopigments tuned to peak wavelengths of approximately 430 nm, approximately 535 nm and approximately 562 nm (refs 1, 2), has evolved convergently in catarrhine primates and one genus of New World monkey, the howlers (genus Alouatta). This uniform capacity to discriminate red-green colours, which is not found in other mammals, has been proposed as advantageous for the long-range detection of either ripe fruits or young leaves (which frequently flush red in the tropics) against a background of mature foliage. Here we show that four trichromatic primate species in Kibale Forest, Uganda, eat leaves that are colour discriminated only by red-greenness, a colour axis correlated with high protein levels and low toughness. Despite their divergent digestive systems, these primates have no significant interspecific differences in leaf colour selection. In contrast, eaten fruits were generally discriminated from mature leaves on both red-green and yellow-blue channels and also by their luminance, with a significant difference between chimpanzees and monkeys in fruit colour choice. Our results implicate leaf consumption, a critical food resource when fruit is scarce, as having unique value in maintaining trichromacy in catarrhines.

Field kit to characterize physical, chemical and spatial aspects of potential primate foods.

An outline is given for a field kit aiming to substantially increase the in situ knowledge gleaned from feeding studies of primates. Measurements are made of colouration (spectrum of non-specular reflection) and many mechanical, chemical and spatial properties of primate foods.

Gender differences in HIV risk behaviour of injecting drug users in Edinburgh.

A multi-site sample of currently-injecting drug users (IDUs) comprising 344 men and 136 women was recruited in Edinburgh. Sixty-seven per cent of the sample said they had at some time used injecting equipment already used by another person and 25% admitted doing so in the 6 months before interview. Whereas women who injected with used equipment obtained it predominantly from a sexual partner, for men the source was more often a close friend or someone whose HIV status they were unlikely to know. In the 6 months before interview, 40% of men, compared with 20% of women, had more than one heterosexual partner. This difference was associated with a higher proportion of men with steady partners also having casual partners. Women IDUs were more likely to have regular partners who injected (57% vs 26%). Though sharing of injecting equipment has already diminished in Edinburgh, further measures are needed to eliminate it. For injectors here, the risk of infection from unprotected heterosexual intercourse may now be greater than that from sharing injecting equipment, particularly for women. Other methods of encouraging changes in sexual behaviour need to be investigated and successful ones promoted.

HIV in injecting drug users in Edinburgh: prevalence and correlates.

A citywide sample of injecting drug users (IDUs) who had injected in the previous 6 months was recruited in Edinburgh. Interviewers administered a questionnaire enquiring about drug use, sharing of injecting equipment, sexual behavior, and imprisonment. A specimen of saliva was assayed for human immunodeficiency virus (HIV) IgG. HIV antibody prevalence in 346 IDUs recruited between June 1992 and October 1993 was 19.7% (95% confidence limits, 15.5 and 23.9%). Univariate analyses indicated that infection was significantly associated with being 27 to 36 years of age, starting to inject between 1975 and 1980, injecting in 1980-1987 and, particularly, 1982-1984, injecting in more than 7 years since 1979, reusing injecting equipment already used by another IDU in 1980-1987, being imprisoned, using equipment used by a fellow prisoner, and residing in north Edinburgh. Multivariate analysis showed that being 27-36 years of age, injecting in 1982-1984, and being imprisoned were independently related to being HIV positive. The risk of being infected increased with the number of times of imprisonment. A quarter of the sample said that they had used injecting equipment already used by another person in the 6 months before interview, and 70% said that they had ever done so. Of IDUs who started injecting after 1986, 4.5% were HIV positive. These findings suggest that the potential for HIV transmission by contaminated equipment still exists in Edinburgh. This is particularly so in prison, where IDUs do not have access to new needles and syringes.