Hormonal correlates of dominance in meerkats (Suricata suricatta)

In cooperatively breeding meerkats (Suricata suricatta), individuals typically live in extended family groups in which the dominant male and female are the primary reproductives, while their offspring delay dispersal, seldom breed, and contribute to the care of subsequent litters. Here we investigate hormonal differences between dominants and subordinates by comparing plasma levels of luteinizing hormone (LH), estradiol and cortisol in females, and testosterone and cortisol in males, while controlling for potential confounding factors. In both sexes, hormone levels are correlated with age. In females, levels of sex hormone also vary with body weight and access to unrelated breeding partners in the same group: subordinates in groups containing unrelated males have higher levels of LH and estradiol than those in groups containing related males only. When these effects are controlled, there are no rank-related differences in circulating levels of LH among females or testosterone among males. However, dominant females show higher levels of circulating estradiol than subordinates. Dominant males and females also have significantly higher cortisol levels than subordinates. Hence, we found no evidence that the lower levels of plasma estradiol in subordinate females were associated with high levels of glucocorticoids. These results indicate that future studies need to control for the potentially confounding effects of age, body weight, and access to unrelated breeding partners before concluding that there are fundamental physiological differences between dominant and subordinate group members.     

Consistent individual differences in cooperative behaviour in meerkats (Suricata suricatta)

Although recent models for the evolution of personality, using game theory and life‐history theory, predict that individuals should differ consistently in their cooperative behaviour, consistent individual differences in cooperative behaviour have rarely been documented. In this study, we used a long‐term data set on wild meerkats to quantify the repeatability of two types of cooperative care (babysitting and provisioning) within individuals and examined how repeatability varied across age, sex and status categories. Contributions to babysitting and provisioning were significantly repeatable and positively correlated within individuals, with provisioning more repeatable than babysitting. While repeatability of provisioning was relatively invariant across categories of individuals, repeatability of babysitting increased with age and was higher for subordinates than dominants. These results provide support for theoretical predictions that life‐history trade‐offs favour the evolution of consistent individual differences in cooperative behaviour and raise questions about why some individuals consistently help more than others across a suite of cooperative behaviours.     

Diet and foraging behaviour of group-living meerkats, Suricata suricatta, in the southern Kalahari

Slender-tailed meerkats ( Suricata suricatta ) are small, diurnal, and gregarious mongooses which inhabit the semi-arid regions of southern Africa. In the south-western Kalahari, substantial fluctuations in productivity are caused by extreme seasonality in rainfall and temperatures. We observed the foraging behaviour of habituated meerkats from January to July, a period covering the entire birth season and stages of high and low prey availability. Insects were the most frequently occurring prey class (78.1%), of which larvae (33.4% total frequency) and adult Coleoptera (27.5% total frequency) were the most important prey items throughout the year. Reptiles were heavily utilized in terms of prey bulk-an index of volume-(19.9%), but not by frequency (9.2%). Consumption of Coleoptera was positively correlated with rainfall, and negatively with temperature. Meerkats used a mean of 6.7 ± 1.1 prey categories daily, and there were significant monthly differences in prey diversity in the diet. Dietary shifts were apparently related to fluctuations in prey availability and the presence of preferred prey. There were no differences between the sexes in dietary diversity or niche breadth, but pregnant and lactating females foraged at significantly higher rates than males. The timing of foraging activity altered over the months in response to changes in daylength and thermoregulatory constraints. Foraging behaviour and seasonality in foraging effort are described, and the implications of an insect prey base for meerkat socioecology are discussed.     

Dispersal and extra-territorial prospecting by slender-tailed meerkats (Suricata suricatta) in the south-western Kalahari

Dispersal in slender-tailed meerkats or suricates, Suricata suricatta, in the south-western Kalahari occurred mainly during the early breeding season, and was age- and sex-dependent. Among yearlings, more males than females were immigrants, but more females than males disappeared. There were no sex differences in dispersal among two-year-olds, but among animals aged three years or older, more males than females emigrated. Most dispersers moved into adjacent bands or joined other transients, and females apparently suffered higher rates of mortality than males. Kinship with the same-sex or opposite-sex breeder had no discernible effect on the likelihood of dispersing. Both males and females made prospecting forays to other groups, apparently to assess dispersal and breeding opportunities. Males made frequent and repeated forays, often in coalitions with other band members or transients, whereas prospecting by females was generally solitary, and they were not known to make multiple forays. Prospecting males successfully took over dominance of two bands, and attempted to take over bands on three other occasions. Animals attempting to join or follow a band ( trailers ) behaved submissively and were readily chased by residents, whereas those attempting a dominance takeover ( invaders ) scent-marked at a high rate and showed no submissive behaviours. Dispersing meerkats maximized reproductive success by increasing their mating opportunities, while animals which delayed dispersal received indirect benefits by helping to raise kin.     

The number of subordinates moderates intrasexual competition among males in cooperatively breeding meerkats

For dominant individuals in cooperatively breeding species, the presence of subordinates is associated with both benefits (i.e. increased reproductive output and other group-living benefits) and costs (i.e. intrasexual competition on reproduction). The biological market theory predicts that dominant individuals are tolerant to same-sex group members when there are only a few subordinates, so as to maximize their own reproductive success. We investigated factors affecting aggression by dominant males and submission by subordinate males for a cooperatively breeding mammal, meerkats, Suricata suricatta. In this species, reproductive conflict occurs between the dominant male and the non-offspring males. As predicted, the number of subordinates in a group was positively associated with the aggression frequency by the dominant male and with the submission frequency by the subordinate males. Relative to the aggression frequency against male offspring, the frequency of aggression against non-offspring males was comparable in small groups, but was higher in large groups. These results indicate that reproductive conflict is present between the dominant male and the non-offspring males but is moderated in groups with small numbers of subordinates. This study provides an empirical data agreeing with the biological market theory in the context of intrasexual competition in cooperatively breeding species.     

A genetic analysis of breeding success in the cooperative meerkat (Suricata suricatta)

Measurement of reproductive skew in social groups is fundamentalto understanding the evolution and maintenance of sociality,as it determines the immediate fitness benefits to helpers ofstaying and helping in a group. However, there is a lack ofstudies in natural populations that provide reliable measuresof reproductive skew and the correlates of reproductive success,particularly in vertebrates. We present results of a study thatuses a combination of field and genetic (microsatellite) dataon a cooperatively breeding mongoose, the meerkat (Suricatasuricatta). We sampled 458 individuals from 16 groups at twosites and analyzed parentage of pups in 110 litters with upto 12 microsatellites. We show that there is strong reproductiveskew in favor of dominants, but that the extent of skew differsbetween the sexes and between different sites. Our data suggestthat the reproductive skew arises from incest avoidance andreproductive suppression of the subordinates by the dominants.     

Dispersal, eviction, and conflict in meerkats (Suricata suricatta): an evolutionarily stable strategy model

Decisions regarding immigration and emigration are crucial to understanding group dynamics in social animals, but dispersal is rarely treated in models of optimal behavior. We developed a model of evolutionarily stable dispersal and eviction strategies for a cooperative mammal, the meerkat Suricata suricatta. Using rank and group size as state variables, we determined state-specific probabilities that subordinate females would disperse and contrasted these with probabilities of eviction by the dominant female, based on the long-term fitness consequences of these behaviors but incorporating the potential for error. We examined whether long-term fitness considerations explain group size regulation in meerkats; whether long-term fitness considerations can lead to conflict between dominant and subordinate female group members; and under what circumstances those conflicts were likely to lead to stability, dispersal, or eviction. Our results indicated that long-term fitness considerations can explain group size regulation in meerkats. Group size distributions expected from predicted dispersal and eviction strategies matched empirical distributions most closely when emigrant survival was approximately that determined from the field study. Long-term fitness considerations may lead to conflicts between dominant and subordinate female meerkats, and eviction is the most likely result of these conflicts. Our model is computationally intensive but provides a general framework for incorporating future changes in the size of multimember cooperative breeding groups.     

Costs of cooperative behaviour in suricates (Suricata suricatta).

Functional interpretations of helping behaviour suggest that it has evolved because helpers increase their direct or indirect fitness by helping. However, recent critiques have suggested that helping may be an unselected extension of normal parental behaviour, pointing to evidence that all mature individuals commonly respond to begging young (whether they are parents, relatives or non-relatives) as well as to the lack of evidence that cooperative activities have appreciable costs to helpers. Here we provide an example of one form of cooperative behaviour that is seldom performed by parents and has substantial energetic costs to helpers. In the cooperative mongoose, Suricata suricatta, non-breeding adults commonly babysit young pups at the natal burrow for a day at a time, foregoing feeding for 24 hours. Parents rarely contribute to babysitting, and babysitting has substantial energetic costs to helpers. Members of small groups compensate for the reduced number of participants by babysitting more frequently, and neither the proportion of time that babysitters are present nor the survival of litters vary with group size.     

Individual contributions to babysitting in a cooperative mongoose, Suricata suricatta

Evolutionary explanations of cooperative breeding based on kin selection have predicted that the individual contributions made by different helpers to rearing young should be correlated with their degree of kinship to the litter or brood they are raising. In the cooperative mongoose or meerkat, Suricata suricatta, helpers babysit pups at the natal burrow for the first month of pup life and frequent babysitters suffer substantial weight losses over the period of babysitting. Large differences in contributions exist between helpers, which are correlated with their age, sex and weight but not with their kinship to the young they are raising. Provision of food to some group members raises the contributions of individuals to babysitting. We discuss the implications of these results for evolutionary explanations of cooperative behaviour.     

Density dependence in group dynamics of a highly social mongoose, Suricata suricatta

1.?For social species, the link between individual behaviour and population dynamics is mediated by group-level demography. 2.?Populations of obligate cooperative breeders are structured into social groups, which may be subject to inverse density dependence (Allee effects) that result from a dependence on conspecific helpers, but evidence for population-wide Allee effects is rare. 3.?We use field data from a long-term study of cooperative meerkats (Suricata suricatta; Schreber, 1776) - a species for which local Allee effects are not reflected in population-level dynamics - to empirically model interannual group dynamics. 4.?Using phenomenological population models, modified to incorporate environmental conditions and potential Allee effects, we first investigate overall patterns of group dynamics and find support only for conventional density dependence that increases after years of low rainfall. 5.?To explain the observed patterns, we examine specific demographic rates and assess their contributions to overall group dynamics. Although per-capita meerkat mortality is subject to a component Allee effect, it contributes relatively little to observed variation in group dynamics, and other (conventionally density dependent) demographic rates - especially emigration - govern group dynamics. 6.?Our findings highlight the need to consider demographic processes and density dependence in subpopulations before drawing conclusions about how behaviour affects population processes in socially complex systems.     

Reproduction and survival of suricates (Suricata suricatta) in the southern Kalahari

In most respects, the demography of Kalahari suricates (Suricata suricatta) resembles that of other social mongooses. Average group size varies from four to nine, and groups typically include several mature females, of which one is responsible for the majority of breeding attempts. Breeding females show a postpartum oestrus; gestation is around 60 days; litter size is three to five pups at emergence and females rarely breed before the age of 24 months. In contrast, annual survival rates (0.20 for pups and 0.43 for animals over one year old) are lower than those recorded in other species. Breeding frequency is related to rainfall and breeding can cease altogether when rainfall is unusually low. In a year when this occurred, group size eroded rapidly and over 60% of groups became extinct. Total numbers were slow to recover during the following year because emigration by females was infrequent and new groups did not form in vacant ranges created by the extinction of groups. High rates of group extinction have been found in other cooperative breeders and may occur because breeding success and survival show inverse density dependence.     

Response of foraging group members to sentinel calls in suricates,Suricata suricatta

In the suricate (Suricata suricatta), a cooperatively breeding mongoose, one individual typically watches out for predators while the rest of the group is foraging. Most of the time these sentinels announce their guarding duty with special vocalizations. The response of foraging group members to these calls was investigated by analysing observational data, and by performing playback experiments. The use of special calls by sentinels, and the responses of the foraging group members to them, suggest that the coordination of vigilance is strongly influenced by vocal communication. Sentinel calls decreased the time spent alert by the foraging group members. Other group members were less likely to go on guard when a sentinel was vocalizing. Both the proportion of time during which guards overlapped, and the proportion of time the group was unprotected without a guard, decreased when sentinels announced their duty, due to better coordination of the rotation of sentinels. Suricates, however, do not appear to use sentinel calls to mediate a strict rotation of guarding duty.     

Co-operative Rearing by Slender-tailed Meerkats (Suricata suricatta) in the Southern Kalahari

Slender-tailed meerkats or suricates, Suricata suricatta, are small, gregarious and largely insectivorous mongooses which inhabit the arid and semi-arid areas of southern Africa. We describe four elements of co-operative rearing of the young: 1. babysitting at the den; 2. creching on foraging trips; 3. provisioning with prey items away from the den; and 4. allonursing , including spontaneous lactation. Individual band members differed markedly in contributions to co-operative rearing. All adults and yearlings guarded the den and helpers actively defended young against predators. Breeders babysat significantly less than did non-breeding adults. Differences in age–sex class contributions were also evident in creching behaviour. The feeding of kittens by provisioners extended from soon after their first emergence from the den at 2–3 wk of age to effective foraging independence at 10–12 wk. Breeding females initially contributed little care other than nursing. Allonursing occurred in six of 25 closely observed litters, including three incidents of spontaneous lactation when subordinates nursed the young of higher-ranking females. Such co-operation is likely to be critical to the survival of these highly sociable mongooses in a semi-arid environment such as the Kalahari where food availability can fluctuate enormously.     

Predation, group size and mortality in a cooperative mongoose, Suricata suricatta

1. In social mammals where group members cooperate to detect predators and raise young, members of small groups commonly show higher mortality or lower breeding success than members of large ones. It is generally assumed that this is because large group size allows individuals to detect or repel predators more effectively but other benefits of group size may also be involved, including reduced costs of raising young and more effective competition for resources with neighbouring groups.
2. To investigate the extent to which predation rate affects survival, we compared mortality rates in two populations of suricates ( Suricata suricatta ), one living in an area of high predator density (Kalahari Gemsbok Park) and one living in an area of relatively low predator density (neighbouring ranchland). Most aspects of feeding ecology and growth (including time spent feeding, daily weight gain, growth, adult body weight, breeding frequency and neonatal mortality) were similar in the two populations. In contrast, mortality of animals over 3 months old was 1·7 times higher in the Park than on ranchland.
3. Mortality of juveniles between emergence from the natal burrow and 6 months of age was higher in small groups than large ones in the Park but significantly lower in small groups than large ones on ranchland. Adult mortality declined in larger groups in both areas.
4. The tendency for survival to be low in small groups had far-reaching consequences for the risk of group extinction. During a year of low rainfall in the Park, all groups of less than nine animals became extinct and population density declined to around a third of its initial level. We argue that high group extinction rates are to be expected in species where survival declines in small groups and mortality rates are high.     

Ontogeny of Playful Contact in a Social Mongoose, the Meerkat, Suricata suricatta

Playful contact interaction within a captive family of six meerkatswas observed using a rotating focal animal observation methodover a 5-month period. Ten interaction patterns are described.The mother interacted playfully with her family members at alow rate while the father and young initeracted together farmore than with the mother. The parents sniffed all family membersabout equally, but all offspring sniffed the father far morethan they sniffed the mother. Dyadic interaction sequences betweenthe youngsters incorporated two patterns that infrequently occurredin fatheryoung sequences. Eighteen-week profiles of biting andforelimb contact displayed large oscillations in rate for eachanimal, but there was little inter-individual concurrence ineach pattern and little similarity in profiles between patterns.Playful interaction was depressed and fluctuations dampenedfollowing the birth of an ill-fated litter. Sniffing fluctuatedover a smaller amplitude than either of the other two patterns.During the 5-month observation period, only the father and oneyoungster were consistent in their choice of recipients of forelimbcontact; the other three youngsters altered the proportion ofcontact delivered to their companions. The youngsters did notexhibit significant changes in the body targets of biting overthe time period of the study.     

Kin discrimination in cooperatively breeding long-tailed tits

Long-tailed tits Aegithalos caudatus are cooperative breeders in which helpers exhibit a kin preference in their cooperative behaviour. We investigated the mechanism through which this preference is achieved by first conducting an experiment for testing whether breeders could recognize the calls of their relatives while controlling for spatial effects. We found that there were significant differences in the responses of breeders to the vocalizations of kin and non-kin, suggesting that vocal cues may be used for kin recognition. We conducted a second experiment in order to investigate whether recognition is achieved on the basis of relatedness per se or through association. Nestlings were cross-fostered between unrelated broods in order to create broods composed of true and foster siblings. In subsequent years, survivors from experimental broods did not discriminate between true and fostered siblings when making helping decisions, indicating that recognition is learned and not genetically determined. We discuss the effectiveness of learning through association as an indirect cue to kinship.