Subordinate Females Research Articles

Reluctant challengers: why do subordinate female meerkats rarely displace their dominant mothers?

In most cooperatively breeding vertebrates, dominant breeders have higher reproductive success and live longer than subordinate helpers, and subordinates might consequently be expected to challenge the dominants in their group for status. However, in contrast to noncooperative species, challenges for dominance are rare. This could be because subordinates are unable to displace dominants or because the risk of attempting to do so is prohibitively high. Alternatively, because subordinates are commonly the offspring of dominants and more established breeders tend to produce more young, subordinates may maximize their inclusive fitness by allowing related dominants to maintain their position and helping them to raise future offspring. Here, we use more than 13 years of data from a wild population of Kalahari meerkats Suricata suricatta to investigate whether subordinate females would be likely to gain higher inclusive fitness by displacing their dominant mothers than by remaining as helpers. We first show that the breeding success of dominant females increases during the first 2–3 years of their tenure and then declines. Combining estimates of breeding success in each year of tenure with age-specific survival probabilities, we then calculate the reproductive value of successful challengers and nonchallengers. Our results show that, in any year, subordinate females would achieve higher inclusive fitness by displacing their dominant mother than by remaining as helpers. We conclude that the low frequency with which displacement occurs probably reflects the potential costs associated with challenging for status and the low probability of success.

The cost of dominance: suppressing subordinate reproduction affects the reproductive success of dominant female banded mongooses

Social species show considerable variation in the extent to which dominant females suppress subordinate reproduction. Much of this variation may be influenced by the cost of active suppression to dominants, who may be selected to balance the need to maximize the resources available for their own offspring against the costs of interfering with subordinate reproduction. To date, the cost of reproductive suppression has received little attention, despite its potential to influence the outcome of conflict over the distribution of reproduction in social species. Here, we investigate possible costs of reproductive suppression in banded mongooses, where dominant females evict subordinates from their groups, thereby inducing subordinate abortion. We show that evicting subordinate females is associated with substantial costs to dominant females: pups born to females who evicted subordinates while pregnant were lighter than those born after undisturbed gestations; pups whose dependent period was disrupted by an eviction attained a lower weight at independence; and the proportion of a litter that survived to independence was reduced if there was an eviction during the dependent period. To our knowledge, this is the first empirical study indicating a possible cost to dominants in attempting to suppress subordinate breeding, and we argue that much of the variation in reproductive skew both within and between social species may be influenced by adaptive variation in the effort invested in suppression by dominants.

Social stress and reproductive success in the female Syrian hamster: Endocrine and behavioral correlates

In many mammal species, reproduction is not shared equally among the members of a social unit. Even though reproductive skew seems unlikely in females of solitary species, this phenomenon could result from environmental factors. Although solitary in the wild, captive Syrian hamsters (Mesocricetus auratus) are generally housed in groups. We investigated whether social stress produces some degree of reproductive skew in this solitary species and whether female reproductive success varies as a function of social rank. To assess the physiological relationship between social stress and fertility, we monitored reproductive hormones and glucocorticoids of solitary and pair-housed females during pregnancy by means of recently established non-invasive methods for measuring hormone metabolites in the feces. The patterns of fecal progesterone, estrogen and glucocorticoid metabolites were similar to those found in blood and reported in the literature for pregnant hamsters. As expected, dominant females had higher breeding success than subordinate females. However the rate of reproductive failure was also very high among the singly housed females of our control group. The number of pups per litter, the average sex-ratio in each group, and the mean weight of pups did not differ significantly among groups. Glucocorticoid concentrations were unaffected by housing and social rank and the few differences between the endocrine profiles of singly- and pair-housed females are not sufficient to explain the observed difference in breeding success. It is likely that social isolation impairs reproduction in the same manner as subordination. Our findings suggest that social isolation of animals accustomed to group living was equally as disturbing as cohabitation with an unknown conspecific.

Favouritism or intrabrood competition? Access to food and the benefits of philopatry for red-cockaded woodpeckers

In species showing delayed natal dispersal, broodmates vary in natal dispersal timing and strategy, where some choose to disperse early while others delay. In the cooperatively breeding red-cockaded woodpecker, Picoides borealis, typically only one juvenile male per brood delays dispersal despite the lifetime fitness benefits associated with delayed dispersal. We sought to determine whether adult favouritism or intrabrood competition over the distribution of natal food resources provides a mechanism for the persistence of individual variation in natal dispersal strategies. We show that fledgling red-cockaded woodpeckers form male-biased, linear dominance hierarchies as a result of frequent aggressive conflicts. For males, high nestling condition relative to male broodmates was a strong predictor of future dominance, and this condition–rank relationship persisted after individuals reached nutritional independence. Adults were never observed interfering with broodmate conflicts, and were only rarely aggressive towards fledglings. Adults showed no overt favouritism towards offspring when targeting individual fledglings during provisioning early in the postfledging period. However, conflict rates increased with decreasing targeted-feeding rates, suggesting that access to resources is an important function of dominance hierarchies. After fledglings were developmentally able to compete for positions near foraging adults, first- and second-ranking males were fed more often than subordinate females. Of the juvenile males surviving to spring, subordinates were more likely to disperse during their first year than were their dominant broodmates. Together, our findings suggest that for young red-cockaded woodpeckers, intrabrood social rank provides a mechanism for prioritized access to natal resources and variation in natal dispersal strategy.

Interrelationship of serum testosterone, dominance and ovarian cyclicity status in female African elephants

The African elephant population in North American zoos is not self-sustaining, in part due to the prevalence of ovarian acyclicity. While little is known about the cause of this condition, earlier research has shown that females without cyclic corpus luteum (CL) function rank higher in the dominance hierarchy than females with cyclic CL function. The goal of this study was to measure longitudinal serum testosterone concentrations in captive female African elephants to determine if there is a relationship among serum testosterone concentrations, social dominance rank and ovarian cyclicity status. Weekly blood samples from 49 female African elephants (24 having and 25 not having cyclic CL function at 22 facilities) were collected over a 12-month period and analyzed for serum testosterone using an enzymeimmunoassay. A progesterone radioimmunoassay was used to quantify serum progestagen concentrations and categorize ovarian cyclicity status. The dominance hierarchy of individual elephants within each herd was assessed by a written temperament survey, which identified 19 dominant, 15 middle and 15 subordinate females. No clear patterns of serum testosterone secretion were observed in females with and without cyclic CL function. Furthermore, no significant relationships were found among serum testosterone concentrations, dominance rank, and ovarian cyclicity status. These data suggest that increased circulating testosterone concentrations are not associated with greater rates of ovarian acyclicity or dominance status in captive female African elephants.

Energetics during reproduction: A doubly labeled water study of lactating baboons

Understanding the costs and regulation of reproduction in primates requires understanding the separate but linked effects of energy availability and total energy expenditure (TEE). We compared variation in TEE and energy intake (EI) between two periods, early lactation and after the resumption of sexual cycling, for eight females from two groups of normally reproducing colony-living baboons (Papio h. anubis). Total energy expenditure was assessed using the doubly labeled water method. TEE was correlated with maternal mass both during early lactation and after the resumption of cycling. TEE after the resumption of cycling was positively related to infant growth rates; mothers with rapidly growing infants had higher energy expenditure. TEE was however unrelated to maternal rank and only weakly associated with reproductive parameters such as delay to conception. EI in early lactation was related to infant mass and interbirth intervals, but unrelated to infant growth or reproductive parameters once cycling had resumed. Energy availability (EA; the difference between intake and expenditure) differed significantly between subordinate and dominant females during early lactation, was highly variable among individuals as a function of body composition, and is suggested to follow a nonlinear relationship as a complex function of social status, lactation stage, infant growth, and female fertility. Thus, as a consequence of reduced energy availability, subordinate females in this captive context may experience reproductive delays even though the total energy expenditure after the return of cycling was similar between high and low ranking females.

Body weight decreases induced by estradiol in female rhesus monkeys are dependent upon social status

Gonadal steroids regulate appetite and thus body weight. In addition, continuous exposure to stressors negatively influences appetite through circuits likely distinct from those of gonadal steroids. The occurrence of adverse metabolic consequences due to chronic exposure to psychosocial stressors is twice as frequent in women as men, implicating a role for ovarian hormones, estradiol (E2) and progesterone (P4), in modulating stress-induced changes in appetite. Using social subordination in female macaques as a model of social stress, the current study tested the hypothesis that subordinate females would lose more weight during E2 treatment and gain less weight during P4 administration than dominant females. Because polymorphisms in the gene encoding the serotonin transporter (5HTT; SCL6A4) are known to alter responsivity to stress, we hypothesized that weight loss during E2 administration would be greatest in females with the short variant (s-variant) allele of 5HTT. Dominant females were significantly heavier than subordinate animals throughout the study, a result consistent with previous accounts of food intake when animals are fed a low-fat, high-fiber diet. Females with the s-variant 5HTT genotype weighed significantly less than l/l animals. Dominant animals lost significantly more weight than subordinate animals during E2 treatment. Administration of P4 blocked the weight-reducing effects of E2 in all females, regardless of social status. These data provide evidence that social subordination modulates the influence of ovarian steroid hormones on body weight in female rhesus monkeys independent of 5HTT genotype. Given the prosocial effects of these steroids, future studies are necessary to determine whether status differences in E2-induced weight loss are due to diminished food intake and or increases in energy expenditure and how the change in energy availability during E2 treatments relates to a female's motivation to interact with conspecifics.

The role of female dominance hierarchies in the mating behaviour of mosquitofish.

While studies of sexual selection focus primarily on female choice and male-male competition, males should also exert mate choice in order to maximize their reproductive success. We examined male mate choice in mosquitofish, Gambusia holbrooki, with respect to female size and female dominance. We found that the number of mating attempts made by a male was predicted by the dominance rank of females in a group, with dominant females attracting more mating attempts than subordinates. The number of mating attempts made by males was independent of the female size. The observed bias in the number of mating attempts towards dominant females may be driven either by straightforward male mate choice, since dominance and female fecundity are often closely related, or via the dominant females mediating male mating behaviour by restricting their access to subordinate females.

Adaptive Suppression of Subordinate Reproduction in Cooperative Mammals

Attempts to account for observed variation in the degree of reproductive skew among cooperative breeders have usually assumed that subordinate breeding has fitness costs to dominant females. They argue that dominant females concede reproductive opportunities to subordinates to retain them in the group or to dissuade them from challenging for the dominant position or that subordinate females breed where dominants are incapable of controlling them. However, an alternative possibility is that suppressing subordinate reproduction has substantive costs to the fitness of dominant females and that variation in these costs generates differences in the net benefits of suppression to dominants which are responsible for variation in the frequency of subordinate breeding that is not a consequence of either reproductive concessions or limitations in dominant control. Here, we show that, in wild Kalahari meerkats (Suricata suricatta), the frequency with which dominants evict subordinates or kill their pups varies with the costs and benefits to dominants of suppressing subordinate breeding, including the dominants' reproductive status, the size of their group, and the relatedness of subordinates. We review evidence from other studies that the suppression of reproduction by subordinates varies with the likely costs of subordinate breeding to dominants.

Just Joking? Investigating Sexual Harassment in a

This study investigates the reasons for sexual harassment, its nature and policy implications in a departmental store in Gweru, Zimbabwe. It also analyses the costs of sexual harassment on both the individual and the organisation. The study is based on a qualitative research conducted between January and July 2008. 24 respondents (14 females and 10 males) were studied using semi structured interviews and questionnaires. Results are analysed using the Miles and Huberman (1994) approach to data analysis. Results reveal that contract employment and lack of skills create vulnerability and dependency, a situation exploited by the powerful male superiors who sexually harass their subordinate females. Sexual harassment is institutionalised at Tatenda where management refuses to acknowledge it as a problem. The reluctance of management to craft policies on sexual harassment and grievance procedures added to women’s fear of reporting sexual harassment perpetuates a culture of silence at Tatenda. Key words: department store; female employees ;humour; jokes; labour turnover; sexual harassment; target.

Benefits and Costs of Dominance in the Angelfish Centropyge bicolor

AbstractSocial groups are often structured by dominance hierarchies in which subordinates consistently defer to dominants. High‐ranking individuals benefit by gaining inequitable access to resources, and often achieve higher reproductive success; but may also suffer costs associated with maintaining dominance. We used a large‐scale field study to investigate the benefits and costs of dominance in the angelfish Centropyge bicolor, a sequential hermaphrodite. Each haremic group contains a single linear body size‐based hierarchy with the male being most dominant, followed by several females in descending size order. Compared to their subordinate females, dominant males clearly benefited from disproportionately high spawning frequencies, but bore costs in lower foraging rates and greater aggressive defence of their large territories. Within the female hierarchy, more dominant individuals benefited from higher spawning frequencies and larger home ranges, but displayed neither higher foraging rates nor spawn order priority. However, dominance in females was also linked to aggressiveness, particularly towards immediate subordinates, suggesting that females were using energetically costly aggression to maintain their high rank. We further showed by experimentally removing dominant females that the linear hierarchy was also a social queue, with subordinates growing to inherit higher rank with its attendant benefits and costs when dominants disappeared. We suggest that in C. bicolor, the primary benefit of high rank is increased reproductive success in terms of current spawning frequency and the prospect of inheriting the male position in the near future, which may be traded off against the cost of aggressively defending rank and territory.

Diet choice, cortisol reactivity, and emotional feeding in socially housed rhesus monkeys

Chronic psychosocial stress produces an array of adverse health consequences that are highly comorbid, including emotional eating, affective disorders, and metabolic syndrome. The consumption of high caloric diets (HCDs) is thought to provide comfort in the face of unrelenting psychosocial stress. Using social subordination in female rhesus monkeys as a model of continual exposure to daily stressors in women, we tested the hypothesis that subordinate females would consume significantly more calories from a HCD compared to dominant females, and this pattern of food intake would be associated with reduced cortisol release and reduced frequency of anxiety-like behaviors. Food intake, parameters of cortisol secretion, and socio-emotional behavior were assessed for 3 weeks during a no choice phase when only a low caloric diet (LCD) was available and during a choice condition when both a LCD and HCD were available. While all animals preferred the HCD, subordinate females consumed significantly more of the HCD than did dominant females. A flattening of the diurnal cortisol rhythm and a greater increase in serum cortisol to an acute social separation occurred during the diet choice condition in all females. Furthermore, the rate of anxiety-like behavior progressively declined during the 3-week choice condition in subordinate but not dominant females. These data provide support for the hypothesis that daily exposure to psychosocial stress increases consumption of calorically dense foods. Furthermore, consumption of HCDs may be a metabolic stressor that synergizes with the psychosocial stress of subordination to further increase the consumption of these diets.

Four Breeding Females in a Free-Ranging Group of Buffy-Headed Marmosets (Callithrix flaviceps)

The reproductive patterns recorded in a free-ranging group of Callithrix flaviceps were unique in a number of ways, including 4 females breeding simultaneously, a non-breeding dominant female, and a well-defined birth season. In addition, all observed copulations involved extragroup individuals. The more socially dominant breeding female had more births and more surviving offspring, on average, than subordinate females, and was implicated in at least 1 infanticide. All 4 females carried their own infants for relatively long periods following the births, apparently as a defence mechanism related to the risk of infanticide. It remains unclear whether the unusual number of breeding females in the group represents a species-specific pattern, or the result of specific local circumstances.

Characteristics of Dominant and Subordinate Led Social Groups of White-tailed Deer in Illinois

This study of dominant and subordinate led social groups of white-tailed deer (Odocoileus virginianus) was designed to investigate longevity and associations among members as well as the reproductive success that determines the durability of these groups. Characteristics of 25 dominant and 17 subordinate female led social groups of white-tailed deer were studied on three areas in Illinois. Group size for dominant led social groups ranged between 3.8 and 5.2 deer/y and for subordinate led groups only 2–2.5 deer. Dominant females survived significantly longer (8.2 y) then did subordinate females (5.4 y) and fawns born to dominants were significantly more sedentary after independence. Fawn recruitment (fawns alive at 1 y) was also significantly higher for fawns born to dominant females. Members of a dominant female's social group generally confined themselves to the home range of the dominant female but as they aged were seen less often with her. Dominant females occupied stable habitats free of environmental problems while subordinates occupied ranges with frequent natural and human induced disturbances. By association, fawns of dominant females inherit a stable home range that fosters improved longevity and successful fawn recruitment

Reproductive control via eviction (but not the threat of eviction) in banded mongooses

Considerable research has focused on understanding variation in reproductive skew in cooperative animal societies, but the pace of theoretical development has far outstripped empirical testing of the models. One major class of model suggests that dominant individuals can use the threat of eviction to deter subordinate reproduction (the ‘restraint’ model), but this idea remains untested. Here, we use long-term behavioural and genetic data to test the assumptions of the restraint model in banded mongooses (Mungos mungo), a species in which subordinates breed regularly and evictions are common. We found that dominant females suffer reproductive costs when subordinates breed, and respond to these costs by evicting breeding subordinates from the group en masse, in agreement with the assumptions of the model. We found no evidence, however, that subordinate females exercise reproductive restraint to avoid being evicted in the first place. This means that the pattern of reproduction is not the result of a reproductive ‘transaction’ to avert the threat of eviction. We present a simple game theoretical analysis that suggests that eviction threats may often be ineffective to induce pre-emptive restraint among multiple subordinates and predicts that threats of eviction (or departure) will be much more effective in dyadic relationships and linear hierarchies. Transactional models may be more applicable to these systems. Greater focus on testing the assumptions rather than predictions of skew models can lead to a better understanding of how animals control each other's reproduction, and the extent to which behaviour is shaped by overt acts versus hidden threats.

GPS assessment of the use of exhibit space and resources by African elephants (Loxodonta africana)

In public discussions of animal rights and welfare, we as members and proponents of zoological institutions often face significant challenges addressing the concerns of our detractors due to an unfortunate deficiency in systematically collected and published data on the animals in our collections. In the case of elephants, there has been a paucity of information describing their use of space within captive environments. Here, using collar-mounted GPS recording devices, we documented the use of exhibit space and resources by a herd of five adult female African elephants (Loxodonta africana) housed at Disney's Animal Kingdom((R)). We found that dominant animals within the herd used a greater percentage of the available space and subordinate females avoided narrow or enclosed regions of the enclosure that we termed "restricted flow areas." In their use of other resources, dominant females demonstrated increased occupation of the watering hole over subordinate females, but all females demonstrated relatively equivalent use of the mud wallow. Overall, our results provide preliminary evidence that position within the dominancy hierarchy impacts the percentage of space occupied in a captive setting and may contribute to resource accessibility. These findings can be applied to future decisions on exhibit design and resource distribution for this species.

Investigating the impact of rank and ovarian activity on the social behavior of captive female African elephants

Over a third of captive female African elephants in North America fail to exhibit normal estrous cycles based on long-term serum progestagen analyses. Why acyclicity occurs is unknown; however, the majority of noncycling females are ranked by keepers as the dominant individual within the group. To investigate the relationship between ovarian cyclicity status and keeper-determined social rank, observations were conducted on 33 female African elephants (18 cycling, 15 noncycling). Based on keeper evaluations, five cycling elephants were ranked dominant, seven in the middle and six as subordinate. In contrast, 10 noncycling elephants were ranked as dominate and five as subordinate with none ranked as middle. When comparing the behavior of the elephants by their keeper-determined rank, the dominant females dominant were significantly more likely to approach, displace and push. Similarly, keeper-determined subordinate females more frequently presented their hind end and held their ears erect. Behaviors initiated by one elephant toward another did not vary between cycling and noncycling females, except when the interaction with social rank was tested. Dominant, noncycling females initiated a higher percentage of "approach" and "displace" behaviors than both cycling and noncycling, subordinate elephants. Subordinate, noncycling elephants displayed the highest percentage of "ears erect." Social rank drives the interactions of ex situ female African elephants more than ovarian cyclicity status. Thus, behavioral interactions cannot be used to predict which cycling elephants are most likely to become acyclic.

Habitat structure directly affects aggression in convict cichlids Archocentrus nigrofasciatus

Abstract Aggressive behavior can be an important factor in determining how animals use and divide space and resources. Previous studies have shown that aggression in fishes can be influenced by a variety of factors, including water temperature and resource levels. In this study, we tested if the amount of habitat structure in the environment affected aggression levels in female convict cichlids Archocentrus nigrofasciatus. We performed a laboratory experiment in which we placed female convict cichlids into an aquarium with low or high amounts of habitat structure and monitored the dominant female's behavior toward the subordinate female. Aggressive behavior in convict cichlids primarily consists of chases and bites. We found that the total time the dominant female spent chasing the subordinate female was greater when there was a low amount of habitat structure as compared to when there was a high amount of habitat structure. We also found that both the average duration of a chasing bout and the number of bites directed at the subordinate fish increased when there was a low amount of structure, but the number of chases did not. These results indicate that increased habitat structural complexity decreases aggressive behavior in convict cichlids.

Unravelling the neurophysiological basis of aggression in a fish model

BackgroundAggression is a near-universal behaviour with substantial influence on and implications for human and animal social systems. The neurophysiological basis of aggression is, however, poorly understood in all species and approaches adopted to study this complex behaviour have often been oversimplified. We applied targeted expression profiling on 40 genes, spanning eight neurological pathways and in four distinct regions of the brain, in combination with behavioural observations and pharmacological manipulations, to screen for regulatory pathways of aggression in the zebrafish (Danio rerio), an animal model in which social rank and aggressiveness tightly correlate.ResultsSubstantial differences occurred in gene expression profiles between dominant and subordinate males associated with phenotypic differences in aggressiveness and, for the chosen gene set, they occurred mainly in the hypothalamus and telencephalon. The patterns of differentially-expressed genes implied multifactorial control of aggression in zebrafish, including the hypothalamo-neurohypophysial-system, serotonin, somatostatin, dopamine, hypothalamo-pituitary-interrenal, hypothalamo-pituitary-gonadal and histamine pathways, and the latter is a novel finding outside mammals. Pharmacological manipulations of various nodes within the hypothalamo-neurohypophysial-system and serotonin pathways supported their functional involvement. We also observed differences in expression profiles in the brains of dominant versus subordinate females that suggested sex-conserved control of aggression. For example, in the HNS pathway, the gene encoding arginine vasotocin (AVT), previously believed specific to male behaviours, was amongst those genes most associated with aggression, and AVT inhibited dominant female aggression, as in males. However, sex-specific differences in the expression profiles also occurred, including differences in aggression-associated tryptophan hydroxylases and estrogen receptors.ConclusionsThus, through an integrated approach, combining gene expression profiling, behavioural analyses, and pharmacological manipulations, we identified candidate genes and pathways that appear to play significant roles in regulating aggression in fish. Many of these are novel for non-mammalian systems. We further present a validated system for advancing our understanding of the mechanistic underpinnings of complex behaviours using a fish model.

Grooming and the value of social relationships in cooperatively breeding meerkats

In social mammals, grooming is used not only for hygienic purposes; it also serves social functions. We examined the grooming patterns of dominant males in groups of cooperatively breeding meerkats, Suricata suricatta, to test the hypothesis that the distribution of grooming reflects the value of social relationships. Grooming between dominant individuals was the most commonly observed interaction. Grooming by the dominant male was less common when the dominant female was in oestrus. Grooming between dominant males and subordinates was asymmetrical, with dominant males receiving more grooming and providing less grooming to subordinates. Because subordinate males defend the group against extragroup males, the dominant male was predicted to groom subordinate males more often than to groom subordinate females. Although the sex of a subordinate did not affect the probability of grooming occurring, dominant males groomed subordinate males for longer than they groomed subordinate females. The duration of grooming by a dominant male was longer in small groups than large groups, suggesting that grooming activity is constrained by time. In contrast, subordinates groomed dominant males for longer in larger groups, and as a result, the asymmetry of grooming exchanges was exaggerated in larger groups. This result is consistent with the biological market theory, which predicts that the value of subordinates is dependent on group size and that subordinates will alter grooming efforts accordingly. These results suggest that meerkat grooming serves several social functions, such as the maintenance of valuable and/or fitness-enhancing relationships.