The Effect of Massage on Maternal Role Adaptation in Mothers with Premature Infants.

Background: Accepting and adapting the maternal role by mothers with premature infants is complicated. Active participation of mothers in neonate massage may facilitate this process. Primary Study Objective: Determining the effect of massage on maternal role adaptation in mothers of premature infants admitted to the neonatal intensive care unit (NICU). Methods/Design: A non-parallel quasi-experimental study with a sequential sampling method. Setting: This study was done in the NICU of Imam Ali Hospital in Amol City, Iran. Participants: 90 mothers of premature infants hospitalized in the NICU participated in this study. Intervention: The mothers in the intervention group after receiving two training sessions massaged their infant for 15 minutes daily from the third day of hospitalization for 5 consecutive days. Primary Outcome Measures: A maternal role adaptation questionnaire was used. Participants completed the maternal role adaptation questionnaire 3 times: before, on the fifth day, and 14 days after the first day of intervention. The maternal role adaptation questionnaire was used to assess the maternal role adaptation. The participants of the control group also filled out the questionnaire at similar time. Results: The mean scores of maternal adaptation were significantly different between the two control groups (5th day and 14th day) and intervention (day 5: 136.88 ± 10.062 (P = .025); day 14: 151.93 ± 6 (P < .001)). Maternal role adaptation showed an upward trend in the two groups during the 14 days of study, but this trend was significantly higher in the intervention group over time, compared to the control group. Conclusion: Massage of premature infants facilitates the adaptation to maternal role. It is recommended, along with other nursing interventions, to empower mothers with premature neonates admitted to the NICU.

Maternal Borderline Personality Disorder Severity and Parenting Behaviors During Conflict Discussions With Adolescent Offspring.

Examining the impact of maternal borderline personality disorder (BPD) on parent-child interactions could elucidate pathways of intergenerational risk and inform intervention. The current study used an expanded version of the Observing Mediational Interactions to investigate (a) associations between maternal BPD symptom severity and mediational parenting behaviors during conflict discussions with clinically referred early adolescent offspring (N = 56, age = 10-15, 54% female) and their mothers, and (b) the potential moderating role of early adolescent BPD symptom severity in those associations. Consistent with hypotheses, mothers with higher levels of BPD symptom severity engaged in fewer positive emotional/attachment-based behaviors and more negative (i.e., invalidating, controlling, coercive, or insensitive) parenting behaviors. Only parent-reported, but not self-reported, adolescent BPD severity moderated these associations; maternal BPD severity was significantly associated only with negative parenting in dyads with low-to-moderate levels of parent-reported adolescent BPD severity. We discuss implications including targeting attachment-based and negative parenting behaviors in intervention.

Maternal Care under Large Clutches with Small Eggs: The Evolution of Life History Traits in Shield Bugs.

AbstractPatterns in the correlated evolution of parental care and life history traits are long established but controversial. Although parental care is related to large egg size in many taxa, conflicting results have also been reported. To test the evolutionary relationships between parental care and life history traits, we performed phylogenetic comparative analyses using shield bugs (Heteroptera: Acanthosomatidae), in which maternal guarding of eggs and young has repeatedly evolved. Our analyses revealed that female body size affected reproductive resource allocation. Contrary to the expectations of current theories, the acquisition of maternal care was associated with small eggs, large clutches, and large egg resource allocation. There was a greater trade-off between egg size and clutch size in caring species than in noncaring species. Egg and hatchling developmental rates were not correlated with egg size but were slower in caring species than in noncaring species. Analyses of evolutionary transitions suggest that the establishment of large clutches, small eggs, and large egg resource allocation preceded the evolution of maternal care. To our knowledge, this is the first study clarifying the evolution of parental care linked with small eggs in invertebrates.

Maternal care leads to the evolution of long, slow lives.

Animals, and mammals in particular, vary widely in their "pace of life," with some species living long lives and reproducing infrequently (slow life histories) and others living short lives and reproducing often (fast life histories). These species also vary in the importance of maternal care in offspring fitness: In some species, offspring are fully independent of their mothers following a brief period of nutritional input, while others display a long period of continued dependence on mothers well after nutritional dependence. Here, we hypothesize that these two axes of variation are causally related to each other, such that extended dependence of offspring on maternal presence leads to the evolution of longer lives at the expense of reproduction. We use a combination of deterministic modeling and stochastic agent-based modeling to explore how empirically observed links between maternal survival and offspring fitness are likely to shape the evolution of mortality and fertility. Each of our modeling approaches leads to the same conclusion: When maternal survival has a strong impact on the survival of offspring and grandoffspring, populations evolve longer lives with less frequent reproduction. Our results suggest that the slow life histories of humans and other primates as well as other long-lived, highly social animals such as hyenas, whales, and elephants are partially the result of the strong maternal care that these animals display. We have designed our models to be readily parameterized with demographic data that are routinely collected by long-term researchers, which will facilitate more thorough testing of our hypothesis.

Postnatal maternal care moderates the effects of prenatal bisphenol exposure on offspring neurodevelopmental, behavioral, and transcriptomic outcomes.

Bisphenols (BP), including BPA and "BPA-free" structural analogs, are commonly used plasticizers that are present in many plastics and are known endocrine disrupting chemicals. Prenatal exposure to BPA has been associated with negative neurodevelopmental and behavioral outcomes in children and in rodent models. Prenatal BPA exposure has also been shown to impair postnatal maternal care provisioning, which can also affect offspring neurodevelopment and behavior. However, there is limited knowledge regarding the biological effects of prenatal exposure to bisphenols other than BPA and the interplay between prenatal bisphenol exposure and postnatal maternal care on adult behavior. The purpose of the current study was to determine the interactive impact of prenatal bisphenol exposure and postnatal maternal care on neurodevelopment and behavior in rats. Our findings suggest that the effects of prenatal bisphenol exposure on eye-opening, adult attentional set shifting and anxiety-like behavior in the open field are dependent on maternal care in the first five days of life. Interestingly, maternal care might also attenuate the effects of prenatal bisphenol exposure on eye opening and adult attentional set shifting. Finally, transcriptomic profiles in male and female medial prefrontal cortex and amygdala suggest that the interactive effects of prenatal bisphenol exposure and postnatal maternal care converge on estrogen receptor signaling and are involved in biological processes related to gene expression and protein translation and synthesis. Overall, these findings indicate that postnatal maternal care plays a critical role in the expression of the effects of prenatal bisphenol exposure on neurodevelopment and adult behavior. Understanding the underlying biological mechanisms involved might allow us to identify potential avenues to mitigate the adverse effects of prenatal bisphenol exposure and improve health and well-being in human populations.

Selection on the joint actions of pairs leads to divergent adaptation and coadaptation of care-giving parents during pre-hatching care.

The joint actions of animals in partnerships or social groups evolve under both natural selection from the wider environment and social selection imposed by other members of the pair or group. We used experimental evolution to investigate how jointly expressed actions evolve upon exposure to a new environmental challenge. Our work focused on the evolution of carrion nest preparation by pairs of burying beetles Nicrophorus vespilloides, a joint activity undertaken by the pair but typically led by the male. In previous work, we found that carrion nest preparation evolved to be faster in experimental populations without post-hatching care (No Care: NC lines) than with post-hatching care (Full Care: FC lines). Here, we investigate how this joint activity evolved. After 15 generations of experimental evolution, we created heterotypic pairs (NC females with FC males and NC males with FC females) and compared their carrion nest making with homotypic NC and FC pairs. We found that pairs with NC males prepared the nest more rapidly than pairs with FC males, regardless of the female's line of origin. We discuss how social coadaptations within pairs or groups could act as a post-mating barrier to gene flow.

Examining infantile facial features and their influence on caretaking behaviors in free-ranging Japanese macaques (Macaca fuscata).

Facial features of immature individuals play a pivotal role in eliciting caretaking behaviors in humans. It has been posited that non-human animals share particular infantile facial features with humans, which can elicit caregivers' attention and caretaking behaviors. Nevertheless, the empirical examination of this hypothesis is extremely limited. In this study, we investigated infantile facial features in Japanese macaques (Macaca fuscata), their developmental processes, and their correlation with caretaking and infant behaviors, based on 470 facial photographs from one free-ranging group. We measured the size of facial parts and evaluated these features using non-contact procedures with the animals. The results indicated that, although some partial species differences were observed, the infantile facial features in Japanese macaques were broadly consistent with those previously observed in humans and great apes. Furthermore, half of the infant subjects displayed non-linear developmental trajectories of infantile faces, similar to those suggested in humans. However, unlike previous studies in humans, infantile faces were not significantly associated with maternal or non-maternal caretaking behaviors, nor were their developmental changes correlated with infant behavioral development. These findings indicate that while many aspects of infantile facial features are shared among particular primates, humans may have evolved a uniquely elevated preference for selecting such features among the primate lineage.

Re-wiring of the bonded brain: Gene expression among pair bonded female prairie voles changes as they transition to motherhood.

Motherhood is a costly life-history transition accompanied by behavioral and neural plasticity necessary for offspring care. Motherhood in the monogamous prairie vole is associated with decreased pair bond strength, suggesting a trade-off between parental investment and pair bond maintenance. Neural mechanisms governing pair bonds and maternal bonds overlap, creating possible competition between the two. We measured mRNA expression of genes encoding receptors for oxytocin (oxtr), dopamine (d1r and d2r), mu-opioids (oprm1a), and kappa-opioids (oprk1a) within three brain areas processing salience of sociosensory cues (anterior cingulate cortex; ACC), pair bonding (nucleus accumbens; NAc), and maternal care (medial preoptic area; MPOA). We compared gene expression differences between pair bonded prairie voles that were never pregnant, pregnant (~day 16 of pregnancy), and recent mothers (day 3 of lactation). We found greater gene expression in the NAc (oxtr, d2r, oprm1a, and oprk1a) and MPOA (oxtr, d1r, d2r, oprm1a, and oprk1a) following the transition to motherhood. Expression for all five genes in the ACC was greatest for females that had been bonded for longer. Gene expression within each region was highly correlated, indicating that oxytocin, dopamine, and opioids comprise a complimentary gene network for social signaling. ACC-NAc gene expression correlations indicated that being a mother (oxtr and d1r) or maintaining long-term pair bonds (oprm1a) relies on the coordination of different signaling systems within the same circuit. Our study suggests the maternal brain undergoes changes that prepare females to face the trade-off associated with increased emotional investment in offspring, while also maintaining a pair bond.

Examining the implications of contextual stress and maternal sensitivity for infants' cortisol responses to the still face paradigm.

Infants' hypothalamic-pituitary-adrenocortical (HPA) axis responses to acute stressors are theorized to be shaped by parents' sensitive responsiveness to infants' cues. The strength and direction of the association between maternal sensitivity and infants' HPA responses may depend on the context in which maternal sensitivity is observed and on broader environmental sources of stress and support. In this preregistered study, we used data from 105 mothers and their 7-month-old infants to examine whether two empirically identified forms of contextual stress-poor maternal psychosocial wellbeing and family socioeconomic hardship-moderate the association between maternal sensitivity and infants' cortisol responses to the Still-Face Paradigm (SFP). Results indicated that maternal sensitivity during the free play and family socioeconomic hardship interacted to predict infants' cortisol responses to the SFP. Specifically, maternal sensitivity during this non-distressing interaction was negatively associated with cortisol responses only among infants whose mothers were experiencing relatively high socioeconomic hardship. Exploratory analyses revealed that poor maternal psychosocial wellbeing was positively associated with overall infant cortisol production during the SFP. Altogether, these findings suggest that experiences within early parent-infant attachment relationships and sources of contextual stress work together to shape infant HPA axis activity.

Puppy whines mediate maternal behavior in domestic dogs.

In mammals, offspring vocalizations typically encode information about identity and body condition, allowing parents to limit alloparenting and adjust care. But how do these vocalizations mediate parental behavior in species faced with the problem of rearing not one, but multiple offspring, such as domestic dogs? Comprehensive acoustic analyses of 4,400 whines recorded from 220 Beagle puppies in 40 litters revealed litter and individual (within litter) differences in call acoustic structure. By then playing resynthesized whines to mothers, we showed that they provided more care to their litters, and were more likely to carry the emitting loudspeaker to the nest, in response to whine variants derived from their own puppies than from strangers. Importantly, care provisioning was attenuated by experimentally moving the fundamental frequency (fo, perceived as pitch) of their own puppies' whines outside their litter-specific range. Within most litters, we found a negative relationship between puppies' whine fo and body weight. Consistent with this, playbacks showed that maternal care was stronger in response to high-pitched whine variants simulating relatively small offspring within their own litter's range compared to lower-pitched variants simulating larger offspring. We thus show that maternal care in a litter-rearing species relies on a dual assessment of offspring identity and condition, largely based on level-specific inter- and intra-litter variation in offspring call fo. This dual encoding system highlights how, even in a long-domesticated species, vocalizations reflect selective pressures to meet species-specific needs. Comparative work should now investigate whether similar communication systems have convergently evolved in other litter-rearing species.

Effect of maternal eating behaviors and attitudes towards the feeding process on feeding problems of pre-school age children.

BACKGROUND & AIMS: Feeding problems in pre-school children are common and negative maternal feeding practices may even worsen the child's problematic eating behavior. Therefore, investigating the effects of maternal eating behaviors and attitudes towards the feeding process on pre-school children's feeding problems may be helpful for preventing feeding problems. This study sought to investigate the effects of maternal eating behaviors and attitudes towards the feeding process on feeding problems of pre-school children. METHODS: Mothers of 373 children aged 3-6 were included in this cross-sectional study and data was collected by an online questionnaire including the scales of three-factor eating questionnaire (TFEQ), mother's attitudes towards the feeding process (MATFPS) and behavioral pediatric feeding assessment (BPFAS), as well as demographics and anthropometric measures (height and weight). Spearman's rho test was used to calculate correlation coefficients between the TFEQ, MATFP and BPFA scales. In order to identify independent predictors of child feeding behaviors, a multiple linear regression model was used. RESULTS: Results showed that uncontrolled eating subscale was positively (r = 0.160, p < 0.001) and cognitive restriction subscale negatively (r = -0.126, p < 0.05) correlated with MATFP. MATFP was also positively correlated with BPFA (r = 0.368, p < 0.001). Regression analysis indicated that BPFA was significantly predicted by MATFP which was the most important contributor of child feeding problems (ß = 0.24, t = 4.88, p < 0.001). CONCLUSIONS: This study indicated that maternal eating behaviors were related to maternal attitudes towards the feeding process and, mothers' attitudes were associated with feeding problems of their pre-school children.

Home-visiting Parenting Programs to Improve Mother-Infant Interactions at Early Ages: A Systematic Review.

Objective: To systematically review studies examining the effects of home-visiting preventive parenting programs (HV-PPs) on improving the quality of mother-child interactions in early childhood. Method: Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses protocol, we identified 3,586 studies published between 2018 and 2022 by searching the following databases: PubMed, Web of Science, BVS/LILACS, SciELO, and PsycNET/PsycINFO. After applying the eligibility criteria, 17 articles were selected for review. Results: Most studies were conducted in high-income countries (53%) and the remainder were conducted in upper-middle-income countries, predominantly using a randomized controlled trial design and with strong methodological quality. The 17 studies applied 13 different HV-PPs, predominantly using video feedback, based on various dosages and schedules. Most studies (77%) showed significant positive effects on mother-child interactions by improving mainly positive maternal behaviors (e.g., sensitivity and responsiveness). Positive effects occurred independent of the study design, sample characteristics, measures, and constructs assessed. However, the findings suggest that the combination of fewer than six sessions, durations shorter than three months, and a very early start did not impact mother-child interactions, as expected. Few studies have explored negative maternal behaviors, children's behaviors, and dyadic interactions such as mutuality and synchrony. Conclusions: HV-PPs positively impacted mother-child interactions in early childhood despite the large heterogeneity across program designs, outcome measures, and overlapping constructs. Based on the results, we discuss the practical and economic implications of using parenting programs as a preventive approach.

Prenatal restraint stress affects early neurobehavioral response and oxidative stress in mice pups.

Prenatal stress (PS), in both humans and animals, presents a potential risk to the mother and her fetus throughout gestation. PS is always associated with physiological changes that alter embryonic development and predispose the individual to lifelong health problems, including susceptibility to mental illness. This study aims to identify the harmful effects of prenatal restraint stress (PRS), commonly employed to induce stress painlessly and without any lasting debilitation during gestation. This stress is applied to pregnant Swiss albino mice from E7.5 to delivery for three hours daily. Our results show that PS affects dams' weight gain during the gestational period; moreover, the PS dams prefer passive nursing, exhibit a lower percentage of licking and grooming, and impair other maternal behaviors, including nesting and pup retrieval. Concerning the offspring, this stress induces neurobehavioral impairments, including a significant increase in the time of recovery of the young stressed pups in the surface righting reflex, the latency to avoid the cliff in the cliff avoidance test, longer latencies to accomplish the task in negative geotaxis, and a lower score in swimming development. These alterations were accompanied by increased Malondialdehyde activity (MDA) at PND17 and 21 and downregulation of AchE activity in the whole brain of pups on postnatal days 7 and 9. These findings demonstrated that PS causes deleterious neurodevelopmental impairments that can alter various behaviors later in life.

Maternal behaviours disrupted by Gprasp2 deletion modulate neurodevelopmental trajectory in progeny.

Autism spectrum disorders (ASDs) are known to present sex-specific differences. At the same time, understanding how maternal behaviours are affected by pathogenic mutations is crucial to translate research efforts since rearing may recursively modulate neurodevelopment phenotype of the progeny. In this work, we focused on the effects of Gprasp2 deletion in females and its impact in progeny care and development. Female mice, wild-type (WT), Gprasp2+/- (HET) or Gprasp2-/- (KO) mutants and their progeny were used and behavioural paradigms targeting anxiety, memory, maternal care, and other social behaviours were performed. Analysis of communication was carried out through daily recordings of ultrasonic vocalizations in isolated pups and cross-fostering experiments were performed to understand the effect of maternal genotype in pup development. We found that Gprasp2-/- females presented striking impairments in social and working memory. Females also showed disruptions in maternal care, as well as physiological and molecular alterations in the reproductive system and hypothalamus, such as the structure of the mammary gland and the expression levels of oxytocin receptor (OxtR) in nulliparous versus primiparous females. We observed alterations in pup communication, particularly a reduced number of calls in Gprasp2 KO pups, which resulted from an interaction effect of the dam and pup genotype. Cross-fostering mutant pups with wild-type dams rescued some of the early defects shown in vocalizations, however, this effect was not bidirectional, as rearing WT pups with Gprasp2-/- dams was not sufficient to induce significant phenotypical alterations. Our results suggest Gprasp2 mutations perturb social and working memory in a sex-independent manner, but impact female-specific behaviours towards progeny care, female physiology, and gene expression. These changes in mutant dams contribute to a disruption in early stages of progeny development. More generally, our results highlight the need to better understand GxE interactions in the context of ASDs, when female behaviour may present a contributing factor in postnatal neurodevelopmental trajectory.

Neuropeptides affecting social behavior in mammals: Oxytocin.

Oxytocin (OXT), a neuropeptide consisting of only nine amino acids, is synthesized in the paraventricular and supraoptic nuclei of the hypothalamus. Although OXT is best known for its role in lactation and parturition, recent research has shown that it also has a significant impact on social behaviors in mammals. However, a comprehensive review of this topic is still lacking. In this paper, we systematically reviewed the effects of OXT on social behavior in mammals. These effects of OXT from the perspective of five key behavioral dimensions were summarized: parental behavior, anxiety, aggression, attachment, and empathy. To date, researchers have agreed that OXT plays a positive regulatory role in a wide range of social behaviors, but there have been controversially reported results. In this review, we have provided a detailed panorama of the role of OXT in social behavior and, for the first time, delved into the underlying regulatory mechanisms, which may help better understand the multifaceted role of OXT. Levels of OXT in previous human studies were also summarized to provide insights for diagnosis of mental disorders.

Effects of sensory overstimulation in postpartum rats.

Research in rodents has shown that exposure to excessive early life audiovisual stimulation leads to altered anxiety-like behaviors and cognitive deficits. Since this period of stimulation typically begins prior to weaning, newborn rodents receive sensory overstimulation (SOS) as a litter within their home cage while the dam is present. However, the effects of SOS during the postpartum period remain unexplored. To this end, we adapted an SOS paradigm for use in rats and exposed rat dams and their litters from postpartum days (PD) 10-23. Maternal observations were conducted to determine whether SOS produced changes in positive and/or negative maternal behaviors. Next, we assessed changes in anxiety-like behavior and cognition by testing dams in the elevated zero maze, open field, and novel object recognition tests. To assess potential effects on HPA-axis function, levels of the stress hormone corticosterone (CORT) were measured approximately 1-week after the cessation of SOS exposure. Our results indicate increased nursing and licking in SOS dams compared to controls, although SOS dams also exhibited significant increases in pup dragging. Moreover, SOS dams exhibited reduced self-care behaviors and nest-building compared to control dams. No differences were found for anxiety-like behaviors, object recognition memory, or CORT levels. This study is the first to assess the impact of postpartum SOS exposure in rat dams. Our findings suggest an SOS-induced enhancement in positive caregiving, but limited impact in all other measures.

Lateral septum as a possible regulatory center of maternal behaviors.

The lateral septum (LS) is involved in controlling anxiety, aggression, feeding, and other motivated behaviors. Lesion studies have also implicated the LS in various forms of caring behaviors. Recently, novel experimental tools have provided a more detailed insight into the function of the LS, including the specific role of distinct cell types and their neuronal connections in behavioral regulations, in which the LS participates. This article discusses the regulation of different types of maternal behavioral alterations using the distributions of established maternal hormones such as prolactin, estrogens, and the neuropeptide oxytocin. It also considers the distribution of neurons activated in mothers in response to pups and other maternal activities, as well as gene expressional alterations in the maternal LS. Finally, this paper proposes further research directions to keep up with the rapidly developing knowledge on maternal behavioral control in other maternal brain regions.

Maternal probiotic Lactocaseibacillus rhamnosus HN001 treatment alters postpartum anxiety, cortical monoamines, and the gut microbiome.

Peripartum mood and anxiety disorders (PMADs) affect 15-20% of peripartum women and are well known to disrupt infant caregiving. A recent study in humans reported that anxiety and depressive symptoms were alleviated by peripartum treatment with the probiotic, Lactocaseibacillus rhamnosus HN001. The current study determined the effects of chronic Lactocaseibacillus rhamnosus HN001 (HN001) treatment on postpartum affective and caregiving behaviors in a laboratory rodent model. Female rats were given probiotic overnight in their drinking water, or untreated water, from the first day of pregnancy through postpartum day 10. To determine whether the HN001 effects were influenced by a background of stress, half the females underwent chronic variable pregnancy stress and the other half remained undisturbed. The results revealed that, even without pregnancy stress, HN001 reduced postpartum anxiety-related behavior, increased variability in behavioral fragmentation when dams interacted with pups, increased time away from pups, and decreased prefrontal cortex norepinephrine (NE), dopamine (DA) and serotonin (5-HT). Probiotic plus stress consistently reduced the latency to float in the forced swim test, increased DA and 5-HT turnovers in the prefrontal cortex, increased hippocampal NE, and reduced hypothalamic DA. Fecal microbe alpha and beta diversities were lower postpartum than prepartum, which was prevented by the probiotic treatment and/or stress. Across the entire sample lower postpartum anxiety behavior was associated with lower fecal Bacteroides dorei. This study reveals novel information about how L. rhamnosus HN001 influences postpartum behavior and microbiota-gut-brain physiology in female laboratory rats, with implications for probiotic supplement use by pregnant and postpartum women.

Prolactin is associated with proximity to incubating partner rather than parental care in black-headed gulls.

The peptide hormone prolactin plays an important role in the expression of parental care behaviours across bird and mammal taxa. While a great deal is known about how plasma prolactin concentrations vary across the reproductive cycle, the few studies that investigate how prolactin relates to individual-level variation in parental care have reported mixed results. We argue that, since parental care is also affected by social interactions and environmental constraints, prolactin may better reflect behaviours that are indirectly related to parenting than the absolute level of care that is eventually expressed. In this study, we tested for associations between plasma prolactin and the expression of both parental care and proximity to the partner in incubating black-headed gulls, Chroicocephalus ridibundus. Baseline prolactin levels increased with calendar date but were unrelated to incubation behaviours. However, parents who showed a weaker decrease in prolactin to an acute stressor spent more time in close proximity to their incubating partner while not on the nest themselves, suggesting that individual variation in stress-induced prolactin changes reflect differences in parents' tendency to be closely associated with their partner and the joint nesting attempt. Baseline and stress-induced levels of the stress hormone corticosterone were unrelated to both prolactin levels and parental behaviours, suggesting that this hormone is not a strong moderator of parental care in black-headed gulls. One potential explanation for the link between prolactin dynamics and partner proximity is that prolactin reflects parental motivation to provide parental care or retain contact with the breeding partner, but further work is needed to directly test this hypothesis.