Parental and Alloparental Care in a Polygynous Mammal

African striped mice (Rhabdomys pumilio) as a neurobehavioral model for male parental care

Parental care is diversely demonstrated across the animal kingdom, such that active practitioners and repertoires of parental behavior vary dramatically between and within taxa. For mammals, maternal care is ubiquitous while paternal and alloparental care are rare. The African striped mouse, a rodent species in the family Muridae, demonstrates maternal, paternal, and alloparental care. Because socio-environmental factors can considerably influence the development of their social behavior, including that of paternal and alloparental care, African striped mice are considered socially flexible. Here, we highlight African striped mice as a new model for the neurobiological study of male parental care. We first provide essential background information on the species' natural ecological setting and reproductive behavior, as well as the species-relevant interaction between ecology and reproduction. We then introduce the nature of maternal, paternal, and alloparental care in the species. Lastly, we provide a review of existing developmental and neurobiological perspectives and highlight potential avenues for future research.

Family dynamics reveal that female house mice preferentially breed in their maternal community

Whether females breed in their natal group is an important factor in the evolution of extended families in animal sociality. Breeding in natal groups comes with costs and benefits, depending on group size and presence of older relatives, including mothers. Studying the consequences of breeding in the natal versus another group provides insight into the decisions and trade-offs governing the formation and structure of family groups. We investigated the family dynamics of a population of free-ranging commensal house mice. Using dynamic community detection on long-term datasets, we determined which females first bred in their natal group. We then looked at how this influenced breeding success. We found most females (77%) exhibited strong philopatry, breeding in their natal groups. Breeding elsewhere was only somewhat predictable at very large and very small group sizes. Despite their philopatric preference, breeding elsewhere made no difference in how quickly and successfully a female bred. However, presence of their mother did lead females to breed sooner when born during high breeding activity, when competition over reproduction is high. Based on these results, potential loss of reproductive success from leaving the natal group does not seem to be the main driver of philopatry in female house mice. The effect of the presence of mothers suggests that benefiting from established social connections promotes breeding in the natal group. Mothers providing benefits also implies a lack of conflict between generations, which will be important for the development of stable social groups.

Allonursing in Wild and Farm Animals: Biological and Physiological Foundations and Explanatory Hypotheses

The dams of gregarious animals must develop a close bond with their newborns to provide them with maternal care, including protection against predators, immunological transference, and nutrition. Even though lactation demands high energy expenditures, behaviors known as allonursing (the nursing of non-descendant infants) and allosuckling (suckling from any female other than the mother) have been reported in various species of wild or domestic, and terrestrial or aquatic animals. These behaviors seem to be elements of a multifactorial strategy, since reports suggest that they depend on the following: species, living conditions, social stability, and kinship relations, among other group factors. Despite their potential benefits, allonursing and allosuckling can place the health and welfare of both non-filial dams and alien offspring at risk, as it augments the probability of pathogen transmission. This review aims to analyze the biological and physiological foundations and bioenergetic costs of these behaviors, analyzing the individual and collective advantages and disadvantages for the dams' own offspring(s) and alien neonate(s). We also include information on the animal species in which these behaviors occur and their implications on animal welfare.

Seasonal variation in reversal learning reveals greater female cognitive flexibility in African striped mice

Cognitive flexibility describes the ability of animals to alter cognitively mediated behaviour in response to changing situational demands, and can vary according to prevailing environemental conditions and individual caracteristics. In the present study, we investigated (1) how learning and reversal learning performance changes between seasons, and (2) how cognitive flexibility is related to sex in a free-living small mammal. We studied 107 African striped mice, Rhabdomys pumilio, in an arid semi-desert, 58 during the hot dry summer with low food availability, and 49 during the cold wet winter with higher food availability. We used an escape box task to test for learning and reversal learning performance. We found that learning and reversal learning efficiency varied seasonally by sex: females tested in summer were faster at solving both learning and reversal tasks than males tested in winter. Performance varied within sex: males tested in winter showed faster learning compared to males tested in summer. During reversal learning, females tested in summer were more efficient and solve the task faster compared to females tested in winter. We suggest that seasonal cognitive performance could be related to sex-specific behavioural characteristics of the species, resulting in adaptation for living in harsh environmental conditions.

Seasonal changes in problem-solving in wild African striped mice

Innovative problem-solving ability is a predictor of whether animals can successfully cope with environmental changes. These environmental changes can test the limits of animals, for example when energy availability decreases seasonally and, hence, problem-solving performance decreases because less energy is available for cognitive processes. Here, we investigated: (1) how problem-solving performance changed between seasons that differed significantly in food availability; (2) whether these changes were related to environmentally induced physiological changes in blood glucose and ketone levels, indicators of energy availability; and (3) whether individual variation in problem-solving was related to sex differences. We studied 99 free-ranging African striped mice, Rhabdomys pumilio, in the Succulent Karoo, South Africa, 55 during the hot dry summer with low food availability and 44 during the cold wet winter with higher food availability. We measured their problem-solving abilities using a food extraction task and found no seasonal differences in problem-solving success. However, mice solved the problem faster in summer versus winter. In summer, food availability was reduced and blood ketones increased but there was no seasonal difference in blood glucose levels. There were no correlation between problem-solving performance and blood glucose or ketone levels. Overall, more males solved the task than females. It appears that in striped mice cognitive functions can be maintained under harsh environmental conditions.

Maternal feeding benefits of allomaternal care in black-and-white colobus (Colobus guereza)

Caring for infants involves lactation, protection, provisioning, and carrying-all energetically taxing states for primate mothers. Holding and carrying clinging infants often constrains mothers from moving and traveling, potentially reducing their food and energy intake; however, when separated from its mother an infant is at risk of predation. This separation therefore requires that mothers be vigilant, further deterring them from feeding. Allomaternal care (AMC) is hypothesized to allow mothers to safely detach from their infants to feed, permitting them to increase energy intake, which is particularly needed for lactation. We examined the nutritional benefits of AMC in black-and-white colobus monkeys (Colobus guereza) by estimating energy intake by lactating mothers during AMC versus non-AMC. We studied seven mother-infant dyads in three groups of C. guereza during six months in Kibale National Park, Uganda. Immature group members handled infants more often than adults, and females handled infants more often than males. An infant's distance to its mother and its nearest neighbor's age and sex best predicted the occurrence of AMC. Lactating mothers fed more often, fed and rested for longer durations, and consumed more metabolizable energy during AMC compared to when they were caring for their infants. These results demonstrate that AMC in C. guereza provides mothers with feeding opportunities that increase their energy intake.

With a little help from her friends (and family) part I: the ecology and evolution of non-maternal care in mammals

In the class Mammalia, most young are cared for exclusively by their mothers. In species where mothers receive help, however, non-maternal caregivers may play a crucial role in development and life history trajectories. In turn, recipients of such care may have important impacts on caregivers of all types. In Part I of this overview, we briefly review the evolutionary barriers to widespread non-maternal care in mammals, and explain why the exceptions are of particular theoretical importance. We also summarize the current understanding of the selective forces leading to non-maternal care, and the taxa and types of caretakers amongst which it occurs. Finally, we argue for a fresh look at the categorization schemes that have traditionally been used to separate various types of mammalian non-maternal caregivers. This two-part introduction is aimed at scientists from multiple disciplines who study diverse organismal systems. It draws from the social and biological sciences literatures to provide an overview of this special issue of Physiology and Behavior's suite of methodological offerings and theoretical underpinnings.

Brain plasticity in pregnancy and the postpartum period: links to maternal caregiving and mental health

Pregnancy and the postpartum period involve numerous physiological adaptations that enable the development and survival of the offspring. A distinct neural plasticity characterizes the female brain during this period, and dynamic structural and functional changes take place that accompany fundamental behavioral adaptations, stimulating the female to progress from an individual with self-directed needs to being responsible for the care of another life. While many animal studies detail these modifications, an emerging body of research reveals the existence of reproduction-related brain plasticity in human mothers too. Additionally, associations with aspects of maternal caregiving point to adaptive changes that benefit a woman's transition to motherhood. However, the dynamic changes that affect a woman's brain are not merely adaptive, and they likely confer a vulnerability for the development of mental disorders. Here, we review the changes in brain structure and function that a woman undergoes during the peripartum period, outlining associations between these neural alterations and different aspects of maternal care. We additionally discuss peripartum mood disorders and postpartum psychosis, and review the neuroimaging studies that investigate the neural bases of these conditions.

Comparative analysis of oxytocin receptor density in the nucleus accumbens: an adaptation for female and male alloparental care?

Parental behavior is commonly displayed by progenitors. However, other individuals, genetically related (e.g. siblings, aunts, uncles) or not with the newborns, also display parental behavior (commonly called alloparental, or adoptive behavior). I hypothesize that species that live in family or social groups where other non-reproductive members (males and females) take care of infants, have brain adaptations to promote or facilitate that behavioral response. The present work revises the evidence supporting the hypothesis that high density of oxytocin receptors (OXTR) in the nucleus accumbens (NA) is one of those adaptations. All species known to have high NA OXTR show not only female, but also male alloparental care. Therefore, I predict that high NA OXTR could be present in all species in which juvenile and adult male alloparental behavior have been observed. Strategies to test this and other alternative working hypothesis and its predictions are presented.

Alternative reproductive tactics in female striped mice: Solitary breeders have lower corticosterone levels than communal breeders

Alternative reproductive tactics (ARTs), where members of the same sex and population show distinct reproductive phenotypes governed by decision-rules, have been well-documented in males of many species, but are less well understood in females. The relative plasticity hypothesis (RPH) predicts that switches between plastic ARTs are mediated by changes in steroid hormones. This has received much support in males, but little is known about the endocrine control of female ARTs. Here, using a free-living population of African striped mice (Rhabdomys pumilio) over five breeding seasons, we tested whether females following different tactics differed in corticosterone and testosterone levels, as reported for male striped mice using ARTs, and in progesterone and oestrogen, which are important in female reproduction. Female striped mice employ three ARTs: communal breeders give birth in a shared nest and provide alloparental care, returners leave the group temporarily to give birth, and solitary breeders leave to give birth and do not return. We expected communal breeders and returners to have higher corticosterone, owing to the social stress of group-living, and lower testosterone than solitary breeders, which must defend territories alone. Solitary breeders had lower corticosterone than returners and communal breeders, as predicted, but testosterone and progesterone did not differ between ARTs. Oestrogen levels were higher in returners (measured before leaving the group) than in communal and solitary breeders, consistent with a modulatory role. Our study demonstrates hormonal differences between females following (or about to follow) different tactics, and provides the first support for the RPH in females.

Intraspecific variation in social organization by genetic variation, developmental plasticity, social flexibility or entirely extrinsic factors

Previously, it was widely believed that each species has a specific social organization, but we know now that many species show intraspecific variation in their social organization. Four different processes can lead to intraspecific variation in social organization: (i) genetic variation between individuals owing to local adaptation (between populations) or evolutionarily stable strategies within populations; (ii) developmental plasticity evolved in long-term (more than one generation) unpredictable and short-term (one generation) predictable environments, which is mediated by organizational physiological effects during early ontogeny; (iii) social flexibility evolved in highly unpredictable environments, which is mediated by activational physiological effects in adults; (iv) entirely extrinsic factors such as the death of a dominant breeder. Variation in social behaviour occurs between individuals in the case of genetic variation and developmental plasticity, but within individuals in the case of social flexibility. It is important to study intraspecific variation in social organization to understand the social systems of species because it reveals the mechanisms by which species can adapt to changing environments, offers a useful tool to study the ultimate and proximate causes of sociality, and is an interesting phenomenon by itself that needs scientific explanation.

Maternal care in the African striped mouse Rhabdomys pumilio: a behaviorally flexible phenotype that is modified by experience

The development of maternal care in mammals can be influenced by the type and quality of maternal care received. Using biparental striped mice Rhabdomys pumilio, we investigated whether development of maternal care is influenced by the mother during early rearing and by an adult female's experience and that of her mate. Offspring were raised in one of three treatments, by: both parents; mothers alone; and mothers separated from the father with a barrier. Since female striped mice increase their care when raising litters alone, which influences expression of parental care of their adult sons, we expected daughters to respond like sons. However, there was no treatment effect in the development of maternal care in daughters. In subsequent experiments, experienced and inexperienced females decreased care when raising their offspring with experienced but not inexperienced males. Therefore, maternal care in striped mice is modulated in response to prevailing environmental and social conditions.

Hormone levels of male African striped mice change as they switch between alternative reproductive tactics

Alternative reproductive tactics occur when individuals of the same species follow alternative ways to maximize reproductive success. Often younger and smaller males follow tactics that result in lower fitness than that of dominant larger males. The relative plasticity hypothesis predicts that hormone levels change as males change tactics, but direct tests of this hypothesis are missing. It has been demonstrated in a number of studies that males following different tactics also differ in hormone levels (unpaired data), but not that individual males change their hormone levels as they change tactic (paired data). We compared hormone levels in the same individuals before and after they changed their tactic, using field samples collected over a period of 6 years. We studied male striped mice (Rhabdomys pumilio) following three alternative reproductive tactics: 1. alloparental philopatric males; 2. solitary roaming males, and 3. group-living dominant breeders. Testosterone levels increased and corticosterone levels decreased when philopatric males became roamers or breeders. The increase in testosterone levels tended to be higher in philopatric males that became roamers than in philopatric males that became breeders. Testosterone levels decreased when roamers became breeders. Prolactin levels increased when males of any other tactic became breeders. Thus, males significantly changed their hormone profiles as they changed tactics. These results are in agreement with the hypothesis that changes in hormone levels are associated with the switch from one alternative reproductive tactic to another.