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1.
In communally breeding animals, there is an evolutionary conflict over the partitioning of reproduction within the group. If dominant group members do not have complete control over subordinate reproduction, this conflict may favour the evolution of infanticidal behaviour (by either subordinates or dominants or both). Elimination of offspring, however, is likely to be constrained by the difficulty of discriminating between an individual's own progeny and those of cobreeders. Here, we develop an evolutionarily stable strategy (ESS) model of reproductive partitioning, which demonstrates that killing of young can be favoured, even if such discrimination is not possible. The model predicts that infanticide will typically be associated with elevated levels of offspring production, and is most likely to prove evolutionarily stable when the coefficient of relatedness between cobreeders is low, and offspring are cheap to produce. The effect of infanticide is to release subordinates from the reproductive restraint they would otherwise be forced to exercise, leading to reduced reproductive skew. When infanticide is possible, addition of numerous young to the joint brood will not lower overall productivity, because progeny in excess of the most productive brood size are eliminated. Subordinates are thus free to contribute more young to the brood than would otherwise be the case. In addition, we show that the possibility of infanticide may influence the pattern of reproduction within a group even if no offspring are actually killed at equilibrium. Copyright 1999 The Association for the Study of Animal Behaviour.  相似文献   

2.
Infanticide, the killing of conspecific young, is commonly recognized as an adaptive behavioural strategy enhancing the fitness of the perpetrator. Infanticide is supposed to be inhibited in several male rodent species after mating with a time lag to the time when perpetrators own offspring would be born. This is because males with no parental care do not recognize their own offspring. It has been suggested that copulation alone is enough to inhibit infanticidal behaviour in male rodents. Infanticidal behaviour occurs in more than 50% of male bank voles (Myodes glareolus), and offspring loss because of infanticide may have a great effect on breeding success and population recruitment. In a laboratory experiment, we studied whether infanticidal male bank voles after successful mating stop the killing of pups. Infanticidal males were paired with a female until successful copulation. After the young were born, the males’ infanticidal behaviour was studied from the time of expected birth of own pups until their post‐weaning age. We predicted that mated infanticidal males are inhibited from committing infanticide especially during the time period when pups are less than 10 d old. Against our prediction, 67% of the infanticidal males continued the killing of pups in the age of 3 d. Infanticidal behaviour remained stable, and half of the males were infanticidal still at the age of weaning of pups. Our results are contradictory to previous studies, as we observed no inhibition of infanticide during early life of pups nor increase in infanticide again when their own offspring would have reached the ‘safe’ age and size after weaning. We suggest that mating alone is not sufficient to inhibit infanticide. Thus, we suggest that other cues of the female with whom the male mated with or on her territory are needed for inhibition to occur.  相似文献   

3.
Infanticide is a violent but successful reproductive strategy found in many mammals, particularly rodents. In male house mice (Mus domesticus and M. musculus) the act of ejaculation provides a reliable neural signal for timing the birth of their offspring. However, a unique chronobiological aspect of this phenomenon is the extraordinary temporal latency that can occur between the stimulus (coital ejaculation) and its adaptive neural response (male mice cease killing pups and behave parentally toward them instead). Specifically, the inhibition of infanticide is often time delayed for many days after a male ejaculates, but virtually always occurs before or around the time his own sired offspring would be born 18-20 days later. Furthermore, infanticide spontaneously reemerges 50-60 days after mating. In CF-1 stock male mice this entire behavioral sequence is synchronized with the female's reproductive cycle, and occurs even in the total absence of social cues or changes in pituitary or gonadal hormones after mating. When entrained and mated at 22 h (lightdark 11:11) or 27 h (lightdark 13.5:13.5) T-cycles, photoperiodic cues appeared to synchronize this dramatic shift in behavior, because a sudden transition from pup killing to parenting was matched with the number of light/dark cycles experienced after ejaculation rather than the amount of real time experienced, suggesting a circadian timing link. Housing in constant light accelerated the postmating transition to parenting, whereas constant dark significantly delayed the transition to parenting, but still occurred by 3 weeks after mating. Most males tend to oscillate between infanticide and parental behavior for several days before locking in to constant parenting, regardless of lighting conditions. Variation in the time delay between ejaculation and the inhibition of infanticide was consistent within young individuals (<10 months of age), but in older males (> 18 months of age) the time interval between ejaculation and parenting was significantly prolonged and attenuated. Another unique aspect of this phenomenon is that variation among individuals in their timing and response to light cues is correlated with phenotypic variation in sex steroid exposure during late fetal development. So far, no simple physiological explanation can account for the neural mechanism triggered by ejaculation that coordinates these time-delayed behavioral changes toward pups.  相似文献   

4.
Infanticide is a violent but successful reproductive strategy found in many mammals, particularly rodents. In male house mice (Mus domesticus and M. musculus), the act of ejaculation provides a reliable neural signal for timing the birth of their offspring. However, a unique chronobiological aspect of this phenomenon is the extraordinary temporal latency that can occur between the stimulus (coital ejaculation) and its adaptive neural response (male mice cease killing pups and behave parentally toward them instead). Specifically, the inhibition of infanticide is often time delayed for many days after a male ejaculates, but virtually always occurs before or around the time his own sired offspring would be born 18-20 days later. Furthermore, infanticide spontaneously reemerges 50-60 days after mating. In CF-1 stock male mice this entire behavioral sequence is synchronized with the female's reproductive cycle, and occurs even in the total absence of social cues or changes in pituitary or gonadal hormones after mating. When entrained and mated at 22 h (light:dark 11:11) or 27 h (light:dark 13.5:13.5) T-cycles, photoperiodic cues appeared to synchronize this dramatic shift in behavior, because a sudden transition from pup killing to parenting was matched with the number of light/dark cycles experienced after ejaculation rather than the amount of real time experienced, suggesting a circadian timing link. Housing in constant light accelerated the postmating transition to parenting, whereas constant dark significantly delayed the transition to parenting, but still occurred by 3 weeks after mating. Most males tend to oscillate between infanticide and parental behavior for several days before locking in to constant parenting, regardless of lighting conditions. Variation in the time delay between ejaculation and the inhibition of infanticide was consistent within young individuals (< 10 months of age), but in older males (> 18 months of age) the time interval between ejaculation and parenting was significantly prolonged and attenuated. Another unique aspect of this phenomenon is that variation among individuals in their timing and response to light cues is correlated with phenotypic variation in sex steroid exposure during late fetal development. So far, no simple physiological explanation can account for the neural mechanism triggered by ejaculation that coordinates these time-delayed behavioral changes toward pups.  相似文献   

5.
Recently, familial abuse and killing of children have been correlated with infanticidal behavior by nonhuman male animals which is postulated to be genetic. However, infanticide by males as an evolutionary mechanism is unlikely to occur in primates, and is equally unlikely in lions. To investigate the sexual selection hypothesis of infanticide for lions, four questions should be considered: (1) because they all mate freely with lionesses, are male pride lions closely related? (often they are not), (2) do males kill the young cubs when they join a pride? (few such cases have been observed), (3) do the females then mate with the new males to produce offspring? (yes), and (4) do the males remain with the pride for over two years to protect this new generation? (often not). Field data indicate that in NO instance do we know that male lions killed cubs in a new pride, mated with their mother, and then remained with the pride to protect their own young. Rather, female lions may kill more cubs than males and certainly cause many more cub deaths by allowing them to starve, [ infanticide by male lions, infanticide hypothesis, faulty science]  相似文献   

6.
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.  相似文献   

7.
Infanticide is easiest to understand when it involves killing the offspring of others [1], but a parent may also kill its own offspring if the sacrifice of currently dependent young leads to higher survival of brood mates [2] or an improvement in the parent's likely future reproduction [3]. However, sex-specific infanticide by parents of their own offspring, although occurring in some human societies [4], is rare across species. Its rarity may be because killing one sex combines wasted parental effort with consequent biases in population sex ratios that are detrimental for the fitness of the overproduced sex [5-7]. We show that killing male offspring can be advantageous to Eclectus parrot (Eclectus roratus) mothers even though frequency-dependent selection then elevates the reproductive value of sons above that of daughters. In poorer-quality nest hollows, broods with a single female nestling had higher reproductive value than broods in which the female had a younger brother. Our data demonstrate frequent targeted removal of male nestlings within 3 days of hatching in these specific brood types and nesting conditions. The ability of Eclectus parrots to perceive the sex of their offspring relatively early may favor decisions to kill one sex before further investment in parental care.  相似文献   

8.
Abstract In species where parents may commit infanticide, temporal kin recognition can help ensure parents kill unrelated young but care for their own offspring. This is not true recognition, but rather depends on accurate timing of the arrival of young and a behavioural switch from killing to caring for offspring. Mistakes have clear fitness consequences; how do species that use temporal kin recognition ensure accurate timing? We manipulated photic cues and show that the switch from infanticide to parental care in the burying beetle Nicrophorus vespilloides depends on day‐length inputs. Extending the light period after carcass discovery influenced timing of both oviposition and the cessation of infanticide. Manipulation of the light : dark cycle after oviposition also influenced timing of the switch to parental care. The timing mechanism is therefore sensitive to photic cues and access to a carcass and is not triggered by oviposition. The behavioural switch is directly related to the timing mechanism rather than changes in reproductive physiology. Given the conserved nature and extensive homology of genetic influences on biological timing, we speculate that the molecular mechanisms regulating circadian behaviour may have been co‐opted to allow beetles to determine how much time has passed after carcass discovery even though this is over 50 h.  相似文献   

9.
Infanticide is the killing of infants by conspecifics, and may be direct or indirect; and parental or non‐parental. Explanations for such behaviours range from forcing females with young back into heat, resource recycling in times of shortage and elimination of competitors. Though moderately well understood in some mammal groups, reports of infanticide in hystricomorph rodents are often contradictory and invariably based on captive observations, raising questions about the naturality of the behaviour and the conclusions derived from them. Here, we report the first wild observation of direct infanticide and cannibalism of two juvenile Azara's Agoutis Dasyptocta azarae by a group of adults in Paraguay, confirming that such behaviours also occur under natural conditions.  相似文献   

10.
In mammals, allocation to reproduction can either be primed or suppressed in relation to cues from other individuals. Some conspecifics (e.g. potential mates) may enhance an individual's ability to reproduce but others may have a detrimental effect on reproductive success. One widely studied response to conspecific cues, the ‘Bruce effect’, occurs when pregnant females abort their pregnancies after exposure to a novel male. It has been suggested that this response has evolved as a counter‐tactic to the threat of infanticide posed by novel males. In some species, like mice, pregnancy termination will only occur if females are exposed to the unfamiliar male during a brief critical period early in pregnancy, which is surprising considering that an unfamiliar male threatens infanticide whenever present, and in particular near to birth. We demonstrate that female mice experiencing novel males during late pregnancy also alter their investment in progeny, but in a more subtle manner than previously observed. Females exposed to an unfamiliar male during late pregnancy give birth to offspring of a comparable weight to those produced by females exposed to the paternal male, but these offspring grow more slowly over lactation. As a consequence, offspring from these females weigh less at weaning. Modification of their growth trajectory, however, allows these offspring to catch up to normal weights by adulthood. Thus, cues of unfamiliar males, and possibly their associated threat of infanticide, can produce more wide‐ranging effects on maternal investment than previously recognized.  相似文献   

11.
The killing of genetically unrelated young by males has been viewed as a strategy that forces victimized females to advance the onset of their next fertile period, thus infanticidal males gain a time advantage that may be crucial to maximize reproductive success. Among females that may raise several broods in a year, a failure occurring relatively earlier in the time-course of the previous breeding attempt may result in an increased investment in the next breeding attempt. This female strategy may be exploited by males in their own interest, and may strongly select for male infanticidal behaviour. I demonstrate that, in the house sparrow, females mated with infanticidal males re-laid earlier, initiated more breeding attempts and fledged more offspring than females mated with non-infanticidal males. These results suggest that both the time saving and the manipulation of female investment are independent mechanisms conferring advantages that may have selected for male infanticide in the studied population.  相似文献   

12.
Infanticide, the killing of conspecific young, has been documented in numerous species of mammals, especially rodents. In that infanticide is costly to the victim mother, natural selection should favour counter-strategies by females to protect their pups. We studied the frequency of infanticide by male and female bank voles (Clethrionomys glareolus) and the effectiveness of dams in recognising and deterring infanticide. In trials in which unprotected pups were exposed to voles of both sexes, one third of male and female intruders killed pups. When mothers were present at the nest site, not a single female and only 2 of 25 males were able to commit infanticide. Females acted aggressively towards all intruders and hence did not discern between infanticidal and non-infanticidal males and females. Aggression of dams against any intruder indicates that all strange individuals near the nest site of a territorial species form an equal threat to pups. However, the presence of the aggressive dam is sufficient to deter most intruders from harming offspring by keeping them at a distance from the nest site. Heat run before mating, in a species with postpartum oestrus and vulnerable pups in the nest, also might lure potential infanticidal males away from the nest site and obscure the nest location. Received in revised form: 17 October 2001 Electronic Publication  相似文献   

13.
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.  相似文献   

14.
Infanticide by males is widespread across mammals and especially prevalent among primates. Considerable research has examined how fitness benefits can explain the occurrence of this behavior; less is known, however, about intrapopulation variation in its occurrence. We evaluated 10 infanticides by males in wild blue monkeys according to the sexual selection hypothesis. To explore intrapopulation variation in occurrence of infanticide, we compared these cases to 38 cases that were contextually similar but in which infanticide did not occur. We examined male reproductive benefit, infant age, maternal parity, postconception estrus, group defense, available mating partners, and context of takeover. We based comparisons on daily or near daily records of male presence in the study groups, infant birth dates, and male-female sexual interactions. Infanticides followed predictions of the sexual selection hypothesis: males were unlikely to kill their own offspring, the period for the mother’s return to conception was reduced by half, and males increased their chance of siring her next offspring. Difference in male reproductive benefit, costs, and motivation did not fully explain the observed variation in infanticide occurrence. Infants were more likely to be spared if they were older when a male first arrived, or if their mother had mated with the male in the second month after conception. The most important determinant of infant fate, however, was male identity, a finding consistent with 2 scenarios: 1) an infanticidal tendency may be influenced by a genetic polymorphism that is not fixed in this population or 2) infanticidal behavior may be a conditional male strategy. Further research on intrapopulation variation in infanticidal behavior should focus especially on characteristics of males.  相似文献   

15.
Strategies and counterstrategies to infanticide in mammals   总被引:4,自引:0,他引:4  
I analyse and summarize the empirical evidence in mammals supporting alternative benefits that individuals may accrue when committing nonparental infanticide. Nonparental infanticide may provide the perpetrator with nutritional benefits, increased access to limited resources, increased reproductive opportunities, or it may prevent misdirecting parental care to unrelated offspring. The possibility that infanticide is either a neutral or maladaptive behaviour also is considered. I devote the second half of this article to reviewing potential mechanisms that individuals may use to prevent infanticide. These counterstrategies include the early termination of pregnancy, direct aggression by the mother against intruders, the formation of coalitions for group defence, the avoidance of infanticidal conspecifics, female promiscuity, and territoriality. I evaluate the support for each benefit and counterstrategy across different groups of mammals and make suggestions for future research.  相似文献   

16.
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.  相似文献   

17.
In nonhuman primates, infanticide by adult males can occur when the leader male is ousted from a one-male, multifemale group, or when male dominance rank changes within a multimale, multifemale group. According to the sexual selection hypothesis, this behavior may be adaptive if perpetrators increase their reproductive success by killing unrelated, unweaned infants, thus shortening the interbirth interval of the mother, and then siring her next infant. Under an alternative hypothesis, infanticide is a byproduct of aggressive male–male competition and these predictions do not hold. Direct observations of the context surrounding infanticide in free-ranging primate populations that allow a test of these predictions are rare. Here, we document four cases of male infanticide and report paternity data for a group of golden snub-nosed monkeys (Rhinopithecus roxellana) at Shennongjia, China. Three cases of infanticide by new leader males supported the predictions of the sexual selection hypothesis, while another provides partial support for the sexual selection hypothesis, but can also be explained via a nonadaptive hypothesis. In this latter case, a male from an all-male group killed an infant during an aggressive episode that appeared to be accidental, as it took place 7 mo before a male takeover happened, and the perpetrator did not obtain any reproductive advantage. We conclude that most male infanticide events in golden snub-nosed monkeys are consistent with the adaptive selection sexual hypothesis.  相似文献   

18.
Evidence of alloparental care during the incubation stage has largely been demonstrated for species that incubate their offspring externally in a nest. Alloparental care in these species generally consists of the rearing of mixed broods which contain a low proportion of “foreign” young alongside the host's own offspring. However, many animals, including sea anemones, incubate offspring either on or within their bodies. The beadlet anemone Actinia equina incubate their young internally, and as many sea anemones are capable of reproducing both sexually and asexually, the origin of these internally brooded young has been the subject of much debate. While genetically identical young are brooded internally under the juvenile stage, it is thought that those produced sexually are released as larvae into the water and must return to the gastric cavity of an adult in order for metamorphosis to occur. As the likelihood of a planula larva finding its way back to its parent is slim, this suggests that alloparental care may play a role in the survival of juveniles in this species, a hypothesis first suggested a century ago but rarely tested. Here, using highly polymorphic microsatellite markers, we find evidence of alloparental care in A. equina. Our results indicate that while a high proportion of juveniles were genetically identical to their brooding adult, the remaining juveniles showed stark genetic differences to their brooding adult. These juveniles shared far fewer alleles with their “parent” than expected under sexual reproduction, indicating that they were not the adult's offspring. Furthermore, we found variation in the genetic composition of broods, which consisted either of (a) entirely genetically identical individuals, (b) a mix of unique individuals and clonemates or (c) entirely unique individuals, that is no shared genotype. Our results thus indicate that adult A. equina tolerate the presence of non-offspring within their gastric cavity and furthermore that they may incubate entirely “foreign” broods.  相似文献   

19.
Females in numerous rodent species engage in communal nesting and breeding, in which they share one or more nests to rear their young. A potential cost of communal nesting and breeding is that mothers divert resources to unrelated offspring. One way mothers could avoid this cost is to recognize and favour their own young over unrelated offspring when allocating maternal effort. We assessed whether female degus (Octodon degus), a communally nesting and breeding caviomorph rodent, discriminate between their own and unrelated offspring during lactation. Female degus previously have been shown to distinguish between their own and unrelated pups when exposed to odours from both. We measured pup discrimination based on differences in the retrieval behaviour of females that were in early or intermediate lactation directed towards their own and unrelated offspring; offspring presented were of similar or different age. Before any event of pup retrieval, lactating females spent similar amounts of time and interacted to a similar extent with their own and unrelated pups. During pup retrieval, all lactating females transported both pups to the nest. Neither relatedness to pups, nor pup‐age differences, influenced the order in which pups were retrieved to the nest. Dams waited similar amounts of time before retrieving the first pup when the first transported young was their own or unrelated. Likewise, females waited similar amounts of time before retrieving the second pup when the pup transported first was their own or unrelated. The time between first and second pup transport events was longer when dams were in early when compared with intermediate lactation, but only when pups were of similar age. All experimental subjects nursed unrelated pups after they were retrieved. Collectively, our results do not support the hypothesis that communally breeding female degus use their recognition ability to discriminate against unrelated offspring in favour of their own young.  相似文献   

20.
Evolutionary theories about parent-offspring relationships have predicted that young will aggressively demand food and care from their parents at the time of weaning - when the parents should, in their own interests, reserve their efforts for future offspring. Detailed studies of the behavioural development of mammals have given only limited support for these expectations. Often the mother is more amenable to the needs of her offspring than evolutionary theory predicts, and often offspring are sensitive to the state of their mother, tuning the pattern of their own development accordingly. Such aggression as is seen between mother and offspring tends to occur at stages other than weaning. The mismatch between theory and evidence may arise because a mother needs to monitor her offspring's state as well as her own and respond appropriately in order to maximize her own reproductive success. Similarly, an offspring needs to monitor its mother and prepare for the world in which it will grow up, in order to maximize its chances of surviving to breed.  相似文献   

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