Secondary sex ratios by maternal rank,parity, and age in captive rhesus macaques (Macaca mulatta)

Analysis of 645 conceptions by captive rhesus macaques (Macaca mulatta) with known reproductive histories indicated that maternal age and parity had little effect on the sex of progeny. There was, however, a slight indication that high-ranking females produced a higher proportion of daughters and relatively fewer sons than did low-ranking females. These results provide only weak support for the “advantaged daughter” hypothesis suggested by three previous studies of cercopithecine monkeys, and therefore they further confound the conflicting results for macaques and baboons in general.     

Sebaceous gland adenoma in a rhesus monkey (Macaca mulatta)

A tumor mass was identified below the shoulder region of a 5-year-old male rhesus monkey (Macaca mulatta). The mass was excised and diagnosed as sebaceous gland adenoma based on the microscopic findings. Morphologically it appeared as an elevated, dome-shaped, circumscribed mass of 3.6 x 2.8 x 3.2 cm in dimension with tan speckled color. Histologically, the tumor was composed of mature, sebaceous cells (sebocytes), basal cells arranged in a mass of irregular shapes and sizes, with a characteristic appearance of poly or multilobular structure. Sebocytes were well differentiated with foamy cytoplasm in the center of the lobules and poorly or undifferentiated densely staining basal cells in the periphery of the lobules. Cellular changes in the adjacent lymph node included hyperplasia of plasma cells, macrophages and lymphoid elements with typical mitosis.     

High-resolution chromosomes of rhesus macaques (Macaca mulatta)

Late-prophase high-resolution chromosomes were successfully cultured for 22 of 27 Macaca mulatta samples. Twelve of the successful cultures were adequate for karyotyping high-resolution spreads. High-resolution chromosome technique provides an important contribution to primate genetics because it can be used to identify chromosomal anomalies undetected in metaphase spreads and may be useful for paternity exclusion analysis.     

Consortships and conceptions in captive rhesus macaques (Macaca mulatta)

A captive group of rhesus macaques (Macaca mulatta) was observed during the breeding season to determine if consortship behavior, rather than promiscuous matings, resulted in higher reproductive success for either partner. The 38 adult females in this group were observed “in consort” with the 5 adult or 4 subadult males on 179 occasions. Most of these consortships were short-term, lasting less than one day. Six females engaged in consortships with one male that spanned more than three days, but the majority of these long-term associations did not result in a pregnancy with that male. The term “consortship” has been traditionally accepted as a specific nonhuman primate mating pattern, but the exact nature of this behavioral pattern and its evolutionary importance have been less clearly understood. Consort behavior could be considered a precursor to a monogamous mating system if long-term exclusive sexual associations resulted in higher reproductive success for the participants. But this study demonstrates that for rhesus macaques, who exhibit both consort behavior and more promiscuous matings, there is no clear reproductive advantage to long-term consortships. In light of the inconsistent use of the term consortship, the possible adaptive significance of an exclusive male-female sexual association for the evolution of human mating patterns needs to be reevaluated.     

Skeptical responding in rhesus monkeys (Macaca mulatta)

Signalers that misinform sufficiently open may become devalued as sources of information; however, “skepticism” and any comparison involved in testing reliability entail a cost that involves delays and energy expenditure. Skepticism may be less costly though, if, as a rule, animals are not equally skeptical of the signals of all conspecifics. Animals with the ability to recognize individual conspecifics and to recall past encounters with them may have the capacity to restrict skepticism to subsets of animals that are most likely to benefit from deception. We played tape-recorded alarm calls of high- and low-ranking rhesus monkeys(Macaca mulatta) to their groups in a feeding context once daily over 8 consecutive days at the Yerkes Primate Center Field Station. Over the sequence of playbacks, response was greater to the calls of high-ranking monkeys, adult response patterns were different from those of juveniles, and for adults especially, decline in responsiveness was punctuated by partial resurgences of response. These differences may be the consequence of the adults’ more extensive histories of interaction with group members that, though generally reliable, vary with respect to the potential benefits of deceptive signaling.     

Brief repot: Interactions with infants by full siblings,paternal half-siblings,and nonrelatives in a captive group of rhesus macaques (Macaca mulatta)

Six mother-infant pairs in a group of captive rhesus monkeys (Macaca mulatta) were observed for six months. “Infant grabs” by others and mothers' resistance to grabs were scored. More full siblings grabbed infants than either paternal half-siblings or nonrelatives. Mothers resisted grabbing by more nonrelatives than by paternal half-siblings. Although the maternal effect suggested by full sib-infant interactions is expected, the paternal effect revealed by mothers' tolerance of paternal half-sibs, but not full siblings, over nonrelatives is unexpected.     

Frequency of the major histocompatibility complex Mamu-A*01 allele in a closed breeding colony of rhesus monkey (Macaca mulatta) from Brazil

Background  Rhesus monkeys are relevant models for human diseases. The simian immunodeficiency virus (SIV) infection is an useful macaque model for assessing human immunodeficiency virus (HIV) vaccine strategies. Susceptibility and resistance to viruses have been associated with particular major histocompatibility complex (MHC) molecules. Several epitopes in the HIV structural and non-structural protein restricted by distinct MHC class I haplotypes are important targets for human cytotoxic T lymphocytes, which mediate protection against SIVmac infection. Mamu-A*01 , for example, is a MHC class I molecule of rhesus monkeys that presents a peptide from SIV gag protein.
Methods  Our study determined the frequency of Mamu-A*01 in a closed colony of rhesus monkeys from Brazil by polymerase chain reaction.
Results  A high frequency of the allele was found in the study colony.
Conclusion  This colony provides a significant source of A*01 -positive animals to investigators.     

Aspects of fight interference in free-ranging and compound-dwelling rhesus macaques (Macaca mulatta)

Patterns of fight interference (agonistic aiding) were compared among three groups of rhesus monkeys (Macaca mulatta) living in two settings: (1) two groups at Cayo Santiago (Caribbean Primate Center); and (2) one group at the Yerkes Regional Primate Research Center (YRPRC). A total of 1,227 interference episodes were recorded in 1,650 hours of observation. The only significant intergroup difference was the increased tendency of males at YRPRC to aid aggressors rather than victims. Among other findings, females aided relatives, interfered against target animals dominant to themselves, aided juveniles, and aided victims more consistently and frequently than did males. Importantly, female interference became more male-like in pattern when aid was given to nonrelatives. Neither the dominant males nor males in general displayed a unique or consistent tendency to interfere in fights in a manner which could be interpreted as controlling aggression. The males' interference patterns also did not suggest they were forming coalitions to either attain or defend status rankings. It is concluded that, overall, observations of compound-dwelling and free-ranging rhesus monkeys reveal similar relationships. Further, while female rhesus monkeys interfered in fights in a manner consistent with the control of aggression and protection of kin, the motives of male interferers remain unknown; however, their behavior is consistent with the hypothesis that they were reducing intermale tensions while, at the same time, minimizing physical risk.     

Social rank and cortisol among female rhesus macaques (Macaca mulatta)

In animal societies, some stressful events can lead to higher levels of physiological stress. Such stressors, like social rank, also predict an increased vulnerability to an array of diseases. However, the physiological relationship between social rank and stress varies between different species, as well as within groups of a single species. For example, dominant individuals are more socially stressed at times, while at other times it is the subordinate ones who experience this stress. Together, these variations make it difficult to assess disease vulnerability as connected to social interactions. In order to learn more about how physiological rank relationships vary between groups of a single species, cortisol measurements from hair samples were used to evaluate the effects of dominance rank on long-term stress levels in despotic and less stringent female rhesus macaque hierarchal groups. In despotic groups, cortisol levels were found not to be correlated with social rank, but a negative correlation was found between social rank and cortisol levels in less stringent hierarchies. Low ranking monkeys in less stringent groups secreted elevated levels of cortisol compared to higher ranking animals. These data suggest that variations in the strictness of the dominance hierarchy are determining factors in rank related stress physiology. The further consideration of nonhuman primate social system diversity and the linear degree of their hierarchies may allow for the development of valid rank-related stress models that will help increase our understanding and guide the development of new therapeutics for diseases related to human socioeconomic status.     

Social rank and sex ratio of captive long-tailed macaque females (Macaca fascicularis)

Variation in birth sex ratios in primates can be accounted for by two hypotheses: the local resource competition hypothesis [Silk: American Naturalist 121:56–66, 1983] and the hypothesis of Trivers & Willard [Science 179:90–92, 1973] concerning the maternal effect on the quality of a male. We examined the effects of female dominance rank on aspects of reproduction in three well-established captive groups of long-tailed macaques (Macaca fascicularis). High-ranking females produced a higher proportion of sons than low-ranking females, and factors other than rank did not have significant effects on birth sex ratios. Interbirth intervals following daughters were longer than those following sons, but they were independent of the mother's rank. The sons of high-ranking mothers had better survival prospects than sons of low-ranking mothers in some of the groups; no such difference was found for daughters. Overall, there was no sex difference in survival up to 5 years of age. These results support the Trivers-Willard hypothesis rather than the local resource competition hypothesis. An analysis of interbirth intervals suggested that the deviation in birth sex ratio is already established at conception.     

Patterns of affiliation among immature rhesus monkeys (Macaca mulatta)

The affiliative interaction patterns of the immature members of a group of rhesus monkeys at the Yerkes Regional Primate Research Center reflected a strong bias toward matrilineal kin, although this effect was modified by age and sex variables. Association with kin decreased with age, particularly for males. Juvenile males showed less of a kin bias in their behavior than did juvenile females, especially for grooming. Juvenile males also exhibited a preference for interaction with other males. The diminished association with kin and the same-sex bias may be reinforced in adolescence as adult males begin to aggressively target adolescent males involved in agonistic encounters with females or immatures. Adolescent males did not decrease their levels of social interaction relative to those of adolescent females; however, these males preferentially associated with other males (predominantly their own age-sex class) and specifically avoided females and younger animals, both kin and nonkin. Avoidance may diminish conflicts with females or immatures which could result from association, thereby decreasing the potential for selective aggressive interference by adult males. Juvenile and adolescent females maintained strong ties with their kin and preferentially associated with other females and immatures. The breadth of interaction of females with other females may facilitate the establishment of dominance relationships as females mature. Familiarity and predictability may also decrease the necessity of more severe agonistic interaction.     

Early maternal recognition of offspring vocalizations in rhesus macaques (Macaca mulatta)

This study investigated the development of maternal recognition of infant calls in rhesus macaques (Macaca mulatta). Fifteen mothers and their offspring, of age ranging from several hours to 28 days, served as subjects of an experiment in which the offspring's distress vocalizations were recorded and then played back to their mothers simultaneously with those of an age-matched control infant. The proportion of time looking at, but not the proportion of orientations to the speaker playing the offspring's vocalizations increased significantly as a function of infant age. Specifically, mothers of infants older than 1 week of age responded longer to the playback of their own infant's calls than did mothers of younger infants. These findings provide the firt evidence that offspring recognition in macaques develops between the first and second week of the infant's life and are consistent with the hypothesis that mothers need to be exposed to their infants' calls in order to learn their acoustic characteristics.     

The human-ABO blood groups of free-ranging long-tailed macaques (Macaca fascicularis) and parapatric rhesus macaques (M. mulatta) in Thailand

BACKGROUND: Long-tailed and rhesus macaques are widely used in biomedical research; therefore, the known blood group is important. METHODS: The human-type ABO blood group was determined in wild or semi-wild long-tailed and rhesus macaques in Thailand. A total of 729 long-tailed and 160 rhesus macaques from 20 localities were temporarily caught. RESULTS: The frequency profiles of blood groups, calculated by averaging the frequency of each troop in long-tailed and rhesus macaques, were AB > O > B > A at 29.6%, 27.4%, 27.2%, and 15.8%, and B > AB > A > O at 39.6%, 33.4%, 18.2%, and 8.8%, respectively. Irrespective of locality, the frequencies were AB > O > B > A of 29.6%, 28.0%, 24.4%, and 18.0%, and AB > B > A > O of 37.5%, 28.7%, 26.9%, and 6.9%, respectively, for all long-tailed and rhesus macaques. The frequency profile of blood groups in Thai rhesus macaques was somewhat similar to that in the parapatric long-tailed macaques; however, it was different from other rhesus populations where only group B was detected. CONCLUSIONS: Our data support the hypothesis that Indochinese rhesus macaques are hybrids between rhesus and long-tailed macaques in the past.     

Breeding performance of a captive colony of rhesus macaques (Macaca mulatta)

For most of the 18 years recorded, fewer than 50% of the adult females gave birth in any one year. The colony, of 6 social groups, showed a clear-cut breeding season. Female parity and dominance had no effect on breeding rate, though 1st infants were born earlier in the year than 2nd-born ones. Only when females gave birth in successive years were the months of giving birth correlated. Mothers and daughters may tend to give birth closer in time within a breeding season than do other females.     

Coat condition, housing condition and measurement of faecal cortisol metabolites--a non-invasive study about alopecia in captive rhesus macaques (Macaca mulatta)

BACKGROUND: Previous studies have characterized alopecia in captive rhesus macaques (Macaca mulatta) by a mixed partial to complete alopecia in a bilateral symmetric pattern. METHODS: In this study, coat condition assessments were related to exogenous and endogenous factors in captive rhesus macaques under different housing conditions in order to identify disturbances in environmental factors controlling or influencing hair growth. Additionally, the degree of alopecia was investigated in relation to adrenal endocrine function as an indicator of social stress using faecal glucocorticoid measurements. RESULTS: Hair loss was found to vary with season and sex, was most pronounced in adult females during the winter and spring months. Generally, infants were not affected, but alopecia developed during adolescence. However, the housing system, available enclosure space and variations in group size and composition also appeared to influence coat condition. Levels of immunoreactive cortisol metabolites (11-oxoetiocholanolone) in faeces were significantly negatively correlated with alopecia, suggesting a relationship between hypothalamic-pituitary-adrenal (HPA) axis activity and hair loss in captive rhesus macaques. CONCLUSIONS: Although the present study demonstrates the influence of the HPA axis on coat condition, it is not known if hair loss is caused by abnormal behaviour or hormonal imbalances of the HPA axis itself. Our data suggest that alopecia in rhesus macaques is a highly complex multicausal disorder.     

Brief report: Outbreak of severe aggression in captive Macaca mulatta

An outbreak of severe aggression occurred among females in a rhesus macaque breeding group at the California Primate Research Center four years after the group was established. During the breeding season in which this occurred, the incidence of injured females in other breeding groups at the Primate Center was significantly higher than in the previous year. This breeding season was the first in which a large number of females reached sexual maturity. The group in which the most severe aggression occurred contained the largest number and proportion of maturing females. Evidence suggests that the simultaneous maturation of a large cohort of adolescent females may be associated with increased levels of aggression, and that this aggression may be intensified by certain aspects of captivity.     

Decrease in sexual initiative and responsiveness in female rhesus macaques (Macaca mulatta) during pregnancy

Although the sexual behavior of female rhesus macaques (Macaca mulatta) has been reported to decrease during pregnancy, systematic studies have been largely confined to reports of male behavior. Therefore, we designed a study to examine changes in female sexual behavior during pregnancy. Six cycling multiparous female rhesus macaques were paired during the periovulatory period of the menstrual cycle and during the first and second halves of pregnancy with six sexually experienced males of the same species. Each female was paired with the same male in all tests. The means of the behavioral measures scored on days 11–13 of the menstrual cycle, 35–56 of pregnancy, and 147–168 of pregnancy were compared. Females showed a significant decrease in the present contact ratio and the rate of threat-aways during pregnancy. Males showed lower rates of threatening-away, contacting, mounting, intromitting, and ejaculating when females were pregnant. The extent to which the decrease in male sexual behavior can be accounted for by an increase in female rejection is uncertain, but it is probably as significant as any loss of attractiveness that might accompany pregnancy.     

Paternity exclusion in six captive groups of rhesus monkeys (Macaca mulatta)

Five genetic markers were employed to attempt to identify the fathers of 135 Macaca mulatta offspring living in large outdoor field cages. Family studies of two of these markers to confirm mode of inheritance of phenotypes had not heretofore been reported. Of the 284 exclusions required to identify the fathers of all 135 monkeys, 198 (or 70 percent) were possible using only these five genetic polymorphisms. For 58 (or 43 percent) of these 135 offspring the father was identified. These data were applied to estimate the association between dominance rank of fathers and reproductive success. Fertility of first- and second-ranking fathers was judged to be about twice as high as that of third- and fourth-ranking fathers.     

Radiographic incidence of spinal osteopathologies in captive rhesus monkeys (Macaca mulatta)

Degenerative spinal disease is a leading cause of chronic disability both in humans and animals. Although widely seen as a normal occurrence of aging, degenerative spinal disease can be caused by various genetic, iatrogenic, inflammatory, and congenital factors. The objective of this study was to characterize the degenerative spine-related diseases and the age at onset in a random subpopulation of 20 captive rhesus monkeys (Macaca mulatta; male, 13; female, 7; age: range, 4 to 27 y; median, 18.5 y). Spinal radiographic evaluation (left lateral, right lateral, and ventrodorsal views) of the spinal column (C1 to S1) was performed, and spinal degenerative disease was scored. The incidence of osteopathology was higher in the 14- to 18-y-old group, but incidence did not differ according to sex. In the studied population, degenerative changes were present in monkeys as young as 9 y of age.