Selection and the transferrin polymorphism in rhesus monkeys (Macaca mulatta)

Genomic resources for rhesus macaques (Macaca mulatta)

Rhesus macaques (Macaca mulatta) are among the most extensively studied of nonhuman primates. This species has been the subject of many investigations concerning basic primate biology and behavior, including studies of social organization, developmental psychology, physiology, endocrinology, and neurodevelopment. Rhesus macaques are also critically important as a nonhuman primate model of human health and disease, including use in studies of infectious diseases, metabolic diseases, aging, and drug or alcohol abuse. Current research addressing fundamental biological and/or applied biomedical questions benefits from various genetic and genomic analyses. As a result, the genome of rhesus macaques has been the subject of more study than most nonhuman primates. This paper briefly discusses a number of information resources that can provide interested researchers with access to genetic and genomic data describing the content of the rhesus macaque genome, available information regarding genetic variation within the species, results from studies of gene expression, and other aspects of genomic analysis. Specific online databases are discussed, including the US National Center for Biotechnology Information, the University of California Santa Cruz genome browser, Ensembl genome browser, the Macaque Genotype and Phenotype database (mGAP), Rhesusbase, and others.

Terminal investment and senescence in rhesus macaques (Macaca mulatta) on Cayo Santiago

Long-lived iteroparous species often show aging-related changes in reproduction that may be explained by 2 non-mutually exclusive hypotheses. The terminal investment hypothesis predicts increased female reproductive effort toward the end of the life span, as individuals have little to gain by reserving effort for the future. The senescence hypothesis predicts decreased female reproductive output toward the end of the life span due to an age-related decline in body condition. Nonhuman primates are ideal organisms for testing these hypotheses, as they are long lived and produce altricial offspring heavily dependent on maternal investment. In this study, we integrated 50 years of continuous demographic records for the Cayo Santiago rhesus macaque (Macaca mulatta) population with new morphometric and behavioral data to test the senescence and terminal investment hypotheses. We examined relationships between maternal age and activity, mother and infant body condition, interbirth intervals, measures of behavioral investment in offspring, and offspring survival and fitness to test for age-associated declines in reproduction that would indicate senescence, and for age-associated increases in maternal effort that would indicate terminal investment. Compared with younger mothers, older mothers had lower body mass indices and were less active, had longer interbirth intervals, and spent more time in contact with infants, but had infants of lower masses and survival rates. Taken together, our results provide strong evidence for the occurrence of reproductive senescence in free-ranging female rhesus macaques but are also consistent with some of the predictions of the terminal investment hypothesis.

Recent studies of iron deficiency during brain development in nonhuman primates

Recent studies of the effects of developmental iron deficiency (ID) and iron deficiency anemia in nonhuman primates have provided new insights into this widespread and well-recognized human nutritional deficiency. The rhesus monkey was the animal model in these experiments, which used extensive hematological and behavioral evaluations in addition to noninvasive brain measures. Two important findings were as follows: 1) different behavioral consequences depending on the timing of ID relative to brain developmental stages and 2) the potential for long-lasting changes in brain iron regulatory systems. Further work in this model, including integration with studies in humans and in laboratory rodents, is ongoing.

On the quantification of suckling intensity in primates

The inhibitory effect that suckling has on the reproductive function of primate mothers varies as a function of the intensity with which they are suckled. Here we present an easily computed index of one parameter of suckling intensity, namely the temporal patterning of suckling bouts. High intensity suckling is characterized by frequent nursing bouts demarcated by short interbout intervals. Therefore, our suckling index is based on the brevity of observed interbout intervals, more specifically the proportion of such intervals that fail to exceed a criterion length. The index is an appropriate means of making interspecific comparisons of the development of infant suckling and is well suited for application to field data that include interbout intervals that were not observed in their entirety. To demonstrate its utility, we apply the index to field data collected on the suckling behavior of free-ranging rhesus monkey (Macaca mulatta) infants in India. In this context, we demonstrate that, in rhesus, between-infant differences in suckling intensity manifest themselves early in the postpartum period and contribute to between-female differences in the timing of first mating postpartum.

Determinants of postnatal weight in infant rhesus monkeys: implications for the study of interindividual differences in neonatal growth

This paper provides an analysis of infant body weights obtained from a sample of 38 rhesus monkey infants (Macaca mulatta) aged 29-165 days, i.e., animals still nutritionally dependent on their mothers. We examine the data on neonatal weights in relation to a number of factors, most notably, the sex of the infants, and the age and adiposity of their mothers. The infant body weights represent cross-sectional rather than longitudinal data; because they were mostly free-ranging animals, the infants were weighted just once each. Nevertheless, the results of our analysis strongly suggest that early postnatal growth in free-ranging rhesus is dependent on both maternal fatness and age. They also suggest that, although male infants are generally heavier than like-aged female infants, they do not grow any faster during the early postnatal period. Here, we speculate that the associations between infant size and both maternal age and adiposity are the result of between-mother differences in lactational output.

Molecular genetic variation and individual survival during population crashes of an unmanaged ungulate population

Theoretical models of the effect of population bottlenecks on genetic variation assume that individuals are removed at random from the population. We investigated this assumption in a naturally regulated, unstable population of Soay sheep (Ovis aries). During rapid population declines or 'crashes', individuals were not removed at random with respect to genotype: we found associations between individual survival and certain genotypes at five polymorphic protein or microsatellite DNA loci (Ada, Got, Tf, MAF18 and OPACAP). Some loci appeared to show simple associations with survival whereas others had more complex interactions with crash year or age: all displayed different patterns of association between the sexes. Simple overdominance was not a general feature of our data; it seems likely that fluctuating selecting, countervailing selection in different fitness components or frequency-dependent selection may explain the pattern and complexity of the associations shown at different loci. Our study cannot distinguish between selection acting at these loci or at other, closely linked loci. However, our empirical study implies that the molecular genetic outcome of population bottlenecks in natural populations does not always follow theoretical expectations based on the random removal of genotypes. Bottlenecks in which individuals are removed at random are distinct from bottlenecks in which there is scope for selection via non-random survival of individuals.

The genetic consequences of primate social organization: a review of macaques, baboons and vervet monkeys

Primates, as long-lived, iteroparous, socially complex mammals, offer the opportunity to assess the effects of behavior and demography on genetic structure. Because it is difficult to obtain tissue samples from wild primate populations, research in this area has largely been confined to terrestrial and semi-terrestrial old world monkeys (e.g., rhesus and Japanese macaques, vervets and several subspecies of baboons). However, these species display a multi-male, multi-female social structure commonly found in many other primate and non-primate mammals. Electrophoretic analyses of blood proteins from individually recognized and/or marked wild Himalayan rhesus monkeys, themselves the subject of long-term behavioral and demographic research, have begun to reveal the genetic consequences of such phenomena as social group fission, male-limited dispersion, non-consanguineous mating patterns, and agonistically defined male dominance. Specifically, rhesus social groups, consisting primarily of clusters of maternal relatives, appear to be non-random samples of a population's genotypes and genes. The genetic effects of social group fission are highly dependent on each group's size, demographic structure, and average degree of relatedness. In all cases fission contributes to the degree of intergroup genetic differentiation. Male-limited dispersion appears both to retard genetic differentiation between social groups and to lead to mating patterns that result in an avoidance of consanguinity. Groups, therefore, appear to be genetically outbred. Comparing these results with studies of other free-ranging or wild cercopithecines allows several generalizations: (a) genetic variation seems to be evenly distributed throughout each local population of multi-male social groups; (b) social groups, however, because they contain clusters of relatives, are distinctive in their specific frequencies of genes; (c) the degree of genetic differentiation between a population's social groups, because of the effects of social group fission and non-deterministic forms of male dispersal, is somewhat greater than expected on the basis of migration rates alone; and (d) the asymmetrical pattern of dispersion with respect to sex effectively precludes inbreeding in any one social group or the population as a whole. These observations have important implications for understanding the unusually rapid rates of evolution among the primates.

Genetics of a wild population of rhesus monkeys (Macaca mulatta): II. The Dunga Gali population in species-wide perspective

Genetic variability in a population of wild rhesus monkeys near the village of Dunga Gali, Northwest Frontier Province, Pakistan (Melnick et al., Am. J. Phys. Anthropol. 63:341-360, 1984) was compared to similar variation in other wild-caught rhesus monkeys. Regional samples of rhesus from different parts of Asia all displayed similar amounts of variation (i.e., P and Hi) and were consistently more variable than the Dunga Gali local population. Despite these differences in the level of genetic variation, genetic diversity is fairly evenly distributed across the species range. Thus only 3-9% of the total gene diversity of Macaca mulatta can be attributed to differences among major regions. The differences that do exist tend toward a weak geographic cline with clustering of populations into an eastern and a western group. Both selection and drift/migration models explain this general genetic homogeneity. More genetic (protein and DNA) and zoogeographic data are necessary to choose between these models.

Segregation distortion at the transferrin locus in Macaca mulatta

The transferrin phenotypes of 256 rhesus monkeys and their parents were identified by polyacrylamide gel electrophoresis. The segregation ratio for phenotypes involving only alleles of high electrophoretic mobility was statistically significantly higher than expected and suggests that selection favors these more negatively charged transferrins. Electrostatic-dependent processes associated with the binding and transportation of iron might be responsible for this outcome.