Observed case of infanticide committed by a resident male central American black howler monkey (Alouatta pigra)

Although infanticide has been witnessed in other species of howler monkey, and has been inferred for Alouatta pigra, an observed case of infanticide has not previously been recorded for this species. Here we describe the killing of a 2-week-old infant by the resident male of a small social group in southern Belize. The infanticide was witnessed as part of an intensive observational study that began in January 2003. The male was known to have resided in the group for at least 4 months, but it is not known whether he was the father of the infant. The literature proposes three main explanations for infanticide: two adaptive hypotheses (sexual selection and resource competition), and one nonadaptive hypothesis (social pathology). Individual cases of infanticide such as this one are important for comparative purposes, but when examined on their own they are difficult to interpret in relation to established theoretical frameworks. The data presented here show some consistency with the sexual-selection and resource-competition hypotheses, but the lack of critical information (i.e., as to paternity) makes it impossible to draw firm conclusions.     

Infanticide and Maternal Offspring Defence in European Rabbits under Natural Breeding Conditions

Infanticide is an important source of mortality of dependent offspring in several mammal species, whereas female conspecifics are often the perpetrators. This has led to maternal counter‐strategies, such as the defence of the nests. However, cases of infanticide are hard to detect in the field, and studies on maternal offspring defence behaviour under natural breeding conditions are scarce. We conducted such a study on the European rabbit (Oryctolagus cuniculus), which is usually considered to show low maternal care. The study was carried out over 5 yr on a field enclosure population. We (1) studied infanticide rates and the impact of potential determinants: the group density and age structure of the females’ rank hierarchy within the groups; we used the latter as an estimator of social group stability. We (2) studied if mothers defend their breeding burrow against approaching, potentially infanticidal females. Overall, we recorded infanticide in 5% of all litters; infanticide was the cause in 12% of cases of litter mortality. The proportion of infanticide was 7% higher in groups where same‐age females occupied successive rank positions than in groups where the females’ rank hierarchy had a more heterogeneous and linear age structure. We hypothesize that social instability in the former groups was the reason for the increased infanticide risk. Infanticide rates were not correlated with group density and did not differ among mothers with different social ranks. Infanticide occurred exclusively during the first 10 d after parturition. During this time, mothers stayed closer to their breeding burrows than shortly before parturition or during later lactation. Moreover, mothers were more aggressive against other females in proximity to their breeding burrow than in more distant areas. We suggest that the pattern of spacing behaviour and intrasexual aggression of rabbit mothers are an adaptive response to the occurrence of female infanticidal behaviour.     

Infanticide and social flexibility in the genus <Emphasis Type="Italic">Gorilla</Emphasis>

Based on the cases of infanticide by male mountain gorillas reported from the Virunga volcanic region, the socioecological and life history features of gorillas satisfy the conditions for which infanticide may be expected. However, there are considerable variations in the occurrence of infanticide between habitats. We analyze the recent reports of infanticides that were directly observed or are suspected based on field evidence in two populations of eastern and western lowland gorillas (Kahuzi and Mbeli Bai, respectively) along with previous reports on mountain gorillas, and consider which social features are linked with and which factors influence the occurrence of infanticide in the gorilla populations. All victims were suckling infants and most of them were killed by males who seemed unrelated to them. Dependent infants are most vulnerable to infanticide when the protector male (its putative father in most cases) is absent, and so male protection ability seems to be important in determining female transfer decisions. Two cases observed in Kahuzi suggest that the infanticidal male may discriminate between infants to accept and those to kill according to his previous interactions with their mothers. Mating for a prolonged period prior to parturition is necessary for immigrant females to avoid infanticide by the new male of the group that they join. Infanticide was usually associated with female transfer, and the patterns of female association at transfer may shape variations in social structure between populations. Female mountain gorillas prefer large groups with multiple males and tend to transfer alone in order to seek more protection against infanticide in Virunga. By contrast, female eastern and western lowland gorillas tend to transfer with other females to small groups or solitary males, and maturing silverbacks take females to establish new groups through group fission in Kahuzi and Mbeli Bai. These differences may result in more multi-male and larger groups in the Virungas than in Kahuzi and Mbeli Bai. Rapid changes in density of gorilla social units and their relations following drastic environmental changes caused by recent human disturbances may also increase the probability of infanticide.     

Impact of Male Infanticide on the Social Structure of Mountain Gorillas

Infanticide can be a major influence upon the social structure of species in which females maintain long-term associations with males. Previous studies have suggested that female mountain gorillas benefit from residing in multimale groups because infanticide occurs when one-male groups disintegrate after the dominant male dies. Here we measure the impact of infanticide on the reproductive success of female mountain gorillas, and we examine whether their dispersal patterns reflect a strategy to avoid infanticide. Using more than 40 years of data from up to 70% of the entire population, we found that only 1.7% of the infants that were born in the study had died from infanticide during group disintegrations. The rarity of such infanticide mainly reflects a low mortality rate of dominant males in one-male groups, and it does not dispel previous observations that infanticide occurs during group disintegrations. After including infanticide from causes other than group disintegrations, infanticide victims represented up to 5.5% of the offspring born during the study, and they accounted for up to 21% of infant mortality. The overall rates of infanticide were 2–3 times higher in one-male groups than multimale groups, but those differences were not statistically significant. Infant mortality, the length of interbirth intervals, and the age of first reproduction were not significantly different between one-male versus multimale groups, so we found no significant fitness benefits for females to prefer multimale groups. In addition, we found limited evidence that female dispersal patterns reflect a preference for multimale groups. If the strength of selection is modest for females to avoid group disintegrations, than any preference for multimale groups may be slow to evolve. Alternatively, variability in male strength might give some one-male groups a lower infanticide risk than some multimale groups, which could explain why both types of groups remain common.     

First direct evidence of infanticide and cannibalism in wild snub-nosed monkeys (Rhinopithecus bieti)

Although infanticide has been witnessed in many species of Colobinae, and a case was observed in a captive group of golden snub-nosed monkeys (Rhinopithecus roxellana), observed cases of infanticide in wild snub-nosed monkeys (Rhinopithecus spp.) have not previously been recorded. Here we describe the killing of a 1-month-old infant by a male in a black-and-white snub-nosed monkey (R. bieti) group at Xiaochangdu in Tibet. The infanticidal attack was witnessed as part of a long-term observational study of ecology and behavior that began in June 2003. The male was observed killing and eating the infant. The literature proposes three main explanations for infanticide: two adaptive hypotheses (sexual selection and resource competition), and one nonadaptive hypothesis (social pathology). Individual cases of infanticide, such as this one, are important for comparative purposes, but when examined on their own they are difficult to interpret in relation to established theoretical frameworks. The cases we describe here show some consistency with the sexual selection hypothesis, but the lack of critical information (i.e., as to paternity) makes it impossible to draw a firm conclusion. This is also the first described case of cannibalism in snub-nosed monkeys.     

Mating Strategies in Relation to Sexually Selected Infanticide in a Non-Social Carnivore: the Brown Bear

Based on the sexually selected infanticide (SSI) hypothesis, infanticide can be an adaptive mating strategy for males, but this is has rarely been documented in non‐social mammals. This phenomenon should not benefit females, so one would expect females to evolve mating counter strategies in order to protect their infants from infanticidal males. Cases of SSI are extremely difficult to document in the field, especially for non‐social species. Using field observations and genetic methods, we describe mating strategies employed by both sexes of brown bears (Ursus arctos) in relation to SSI. We present evidence for the first time suggesting that infanticide is an adaptive male mating strategy in this non‐social carnivore, as all requirements for SSI are fulfilled (1) infanticide shortens the time to the mother's next estrus, (2) the perpetrator is not the father of the killed infants, and (3) putative perpetrators sire the next litter. Moreover, all infanticide cases occurred during the mating season. We expected that primarily immigrant males were infanticidal, as in social species. However, we found that resident adult males commonly committed infanticide. Perhaps they recognize females they have mated with previously. Moreover, we used DNA‐based parentage testing to demonstrate a minimum of 14.5% of multiple paternities (up to 28% for litters with at least three young). Female promiscuity to confuse paternity may be an adaptive counter strategy to avoid infanticide.     

Changes in incidence of infanticidal and parental responses during the reproductive cycle in male and female wild mice Mus musculus

Most studies of infanticide in rodents have been carried out on laboratory animals. In the present study, pairs of infanticidal male and female wild mice were observed for changes in their responsiveness to alien pups during the reproductive cycle. Females killed pups during pregnancy, adopted alien pups during the lactation period, and killed pups again a month after the weaning of their offspring. In males, the transition from infanticidal to parental responses occurred as early as the first half of their mates' pregnancy, and only half of them resumed infanticide a month after the weaning of their litters. Subsequent experiments showed that two independent factors, the experience of copulation and cues from the pregnant female, accounted for the cessation of infanticide and onset of parental care in the male. The adaptive value of the co-existence of multiple mechanisms underlying the cessation of infanticide in male and female house mice is discussed with respect to the social life of this species.     

Observed infanticides following a male immigration event in black howler monkeys, Alouatta pigra, at Palenque National Park, Mexico

This study describes two cases of directly observed and one case of nearly observed infanticide after an adult male immigrated into a multimale–multifemale group of black howler monkeys (Alouatta pigra) at Palenque National Park, Mexico. The immigrant male entered the group alone, injured the central adult male, presumably evicted the noncentral adult male, and killed all three young infants present over the course of three consecutive days in February 2010. Three weeks after the infanticide events, the three adult females who lost their infants were observed to sexually solicit and copulate with both the infanticidal male and the injured central male. Multimale mating is an effective reproductive strategy that females employ to confuse paternity and reduce the risk of infanticide, but the extent to which promiscuous mating after infanticide events is part of a counterstrategy in this species is still unknown. More cases of infanticide will need to be observed to assess the degree to which infanticide avoidance shapes the social system of the black howler monkey.     

Female dispersal,social organization,and infanticide in langurs: Are they linked to human disturbance?

Female dispersal in gregarious animals can involve the desertion of a site, desertion of a social group, or both. Group desertion may be related to inbreeding avoidance. Group fidelity may result from cooperation among females in a group. Site fidelity will be more likely when food can be monopolized and when the population density is close to habitat saturation. The degree of habitat saturation was approximated with a measure of human disturbance. The influence of these various factors on the incidence of female dispersal was investigated for langur populations using data from the literature. The results suggest that female dispersal in langurs involved site desertion, not group desertion. The incidence of female dispersal may affect the social organization of langurs. I propose that when females do not disperse, male takeovers prevail, whereas in populations where female dispersal regularly occurs bisexual groups are disbanded or new groups are formed, a process I call female split-merger. Male takeover is thought to occur when site fidelity is high, female split-merger when site fidelity is low. These processes were indeed found to occur in these circumstances. The dispersal of females might prevent infanticide, whereas male takeover might promote it. Indeed, in studies with male takeover, more infants fell victim to infanticide than in studies with female split-merger. Therefore, female dispersal in langurs is an effective female counterstrategy to infanticide. The factor that had the most profound effect on female dispersal, social organization, and infanticide was habitat saturation. Habitat saturation was measured as the degree of human disturbance, and its influence on the behavior of langurs is probably of relatively recent date. This may lead to an evolutionary transient situation and may explain the discrepancy between current socioecological theories and the behavior of langurs in populations lacking female dispersal. Am. J. Primatol. 44:235–254, 1998. © 1998 Wiley-Liss, Inc.     

New Case of Intragroup Infanticide in the Chimpanzees of Gombe National Park

Researchers have reported a total of 31 infanticides in 4 different chimpanzee (Pan troglodytes) populations. Though infanticide is infrequent, low reproductive rates of females likely make it a strong selective pressure in the species. We report a new incident of intragroup infanticide in Gombe National Park, Tanzania, in which a community male attacked a 3.5-yr-old male. We then consider the infanticide in terms of adaptive and nonadaptive explanations for infanticide including the social pathology, by-product of male aggression, nutritive benefits, resource competition, and sexual selection hypotheses. The incident reported here is not well explained by any of them. While the infanticide is puzzling in terms of ultimate explanations for infanticide, it provides a good context in which to consider proximate mechanisms for offspring recognition. The incident provides some evidence that males may use their mating history with the mother to assess paternity likelihood.     

Infanticide in Propithecus diadema edwardsi: An Evaluation of the Sexual Selection Hypothesis

Infanticide might be described as a reproductive strategy employed by anthropoid primate males when they immigrate into new groups. But infanticide has rarely been observed in wild prosimian primates. For the Malagasy lemurs this may reflect one or more of the following: strict breeding seasons; relative monomorphism in canine tooth and body size; small group sizes; male–female dominance relations; and male–female dyads within groups. We addressed the following questions: Do prosimian males commit infanticide in circumstances similar to those in which anthropoids do? and Is there any reproductive advantage for a highly seasonal breeder to commit infanticide? To help answer these questions, we describe the death of a 24-hr-old infant male Propithecus diadema edwardsi from wounds received during a fight between his mother, her adult daughter, and a newly immigrant male. Interbirth intervals between surviving offspring are 2 years for Propithecus diadema edwardsi; therefore, a male could dramatically shorten the time between reproductive windows by killing an infant. Whether this tactic would be favored by sexual selection cannot be addressed until more information has been collected on the length of interbirth interval due to infanticide relative to that of infant death by other causes; how social factors such as stability of breeding relationships affect long-term male reproductive success; how effective female counterstrategies are to prevent infanticide and/or whether they choose to mate with males that commit infanticide; and how often males that kill infants subsequently sire infants, particularly in groups that contain a resident male.     

Gender Differences in Homicide of Neonates,Infants, and Children under 5 y in South Africa: Results from the Cross-Sectional 2009 National Child Homicide Study

BackgroundHomicide of children is a global problem. The under-5-y age group is the second largest homicide age group after 15–19 y olds, but has received little research attention. Understanding age and gender patterns is important for assisting with developing prevention interventions. Here we present an age and gender analysis of homicides among children under 5 y in South Africa from a national study that included a focus on neonaticide and infanticide.ConclusionsHomicide of children is an extreme form or consequence of violence against children. This national study provides one of the first analyses of neonaticide and infanticide by age and gender and shows the failure of reproductive and mental health and social services to identify and help vulnerable mothers. Multi-sectoral prevention strategies are needed.     

Infanticide in hamadryas baboons

The results of 20-year study of infanticide cases in hamadryas baboon troop of the Sukhumi colony and 10-year observations in Gumista Natural Reserve are presented. The allopatric behaviour which may be the cause of infant death, is shown to be common for 4-7 year old males. In behaviour of older males directed to the infants the elements of aggression predominate. The majority of injuries and infanticide by males takes place in the situations associated with a dominant male change in the group or with the introduction of new females into the groups. In the groups where the social relationships are not fully organized, the appearance of infant leads to decrease of dominant male function and to appropriation of infant by a male and its traumatizing. As a result of infanticide the infants of young 4-7 year old females die most of all. The death of infants commonly occurs during the introduction of young males into the group. The probability of infanticide during the introduction of older males is lower.     

Infanticide and Population Growth in the Bank Vole (Myodes glareolus): The Effect of Male Turnover and Density

One major intrinsic factor affecting recruitment of young into a population is infanticide, the killing of conspecific young by adult males. It occurs in most mammal species, like our study species the bank vole (Myodes glareolus), and is widely accepted as an adaptive behavior, which may increase male fitness via nutritional gain, decreased competition, or an increased access to mates. A turnover of males in a population increases the risk of infanticide owing to a disruption of social structures. In a controlled field study, we tested the effects of total male turnover and density on juvenile recruitment and female space use in experimental bank vole populations. Juvenile recruitment declined significantly in low‐density populations with male turnover, while growth of high‐density populations seemed unaffected. The females’ spatial behavior seemed unaffected by both male turnover and density. Our results suggest that male infanticide may considerably affect population growth and it is more likely to do so at lower densities.     

Infanticide and control of reproduction in cooperative and communal breeders

Many communal breeders are characterized by a conflict over who gets to reproduce, with dominant individuals often claiming the largest share of reproduction in the group. How do dominants control breeding in these species? Although infanticide has often been invoked as a means of control, previous theoretical work on indiscriminate killing of young did not support this idea. There is, however, increasing evidence from field studies in both vertebrates and insects that infanticidal individuals can discriminate between their own offspring and those of other group members, and thus avoid the risk of accidentally killing their own progeny. In a simple game-theoretical model we demonstrate that the capacity for discriminate infanticide can promote high reproductive skew even though few or no offspring are actually killed. When discrimination is good and offspring are cheap to produce, the threat of infanticide prevents the subordinate cobreeder from adding many young to the joint brood, and no killing need occur. High levels of infanticide tend to occur only when discrimination is poor, costs of offspring production are low and/or relatedness is low.     

Infanticide among free-ranging langurs (Presbytis entellus) at jodhpur (Rajasthan/India): Recent observations and a reconsideration of hypotheses

Considerable disagreement characterizes the debate concerning frequency, causation, and function of infanticide in connection with adult male replacements in bisexual one-male troops of hanuman langurs (Presbytis entellus). Detailed observations are presented about two noninfanticidal and three infanticidal male changes including six eye-witness and five presumed cases of infanticide within three langur troops during a long-term study at Jodhpur, Rajasthan, India. The results do not support any explanatory hypotheses focussing on social crowding, regulation of population density, social stress, sexual frustration, incest avoidance, or social bonding, but are in general though not total agreement with the reproductive advantage hypothesis: mainly unrelated infants were killed (one possible exception), the infanticidal male generally sired the subsequent offspring (one exception), and the mean interbirth interval subsequent to infanticide is by 2.1 months shortened. Likewise, several cases of stress induced abortions occurred. It is demonstrated that postconception estrous behaviour is by no means a female counterstrategy to infanticide in order to confuse males concerning the issue of paternity, since an infanticidal male did not spare the subsequent offspring of mothers who copulated with him during pregnancy and pregnant females did not discriminate between fathers and non-fathers.     

Primate group size and interpreting socioecological models: Do folivores really play by different rules?

Because primates display such remarkable diversity, they are an ideal taxon within which to examine the evolutionary significance of group living and the ecological factors responsible for variation in social organization. However, as with any social vertebrate, the ecological determinants of primate social variability are not easily identified. Interspecific variation in group size and social organization results from the compromises required to accommodate the associative and dissociative forces of many factors, including predation, 1 - 3 conspecific harassment and infanticide, 4 - 6 foraging competition 1 , 7 and cooperation, 8 dominance interactions, 9 reproductive strategies, and socialization. 10 - 12 Causative explanations have emerged primarily through the construction of theoretical models that organize the observed variation in primate social organization and group size relative to measurable ecological variation.     

Infanticide in male laboratory mice: Effects of social status,prior sexual experience,and basis for discrimination between related and unrelated young

Several aspects of infanticide, including effects of social status, prior sexual experience, and the basis for discrimination between related and unrelated young, were examined in Swiss-Webster laboratory mice (Mus musculus). Strange males introduced into the female's cage for 24 h on day 1 postpartum significantly reduced pup survival whereas the introduction of sires did not. Direct observations of infanticide were frequent, and the motor patterns used by males to kill pups are described. Males killed their own offspring when those young were in the nest of a strange female, whereas most males did not kill unrelated young in the nest of a familiar female. Thus, past association with the mother appears to be the single most important factor mediating male discrimination of young. Prior contact with a specific female's urine reduced a male's propensity for subsequently killing her young. The act of copulation itself also reduced infanticide. Infanticidal behaviour was correlated with the male's social status: most dominant males killed unrelated pups, whereas none of the subordinates engaged in infanticide. These results are discussed in terms of the population biology of this species.     

Intra-specific variation in social organization of gorillas: implications for their social evolution

We analysed intra-specific variation in the social organization of gorillas and ecological and social factors influencing them, based on recent data on diet, day journey length, home range size, group size and proportion of multi-male groups in three subspecies [western lowland gorillas (WLG); eastern lowland gorillas (ELG); mountain gorillas (MG)]. Median group size was similar across subspecies and across habitats, but the extraordinarily large group including >30 gorillas was only found in habitat with dense terrestrial herbaceous vegetation. Within-group competition may determine the upper limit of group size in frugivorous WLGs and ELGs in lowland habitats with scarce undergrowth. A frugivorous diet may be a causal factor of subgrouping in multi-male groups of WLGs and ELGs, while a folivorous diet may prevent subgrouping in multi-male groups of MGs. Social factors, rather than ecological factors, may play an important role in the formation of multi-male groups and their cohesiveness in MGs. High gregariousness of female gorillas and their prolonged association with a protector male are explained by their vulnerability to both infanticide (MGs) and predators (ELGs). Comparison of long-term changes in group composition and individual movements between ELGs in Kahuzi and MGs in the Virungas suggest that the occurrence of infanticide may promote kin-male association within a group. Threat of infanticide may stimulate MG females to transfer into multi-male groups to seek reliable protection and maturing MG males to stay in their natal groups after maturity. By contrast, the absence of infanticide may facilitate ELG females to associate with infants and other females at transfer and ELG males to establish large groups in a short period by taking females from their natal groups, by luring females from neighbouring groups, or by takeover of a widow group after the death of its leading male. These conditions may prevent ELG and WLG maturing males from remaining to reproduce in their natal groups and possibly result in a rare occurrence of multi-male groups in their habitats. Similar reproductive features of MG and ELG females suggest both female strategies have been adaptive in their evolutionary history.     

Distinct preoptic‐BST nuclei dissociate paternal and infanticidal behavior in mice

Paternal behavior is not innate but arises through social experience. After mating and becoming fathers, male mice change their behavior toward pups from infanticide to paternal care. However, the precise brain areas and circuit mechanisms connecting these social behaviors are largely unknown. Here we demonstrated that the c‐Fos expression pattern in the four nuclei of the preoptic‐bed nuclei of stria terminalis (BST) region could robustly discriminate five kinds of previous social behavior of male mice (parenting, infanticide, mating, inter‐male aggression, solitary control). Specifically, neuronal activation in the central part of the medial preoptic area (cMPOA) and rhomboid nucleus of the BST (BSTrh) retroactively detected paternal and infanticidal motivation with more than 95% accuracy. Moreover, cMPOA lesions switched behavior in fathers from paternal to infanticidal, while BSTrh lesions inhibited infanticide in virgin males. The projections from cMPOA to BSTrh were largely GABAergic. Optogenetic or pharmacogenetic activation of cMPOA attenuated infanticide in virgin males. Taken together, this study identifies the preoptic‐BST nuclei underlying social motivations in male mice and reveals unexpected complexity in the circuit connecting these nuclei.