Male Cayo Santiago rhesus macaques (Macaca mulatta) tend to have greater molar wear than females at comparable ages: exploring two possible reasons why

Objectives

(1) To investigate sex differences in molar wear in known-age Cayo Santiago rhesus macaques (Macaca mulatta) and, (2) To explore sex differences in body weight and molar eruption timing as factors influencing sex differences in molar wear.

Materials and Methods

Data set I comprises wear scores, ages and body weights of 212 living monkeys included in the 1985 roundup. Data set II consists of molar wear measurements taken on 2D images of 103 of these monkeys' dental remains. Ordinal logistic regression was used to analyze the first data set. General linear models were used to analyze the second.

Results

Males generally exhibited more wear than females at equivalent chronological ages, though results varied by tooth type for the second data set. Male body weight in the full 1985 living sample was significantly related to dental wear, when age was taken into account; however, when males less than eight years of age were eliminated from the sample, the association between dental wear and weight became statistically insignificant. Analysis of the second data set suggested no statistically significant sex difference in dental wear for third molars, despite the approximately two year sex difference in eruption age for this tooth type.

Discussion

This study suggests that body weight in males might be a predictor of dental wear and that if it is, body weight might also influence sex differences in dental wear. Sex differences in dental eruption timing do not appear to explain sex differences in dental wear in this sample.

Morphological variation in Homo erectus and the origins of developmental plasticity

Homo erectus was the first hominin to exhibit extensive range expansion. This extraordinary departure from Africa, especially into more temperate climates of Eurasia, has been variously related to technological, energetic and foraging shifts. The temporal and regional anatomical variation in H. erectus suggests that a high level of developmental plasticity, a key factor in the ability of H. sapiens to occupy a variety of habitats, may also have been present in H. erectus. Developmental plasticity, the ability to modify development in response to environmental conditions, results in differences in size, shape and dimorphism across populations that relate in part to levels of resource sufficiency and extrinsic mortality. These differences predict not only regional variations but also overall smaller adult sizes and lower levels of dimorphism in instances of resource scarcity and high predator load. We consider the metric variation in 35 human and non-human primate 'populations' from known environmental contexts and 14 time- and space-restricted paleodemes of H. erectus and other fossil Homo Human and non-human primates exhibit more similar patterns of variation than expected, with plasticity evident, but in differing patterns by sex across populations. The fossil samples show less evidence of variation than expected, although H. erectus varies more than Neandertals.This article is part of the themed issue 'Major transitions in human evolution'.

Free-ranging Cayo Santiago rhesus monkeys (Macaca mulatta): III. Dental eruption patterns and dental pathology

This article describes the dental eruption patterns, dentition, and dental wear, including tooth loss and breakage, of the free-ranging population of rhesus monkeys (Macaca mulatta) on Cayo Santiago (CS), Puerto Rico, ranging from 24 hr to 25 years old. Of the 694 monkeys on the island in the year 1985, 688 (99.1%; 366 males, 322 females) were captured and the dentition of 685 subjects (98.7% of the total population; 366 males, 319 females) was examined. Animals ranged in age from less than 24 hr to 331 months (27.58 years), encompassing the entire life span of the CS macaques. Results demonstrated that the first deciduous teeth appeared as early as the third day of life and that the sequence of dental eruption was comparable to the pattern observed in laboratory rhesus. However, there were slight differences in the age of eruption of individual teeth. For example, the canines and third molars erupted about a year later in the CS macaques compared to some laboratory rhesus. Overall, CS rhesus had good oral health and dental condition although tooth wear, loss, and breakage were common in aged animals, especially in males. This report, combined with earlier studies on morphological characteristics and skeletal remains of the CS macaques, provides the basis for further studies on the biology, genetics, life history, and effects of the environment on rhesus monkeys.

Selection on adult female body size in rhesus macaques

Body size is a critical descriptor of animal biology with many ecological, behavioral, and physiological correlates. Size differences among species or between populations are often explained by adaptive scenarios invoking the action of selection, although studies of selection in action on primate body size, or other phenotypic traits, are very rare. We document directional selection for larger skull and postcranial size in the skeletons of female semi-free ranging rhesus macaques (Macaca mulatta) from Cayo Santiago, born between 1957 and 1982. Larger females live to later ages and consequently give birth to more offspring. Despite selection for larger size, there are indications of a trend toward generally smaller size in the same birth cohorts. This trend is provisionally attributed to increasing population density, though other environmental factors may play a role. Small selection differentials and low heritabilities also limit the genetic response to selection. Alternative explanations for increasing adult size in the skull and postcranium, such as continued adult growth or pathological bone deposition, do not adequately explain the observed age-related trends and are inconsistent with longitudinal studies of adult skeletal change.

Role of the prehensile tail during ateline locomotion: Experimental and osteological evidence

The dynamic role of the prehensile tail of atelines during locomotion is poorly understood. While some have viewed the tail of Ateles simply as a safety mechanism, others have suggested that the prehensile tail plays an active role by adjusting pendulum length or controlling lateral sway during bimanual suspensory locomotion. This study examines the bony and muscular anatomy of the prehensile tail as well as the kinematics of tail use during tail-assisted brachiation in two primates, Ateles and Lagothrix. These two platyrrhines differ in anatomy and in the frequency and kinematics of suspensory locomotion. Lagothrix is stockier, has shorter forelimbs, and spends more time traveling quadrupedally and less time using bimanual suspensory locomotion than does Ateles. In addition, previous studies showed that Ateles exhibits greater hyperextension of the tail, uses its tail to grip only on alternate handholds, and has a larger abductor caudae medialis muscle compared to Lagothrix. In order to investigate the relationship between anatomy and behavior concerning the prehensile tail, osteological data and kinematic data were collected for Ateles fusciceps and Lagothrix lagothricha. The results demonstrate that Ateles has more numerous and smaller caudal elements, particularly in the proximal tail region. In addition, transverse processes are relatively wider, and sacro-caudal articulation is more acute in Ateles compared to Lagothrix. These differences reflect the larger abductor muscle mass and greater hyperextension in Ateles. In addition, Ateles shows fewer side-to-side movements during tail-assisted brachiation than does Lagothrix. These data support the notion that the prehensile tail represents a critical dynamic element in the tail-assisted brachiation of Ateles, and may be useful in developing inferences concerning behavior in fossil primates.

Effect of parity on bone mineral density in female rhesus macaques from Cayo Santiago

This cross-sectional study investigates the relationship between parity, bone mineral density, and spontaneous osteopenia/osteoporosis in a large skeletal population of female rhesus macaques (Macaca mulatta) from the free-ranging colony of Cayo Santiago, Puerto Rico. The sample consists of 119 mature female monkeys aged 4.0-22.2 years at time of death. The data consist of measurements of bone mineral content (BMC) and bone mineral density (BMD), obtained from dual-energy X-ray absorptiometry (DEXA) of the last lumbar vertebra. After controlling for age, there is a significant increase in BMD of the spine with increasing parity (P = 0.0006), up to a parity of 7 offspring. Thus, high parity initially has a positive effect on BMD in female rhesus monkeys, but this positive effect disappears with parities that are greater than 7 offspring. After controlling for parity, however, age has a negative (P = 0.015) effect on BMD, beginning several years after the attainment of peak BMD (age 9.5 years). Thus, it appears that parity initially mitigates the effects of aging, but the positive effect of parity on BMD is eventually overwhelmed by the aging process. Mean BMC and BMD values are higher in parous females compared to nulliparous females in the same age range. Similarly, females with low parity have significantly lower mean BMD values than do age-matched high-parity controls, and the frequency of osteopenia and osteoporosis is greater in low-parity females. Forty-three percent (43%) of the osteopenic/osteoporotic females in the sample are members of the low-parity group, even though it composes only 13% (16/119) of the entire sample. This study demonstrates that the free-ranging female rhesus monkeys from Cayo Santiago are a good nonhuman primate model for the study of bone mineral density, parity, osteopenia, and osteoporosis.

Ontogeny of locomotion in rhesus macaques (Macaca mulatta): II. Postural and locomotor behavior and habitat use in a free-ranging colony

This study quantifies changes in postural and locomotor behavior as well as habitat use across the life span of free-ranging rhesus macaques (Macaca mulatta) in the Cayo Santiago colony in Puerto Rico. It focuses on developmentally related changes from birth to adulthood, and complements an earlier study by Turnquist and Wells ([1994] J Hum Evol 26:487-499) on the early postnatal ontogeny of the musculoskeletal system of the same colony. A total of 6,551 locomotor and postural events was analyzed. Selection and use of substrate correlated well with age. The more sedentary adult and dependent infant select safe, wide, horizontal arboreal settings in contrast to the older Infant IIs and Juveniles, who are learning locomotor and postural skills through independent chase and play. Infant macaques, when independent, often employ a low center of gravity and widely abducted limbs in order to broaden their contact with the base of support. This study shows that the previously reported ontogenetic changes in morphology are closely paralleled by changes in postural and locomotor behavior, and these in turn are correlated to changes in habitat use, particularly during the formative years.

Bone mineral density, osteopenia, and osteoporosis in the rhesus macaques of Cayo Santiago

This cross-sectional study investigates metabolic bone disease and the relationship between age and bone mineral density (BMD) in males and females of a large, well-documented skeletal population of free-ranging rhesus monkeys (Macaca mulatta), from the Caribbean Primate Research Center Museum collection from Cayo Santiago, Puerto Rico. The sample consists of 254 individuals aged 1.0-20+ years. The data consist of measurements of bone mineral content and bone mineral density, obtained from dual-energy X-ray absorptiometry (DEXA), of the last lumbar vertebra from each monkey. The pattern of BMD differs between male and female rhesus macaques. Females exhibit an initial increase in BMD with age, with peak bone density occurring around age 9.5 years, and remaining constant until 17.2 years, after which there is a steady decline in BMD. Males acquire bone mass at a faster rate, and attain a higher peak BMD at an earlier age than do females, at around 7 years of age, and BMD remains relatively constant between ages 7-18.5 years. After age 7 there is no apparent effect of age on BMD in the males of this sample; males older than 18.5 years were excluded due to the presence of vertebral osteophytosis, which interferes with DEXA. The combined frequency of osteopenia and osteoporosis in this population is 12.4%. BMD values of monkeys with vertebral wedge fractures are generally higher than those of virtually all of the nonfractured osteopenic/osteoporotic individuals, thus supporting the view that BMD as measured by DEXA is a useful but imperfect predictor of fracture risk, and that low BMD may not always precede fractures in vertebral bones. Other factors such as bone quality (i.e., trabecular connectivity) should also be considered. The skeletal integrity of a vertebra may be compromised by the loss of key trabeculae, resulting in structural failure, but the spine may still show a BMD value within normal limits, or within the range of osteopenia.

Pendular motion in the brachiation of captive Lagothrix and Ateles

Pendular motion during brachiation of captive Lagothrix lagothricha lugens and Ateles fusciceps robustus was analyzed to demonstrate similarities, and differences, between these two closely related large bodied atelines. This is the first captive study of the kinematics of brachiation in Lagothrix. Videorecordings of one adult male of each species were made in a specially designed cage constructed at the DuMond Conservancy/Monkey Jungle, Miami, FL. Java software (Jandel Scientific Inc., San Rafael, CA) was used for frame-by-frame kinematic analysis of individual strides/steps. Results demonstrate that the sequence of hand and tail contacts differ significantly between the two species with Lagothrix using a new tail hold with every hand hold, while Ateles generally utilizes a new tail hold with only every other hand hold. Stride length and stride frequency, even after adjusting for limb length, also differ significantly between the two species. Lagothrix brachiation utilizes short, choppy strides with quick hand holds, while Ateles uses long, fluid strides with longer hand holds. During brachiation not only is Lagothrix's body significantly less horizontal than that of Ateles but also, within Ateles, there are significant differences between steps depending on tail use. Because of the unique nature of tail use in Ateles, many aspects of body positioning in Lagothrix more closely resemble Ateles steps without a simultaneous tail hold rather than those with one. Overall pendulum length in Lagothrix is shorter than in Ateles. Tail use in Ateles has a significant effect on maximum pendulum length during a step. Although neither species achieves the extreme pendulum effect and long period of free-flight of hylobatids in fast ricochetal brachiation, in captivity both consistently demonstrate effective brachiation with brief periods of free-flight and pendular motion. Morphological similarities between ateline brachiators and hylobatids are fewer and less pronounced in Lagothrix than in Ateles. This study demonstrates that Lagothrix brachiation is also less hylobatid-like than that of Ateles.

Skeletal survey of Cayo Santiago rhesus macaques: osteoarthritis and articular plate excrescences

OBJECTIVES

This study was performed to complement studies on spondyloarthropathy in rhesus macaques by quantifying and characterizing another major form of arthritis and contrasting it with osteoarthritis.

METHODS

Skeletons of 269 macaques of known age and troop affiliation from the free-ranging Cayo Santiago colony (Caribbean Primate Research Center) were macroscopically surveyed for the presence of articular changes of osteoarthritis, articular plate excrescences, and calcifications that project back over the joint surface in all diarthrodial joints. Statistical tests were used to establish the independence of pathological conditions, age, gender, troop membership, and specific joint involvement.

RESULTS

Subchondral articular surface excrescences or calcific plate-like articular surface overgrowth were noted in 17% and osteoarthritis in 18% of Cayo Santiago macaques. Distribution of joint involvement and sex ratio (1:1) of the former condition were independent of either troop membership or the distribution of osteoarthritis.

CONCLUSION

Three major forms of arthritis are common in rhesus macaques: osteoarthritis, spondyloarthropathy, and a category that might be referred to as apical plate excrescences (APE). The latter is very different from spondyloarthropathy, rheumatoid arthritis, osteoarthritis, gout, and infectious arthritis. It is quite similar to what in the past has been referred to as the radiographic form of calcium pyrophosphate deposition disease (CPPD) in humans. A new name has not been offered for the identification/categorization of this phenomenon in dry bone. Its occurrence in rhesus macaques appears to present a natural model for characterization of genetic, immunologic, and environmental aspects of this phenomenon. The acronym APE is offered for consideration in naming this category of arthritis in skeletal material.

Naturally occurring inflammatory arthritis of the spondyloarthropathy variety in Cayo Santiago rhesus macaques (Macaca mulatta)

OBJECTIVE

The establishment of an animal model is a major priority in the battle to control inflammatory arthritis. Exploration to date has not yet identified a viable model for rheumatoid arthritis (RA), while artificial (e.g., collagen-induced) models do not seem to accurately represent RA. They, at least superficially, resemble human spondyloarthropathy. This study assesses the evidence for a common naturally-occurring spondyloarthropathy in a colony of free-ranging rhesus macaques.

METHODS

Skeletal elements of 275 Macaca mulatta of known age and troop affiliation from the Cayo Santiago colony [Caribbean Primate Research Center (CPRC)] were surveyed for the presence of spondyloarthropathy and osteoarthritis. Fisher exact tests established the independence of each pathological condition, age, sex, troop and specific joint.

RESULTS

Spondyloarthropathy was evident in 10% of females and 7% of males. In surviving troops, its frequency in 82 animals over 8 years of age was 20%. The skeletal distribution of spondyloarthropathy was independent of troop membership. Osteoarthritis affected 20% of females and 4% of males and was independent of their troop. Significant differences in the frequencies of specific joint involvement were found when the natural model, particularly in the polyarticular subgroup, was compared to the collagen-induced model.

CONCLUSIONS

Naturally-occurring spondyloarthropathy afflicts 20% of susceptible-aged individuals in surviving macaque troops at the CPRC. This phenomenon appears to present a unique natural model for the characterization of the genetic, immunological and environmental contributions to this disease, which afflicts 0.5-5% of the human population. This natural model would appear to supplant the need for the collagen-induced large animal model.

Osteoarthritis of the hand in nonhuman primates: a clinical, radiographic, and skeletal survey of Cayo Santiago rhesus macaques

We describe the relative prevalence and pattern of distribution of osteoarthritis (OA) in the hands of elderly (> 15 years) rhesus macaques using clinical, radiographic, and skeletal examinations. In the clinical study the prevalence of nodes was 72% and 16% in the distal inter-phalangeal joints (DIPJ) and proximal inter-phalangeal joints (PIPJ), respectively, 31% of all monkeys had polyarticular nodes. Radiographic OA was present in 55%, 9.1%, and 0% of the DIPJs, PIPJs, and thumb base, respectively. Skeletal OA as defined by joint surface eburnation for the DIPJ, PIPJ, and thumb base were 16%, 8%, and 2%, respectively. A similar pattern of hand OA with humans is described except for the thumb base OA. This may be due to the relatively rudimentary manipulative role of the macaque thumb. The finding of polyarticular nodal OA raises the possibility of a common pathogenensis for IPJ OA amongst primates.

Current status of the Caribbean Primate Research Center Museum

The history of the Caribbean Primate Research Center Museum, including the Cayo Santiago Skeletal Collection, is briefly reviewed. Since 1971 skeletons of free-ranging rhesus monkeys from Cayo Santiago have been systematically collected for osteological research. Since 1981 the skeletons from the six species of New and Old World monkeys maintained at Sabana Seca have also been collected. The CPRC Museum was established the following year to house this comparative skeletal collection, as well as alcohol-stored tissue specimens and a library. The current status of the collection, including numbers and types of specimens, and use policies, are presented to give an overview of the research potential of the Museum for biological, anthropological, pathological, and biomedical research.

Passive joint mobility in patas monkeys (Erythrocebus patas): rehabilitation of caged animals after release into a free-ranging environment

A previous study of passive joint mobility in patas monkeys (Erythrocebus patas) showed that laboratory-caged animals had significantly greater mobility in most joints than age/sex matched free-ranging monkeys. Passive joint mobility on 27 of the same animals was measured 6 months after the caged animals were released onto a 40-hectare island. The results show that within 6 months of becoming free-ranging, typical passive joint mobility is restored. Thus, although caging directly affects measurements of morphologically-determined features in patas monkeys, confinement itself does not necessarily prevent rehabilitation if the immature monkeys are released into a free-ranging environment.

Forelimb musculature and ligaments in Ateles, the spider monkey

The forelimb anatomy of Ateles, the spider monkey, is a key factor in its locomotor adaptation because of its extensive use of bimanual suspensory locomotion in addition to climbing and quadrupedal walking (Mittermeier, 1978; and Fleagle and Mittermeier, 1980). The detailed description of the muscles and ligaments of the forelimb of Ateles provided in this paper can be of considerable use not only to primate morphologists interested in both extant and fossil primates but also to functional anatomists. All measurements were made on fresh, unembalmed specimens. Standard anatomical descriptions of the musculature, cross-sectional areas of the muscles, dry weights of muscle bellies, and relative proportions of antagonistic muscles are reported as are the joint ligaments and potential range of motions of the joints. These anatomical data are compared briefly to published data on Alouatta, the howler monkey, which is predominantly a quadruped (Fleagle and Mittermeier, 1980; and Schön Ybarra, 1982).

Influence of age, sex, and caging on joint mobility in the patas monkey (Erythrocebus patas)

Normal range of joint mobility in the extremities of the patas monkey, Erythrocebus patas, was established for a free-ranging colony of 64 animals at La Parguera, Puerto Rico (Caribbean Primate Research Center). Eighty-five animals that had been caged (30" X 30" cages) for up to 5 years were used for comparison. Passive joint mobility of anesthetized animals was measured with a goniometer. Nine parameters (five on the forelimb and four on the hindlimb) were measured on each animal. The data were sorted into subsets according to the animal's age, sex, place of birth, and type of confinement, if any. The number of animals in each subset was recorded and the mean (in degrees) and standard deviation for each parameter were calculated. A P less than or equal to 0.05 on two-tailed Student's t-tests was considered significant. Comparisons between free-ranging males and females showed significant differences in one or two parameters for all age groups. A cross-sectional sample of free-ranging animals of both sexes showed that significant changes in joint mobility occurred only in the first 18 months of life. Joint mobility of all caged animals, however, was highly variable, and even between the more mature animals there were significant differences in several parameters. Almost all comparisons of subsets of the same age and sex showed significant differences between caged and free-ranging animals in at least one parameter. When the caged animals were laboratory-born, however, these differences were significant in five out of nine parameters. The results suggest that, although caging itself affects joint mobility, the age of first confinement may have an even greater effect than the length of the confinement.