Maternal response to neonatal sibling conflict in the spotted hyena, <Emphasis Type="Italic">Crocuta crocuta</Emphasis>

Among spotted hyenas, Crocuta crocuta, neonatal aggression in twins is a well-known phenomenon and serves to establish intra-litter dominance soon after birth. As the stronger more aggressive cub presumably attains dominance over its twin, intra-litter dominance presents mothers with an ideal opportunity to assess individual cub fitness and, thereafter, to selectively favor one cub over the other. This study quantified maternal response to sibling conflict in 26 sets of twins born to 16 wild-living females to determine whether mothers of different social ranks exhibited favoritism towards sons or daughters, or in the case of same-sex twins, the dominant or subordinate cub. Maternal response to sibling conflict did not vary with litter sex composition, suggesting that mothers do not favor offspring of one sex over the other. All mothers intervened when their cubs fought and sometimes punished their cubs. Higher-ranking mothers more often punished both cubs, while lower-ranking mothers were more selective and punished the dominant cub. Where sibling aggression was most extreme, rather than favor the dominant sibling, mothers of all ranks made concessions to the subordinate cub that included procuring private nursing bouts for the subordinate and temporarily housing twins in separate dens, presumably to decrease sibling conflict. These findings represent a complex example of parent–offspring conflict and support both the insurance cub hypothesis and resource tracking hypothesis that mothers endeavor to keep all offspring alive for as long as possible in the event that the dominant sibling dies or that resources provide for the rearing of twins. This contribution is part of the special issue “Sibling competition and cooperation in mammals” (guest editors: Robyn Hudson and Fritz Trillmich).     

Low aggression levels and unbiased sex ratios in a prey-rich environment: no evidence of siblicide in Ngorongoro spotted hyenas (<Emphasis Type="Italic">Crocuta crocuta</Emphasis>)

Avian models of facultative siblicide predict that rates of sibling aggression and the incidence of siblicide should be lower in prey-rich than prey-poor environments, and that siblicide should only occur when fitness benefits outweigh costs. We tested these predictions by comparing data from spotted hyena (Crocuta crocuta) twin litters in the Ngorongoro Crater, Tanzania, a habitat with a high density of resident prey (176 animals/km²) with similar data from the adjacent Serengeti National Park where density of resident prey is low (3.3 animals/km²). As predicted, rates of sibling aggression in Crater twin litters were substantially lower than those among twin siblings in the Serengeti. There was no evidence of siblicide in the Crater, in contrast to the Serengeti, where facultative siblicide occurs frequently. The growth rate of Crater cubs in singleton litters was similar to that of cubs in twin litters, whereas the growth rate of Serengeti singletons was higher than that of cubs in twin litters. Thus despotic behavior by dominant Crater cubs was unlikely to provide fitness benefits, while dominant Serengeti cubs that eliminated their sibling benefited from increased growth and enhanced survival. Previous studies have demonstrated biases in the sex-composition of hyena litters due to facultative siblicide. No such biases were apparent in Crater litters. Our results provide strong evidence that levels of sibling aggression in spotted hyenas are adjusted in an adaptive manner, and that siblicide is facultative and resource dependent. Our results do not support the idea of pre-natal manipulation of offspring sex by female spotted hyenas in response to changes in resource abundance.     

Parent–offspring and sibling conflict in Galápagos fur seals and sea lions

Parent–offspring conflict theory is well supported by theoretical arguments. However, empirical observations are often difficult to interpret and have contradicted one of its most appealing predictions that parent and offspring should disagree over killing of nest or littermates. We present the first examples of deadly conflict between siblings of different cohorts. In Galápagos fur seals (Arctocephalus galapagoensis) and sea lions (Zalophus wollebaeki), mothers often wean their single offspring at 2 years. This leads to a situation where up to 23% of all pups are born while the older sibling is still being nursed. Younger siblings are disadvantaged by being born lighter than neonates without older still dependent siblings. Pups born while an older sib is still dependent grow less in early life (fur seal) and suffer increased early mortality (both species) through direct aggression or scramble competition with the older sibling. This effect is much stronger in years of high sea surface temperature (El Niño) indicating low marine productivity and if the older offspring is a male. In both species, mothers interfere aggressively in this conflict by defending the younger offspring. In years of El Niño, intense resistance to maternal aggression by the older offspring happens frequently in the fur seal. Such resistance against weaning can induce maternal neglect of the newborn. Given substantial year to year variation in offspring growth, maternal aggression forces weaning in the older sibling only if it has reached sufficient size to support itself by foraging. In Galápagos fur seals, pups with older siblings can either represent insurance against loss of older offspring or extra reproductive value.     

Siblicide in Serengeti spotted hyenas: a long-term study of maternal input and cub survival

In the Serengeti National Park, Tanzania, large fluctuations of prey abundance alters the frequency at which spotted hyena (Crocuta crocuta) cubs are nursed and thus the total level of maternal input available to them. Maternal input is high when mothers feed on high densities of locally available migratory herbivores and low when mothers travel up to 70 km to forage. Using data from 19 cub cohorts on the incidence of siblicide (from monitoring the survival of 609 cubs in twin litters) and cub growth rates (from 195 cubs in twin litters) as a measure of maternal input, we demonstrate that the incidence of siblicide increased as average cohort growth rate declined. In total, there were 37 siblicides in 384 litters (9% of litters). When both cubs were alive, total maternal input in siblicidal litters was significantly lower than in non-siblicidal litters and the mean share of the dominant sib of 64.6% was significantly higher than the mean of 52.1% for dominant sibs of non-siblicidal litters. After siblicide, growth rates of siblicide victors substantially increased, demonstrating that mothers did not reduce maternal input after litter reduction. As a result, siblicide victors achieved a long-term growth rate similar to that of singletons and thus significantly increased their expected survival. We conclude that in spotted hyenas, high maternal input in lactation has favoured the evolution of facultative siblicide in populations inhabiting areas with low or fluctuating food resources.     

The appeasement effect of sterility signaling in dominance contests among Bombus terrestris workers

The establishment of dominance hierarchies through aggressive interactions is very common in insect societies. In many cases, it is also mediated through pheromone emissions that enable individuals to evaluate the reproductive quality and level of aggressiveness of the dominant individual, thereby reducing the number and intensity of costly fights. Here, we studied these processes in the primitively eusocial bee Bombus terrestris, using a paired bee system. Specifically, we investigated the behavioral, reproductive, and pheromonal correlates of dominance establishment. Workers were shown to establish dominance hierarchies using overt aggression within 3–4 days. Thereafter, the aggression drastically decreased, and dominance was maintained mostly by ritualized agonistic behavior. The behaviorally dominant bee lost the ester compounds that workers produce in their Dufour's gland (the so-called “sterility signal”) concomitantly with the development of her ovaries. The other bee announced as subordinate by continuously producing high amounts of those esters. The hypothesis that sterility signaling serves as an appeasement signal to pacify the dominant bees is supported by the negative correlation found between the proportion of these esters and the level of aggression that the subordinate received from the dominant worker. Physical interactions, and presumably also the ensuing overt aggression between the bees, were essential for the above pheromonal change to take place and enabled the dominant workers to develop their ovaries and to lay eggs. The subordinate bee’s signaling of non-reproductive status may minimize energy expenditure in costly fights and help stabilize the reproductive division of labor among workers.     

The rarity of twins: a result of an evolutionary battle between mothers and daughters—or do they agree?

The aim of this study was to test the hypothesis that parent–offspring conflict over parental investment might have led to the rarity of dizygotic twins in humans. We explored the theoretical prediction that twins maximize their inclusive fitness by the death of a co-twin, while mothers of twins maximize fitness by raising both twins to independence. We used life history data (1700–1900) from two parishes in Central Norway to compare differences in inclusive fitness (measured as number of children reared to the age of 16 years, using Hamilton's rule) between twins and mothers of twins. Our results show that twins maximize their inclusive fitness by the death of a co-twin, while mothers of twins raise more children by rearing both twins to adulthood. However, because twins growing up as singletons may produce higher or at least equal number of offspring than the sum of the two twins growing up together, mothers might gain more grandchildren by allowing twins to grow up as singletons. To conclude, both selfish twins and their mothers might benefit by the death of a co-twin, indicating that there is no parent–offspring conflict responsible for the rareness of twins in these human populations. Finally, we discuss the results in the light of “The Insurance Egg Hypothesis” and “The Natural Selection Hypothesis”.     

Population trend alters the effects of maternal dominance rank on lifetime reproductive success in yellow baboons (<Emphasis Type="Italic">Papio cynocephalus</Emphasis>)

We evaluated the association between dominance rank and lifetime reproductive success of 75 free-ranging female baboons in Mikumi National Park, Tanzania. Data were evaluated over a 22-year period that included a period of troop increase (1975–1987) associated with two troop splits in 1978 and 1979, followed by a precipitous population crash (1987–1996) where the troops successively fused back together in 1989 and 1994. Lifetime reproductive success was significantly greater for high- versus low-ranking females when examined across the entire study period. High-ranking females had a longer reproductive life span (7.4 vs 3.6 years after first birth), reached menarche earlier (4.6 vs 5.2 years), lived longer (12.0 vs 8.8 years), and had more offspring of both sexes (2.25 vs 1.33 for male offspring; 3.25 vs 0.94 for female offspring), with four times the number of offspring of each sex surviving to 4 years of age compared to low ranking females. Greater offspring production was associated with shorter interbirth intervals of dominant versus subordinate females (545 vs 723 days), partly owing to lower miscarriage rates (0.05 vs 0.2) and a shorter duration of lactation (244 vs 330 days). Rank effects were then partitioned by mothers experiencing the majority of their reproductive life prior to, versus during, the population decline. The majority of rank effects on measures of lifetime reproductive success were virtually eliminated for mothers reproducing during the troop decline, indicating that the considerable impacts of social status on lifetime reproductive success can be markedly altered by intrinsically and extrinsically mediated demographic events.Ramon Rhine is deceasedCommunicated by C. Nunn     

No reduction in aggression after loss of a broodmate: a test of the brood size hypothesis

In some vertebrate species, parents create a large brood or litter then, in the event of unfavourable ecological conditions, apparently allow the number of offspring to be adaptively reduced through siblicide. But how is sibling aggression regulated so that deaths occur only in unfavourable conditions? One proposed mechanism is brood size-dependent aggression. Two experiments tested for this mechanism by reducing three-chick broods of blue-footed boobies either during or after the period of dominance hierarchy establishment. In neither experiment did aggression of the two eldest and highest ranking chicks decline after removal of the youngest broodmate, in comparison with controls. These results suggest that dominant booby chicks do not become less aggressive to each other after disappearance of their youngest broodmate and that this species does not show brood size dependent aggression. Elder blue-footed booby chicks increase their attacks on broodmates when they receive less food, and this mechanism may be sufficient to tailor brood size to food availability.     

Do female bank voles (Clethrionomys glareolus) mate multiply to improve on previous mates?

Contrary to classical sexual selection theories, females of many taxa mate with multiple males during one reproductive cycle. In this study, we conducted an experiment on the “trade-up hypothesis”, which proposes that females remate if a subsequently encountered male is potentially superior to previous mates to maximize the genetic quality of their offspring. We presented bank vole females (Clethrionomys glareolus) sequentially with two males of known dominance rank in different orders, i.e., either first subordinate and second dominant, first dominant and second subordinate, or two males that were equal in dominance (high ranking) and observed their mating behavior. We found that 92% of the females mated multiply and did not base their remating decision on male social status. Therefore, polyandry cannot be explained by the “trade-up hypothesis” based on dominance rank in this species. However, we found that dominant males sired significantly more offspring than subordinate males. This varied according to mating order: dominant males sired more offspring when they were second than when they were first. Moreover, litter sizes were significantly smaller when the dominant male was first (smallest relative success of dominant males) compared to litter sizes when mating order was reversed or both males equal in status. Our results suggest that even though multimale mating includes males that are of poorer quality and thus potentially decreases the fitness of offspring, most of a female’s offspring are sired by dominant males. Whether this is due to cryptic female choice, sperm competition, or a combination of both, remains to be tested.     

Sex-specific maternal effect on egg mass,laying order,and sibling competition in the Bengalese finch (<Emphasis Type="Italic">Lonchura striata</Emphasis> var. <Emphasis Type="Italic">domestica</Emphasis>)

Maternal effects, such as investment in eggs, have profound effects on offspring fitness. Mothers are expected to skew their investment depending on the laying order and sex when unequal sibling competition occurs within a brood because of sex-specific vulnerability and age hierarchy caused by asynchronous hatching. The Bengalese finch hatches asynchronously and shows a moderate reversed sexual size dimorphism. However, contrary to commonly accepted assumptions of size-dependent vulnerability, the smaller sex (male) is more vulnerable to developmental stress caused by sibling competition. We investigated whether maternal investment would be biased by the position in laying order and the sex of eggs, and also explored the possible differences in growth patterns depending on sex, laying order, and age hierarchy by observing chicks fostered to experimentally manipulated broods where brood composition was controlled and age hierarchy was more enhanced than in natural breeding conditions. We found that overall patterns of maternal investment favored the disadvantageous sectors of sibling competition, i.e., eggs of later laying order and sons over those of early laying order and daughters. We also examined the effect of laying order on adult body size and sex differences in growth patterns. When reared in the subordinate age hierarchy, females could compensate for the deficit of decreased growth rate by taking longer to mature, whereas males could not. We suggest that this sex-specific growth pattern could be the cause of sex differences in vulnerability to early developmental stress.     

Social organization and division of labour in colonies of the polistine wasp,Belonogaster petiolata

Summary Foundresses in pre-emergence and post-emergence nests of Belonogaster petiolata were organized into linear dominance hierarchies according to their level of physical aggression towards cofoundresses. The female at the top of the hierarchy became the queen, while foundresses ranked below her became worker-like subordinates. In pre-matrifilial colonies, worker offspring were socially subordinate to both their queen and the subordinate foundresses. Queens of matrifilial colonies retained full social dominance over their workers. Queens were reproductively dominant over subordinates and workers, and laid the majority of, if not all, surviving eggs. Subordinate-laid eggs were invariably discovered and destroyed by the queen through oophagy; workers in pre-matrifilial and matrifilial colonies never laid or ate eggs. Colonies contained a single (and the same) functional queen throughout the pre- and post-emergence periods and were, therefore, long-term monogynous.In both established pre-emergence colonies and post-emergence colonies, virtually all foraging for food and nesting material was performed by the subordinates and workers. More dominant subordinates generally foraged less than low-ranked subordinates. Queens were more active builders than subordinates or workers in pre-matrifilial and matrifilial colonies. Queens enjoyed a surplus in exchanged food loads, while subordinates and workers did not. Among cofoundresses, an advantage in food exchange was also positively associated with dominance rank. Queens solicited larvae for their salivary fluid more often than did subordinates and workers. Among cofoundresses, frequency of adult-larva trophallaxis was positively associated with rank. Queens rested most often in the central zones of the nest containing late instar larvae and pupae, while subordinates and particularly workers spent more time in the peripheral, broodless regions of the nest.This paper is dedicated to the late Professor Leo Pardi, whose pioneering studies of Belonogaster served as a constant source of inspiration and reference for the present work     

Effects of food availability on dispersal and cub sex ratio in the Mednyi Arctic fox

Since the Pleistocene, Arctic foxes, Alopex lagopus, on Mednyi Island in the North Pacific have been isolated in a small area with rich food resources and no other terrestrial carnivores. This situation provides an unusually simple system within which the effect of food dispersion on demography and social organisation was examined. We studied the composition, location and dispersal of 67 Arctic fox groups and mapped their major food resources (seabird colonies) during 1994–2000 on Mednyi. We compared our observations with the predictions of models of sex-ratio determination. Our observations are most consistent with the predictions of Julliard's (2000) model, where mothers are expected to produce more offspring of the most dispersing sex in low-quality habitats, and more offspring of the most philopatric sex in high-quality habitats. The polygynous foxes on Mednyi Island lived where the principal food resources were patchily distributed (present on 11% of the shoreline), and cub survival to dispersal age or reproductive adult was higher in rich (25/45) than in poor (24/79) home ranges. Furthermore, dispersal was strongly sex-biased: most females (60%) remained on their natal ranges, whereas very few males (9%) did so. Significantly more female than male cubs (54 compared with 24) emerged from dens in resource rich ranges, whereas the sex ratio on poor ranges was approximately equal (51 females and 56 males). While our observations are also to some extent consistent with the local resource enhancement (LRE) hypothesis (which predicts a bias towards the sex most likely to cooperate with parents), this does not account for the observed spatial variability.     

Aggression and submission reflect reproductive conflict between females in cooperatively breeding meerkats Suricata suricatta

In many cooperatively breeding species, dominant females suppress reproduction in subordinates. Although it is commonly assumed that aggression from dominant females plays a role in reproductive suppression, little is known about the distribution of aggressive interactions. Here, we investigate the distribution of aggressive and submissive interactions among female meerkats (Suricata suricatta). In this species, dominant females produce more than 80% of the litters, but older subordinates occasionally breed. Dominant females commonly kill the pups of subordinates and usually evict older female subordinates from the group 1–3 weeks before the birth of the dominant female's litter. The aggression frequency of the dominant female toward subordinates and the submission frequency that each subordinate female showed to the dominant female increased as the age of the subordinate female increased and as the birth of the dominant female's pups approached. Moreover, as birth approached, both of these behaviors intensified more quickly between the dominant female and older subordinates than between the dominant female and younger subordinates. The aggression frequency of the dominant female toward each subordinate female predicted whether that subordinate female was evicted from the group; the submission frequency by each subordinate female predicted the timing of their eviction during the pregnancy period of the dominant female. These results support the idea that conflict between dominant and subordinate females increases with the age of subordinates and, since older subordinate females are most likely to reproduce, suggest that dominant females may less easily control reproductive attempts by older subordinate females.     

Sex differences in the ontogeny of social behavior in pikas: possible relationships to dispersal and territoriality

Summary A laboratory study on the ontogeny of social behavior in pikas (Ochotona princeps), an alpine lagomorph, was conducted to determine the role of early relationships between adult females and young and among siblings in the development of territorial and dispersal behaviors. Sex differences during development were examined because field studies have reported greater dispersal distances in young females than young males. At birth, females were significantly heavier than males. There were no sex differences in nursing frequency until after the 2nd week of age, when males initiated more nursing attempts than females. By the end of the weaning period (weeks 5 and 6), adult females became non-interactive with young, but aggression of young toward littermates and the mother increased until the eighth week. At this time, young males outweighed their sibling females. Young were dominant over their mothers by the age of 5 weeks, and young males were dominant over their sibling females.Sex differences were observed in aggression, scent-marking, exploratory activity, and submissive vocalizations, with higher rates in young males, except for submissive vocalizations, which were higher in females (Table 2). Vocalizations and scent-marking behavior increased over time, and were positively correlated with interaction rates.These data support the hypothesis that female young disperse farther than male young largely as the result of unsuccessful competition with male siblings for available territories close to the birthplance. A dispersal strategy for pkkas is proposed.     

Use of different signaling modalities to communicate status by dominant and subordinate Heermann’s kangaroo rats (<Emphasis Type="Italic">Dipodomys heermanni</Emphasis>)

Dominance relationships in solitary species may be an important factor in the maintenance of long-term, stable relationships among territorial neighbors. We examined the mediation of intraspecific interactions in a solitary, territorial kangaroo rat, Dipodomys heermanni, and tested whether unfamiliar kangaroo rats establish a dominance hierarchy and then decrease aggression and increase communication (via footdrumming and sandbathing) after initial interactions and the establishment of a social structure. Results revealed that both dominance hierarchies and familiarization with particular individuals are likely to mediate social interactions. After only one pairing per dyad, an almost linear dominance hierarchy emerged, which became perfectly linear after a 90-min familiarization period. During the course of subsequent interactions between dyad partners, fighting decreased and non-agonistic communication increased. Dominant kangaroo rats sandbathed at higher rates than subordinates, possibly to deposit scent to advertise competitive ability, whereas subordinate kangaroo rats footdrummed from inside the burrow, which seemed to indicate an unwillingness to interact. We suggest the kangaroo rats use a conditional strategy when deciding to fight (be dominant) or withdraw (be subordinate) by employing different modes to communicate status and minimize the potential risk of injury during unnecessarily prolonged fights.     

Sex differences in fitness following a group take-over among Toque macaques: testing models of social evolution

Summary A group of toque macaques took-over the home range of one of its subordinate neighboring groups and fused with it to form a larger cohesive group. In the 7 years before the take-over, the dominant group had consistently won all contests at common feeding sites, yet the fitnesses of the females of these two groups did not differ significantly (Fig. 2A). After the take-over the females of the subjugated group occupied the lowest ranks in the combined dominance hierarchy of the merged groups (Fig. 1) and thereby lost the advantages of an own home range, such as priority of access to food. Consequently, in the merged group, survivorship and reproductive success among the subjugated females were significantly less than among the females of the dominant subgroup (Table 2, 4). The dominant matrilines grew numerically and replaced all of the subjugated females, and all but one of their offspring, within 8 years after the take-over (Fig. 2B). These data support the hypothesis that cooperation among female kin in defending resources against strange females is important in the evolution of female-bonded groups. Before the merger all 5 natal males of the subordinate group had transferred to the dominant group, where they occupied high and mid-level dominance ranks (Fig. 1). These males survived at a significantly greater rate than their subordinate female kin. Thus, the cost of group transfer seems to be greater for females than for males, and this may be one reason that females generally do not emigrate or that groups do not fuse. The data suggested three hypotheses. First, since large body size and other adaptations for fighting, giving males an advantage in male-male competition for mates, are also of advantage in resource competition with males and females, such male characters may also be favored by non-sexual selection, especially where male reproductive strategy involves group transfer. Second, female bonded groups evolved as female defensive coalitions against not only female but also male resource competitors, there having been a mutual influence in the coevolution of large-sized males and female gregariousness. Third, female defensive coalitions against large-sized aggressive males are also advantageous out-side the context of food competition, or, independent of foraging strategy.     

Cheetah mothers' vigilance: looking out for prey or for predators?

Summary Free-living cheetah (Acinonyx jubatus) cubs are killed by a number of predators, thus vigilance in cheetah mothers may be a form of anti-predator behaviour as well as a means of locating prey. Mothers' vigilance during the day was closely associated with measures of hunting but not with measures of anti-predator behaviour. In contrast, mothers' vigilance at kills was not related to hunting but was related to anti-predator behaviour. Both forms of vigilance decreased as cubs grew older. Vigilance during the day increased with litter size which supports a model of shared parental investment (Lazarus and Inglis 1986) because after prey had been located and caught by mothers, cubs shared the prey between them. Vigilance at kills did not increase with litter size when cubs were young; in these situations predators stole cheetahs' prey and rarely chased cubs so, at most, only a single cub would be taken. Mothers' anti-predator behaviour away from kills did increase with litter size at young cub ages however; more cubs are killed in these circumstances the greater is the size of the litter. When cubs were older and could outrun predators, neither vigilance at kills nor anti-predator behaviour increased with litter size. These results strongly support two models of unshared investment (Lazarus and Inglis 1986) and demonstrate, not only that superficially similar behaviour has different functions in different contexts, but that parental investment is shaped by the type of benefits accrued from it.     

Social behavior of free-ranging juvenile sooty mangabeys (Cercocebus torquatus atys)

Sooty mangabeys are terrestrial monkeys exhibiting female philopatry and male dispersal. Studies in captivity as well as in the wild have found that adult females form linear dominance hierarchies. However, while captive studies found no evidence for a matrilineal social system, a previous study in Taï National Park, Ivory Coast, suggested that relatedness could influence both dominance rank and affiliation pattern among adult females. Here I test whether the dominance rank, coalitionary behavior, and affiliative behavior of juveniles in a group of free-ranging mangabeys in the Taï National Park are in accordance with a matrilineal, individual, or age-related dominance system. I found that juvenile females' dominance ranks remained stable over time and were highly correlated with the dominance ranks of their mothers, whereas juvenile males' dominance ranks were initially correlated with the ranks of their mothers, but showed greater instability with increasing age. Moreover, coalitions occurred mainly between juveniles and animals that were close in rank, including their mothers and siblings. Finally, juvenile females associated and groomed preferentially with close-ranking juvenile and adult females. Juvenile males showed similar preferences in affiliation with adult females, but when associating with juvenile males, they preferred peers. The observed social behavior of free-ranging juvenile sooty mangabeys resembled the social behavior described for juveniles of many matrilineal primate species.     

Determinants of social dominance and inheritance of agonistic behavior in an island population of silvereyes,Zosterops lateralis

Summary We examined components of agonistic behavior and dominance in parents and offspring of silvereyes on Heron Island, Great Barrier Reef, to discover their determinants. The data were collected over four years on 1,235 juveniles and their parents. Of four behavioral characters used to compare juveniles and their parents, bill clattering was seen significantly more among young from female parents that exhibited bill clattering. The total absence of submissive behavior and the total absence of aggressive behavior were shown more often than not by young from dominant male parents and subordinate female parents, respectively. Young fledging early in the breeding season tended to be more dominant than those fledging late in the season. The number of brood-mates or the local nest density did not affect the dominance of young. Dominance status appears to be little affected by the performance of parents.     

Short-term consequences of different breeding histories for captive rhesus macaque mothers and young

Summary Life histories of rhesus monkey mothers (Macaca mulatta) were classified in terms of (1) whether the mothers were top ranking or not, (2) gave birth to more daughters than sons or vice versa, and (3) gave birth at intervals of one year or of more than a year. Bearing daughters at intervals of more than a year was the most common history among top ranking mothers, while bearing sons annually was most common among other mothers. The consequences for the infants and mothers of such histories were examined and (1) infants were more likely to die as neonates if they had an older sister, especially if the sister had been born in the previous birth season; (2) dyads with daughters received more aggression from other adults in the daughter's first year, but not necessarily through the year following the birth of the next infant (3) when mothers of daughters gave birth of the next infant after at least one fallow year, their daughters directed considerable amounts of harassing aggression to their next-born sibling; and (4) mothers of sons but not of daughters delayed longer when they received more aggression from other adults.We discuss the views that birth sex ratios may be affected by a mother's rank rather than how often she is involved in aggressive encounters with other adults; and that in top-ranking mothers, birth intervals may be controlled more by the infant's sex than aggression the family received. Fitting the data into a life history strategy model is done as a provisional and speculative exercise