Communal Nesting among Genetically Similar House Mice

Species differences in the effect of oxytocin on maternal behavior: A model incorporating the potential for allomaternal contributions

Oxytocin has historically been linked to processes involved with maternal behavior. However, the relative importance of oxytocin for maternal behavior widely varies among mammalian species, from indispensable to apparently nonessential. This review proposes a new model in which the relative importance of oxytocin for mothering across species is explained by an evolutionary pressure which we term "allomaternal potential", or the degree to which other conspecifics are capable and likely to assist with caregiving. It is notable that in animals where allomaternal potential is high (i.e., many quality helpers are available), oxytocin is decoupled from mothering. However, in animals where allomaternal potential is low (i.e., conspecifics refuse to, or do not provide, quality help), oxytocin is crucial for mothering. We posit that this relationship is a form of kin selection, whereby oxytocin is a signal that leads mothers to preferentially dispense resources to their own young when quality helpers are unlikely.

Neural Circuit Mechanisms That Underlie Parental Care

In mammals, parental care is essential for the survival of the young; therefore, it is vitally important to the propagation of the species. These behaviors, differing between the two sexes, are innate, stereotyped, and are also modified by an individual's reproductive experience. These characteristics suggest that neural mechanisms underlying parental behaviors are genetically hardwired, evolutionarily conserved as well as sexually differentiated and malleable to experiential changes. Classical lesion studies on neural control of parental behaviors, mostly done in rats, date back to the 1950s. Recent developments of new methods and tools in neuroscience, which allow precise targeting and activation/inhibition of specific populations of neurons and their projections to different brain structures, have afforded fresh opportunities to dissect and delineate the detailed neural circuit mechanisms that govern distinct components of parental behaviors in the genetically tractably organism, the laboratory mouse (Mus musculus). In this review, we summarize recent discoveries using modern neurobiological tools within the context of traditional lesion studies. In addition, we discuss interesting cross talk between neural circuits that govern parent care with those that regulate other innate behaviors such as feeding and mating.

Fitness Consequences of Female Alternative Reproductive Tactics in House Mice (Mus musculus domesticus)

Alternative reproductive tactics (ARTs) are defined as discrete differences in morphological, physiological, and/or behavioral traits associated with reproduction that occur within the same sex and population. House mice provide a rare example of ARTs in females, which can rear their young either solitarily or together with one or several other females in a communal nest. We assessed the fitness consequences of communal and solitary breeding in a wild population to understand how the two tactics can be evolutionarily stable. Females switched between the two tactics (with more than 50% of all females having two or more litters using both tactics), pointing toward communal and solitary breeding being two tactics within a single strategy and not two genetically determined strategies. Communal breeding resulted in reduced pup survival and negatively impacted female reproductive success. Older and likely heavier females more often reared their litters solitarily, indicating that females use a condition-dependent strategy. Solitary breeding seems the more successful tactic, and only younger and likely less competitive females might opt for communal nursing, even at the cost of increased pup mortality. This study emphasizes the importance of analyzing phenotypic plasticity and its role in cooperation in the context of female ARTs.

Female Chemical Signalling Underlying Reproduction in Mammals

Chemical communication plays many key roles in mammalian reproduction, although attention has focused particularly on male scent signalling. Here, we review evidence that female chemical signals also play important roles in sexual attraction, in mediating reproductive competition and cooperation between females, and in maternal care, all central to female reproductive success. Female odours function not only to advertise sexual receptivity and location, they can also have important physiological priming effects on male development and sperm production. However, the extent to which female scents are used to assess the quality of females as potential mates has received little attention. Female investment in scent signalling is strongly influenced by the social structure and breeding system of the species. Although investment is typically male-biased, high competition between females can lead to a reversed pattern of female- biased investment. As among males, scent marking and counter-marking are often used to advertise territory defence and high social rank. Female odours have been implicated in the reproductive suppression of young or subordinate females across a range of social systems, with females of lower competitive ability potentially benefiting by delaying reproduction until conditions are more favourable. Further, the ability to recognise individuals, group members and kin through scent underpins group cohesion and cooperation in many social species, as well as playing an important role in mother-offspring recognition. However, despite the diversity of female scent signals, chemical communication in female mammals remains relatively understudied and poorly understood. We highlight several key areas of future research that are worthy of further investigation.

Impact of male presence on female sociality and stress endocrinology in wild house mice (Mus musculus domesticus)

In group living animals, reproductive competition plays an important role in shaping social relationships and associations among female group members. In this study, we investigated the impact of male presence on the development of female-female competition and female sociality in groups of female wild house mice, using physiological and behavioral parameters. We predicted that, by eliciting intra-sexual competition, males influence social relationships among female group members and thus affect female associations to potential cooperation partners. To test this hypothesis we compared stress hormone production, the frequency of agonistic interactions, social hierarchies and social partner preferences in groups of unrelated, unfamiliar females in the absence and presence of males. Our results revealed no indication that the introduction of males into all-female groups of wild house mice elicited increased competition among female group members, neither on the physiological nor on the behavioral level. We found no effect of male presence on female glucocorticoid secretion, aggression, dominance hierarchies or on the females' sociability. Females thus seem not to intensely compete over access to males. This female ability to behaviorally and physiologically deal with even previously unfamiliar same-sex group members may be an important feature of female house mouse societies. In fact, it could be a necessary prerequisite to establish cooperative relationships between females in the context of reproduction, such as communal nursing of young.

No evidence for punishment in communally nursing female house mice (Mus musculus domesticus)

Punishment is claimed as an important mechanism to stabilise costly cooperation in humans, but its importance in social animals has been questioned recently due to both conceptual considerations and a lack of empirical evidence (only few published studies). We empirically tested whether there is evidence for punishment in communally nursing house mice (Mus musculus domesticus, direct descendants of “wild” animals). Communally breeding females pool their litters and raise all offspring together, indiscriminately caring for own and other offspring. Such a situation resembles a public good and provides scope for exploitation if females vary in their relative contributions to the joint nest (offspring number). We allowed two females to communally breed and conducted removal experiments both in the presence and absence of pups. We aimed to test whether reduced investment by one of the females (induced through separation from the partner and their combined offspring for 4 or 12 hours) leads to increased aggression by the other female after the reunion. We found no evidence for punishment, on the contrary, females increased socio-positive behaviours. The costs of losing a partner in a communally breeding species might be too high and hinder the evolution of punishment. Our findings add to a growing list of examples questioning the role of punishment in cooperating non-human animals and emphasise the importance of empirical testing of its assumptions and predictions.

Low temperatures during ontogeny increase fluctuating asymmetry and reduce maternal aggression in the house mouse, Mus musculus

Maternal aggression is behavior displayed by post-partum lactating female mice toward unfamiliar conspecifics, presumably as a defense against infanticide. A variety of perinatal stressors can impair maternal care in adulthood. Previous studies on associations between developmental perturbations and maternal aggression have produced mixed results. To address this issue, we employed a proxy for developmental instability, fluctuating asymmetry (FA) to further elucidate the relationship between low temperature stress and maternal aggression. FA, small, random deviations from perfect symmetry in bilateral characters is used as a quantitative measure of stress during ontogeny. Dams were either maintained in standard laboratory temperatures (21 ± 2 °C), or cold temperatures (8 ± 2 °C) during gestation. During lactation, their progeny either remained in the temperature condition in which they were gestated or were transferred to the other temperature condition. Four individual measures of FA, a composite of these measures, and three measures of maternal aggression were assessed in the female progeny in adulthood. Exposure to low temperatures during both pre- and early post-natal development increased composite FA and reduced all three measures of maternal aggression compared to controls. Exposure to low temperatures during the pre- or postnatal period alone did not induce either high FA or altered maternal aggression. Certain measures of FA and nest defense were negatively correlated. Our results suggest that low temperatures experienced during gestation and lactation may have important fitness costs. Low maternal aggression towards infanticidal conspecifics is likely to limit the number of offspring surviving into adulthood. Overall, FA appears to be a reliable indicator of chronic developmental stress with implications for fitness.

A reduced propensity to cooperate under enhanced exploitation risk in a social mammal

Conditional adjustment of cooperativeness to the expected pay-off might be a useful strategy to avoid being exploited in public good situations. Parental care provided towards all offspring in a communal nest (containing offspring of several females) resembles a public good. Females indiscriminately caring for all young share the costs equally, but the pay-off may vary depending on their contribution to the joint nest (number of own offspring). Females with fewer offspring in the joint nest will be exploited and overinvest relative to their contribution. We experimentally created a situation of high conflict in communally nursing house mice, by using a genetic tool to create a difference in birth litter sizes. Females in the high conflict situation (unequal litter sizes at birth) showed a reduced propensity to give birth as part of a communal nest, therefore adjusting their cooperativeness to the circumstances.

The Genetic Basis of Kin Recognition in a Cooperatively Breeding Mammal

Cooperation between relatives yields important fitness benefits, but genetic loci that allow recognition of unfamiliar kin have proven elusive. Sharing of kinship markers must correlate strongly with genome-wide similarity, creating a special challenge to identify specific loci used independently of other shared loci. Two highly polymorphic gene complexes, detected through scent, have been implicated in vertebrates: the major histocompatibility complex (MHC), which could be vertebrate wide, and the major urinary protein (MUP) cluster, which is species specific. Here we use a new approach to independently manipulate sharing of putative genetic kin recognition markers, with the animal itself or known family members, while genome-wide relatedness is controlled. This was applied to wild-stock outbred female house mice, which nest socially and often rear offspring cooperatively with preferred nest partners. Females preferred to nest with sisters, regardless of prior familiarity, confirming the use of phenotype matching. Among unfamiliar relatives, females strongly preferred nest partners that shared their own MUP genotype, though not those with only a partial (single-haplotype) MUP match to themselves or known family. In the absence of MUP sharing, females preferred related partners that shared multiple loci across the genome to unrelated females. However, MHC sharing was not used, even when MHC type completely matched their own or that of known relatives. Our study provides empirical evidence that highly polymorphic species-specific kinship markers can evolve where reliable recognition of close relatives is an advantage. This highlights the potential for identifying other genetic kinship markers in cooperative species and calls for better evidence that MHC can play this role.

Newborns prefer the odor of milk and nipples from females matched in lactation age: Comparison of two mouse strains

Newborn mice are attracted to mammary odor cues carried in murine milk and nipple secretions. However, murine milk odor is not equally attractive along lactation. The present study focuses on the differential response of 2day-old mouse pups of C57Bl/6 (C) and Balb/C (B) strains to the odor of milk (Experiment 1) and nipples (Experiment 2) that are matched/unmatched in terms of pup's age or strain. In Experiment 1, C and B pups were tested in a series of tests simultaneously opposing either murine milk and a blank (water), or two milks collected in early and late lactation (lactation days 2 and 15, respectively) from females belonging to their own or the other strain. Results showed that C and B pups were attracted to the odor of the different milks regardless of the lactation age and the strain of the donor female. Nevertheless, C and B pups preferred the odor conveyed by early- than late-lactation milk of either strain. Moreover, early-lactation milk from C females was more attractive than early-lactation milk from B females for pups of either strain. In Experiment 2, differential nipple grasping response of C and B pups was measured when they were exposed to nipples of females in early or late lactation. The proportion of C pups that grasped a nipple was greater when they were exposed to a nipple in early lactation regardless of the strain of the donor females, whereas the proportion of B pups that grasped a nipple was greater when they were exposed to a nipple in early lactation, but only from own strain. Thus, newborn mice prefer the odor of milk and nipples from females that are matched in lactation age. This result is discussed in terms of reciprocally adaptive mechanisms between lactating females and their newborn offspring.

Allosuckling in reindeer (Rangifer tarandus): milk-theft, mismothering or kin selection?

Allosuckling, the suckling of offspring from females other than their own mother, has been reported in a number of mammalian species, including reindeer. The causes and function of this behaviour are still being investigated. We monitored 25 doe-calf pairs of semi-domestic reindeer Rangifer tarandus over 10 weeks to test three allosuckling/allonursing hypotheses: (1) milk theft, calves opportunistically allosuckle; (2) mismothering, misdirected maternal care; and (3) kin-selected allonursing. A calf soliciting an allosuckling bout was categorized as non-filial (NF), and a calf soliciting a suckling bout from its mother was categorized as filial (F). We recorded 9757 solicitations, of which 5176 were successful F bouts and 1389 were successful NF bouts. The rejection rates were greater for NF than F calves. The proportions of antiparallel positions adopted were greater for F than NF calves. The odds of an allobout were lower for calves arriving 1st, 3rd, 4th, 5th or 6th than for those arriving 2nd, but the odds did not vary with position adopted and relatedness. Our results provided support to the milk-theft hypothesis, whereas limited support for the mismothering hypothesis was found. Our results did not support the hypothesized kin selection function of allosuckling in reindeer. This article is part of a Special Issue entitled: insert SI title.

Maternal investment of communally nursing female house mice (Mus musculus domesticus)

Female house mice (Mus musculus domesticus) belonging to the same polygynous breeding unit rear their litters communally. This paper analyzes the consequences of communal nursing on the number and weight of offspring produced. The reproductive behaviour of monogamous females was compared to that of females living in polygynous groups, consisting of either two familiar sisters or of two genetically unrelated females (unfamiliar until the age of 7 weeks). The lifetime reproductive success of a female was measured as the total number of offspring weaned during a lifespan of 6 months (standardized as 120 days after mating at the age of 8 weeks). The number of litters produced and average litter size per female did not differ significantly between the 3 groups of females. However, females communally nursing with a sister weaned significantly more young than a monogamously paired female. Those sharing a nest with an unrelated female weaned an intermediate number of offspring. Sharing a communal nest with a sister significantly increased the total mass of offspring weaned in comparison with both monogamous females and unrelated females. Furthermore, communal nests improved the birth weight of the young when compared with young in solitary nests. By cooperative brood care and communal nursing, females improved the weight of the young produced. By having a sister for cooperation, a female futher improved the number of offspring weaned when compared with a female rearing litters in solitary nests, as well as the combined weight of offspring weaned compared with all other females studied.

The response of newly born mice to odors of murine colostrum and milk: unconditionally attractive, conditionally discriminated

It is a general rule that milk conveys chemosensory cues that are attractive to mammalian neonates. This study investigated whether compositional fluctuations in milk along lactation induce variations in newborn mouse pups' (Mus musculus, strain BALB/c) attraction to milk odor. Pups differing in suckling experience were exposed to the odor of milk sampled from females varying in lactational stage. Immediately after birth, suckling-inexperienced (P0) and suckling-experienced (P0suck ) pups were assayed in a series of paired-choice tests contrasting murine milk [of lactation days 0, 3, 15 (abridged L0, L3, L15, respectively)] and a blank (water) to evaluate olfactory detection and attraction of milk odor. Preference tests further paired these milk two-by-two to assess their relative attraction. Results showed first that P0 and P0suck pups detect and positively orient to any milk odor. When L0 is presented against L15 milk, P0 pups orient for a similar duration towards these odor stimuli, whereas P0suck pups spend more time toward the odor of L0 than of L15 milk. Finally, P0suck pups orient similarly to odors of L0 milk collected before/after the first suckling episode (L0 and L0suck , respectively), but the odor of L0 milk was more attractive than that of L3 milk. Thus, mouse pups' positive orientation toward the odors of murine colostrum (assumed to correspond to L0/L0suck milk) and later-lactation milk appears unconditional of previous suckling experience, whereas their ability to discriminate or display preference between milk differing in lactation stage appears conditional on postnatal exposure effects.

Communal nursing in wild house mice is not a by-product of group living: females choose

Communal nursing, the provision of milk to non-offspring, has been argued to be a non-adaptive by-product of group living. We used 2 years of field data from a wild house mouse population to investigate this question. Communal nursing never occurred among females that previously lacked overlap in nest box use. Females nursed communally in only 33 % of cases in which there was a communal nursing partner available from the same social group. Solitarily nursing females were not socially isolated in their group; nevertheless, high spatial associations prior to reproduction predict which potential female partner was chosen for communal nursing. An increase in partner availability increased the probability of communal nursing, but population density itself had a negative effect, which may reflect increased female reproductive competition during summer. These results argue that females are selective in their choice of nursing partners and provide further support that communal nursing with the right partner is adaptive.

Development of the social behavior of two mice species with contrasting social systems

The house mouse (Mus musculus) and the mound-building mouse (M. spicilegus) differ in their mating and social systems. The M. musculus is polygynous and females tend to breed cooperatively while M. spicilegus is known to be monogamous and famous for its unique cooperative behavior; the communal overwintering. Mus spicilegus is considered as a highly aggressive species in the genus Mus. In the present study, we attempted to analyze the development of aggressive and sociable behavior in these species and to discover how familiarity with the target moderates the development of sociable and aggressive behaviors and moderates the differences between the species. Dyadic social interaction tests in neutral cages were performed on 21-, 60-, and 120-day-old mice of both genders and both species. Each individual was tested against a sibling and an unfamiliar individual at all three ages. Our results showed that the development of aggressive and sociable behavior with age differed between the species and sexes; however, familiarity with the other mouse moderated the effect of species on aggression. At 21 days, both genders of M. spicilegus were more aggressive against strangers than siblings. This became true of both species at 60 days. When facing a stranger, both sexes of M. spicilegus were more aggressive than M. musculus at 120 days. However, when facing a sibling, neither gender of M. spicilegus was more agonistic than M. musculus, indicating that either kinship or early social experiences elicit tolerance.

A model for genomic imprinting in the social brain: adults

Genomic imprinting refers to genes that are silenced when inherited via sperm or via egg. The silencing of genes conditional upon their parental origin requires an evolutionary explanation. The most widely accepted theory for the evolution of genomic imprinting-the kinship theory-argues that conflict between maternally inherited and paternally inherited genes over phenotypes with asymmetric effects on matrilineal and patrilineal kin results in self-imposed silencing of one of the copies. This theory has been applied to imprinting of genes expressed in the placenta, and infant brain determining the allocation of parental resources being the source of conflict parental promiscuity. However, there is growing evidence that imprinted genes are expressed in the postinfant brain where parental promiscuity per se is no longer a source of conflict. Here, we advance the kinship theory by developing an evolutionary model of genomic imprinting in adults, driven by intragenomic conflict over allocation to parental versus communal care. We consider the role of sex differences in dispersal and variance in reproductive success as sources of conflict. We predict that, in hominids and birds, parental care will be expressed by maternally inherited genes. In nonhominid mammals, we predict more diversity, with some mammals showing the same pattern and other showing the reverse. We use the model to interpret experimental data on imprinted genes in the house mouse: specifically, paternally expressed Peg1 and Peg3 genes, underlying maternal care, and maternally expressed Gnas and paternally expressed Gnasxl genes, underlying communal care. We also use the model to relate ancestral demography to contemporary imprinting disorders of adults, in humans and other taxa.

Kin recognition versus familiarity in a solitary mustelid, the European polecat Mustela putorius

The aim of this experimental study was to investigate kin discrimination in the polecat and to analyse the ontogeny of interactions. Juvenile polecats (ten males and nine females) had been raised under four distinct experimental conditions: 1, kin, familiar; 2, kin, unfamiliar; 3, non-kin, familiar; 4, non-kin, unfamiliar. During dyadic encounters between polecats in neutral enclosures, the number of positive (tolerance), negative (aggression), intermediate (intimidation), and neutral interactions (no direct interactions) were recorded at two different ages of the animals (50 and 70 days old). Male-male encounters were characterised by more aggressive behaviour than female-female ones. The proportion of these negative interactions increased with age, while the proportion of positive interactions decreased. Although aggressive behaviours varied among groups, the reaction did never differ with the kinship. Kin selection theory provides successful explanations for a wide range of phenomena, but our results suggest that multiple mechanisms running simultaneously might be involved in social behaviours. Familiarity clearly influenced the social behaviour of polecats and might be involved in a kin facilitation effect favouring interactions. Animals raised together demonstrated more positive and less negative interactions, so that, despite the individualistic way of life of the polecat, familiarisation may result in more tolerance, emphasising that solitary species may provide significant information on social life. Anyway, familiarisation in polecat may be regarded as a cognitive form of recognition.

Information processing in the mammalian olfactory system

Recently, modern neuroscience has made considerable progress in understanding how the brain perceives, discriminates, and recognizes odorant molecules. This growing knowledge took over when the sense of smell was no longer considered only as a matter for poetry or the perfume industry. Over the last decades, chemical senses captured the attention of scientists who started to investigate the different stages of olfactory pathways. Distinct fields such as genetic, biochemistry, cellular biology, neurophysiology, and behavior have contributed to provide a picture of how odor information is processed in the olfactory system as it moves from the periphery to higher areas of the brain. So far, the combination of these approaches has been most effective at the cellular level, but there are already signs, and even greater hope, that the same is gradually happening at the systems level. This review summarizes the current ideas concerning the cellular mechanisms and organizational strategies used by the olfactory system to process olfactory information. We present findings that exemplified the high degree of olfactory plasticity, with special emphasis on the first central relay of the olfactory system. Recent observations supporting the necessity of such plasticity for adult brain functions are also discussed. Due to space constraints, this review focuses mainly on the olfactory systems of vertebrates, and primarily those of mammals.

The Striped Mouse (Rhabdomys pumilio) From the Succulent Karoo, South Africa: A Territorial Group-Living Solitary Forager With Communal Breeding and Helpers at the Nest

The authors studied the striped mouse (Rhabdomys pumilio) in the semiarid succulent karoo of South Africa. Mice forage alone, but they live in groups that share a common nest. Groups consist of 1 to 4 breeding females, 1 to 2 breeding males, and their offspring of both sexes, which remain in their natal group even after reaching adulthood, participating in territorial defense and nest building without showing signs of reproductive activity. Interactions are typically amicable and take place inside or in front of the nest. In contrast, encounters with mice from other groups are aggressive. Group living in the succulent karoo is possibly due to ecological constraints imposed by habitat saturation because of a year-round stable food supply as well as associated benefits of philopatry.

Experimental tests of spatial association and kinship in monogamous mice (Mus spicilegus) and polygynous mice (Mus musculus domesticus)

The mound-building mouse (Mus spicilegus) and house mouse (Mus musculus domesticus) are closely related species that exhibit putative characteristics of social monogamy and mate-defense polygyny, respectively. Social behaviours and group composition in these species have been well studied in the laboratory under controlled conditions, and the purpose of our study was to examine conclusions drawn from laboratory data in less constrained seminatural enclosures. Specifically, we examined spatial associations and disassociations, which we used as indices of attraction and avoidance, respectively, in both species of mice. In each enclosure and for each species, we introduced small treatment groups of either 2 or 3 female kin (sisters) or 2 or 3 unrelated females, along with an equal number of unrelated males. Initial group composition and physical environments in our enclosures were similar for the two species, therefore we preformed a modified "common garden" experiment. We expected genetically based behavioural differences between species to be revealed. Mound-building mice exhibited strong spatial associations of male–female pairs, and also exhibited spatial avoidance of some of the other mice. House mice exhibited strong female groups of close kin that were significantly associated in space, but this species showed little spatial avoidance compared with mound-building mice. Our results support the idea of social monogamy in mound-building mice, where close reproductive associations of a paired male and female have been hypothesized from laboratory data. Our results also support more extensive evidence suggesting mate-defense polygyny in house mice.

An experimental test of kin association in the house mouse

Studies of genetic markers have suggested that female house mice (Mus musculus domesticus) prefer spatial association and nest sharing with close kin. Further, observations of mothers in single and communal nests suggest a potential advantage of association with kin, namely, improved reproductive success through cooperative defense of young against infanticide. In semi-natural enclosures, we tested for spatial association of female mice in small groups of sisters versus small groups of virtually unrelated females. We also examined success in producing and weaning litters by sisters versus mothers that were not close kin. Sisters exhibited greater spatial association than expected, although some groups of nonsisters showed close associations as well. All 14 sisters in the enclosures produced and weaned young in communal nests. Among 15 mothers that did not have sisters available, 4 did not produce litters, 2 shared a nest, and only 3 weaned young. Although infanticide occurred for both kinds of mothers, it was significantly more common in the single nests of nonsister mothers than for sisters. Thus, sisters were more successful at weaning young, probably owing to advantages of communal nesting. These results suggest that close female kin may associate spatially, and that there are distinct reproductive advantages due to the presence of close kin. The society of house mice is generally described as male dominated, but association of female kin may constitute the basis of social grouping in house mice.

To nest communally or not to nest communally: a review of rodent communal nesting and nursing

Communal nesting, the sharing of parental responsibilities between multiple individuals in a nest, is common in many rodents. Upon first glance, this behaviour seems to be selectively disadvantageous. Communal care not only involves energetic costs, but may also be subject to cheating behaviour. Despite abundant literature, many questions remain regarding advantages gained by females that form nesting groups. I discuss the communal nesting of eusocial, singular and plural breeding rodents. I first clarify the distinction between communal nesting and thermoregulatory huddling. I then review two major groups of hypotheses ('ecological constraints' and 'benefits of philopatry') that are used to explain the occurrence of communal nesting in rodents. Most likely, these hypotheses are not mutually exclusive. Regardless of the main selective pressure(s) acting on communal nesting, the indirect components of inclusive fitness that result from nest sharing most likely influence the formation and maintenance of communal nests. Communal nesting and nursing (the sharing of milk with nonoffspring) are under different selective regimes and thus, must be evaluated separately. I review adaptive and nonadaptive hypotheses for rodent communal nursing. I argue that communal nursing may not be adaptive as mothers may be forced to share milk with nonoffspring in large communal nests (i.e. communal nursing may be a cost associated with communal nesting). In conclusion, I propose directions for future study that may improve our understanding of communal nesting and nursing in the wild. Copyright 2000 The Association for the Study of Animal Behaviour.

Preweaning experience as a modifier of prenatal drug effects in rats and mice--a review

The effects of preweaning experience in rats and mice on neuroendocrine and behavioral end points and their implications for prenatal drug effects are reviewed. The hypothalamo-pituitary-adrenal axis and the dopaminergic system were shown to be affected. Behavior related to hippocampal, adrenocortical functions and to the benzodiazepine receptor system was also modified. Other paradigms (nociception, conditioned taste aversion) exhibited susceptibility to such preweaning manipulations also. The effects of these early experiences seem to be mediated through complex factors including neuroendocrine responses of the pup to hypothermia and a permanent alteration of mother-infant interactions, with subsequent effects on neuroendocrine functions that are important for postnatal brain organization. Studies of interactions between prenatal drug effects and preweaning manipulations have been performed only with ethanol. When extending this work to other compounds, the systems and functions described above may provide some guidance in looking for possible interactions. In most cases the preweaning manipulations alleviated the effects of prenatal ethanol exposure. These findings may have important implications regarding the controversy about environmental influences affecting the outcome of exposure to neurobehavioral teratogens.

Effects of social organization, age and aggressive behaviour on allosuckling in wild fallow deer

I investigated the occurrence, frequency and distribution of allosuckling in a wild population of fallow deer, Dama dama, throughout the lactation period during 1992 in southern Sweden. A total of 292 suckling bouts were observed in four groups; in 43% of these, fawns were seen sucking from a female that was not the mother. Allosuckling occurred in a higher percentage of suckling bouts as the lactation period progressed and all 16 fawns participated to various degrees. Of the 16 females, 13 suckled nonoffspring fawns but their behaviour towards these fawns varied greatly. Allosuckling was positively correlated with the age of the females and negatively correlated with the rate of their aggressive behaviour. Since allosuckling was not performed between groups but was common between related members in a stable social unit and was expressed reciprocally between the oldest individuals in the group, allosuckling could be a result of kin selection and/or reciprocal altruism. Copyright 1998 The Association for the Study of Animal Behaviour.

MHC-disassortative mating preferences reversed by cross-fostering

House mice (Mus musculus domesticus) avoid mating with individuals that are genetically similar at the major histocompatibility complex (MHC). Mice are able recognize MHC-similar individuals through specific odour cues. However, to mate disassortatively for MHC genes, individuals must have a referent, either themselves (self-inspection) or close kin (familial imprinting), with which to compare the MHC identity of potential mates. Although studies on MHC-dependent mating preferences often assume that individuals use self-inspection, laboratory experiments with male mice indicate that they use familial imprinting, i.e. males learn the MHC identity of their family and then avoid mating with females carrying 'familial' MHC alleles. To determine if female mice use familial imprinting, we cross-fostered wild-derived female mouse pups into MHC-dissimilar families, and then tested if this procedure reversed their mating preferences compared with in-fostered controls. Our observations of the female's mating behaviour in seminatural social conditions and the genetic typing of their progeny both indicated that females avoided mating with males carrying MHC genes of their foster family, supporting the familial imprinting hypothesis. We show that MHC-dependent familial imprinting potentially provides a more effective mechanism for avoiding kin matings and reducing inbreeding than self-inspection.

Differential effects of communal rearing and preweaning handling on open-field behavior and hot-plate latencies in mice

On day 2 after delivery, dams of the DBA/1 mouse inbred strain (n = 20/group) with their litter were allocated to one of the following groups: NH21, nonhandling, housed 1 litter/cage, weaned on postnatal day (PND) 21;H21, handling, housed 1 litter/cage, weaned on PND 21; NH30, nonhandling, group-housed (5 litters/cage), weaned on PND 30; H30, handling, group-housed (5 litters/cage), weaned on PND 30. Two male pups of each litter were color marked on PND 2. From PND 8-21 they were removed from their cage, gently held in the experimenter's hand for 5 min/day. The two marked males of each litter were housed together after weaning, and tested in the open-field on PNDs 51-53, and one of each of these siblings was tested for hot-plate latencies on PND 54. Being raised in group-housing and weaned on PND 30 resulted in offspring exhibiting shorter latencies to initiate behavior and higher percentages of centerfield entries in the open field, hot-plate latencies, however, remained unaffected. Preweaning handling increased hot-plate latencies and the number of grooming episodes in the open field, and it decreased defecation, percent centerfield entries and open-field activity in general. It is concluded that the two forms of early experience have different effects on neurobehavioral endpoints 8 weeks after birth.

Effects of prenatal ethanol exposure and early experience on home-cage and open-field activity in mice

-C57BL/6 mice were intubated from gestational day 14-18 twice daily with 1.58 g/kg ethanol, 4.2 g/kg sucrose, or remained untreated. Offspring of ethanol treated or lab chow control groups were raised either by group-housed dams and weaned on postnatal day (PND) 28 or by individually housed dams and weaned on PND 21. Offspring of the sucrose control group were raised by individually housed dams and weaned on PND 21. Groups did not differ in pup weight or litter size. Offspring were assessed for home-cage activity (PND 36-38) and open-field behavior (PND 40-42). Mice prenatally exposed to ethanol showed increased activity in their home cages, whereas open-field behavior was generally not different from that of control groups. Conversely, different preweaning rearing conditions had affected open-field behavior, but not home-cage activity. In conclusion, home-cage behavior was a sensitive paradigm for detecting hyperactivity subsequent to a relatively low dose of prenatal ethanol in mice, and communal nesting/late weaning vs. individual nesting/ standard weaning may be a useful preweaning environmental manipulation to study possible modifications of prenatal neurobehavioral effects.