Androgen and Corticoid Levels in Blood and Body Extracts of High- and Low-ranking Swordtail Males (Xiphophorus helleri) before and after Social Isolation

The two highest- and the two lowest-ranking swordtail males were determined by the criterion of number of attacks directed at and received from every other male in their breeding tanks. The events were recorded until 50 bites were given (high-ranking males) or received (low-ranking males). 40 high- and 40 low-ranking males were bled either after being socially isolates for 4 weeks or after reaching the target number. Androgen and corticoid concentrations both in their blood and their body extracts were measured by means of radioimmunoassay. Although the agonistic behaviour patterns and social experience of high- and low-ranking males were totally different, the baseline hormonal states of the animals were indistinguishable both in body extracts and blood. Isolation led to decreased blood androgen and corticoid levels in high- and low-ranking males. In the body extracts, only the corticoids were reduced. A significant correlation between blood and tissue concentrations was found only in the case of corticoids. I would suggest that the contradictory findings in the literature dealing with the relationship between hormones and dominance result from differences in experimental procedure.     

Age-related differences in social grooming among adult female Japanese monkeys ( Macaca fuscata)

The present study investigated the influence of dominance rank in combination with kinship on age-related differences in social grooming among adult females in a free-ranging group of Japanese monkeys (Macaca fuscata). Eighty-three adult females were divided into six sub-groups according to age-class (younger: 5–9 years old; middle: 10–14 years old; older: 15–22 years old) and dominance rank (high and low rank). The ratio of the number of unrelated females that each female groomed to the total number of available unrelated females and grooming bouts which she gave to unrelated females decreased with increasing age for both high- and low-ranking females, whereas age did not appear to affect corresponding values for related females. On the other hand, compared with low-ranking females, high-ranking females of all age-classes received grooming more often from a larger number of unrelated females. Moreover, older females of low rank received grooming less often from a smaller number of unrelated females than younger females of low rank. These results indicate that with increasing age females are more likely to concentrate on related females when they have grooming interactions with other females. This tendency seems to be more apparent for low-ranking females. Moreover, the present findings also indicate that older high-ranking females could maintain their social attractiveness as high as younger high-ranking females.     

Allogrooming, partner choice, and dominance in male anubis baboons

This study was designed to test the hypothesis that among unrelated male baboons (Papio cynocephalus anubis) in single-gender social groups there is no significant association between dominance status and allogrooming performance. The hypothesis was tested using behavioral measures obtained by focal animal sampling techniques. The results indicate that unrelated male baboons established well-defined linear dominance hierarchies, formed allogrooming relationships with one another, and exhibited a nonrandom distribution of allogrooming; however, there were no significant relationships between dominance rank and the frequency of allogrooming. We further tested our results by grouping individuals into three dominance status classes (high, middle, and low) and comparing the classes. Analysis of variance demonstrated no significant differences in rates of allogrooming by dominance class. These results suggest that dominance did not account for the variation in observed allogrooming behavior: Dominance status did not appear to determine the frequency with which animals groomed others, the number of grooming partners, or frequency of grooming that any individual received in comparison to that performed. High-ranking animals did not have significantly more grooming partners than low-ranking animals, and there appeared to be little competition within the groups for subordinates to groom high-ranking animals. When age, kinship, and group tenure are controlled, performance and reception of allogrooming are not strongly associated with dominance in single-gender social groups of male anubis baboons.     

Acquisition of dominance status affects maze learning in mice

Learning is likely to be costly and thus subject to trade-off with other components of life history. An obvious prediction, therefore, is that investment in learning, and thus learning performance, will vary with individual life history strategy and the reproductive value of the learning outcome. We tested this idea in the context of social dominance in male laboratory mice, using a simple radial maze paradigm to compare the ability of high- and low-ranking male mice to track changing food location. We tested animals in randomly selected pairs before and after establishing aggressive rank relationships to distinguish intrinsic differences in learning ability from those attributable to acquiring high or low rank. There was no difference in learning between later dominants and subordinates prior to establishing rank relationships. After pairing, however, dominants showed a significantly greater percentage of correct responses, with the difference being greatest earlier in a sequence of trials. The percentage of correct responses also increased with the amount of aggression initiated during pairing. The results thus appeared to reflect a state-dependent change in learning associated with the aggressive social relationships formed during pairing.     

Social inertia in white-throated sparrows results from recognition of opponents

Social inertia is a term for the stability of dominance relationships despite changes in the intrinsic dominating abilities of opponents. In a standard test for social inertia, low-ranking birds in an established hierarchy receive implants with testosterone (treated) and high-ranking birds receive empty implants (untreated). Social inertia occurs when the treated birds remain subordinate to untreated opponents in these groups, despite evidence that similarly treated birds dominate untreated strangers. In previous demonstrations of social inertia, however, treated and untreated birds were returned to their original aviaries and tested with familiar opponents, and thus the effects of familiarity with the location and those of familiarity with opponents were not separated. To address this issue, we investigated social inertia in 16 groups of white-throated sparrows Zonotrichia albicollis. When low-ranking treated birds were placed in new aviaries with familiar high-ranking, untreated opponents (treatment S, same opponents), dominance relationships showed social inertia. When such birds were placed in new aviaries with unfamiliar opponents (treatment N, new opponents), testosterone influenced dominance. When groups of high-ranking, untreated birds acquainted with each other were placed with unfamiliar treated opponents (treatment G, grouped dominants), 'coat-tail' effects (dominance by association with high-ranking individuals) sometimes outweighed the effects of testosterone. Social inertia in this species is thus a result of familiarity with opponents, rather than familiarity with locations of encounters. Measurements of aggressive tendencies confirmed a previous report that social inertia suppresses activation of aggression by testosterone. White-throated sparrows can thus recognize their opponents, and this ability affects the expression of both dominance and aggression. Copyright 1999 The Association for the Study of Animal Behaviour.     

Allofeeding in Arabian Babblers (Turdoides squamiceps)

Allofeeding is a common social display among adult Arabian babblers (Turdoides squamiceps). The sociology and rates of allofeeding were studied with a tame population of babblers at the Shezaf Nature Reserve in the Rift Valley, Israel. Allofeeding rate varies with the season and food availability. Experimental supplementation to the whole group or to certain individuals greatly increased the rate of allofeeding, but it did not change the social order of the interactions. The interactions were almost always unidirectional: the donor allofed an individual lower in rank. Most of the few exceptions were reciprocal allofeeding among pairs of low-ranking individuals, correlated with a change in dominance between a young male and a young female. Higher-ranking individuals sometimes interfered with allofeedings by lower-ranking ones, and receivers frequently refused to accept the food offered. Allofeeding may therefore be considered as a display of dominance. However, as dominance rank rarely changes, except in very young birds, we suggest that allofeeding interactions display the prestige of the donors, that is, the degree of dominance of one individual over the other.Electronic Supplementary Material Supplementary material is available for this article at .     

Life history in male mandrills (Mandrillus sphinx): physical development, dominance rank, and group association

We assess life history from birth to death in male mandrills (Mandrillus sphinx) living in a semifree-ranging colony in Gabon, using data collected for 82 males that attained at least the age of puberty, including 33 that reached adulthood and 25 that died, yielding data for their entire lifespan. We describe patterns of mortality and injuries, dominance rank, group association, growth and stature, and secondary sexual character expression across the male lifespan. We examine relationships among these variables and investigate potential influences on male life history, including differences in the social environment (maternal rank and group demography) and early development, with the aim of identifying characteristics of successful males. Sons of higher-ranking females were more likely to survive to adulthood than sons of low-ranking females. Adolescent males varied consistently in the rate at which they developed, and this variation was related to a male's own dominance rank. Males with fewer peers and sons of higher-ranking and heavier mothers also matured faster. However, maternal variables were not significantly related to dominance rank during adolescence, the age at which males attained adult dominance rank, or whether a male became alpha male. Among adult males, behavior and morphological development were related to a male's own dominance rank, and sons of high-ranking females were larger than sons of low-ranking females. Alpha males were always the most social, and the most brightly colored males, but were not necessarily the largest males present. Finally, alpha male tenure was related to group demography, with larger numbers of rival adult males and maturing adolescent males reducing the time a male spent as alpha male. Tenure did not appear to be related to characteristics of the alpha male himself.     

Rank relations of juvenile and subadult natal males of Barbary macaques (Macaca sylvanus) at Affenberg Salem

Rank relations of more than 100 juvenile and subadult natal Barbary macaque males were analyzed. Hierarchical relations among individuals of the same age were established early during the first year of life. With few exceptions concerning infants from very high-ranking genealogies, males dominated female peers regardless of maternal rank. Males started to outrank females from older cohorts during the second year of life and completed the process of rank reversal with adult females at 5-6 years of age. An age-graded dominance pattern existed among males from different birth cohorts. Only 3 rank reversals between males from different cohorts were observed. Rank reversals among males of the same birth cohort occurred more frequently. Rank position of a male among his male peers was influenced by birth order, by maternal rank, and by the presence of juvenile brothers. Most males without juvenile brothers had low positions, regardless of maternal rank. Males born late in the birth season were also low-ranking, even when juvenile brothers were present. There was no cohort where ranking among males was determined by maternal rank alone, as is the case in rhesus monkeys and Japanese macaques. Adult/subadult male carriers had no noticeable effect on rank positions of 'their' infants. It is suggested that a weaker influence of Barbary macaque mothers on rank of their sons is related to very early integration of male infants in male social/play groups.     

Social implications of fission in wild Formosan macaques at Mount Longevity,Taiwan

Group fission in non-human primates has long been proposed to result from interactions between ecological and social factors. Several studies have documented possible causes for group fission, but its proximate causes and ultimate adaptive values are not yet fully understood. We have examined the existing hypotheses on fission from long-term demographic data of Formosan macaques inhabiting the lowland rainforest at Mt Longevity, Taiwan. Five cases of fission occurred in four social groups. We have recorded two types of fission: one involving the separation of a high-ranking adult male and multiple adult females, the other initiated by adult females from main groups. Five adult females immigrated and emigrated a few times between the main and branch groups (oscillation) in three fission events. Data presented in this study are consistent with the prediction that low-ranking females split from main groups when their fitness costs increase due to ecological pressure or population growth. However, their reproductive success may decrease after fission due to a high rate of intra-group competition. Nevertheless, it is beneficial for males to be involved in fission since this increases reproductive benefits by decreasing the sex ratio in small newly formed groups.     

Male Social Behavior and Dominance Hierarchy in the Sulawesi Crested Black Macaque (Macaca nigra)

In a 6-week study of the social behavior of wild Sulawesi crested black macaques (Macaca nigra), we found a linear and transitive dominance hierarchy among the six adult males in one social group. Dominance rank, as determined by the direction of supplantations, correlated strongly with percentage of time near more than four neighbors, frequency of grooming received from adult females, and percentage of time with an adult female as nearest neighbor. These results suggest that high-ranking males are socially attractive. Adult females sexually solicited high-ranking males more often than low-ranking males, but frequency of copulation was not correlated with dominance rank. Frequency and intensity of aggression between males are strongly correlated with rank distance, but aggression toward females was greatest for mid-ranking males. Males of all rank displayed significantly more aggression toward sexually receptive females than toward females in other estrous states. These data indicate that male Sulawesi crested black macaques display a social organization similar to that reported for multimale groups in other macaque species rather than the egalitarian social organization described for female Sulawesi macaques.     

Dominance hierarchy and social relationships in a group of Captive black-and-white snub-nosed monkeys (Rhinopithecus bieti)

Different types of dominance hierarchies reflect different social relationships in primates. In this study, we clarified the hierarchy and social relationships in a one-male unit of captive Rhinopithecus bieti observed between August 1998 and March 1999. Mean frequency of agonistic behaviour among adult females was 0.13 interactions per hour. Adult females exhibited a linear hierarchy with a reversal of 10.9%, indicating an unstable relationship; therefore, R. bieti appears to be a relaxed/tolerant species. The lack of a relationship between the agonistic ratio of the adult male towards adult females and their ranks indicated that males did not show increased aggression towards low-ranking females. Differentiated female affiliative relationships were loosely formed in terms of the male, and to some extent influenced by female estrus, implying that relationships between the male and females is influenced by estrus and not rank alone. A positive correlation between the agonistic ratio of adult females and their ranks showed that the degree to which one female negatively impacted others decreased with reduction in rank. Similarly, a positive correlation between the agonistic ratio of females and differences in rank suggests that a female had fewer negative effects on closely ranked individuals than distantly ranked ones. These data indicate that rank may influence relationships between females. A steeper slope of regression between the agonistic ratio and inter-female rank differences indicated that the extent of the power difference in high-ranking females exerting negative effects on low-ranking ones was larger during the mating season than the birth season, suggesting that rank may influence the mating success of females.     

Allogrooming Behavior and Grooming Site Preferences in Captive Bonobos (Pan paniscus): Association with Female Dominance

I tested the utility of Seyfarth's (1977) model of rank-related attractiveness to explain the distribution of allogrooming behavior among captive bonobos (Pan paniscus). Adult female bonobos generally have high social status and may be dominant over males. As predicted by the model, I found that high-ranking adult females received most allogrooming within each of the four investigated groups. Among adult female-adult female dyads, however, allogrooming was not clearly associated with dominance rank. Contradictory to predictions of the model, the highest-ranking females were responsible for most displacements over allogrooming, and grooming competition is positively correlated with dominance rank. In the second part of this study, I investigated the social significance of allogrooming body site preferences. Bonobos direct significantly most allogrooming to the face of conspecifics, and high- and low-ranking individuals, as well as males and females, differ significantly in their preferences for certain allogrooming sites. Subordinates and males tended to avoid facial grooming and preferred the back and anogenital region, while high-ranking individuals and females directed most allogrooming to the face and head of grooming partners. Data from this study support the hypothesis that high-ranking females are the most attractive grooming partners within a female-centered bonobo society. Many other aspects of allogrooming behavior, however, are not consistent with the model of rank-related attractiveness.     

Age, social rank and lactational status influence ovulatory patterns in seasonally breeding rhesus monkeys

Rhesus monkeys housed outdoors exhibit a distinct breeding season limited to the fall and winter months. Four groups of female rhesus monkeys, multiparous nonlactating (MNL; n = 8), multiparous lactating (ML; n = 6), primiparous lactating (PL; n = 3) and nulliparous first-time ovulators (N; n = 6) were studied to investigate the influence of age, parity, and social dominance rank on the parameters of the breeding season. MNL exhibited the longest season (146 days), and PL the shortest (70 days), with N (106 days) and ML (89 days) intermediate. PL females also had a significantly reduced percentage of normal ovulations compared to other groups. Neither body weight nor estimates of body fat were related to either the timing of the ovulatory season or the quality of ovulations within the season. Parity and social dominance rank were significantly related to the percentage of normal ovulations (r = 0.85), with low-ranking, primiparous females exhibiting the fewest normal ovulations. These data indicate that the presence of a suckling infant acts synergistically with environmental factors to determine the parameters of the breeding season. Furthermore, postpubertal females may be more responsive to those factors that terminate the breeding season, and some factor independent of body weight but associated with low social dominance rank and/or primiparity renders females less capable of normal luteal function during the breeding season.     

Determinants of fecundity and reproductive success in captive vervet monkeys

Between 1975 and 1983, adult female vervet monkeys (Cercopithecus aethiops sabaeus) over 3.5 years of age, living in two undisturbed social groups in a captive colony in Sepulveda, California, have averaged 1.0 births per female year with a mean interbirth interval of 10.7 months. Increased fecundity did not result in decreased survival rates of offspring in this population. Fecundity was influenced by the mother's age and dominance rank. The primary factor in the age-fecundity relationship was the age at first birth, which varied from three to five years. High-ranking females contributed the most to the high rate of fecundity, with significantly shorter interbirth intervals, more births per female year, and more surviving infants compared to low-ranking females.     

The Red Fox,Vulpes vulpes,as a Predator upon Earthworms,Lumbricus terrestris

The tiny (3.1–3.8 g) vespcrtilionid bat Pipistrellus nanus was studied in Kenya palm-thatched roofs from May 1973 to July 1974. Roosting social organization and related activities and behavior are described. ♂♂ held diurnal roosting territories where ♀♀ gathered in small and compositionally labile groups, attracted to the most vocal ♂♂. Annual variation in population-wide aspects of social organization follows predictable seasonal changes in climate and predator abundance. Variability between individuals follows a common mammalian pattern: high male competition for ♀, variance in presumed male reproductive success, and a mating system resembling one based on resource defense polygyny. Social organization in this population contrasts with that known from studies of other P. nanus populations.     

Remarks on the conservatism of sigma(0 -- E)2/E in survival data.

This note presents theoretical and numerical calculations which investigate the adequacy of the sigma(0 -- E)2/E approximation (Peto and Pike [1973]) when applying the Mantel/Haenszel summary chisquare statistic to the comparison of r life tables in the manner suggested by Mantel [1966], Peto and Peto [1972], and Cox [1972]. These indicate that conservatism is mild unless there are marked differences in the withdrawal patterns in the r tables. Such differences may, however, be anticipated in the case of a generalization of the life table procedure suggested by Crowley [1973], Mantel and Byar [1974], and Turnbull, Brown, and Hu [1974], wherein individuals are moved from one life table to another according to changes in their treatment (or other) statuses.     

Dominance Rank and Parental Investment in Swine (Sus scrofa domesticus)

Using domestic swine, we tested the general prediction from life history theory that females increase their investment in offspring with increasing age and parity. Because increased investment may have a greater beneficial impact on the lifetime reproduction of sons than daughters, we also tested the prediction that older females would invest more in sons than in daughters compared to younger females. Finally, we examined whether age- or parity-related patterns of change in reproductive effort were associated with differences in the social dominance ranks of females. Female swine from a large number of domestic breeds were assigned to social groups, and their dominance ranks were determined based on the outcome of agonistic encounters. The prediction that older females produce larger litters was supported, but the increase was related only to age, not to parity. Across all ages, high-ranking females produced a greater proportion of sons than low-ranking females. Contrary to our prediction, there was no rank-related change in the proportion of sons born with increasing age or parity. However, the mean body masses offspring born to high-ranking females increased with increasing maternal age and parity, but this was not the case for offspring of low-ranking females. Studies of free-ranging groups of swine are needed to determine whether an increase in body mass at birth would have different effects on the reproduction of sons or daughters.     

The effects of dominance rank and group size on female lifetime reproductive success in wild long-tailed macaques,Macaca fascicularis

Demographic changes were recorded throughout a 12-year period for three social groups ofMacaca fascicularis in a natural population at Ketambe (Sumatra, Indonesia). We examined the prediction that females' lifetime reproductive success depended on dominance rank and group size. Average birth rate was 0.53 (184 infants born during 349 female years). For mature females (aged 8–20 yr) birth rate reflected physical condition, being higher in years with high food availability and lower in the year following the production of a surviving infant. High-ranking females were significantly more likely than low-ranking ones to give birth again when they did have a surviving offspring born the year before (0.50 vs 0.26), especially in years with relatively low food availability (0.37 vs 0.10). Controlled comparisons of groups at different sizes indicate a decline in birth rate with rroup size only once a group has exceeded a certain size. The dominance effect on birth rate tended to be strongest in large groups. Survival of infants was rank-dependent, but the survival of juveniles was not. There was a trend for offspring survival to be lower in large groups than in mid-sized or small groups. However, rank and group size interacted, in that rank effects on offspring survival were strongest in large groups. High-ranking females were less likely to die themselves during their top-reproductive years, and thus on average had longer reproductive careers. We estimated female lifetime reproductive success based on calculated age-specific birth rates and survival rates. The effects of rank and group size (contest and scramble) on birth rate, offspring survival, age of first reproduction for daughters, and length of reproductive career, while not each consistently statistically significant, added up to substantial effects on estimated lifetime reproductive success. The group size effects explain why large groups tend to split permanently. Since females are philopatric in this species, and daughters achieve dominance rank positions similar to their mother, a close correlation is suggested between the lifetime reproductive success of mothers and daughters. For sons, too, maternal dominance affected their reproductive success: high-born males were more likely to become top-dominant (in another group). These data support the idea that natural selection has favored the evolution of a nepotistic rank system in this species, even if the annual benefits of dominance are small.     

Costs and benefits of maternal aggression in lactating female rhesus macaques

Data from over 400 hr of observation of mother-infant rhesus macaques indicate that during the first 12 weeks of lactation infants are at risk from other group members and that mothers use aggression as well as restraining to protect them. Maternal aggression was negatively correlated with infant restraining. High-ranking mothers reacted aggressively to individuals handling their infants more than did middle- and low-ranking mothers. Conversely, middle- and low-ranking mothers restrained their infants more than did high-ranking mothers. Maternal aggression did not vary with infant age. Maternal aggression was directed toward a higher proportion of higher-ranking adult females and their immature offspring and was more likely to be followed by counter-aggression than nonmaternal aggression, i.e. aggression not related to interactions involving the infant. Middle-and low-ranking mothers suffered higher costs in terms of retaliation than high-ranking mothers. It is argued that the occurrence and distribution of maternal aggression among species and individuals should depend on the risk posed to infants by conspecifics as well as on the characteristics of the social structure (e.g. degree of asymmetry of agonistic contests) and of the mother (e.g. her dominance rank) which may affect the probability of retaliation.     

Variation in mating system and group structure in two populations of swift foxes, Vulpes velox

We studied 26 reproductive groups of swift foxes, Vulpes velox, from both high- and low-density areas during three field seasons in northwestern Texas, U.S.A., to examine whether differences in population density affect mating system and group structure. Although high- and low-density populations were only separated by 40 km and vegetation and diets were similar between sites, polygynous groups, communal denning and nonbreeding females occurred in the area of high density, whereas only monogamous pairs occurred in the area of low density. Annual survival of adult swift foxes was 66% in the area of high density, but 44% in the area of low density. Predation from coyotes, Canis latrans, was the only mortality factor that differed (P=0.01) between sites and contributed most to differences in survival. Although previous research indicated that variation in social systems among canids is related to bottom-up forces (i.e. food, habitat), the results of our study indicate that variation in social systems can also be related to top-down forces (i.e. predation, displacement by larger competitor).