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.

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.

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.

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): II. Passive joint mobility.

Recent studies on the effects of caging on joint mobility and the correlations between joint mobility and use of the extremities have pointed out the need for baseline values that are readily available in the literature. This report provides normative data on the passive mobility of the major joints of free-ranging Cayo Santiago rhesus monkeys (Macaca mulatta). The sample in this cross-sectional study is large (661 animals including 315 males, 346 females), and it spans the entire age spectrum (24 hours to 25 years) of the population. Included are data on motion in the sagittal plane at six joints: shoulder, elbow, wrist, hip, knee, and ankle. Results indicated that passive joint mobility changes in a nonlinear fashion throughout the life cycle. The apparent rapid decline in mobility from birth through puberty parallels rapid changes in body size and proportions in young animals. Joint mobility is relatively stable in prime-age adults, whereas it is generally more restricted in older monkeys. Both genders follow a similar pattern, but timing differs somewhat. Although the primary purpose of this paper is to present numerical data on the Cayo Santiago population, the results are compared with previous, more limited studies of both captive and free-ranging rhesus macaques.

Free-ranging Cayo Santiago rhesus monkeys (Macaca mulatta): I. Body size, proportion, and allometry.

This paper presents comprehensive baseline data on body size and proportion of 661 (315 male, 346 female) free-ranging Cayo Santiago rhesus monkeys (Macaca mulatta) ranging in age from 24 hours to 25 years. All animals were born and raised in the free-ranging colony on Cayo Santiago, and exact ages were known for all. Tabular data from this cross-sectional study are provided to enable comparisons with data from laboratory, wild, and other captive populations of rhesus monkeys, as well as with other species. Despite the extensive literature on rhesus monkey behavior and biology, to date published accounts of its morphometrics have been limited to only a few measurements from animals of unknown age, small sample sizes, or caged colonies. Results of this study showed a distinct intraspecific pattern for body proportions throughout the life cycle. Relative linear increases in overall body proportions of maturing animals appeared to be from greatest to least in the trunk, hindlimb, and forelimb, respectively. Within the limbs, allometric scaling appeared to be fastest in the proximal segment and slowest in the distal segment. Males and females differed in the duration of growth, and gender dimorphism was associated primarily with differences in size rather than proportion. Although the primary purpose of this paper is to present numerical data on the Cayo Santiago colony, the results are compared with previous studies of both laboratory and free-ranging rhesus monkeys.

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.