Can low-quality parents exploit their high-quality partners to gain higher fitness?

An individual's optimal investment in parental care potentially depends on many variables, including its future fitness prospects, the expected costs of providing care and its partner's expected or observed parental behaviour. Previous models suggested that low-quality parents could evolve to exploit their high-quality partners by reducing care, leading to the paradoxical prediction that low-quality parents could have higher fitness than their high-quality partners. However, these studies lacked a complete and consistent life-history model. Here, we challenge this result, developing a consistent analytical model of parental care strategies given individual variation in quality, and checking our results using agent-based simulations. In contrast to previous models, we predict that high-quality individuals always outcompete low-quality individuals in fitness terms. However, care effort may differ between high- and low-quality parents in either direction: low-quality individuals care more than high-quality individuals if their baseline mortality is higher, but less if their mortality increases more steeply with increasing care. We also highlight the ambiguity of the term ‘quality’ and stress the need for ‘genealogical consistency’ in evolutionary models.     

What are the benefits of parental care? The importance of parental effects on developmental rate

The evolution of parental care is beneficial if it facilitates offspring performance traits that are ultimately tied to offspring fitness. While this may seem self‐evident, the benefits of parental care have received relatively little theoretical exploration. Here, we develop a theoretical model that elucidates how parental care can affect offspring performance and which aspects of offspring performance (e.g., survival, development) are likely to be influenced by care. We begin by summarizing four general types of parental care benefits. Care can be beneficial if parents (1) increase offspring survival during the stage in which parents and offspring are associated, (2) improve offspring quality in a way that leads to increased offspring survival and/or reproduction in the future when parents are no longer associated with offspring, and/or (3) directly increase offspring reproductive success when parents and offspring remain associated into adulthood. We additionally suggest that parental control over offspring developmental rate might represent a substantial, yet underappreciated, benefit of care. We hypothesize that parents adjust the amount of time offspring spend in life‐history stages in response to expected offspring mortality, which in turn might increase overall offspring survival, and ultimately, fitness of parents and offspring. Using a theoretical evolutionary framework, we show that parental control over offspring developmental rate can represent a significant, or even the sole, benefit of care. Considering this benefit influences our general understanding of the evolution of care, as parental control over offspring developmental rate can increase the range of life‐history conditions (e.g., egg and juvenile mortalities) under which care can evolve.     

Family background characteristics and relationship satisfaction in a native community in Canada

Abstract

Using data collected from a Native Canadian community by Embree (1993), we examine the influence of personal and family background characteristics on satisfaction with spousal relationships, both legal marriages and cohabitations. Of special interest are the quality of relationships with parents while growing up, alcohol abuse by the parent(s), and the experience of sexual abuse during childhood. Personal traits such as age, sex, and gender role attitudes and the respondent's own drinking behavior are also considered. Path analytic techniques model both the direct effects of independent variables on relationship satisfaction as well as the role of personal consumption of alcohol as an intervening variable in level of satisfaction with a relationship. The results of the analysis indicate that personal consumption of alcohol and the experience of sexual abuse during childhood are the best direct predictors of level of satisfaction with the current relationship, with higher alcohol consumption and experience of sexual abuse related to lower satisfaction. Age also has a significant direct, though smaller, positive influence on relationship satisfaction. Sexual abuse and the respondent's sex are also linked to level of satisfaction through personal alcohol consumption. With personal alcohol use, both the respondent's sex and the experience of sexual abuse during childhood have a significant effect, with males and those sexually abused as children reporting higher levels of alcohol consumption. The socialization explanation of the intergenerational consequences of parental behavior argues that parental role models are primary to the future family formation behavior of children. Consistent with this hypothesis, the findings concerning sexual abuse, in particular, as a predictor of both personal alcohol use and relationship satisfaction seem to underscore the importance of antecedent family characteristics in influencing later adjustment to adult roles and responsibilities.     

Rethinking Stress in Parents of Preterm Infants: A Meta-Analysis

Background

With improved medical outcome in preterm infants, the psychosocial situation of their families is receiving increasing attention. For parents, the birth of a preterm infant is generally regarded as a stressful experience, and therefore many interventions are based on reducing parental stress. Nevertheless, it remains unclear whether parents of children born preterm experience more stress than parents of term-born children, which would justify these interventions. This meta-analysis provides a comprehensive account of parental stress in parents of preterm infants, from birth of the infant through to their adolescence. Mean levels of stress in specific domains of family functioning were investigated, and stress levels in parents of preterm and term infants, and fathers and mothers of preterm infants, were compared. Furthermore, we investigated moderators of parental stress.

Methods and Findings

A random-effects meta-analysis was conducted including 38 studies describing 3025 parents of preterm (<37 wk) and low birth weight (<2500 g) infants. Parental stress was measured with two parent-reported questionnaires, the Parenting Stress Index and the Parental Stressor Scale: Neonatal Intensive Care Unit. The results indicate that parents of preterm-born children experience only slightly more stress than parents of term-born children, with small effect sizes. Furthermore, mothers have slightly more stress than fathers, but these effect sizes are also small. Parents report more stress for infants with lower gestational ages and lower birth weights. There is a strong effect for infant birth year, with decreasing parental stress from the 1980s onward, probably due to increased quality of care for preterm infants.

Conclusions

Based on our findings we argue that prematurity can best be regarded as one of the possible complications of birth, and not as a source of stress in itself.     

Parental genetic characteristics and hatching success in the spotless starling, Sturnus unicolor

Several studies have shown that inbreeding causes low hatching success. However, it is not always clear under which parental genetic characteristics hatching failure occurs. We examined the effects of parental homozygosity and parental genetic similarity on egg hatchability in the spotless starling. We evaluated whether low hatchability was a consequence of genetic similarity of the parents producing a zygote or because the parents themselves had reduced fertility because of their own genetic characteristics. We found a significant detrimental effect of both highest and lowest female homozygosity on hatchability. Parental genetic similarity was negatively related to egg hatchability. In contrast, we found no significant effect of male homozygosity on hatching success. Our results suggest that effects of homozygosity on hatching success may be relevant even in populations of abundant and colonial wild bird species without geographical barriers that could limit immigration or dispersal. We also highlight the importance of the analyses of male and female homozygosity and parental genetic similarity when investigating related fitness consequences of inbreeding.     

Glassfrog embryos hatch early after parental desertion

Both parental care and hatching plasticity can improve embryo survival. Research has found that parents can alter hatching time owing to a direct effect of care on embryogenesis or via forms of care that cue the hatching process. Because parental care alters conditions critical for offspring development, hatching plasticity could allow embryos to exploit variation in parental behaviour. However, this interaction of parental care and hatching plasticity remains largely unexplored. We tested the hypothesis that embryos hatch early to cope with paternal abandonment in the glassfrog Hyalinobatrachium fleischmanni (Centrolenidae). We conducted male-removal experiments in a wild population, and examined embryos'' response to conditions with and without fathers. Embryos hatched early when abandoned, but extended development in the egg stage when fathers continued care. Paternal care had no effect on developmental rate. Rather, hatching plasticity was due to embryos actively hatching at different developmental stages, probably in response to deteriorating conditions without fathers. Our experimental results are supported by a significant correlation between the natural timing of abandonment and hatching in an unmanipulated population. This study demonstrates that embryos can respond to conditions resulting from parental abandonment, and provides insights into how variation in care can affect selection on egg-stage adaptations.     

Facial attractiveness judgements reflect learning of parental age characteristics

Mate preferences are shaped by infant experience of parental characteristics in a wide variety of species. Similar processes in humans may lead to physical similarity between parents and mates, yet this possibility has received little attention. The age of parents is one salient physical characteristic that offspring may attend to. The current study used computer-graphic faces to examine how preferences for age in faces were influenced by parental age. We found that women born to 'old' parents (over 30) were less impressed by youth, and more attracted to age cues in male faces than women with 'young' parents (under 30). For men, preferences for female faces were influenced by their mother's age and not their father's age, but only for long-term relationships. These data indicate that judgements of facial attractiveness in humans reflect the learning of parental characteristics.     

Predator-induced maternal and paternal effects independently alter sexual selection

Parental experience alters survival-related phenotypes of offspring in both adaptive and nonadaptive ways, yielding rapid inter- and transgenerational fitness effects. Yet, fitness comprises survival and reproduction, and parental effects on mating decisions could alter the strength and direction of sexual selection, affecting long-term evolutionary trajectories. We used a full factorial design in which threespine stickleback (Gasterosteus aculeatus) mothers, fathers, both, or neither were exposed to a model predator at developmentally appropriate times to test for predator-induced maternal, paternal, and joint parental effects on daughters’ mating behavior. We tested the responsiveness, preferences, and mate choices of adult daughters in no-choice trials with wild-caught males who had varied sexual signals. Maternal and paternal predator exposure independently yielded daughters who preferred males who were intermediate in conspicuousness (with duller nuptial coloration and who courted less vigorously), relaxing the typical preference for the most conspicuous males. The combined effects of maternal and paternal predator exposure were not cumulative; when both parents were predator exposed, single-parent effects on mate preferences were reversed. Thus, we cannot assume that maternal and paternal effects additively combine to produce “parental” effects. Further, joint parental predator exposure yielded daughters who were three times less likely to mate at all. Stress-induced intergenerational parental effects on reproductive decisions such as those observed here may potentiate rapid transgenerational responses to novel and changing mating environments.     

Parent-infant bed-sharing behavior

An evolutionarily informed perspective on parent-infant sleep contact challenges recommendations regarding appropriate parent-infant sleep practices based on large epidemiological studies. In this study regularly bed-sharing parents and infants participated in an in-home video study of bed-sharing behavior. Ten formula-feeding and ten breast-feeding families were filmed for 3 nights (adjustment, dyadic, and triadic nights) for 8 hours per night. For breast-fed infants, mother-infant orientation, sleep position, frequency of feeding, arousal, and synchronous arousal were all consistent with previous sleep-lab studies of mother-infant bed-sharing behavior, but significant differences were found between formula and breast-fed infants. While breast-feeding mothers shared a bed with their infants in a characteristic manner that provided several safety benefits, formula-feeding mothers shared a bed in a more variable manner with consequences for infant safety. Paternal bed-sharing behavior introduced further variability. Epidemiological case-control studies examining bed-sharing risks and benefits do not normally control for behavioral variables that an evolutionary viewpoint would deem crucial. This study demonstrates how parental behavior affects the bed-sharing experience and indicates that cases and controls in epidemiological studies should be matched for behavioral, as well as sociodemographic, variables.     

Inclusive fitness effects can select for cancer suppression into old age

Natural selection can favour health at youth or middle age (high reproductive value) over health at old age (low reproductive value). This means, all else being equal, selection for cancer suppression should dramatically drop after reproductive age. However, in species with significant parental investment, the capacity to enhance inclusive fitness may increase the reproductive value of older individuals or even those past reproductive age. Variation in parental investment levels could therefore contribute to variation in cancer susceptibility across species. In this article, we describe a simple model and framework for the evolution of cancer suppression with varying levels of parental investment and use this model to make testable predictions about variation in cancer suppression across species. This model can be extended to show that selection for cancer suppression is stronger in species with cooperative breeding systems and intergenerational transfers. We consider three cases that can select for cancer suppression into old age: (i) extended parental care that increases the survivorship of their offspring, (ii) grandparents contributing to higher fecundity of their children and (iii) cooperative breeding where helpers forgo reproduction or even survivorship to assist parents in having higher fecundity.     

Does Parental Fin Digging Improve Feeding Opportunities for Offspring in the Convict Cichlid?

The function of the fin digging behaviour in increasing food availability for the offspring was analysed in the convict cichlid, Cichlasoma (Archocentrus) nigrofasciatum. Consistent individual differences in the frequency of fin digging were found in the parental fish. Examination of the gastrointestinal tract of young revealed that higher frequency of parental fin digging was associated with higher consumption of large and more profitable prey (Diptera larvae), which inhabited deep horizons of the bottom substrate and possibly were difficult to access without parental assistance. Thus, parental fin digging was initially associated with a significant increase of the offspring growth rate. However, at later brood intervals, when parental care ceased, the young of the high-digging parents were characterised by a poorer consumption of small larvae that were most accessible for them without parental aid and represented an increasingly more important component of their ration than large larvae. Offspring of the low-digging parents, on the other hand, presumably as a result of their individual experience, showed a considerably better consumption of small larvae, increasing their growth rate. As a consequence, prior parental fin digging did not affect the offspring body size after independence. Thus, there exist pronounced individual differences and alternative parental styles in the convict cichlid.     

Variations in care for cottontop tamarin, Saguinus oedipus, infants as a function of parental experience and group size

We examined the effects of parental experience and group size on infant care and development. Ten cottontop tamarin families were followed across three consecutive births of offspring to examine differences in survival, quality of care, developmental maturation and physical development for infants in two experimental conditions: (1) in large groups with previous parenting experience and (2) in small groups with little or no parenting experience. Although we found no differences in infant mortality, parents treated infants differently between conditions. However, when we examined the cumulative care provided by parents and sibling helpers together across experimental conditions, there were no differences in the rates of retrieval or rejection of infants. Overall levels of infant transport and food transfers were similar between conditions, with fathers and sibling helpers contributing the bulk of care. Fathers in small groups carried infants and transferred food with infants much more than helpers but, as group size increased, helpers augmented this role. Infant development varied with the experience of the family both between conditions and within a family. The results indicate that infants receive similar levels of care regardless of group size and parenting experience, although the individual contributions of family members change with both factors. Parental experience with previous infants had effects on early infant development, but only for the first sets of infants. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Parental effects on inbreeding depression in a beetle with obligate parental care

Inbreeding depression occurs when individuals who are closely related mate and produce offspring with reduced fitness. Although inbreeding depression is a genetic phenomenon, the magnitude of inbreeding depression can be influenced by environmental conditions and parental effects. In this study, we tested whether size-based parental effects influence the magnitude of inbreeding depression in an insect with elaborate and obligate parental care (the burying beetle, Nicrophorus orbicollis). We found that larger parents produced larger offspring. However, larval mass was also influenced by the interaction between parental body size and larval inbreeding status: when parents were small, inbred larvae were smaller than outbred larvae, but when parents were large this pattern was reversed. In contrast, survival from larval dispersal to adult emergence showed inbreeding depression that was unaffected by parental body size. Our results suggest that size-based parental effects can generate variation in the magnitude of inbreeding depression. Further work is needed to dissect the mechanisms through which this might occur and to better understand why parental size influences inbreeding depression in some traits but not others.     

Perinatal sadness among Shuar women: support for an evolutionary theory of psychic pain

Psychiatry faces an internal contradiction in that it regards mild sadness and low mood as normal emotions, yet when these emotions are directed toward a new infant, it regards them as abnormal. We apply parental investment theory, a widely used framework from evolutionary biology, to maternal perinatal emotions, arguing that negative emotions directed toward a new infant could serve an important evolved function. If so, then under some definitions of psychiatric disorder, these emotions are not disorders. We investigate the applicability of parental investment theory to maternal postpartum emotions among Shuar mothers. Shuar mothers' conceptions of perinatal sadness closely match predictions of parental investment theory.     

Strain‐specific effects of parental age on offspring in Drosophila melanogaster

Maternal age is generally known to be negatively correlated with the lifespan of offspring in several animal models including yeast, rotifers, flies, and possibly in humans. However, several reports have shown positive effects of parental age on offspring lifespan. Thus, there was a need to investigate further the inconsistent results on the effect of parental age on lifespan. In this study, the effects of parental age on offspring fitness and lifespan were examined by using Drosophila melanogaster. The lifespan of offspring from old parents was significantly increased compared with that of the young counterparts in the Canton‐S (CS) strain but not in other D. melanogaster strains, such as Oregon‐R (OR) and w¹¹¹⁸. To find out why the lifespan is increased in the offspring from old parents in CS flies, fitness components that could modulate lifespan were examined in CS flies. Egg weight and body weight were reduced by parental aging and the offspring of old fathers or old mothers developed faster than that of the young. In addition, the offspring of old parents had increased resistance to oxidative and heat shock stresses. However, reproductive capacity, mating preference, and food intake were unaffected by parental aging. These results indicate that parental aging in CS strain D. melanogaster has beneficial effects on the lifespan and fitness of offspring. The presence of strain‐specific manner effects suggests that genetic background might be a significant factor in the parental age effect.     

Interaction between parental care and sibling competition: parents enhance offspring growth and exacerbate sibling competition

Species with elaborate parental care often also show intense sibling competition over resources provided by parents, suggesting joint evolution of these two traits. Despite this, the evolution of elaborate parental care and the evolution of intense sibling competition are often studied separately. Here, we examine the interaction between parental food provisioning and sibling competition for resources through the joint manipulation of the presence or absence of parents and brood size in a species with facultative parental care: the burying beetle Nicrophorus vespilloides. The effect of the interaction between the presence or absence of parents and brood size was strong; brood size had a strong effect on growth when parents provided care, but no effect when parents were absent. As in previous studies, offspring grew faster when parents were present than when parents were absent, and offspring grew faster in smaller broods than in larger broods. Our behavioral observations showed that brood size had a negative effect on both the amount of time parents spent providing resources to individual offspring and the offspring's effectiveness of begging, confirming that the level of sibling competition increased with brood size. Furthermore, offspring in larger broods shifted more from begging toward self-feeding as they grew older compared to offspring in small broods. Our study provides novel insights into the joint evolution of parental care and sibling competition, and the evolution of offspring begging signals. We discuss the implications of our results in light of recent theoretical work on the evolution of parental care, sibling competition, and offspring begging signals.     

Transgenerational memory effect of ageing in Drosophila

Children born to older parents tend to have lower intelligence and are at higher risk for disorders such as schizophrenia and autism. Such observations of ageing damage being passed on from parents to offspring are not often considered within the evolutionary theory of ageing. Here, we show the 25% memory impairment in Drosophila melanogaster offspring solely dependent on the age of the parents and also passed on to the F2 generation. Furthermore, this parental age effect was not attributed to a generalized reduction in condition of the offspring but was specific to short‐term memory. We also provide evidence implicating oxidative stress as a causal factor by showing that lines selected for resistance to oxidative stress did not display a memory impairment in offspring of old parents. The identification of the parental age‐related memory impairment in a model system should stimulate integration between mechanistic studies of age‐related mortality risk and functional studies of parental age effects on the fitness of future generations.     

Sex‐Specific Parental Care in Response to Predation Risk in the European Roller,Coracias garrulus

Sublethal effects of predation constitute an important part of predation effects, which may modulate prey population and community dynamics. In birds, the risk of nest predation may cause a reduction in parental activity in the care of offspring to reduce the chance of being detected by predators. In addition, parents may modify their parental food allocation preferences within the brood in response to predation risk. Our aim in this study was to evaluate the effects of risk of nest predation on parental care and within‐nest food allocation in the European Roller (Coracias garrulus), an asynchronously hatching bird. We manipulated brood predation risk by placing a snake model near the nests that simulates the most common nest predator in the Mediterranean region. Our results show that males but not females increased their provisioning rate when they were exposed to the model and that despite this, nestlings’ body mass decreased in response to this temporary increase in predation risk. We did not find evidence that parents changed their food allocation strategy towards senior or junior nestlings in their nests in response to predation risk. These results show that the European roller modifies parental care in response to their perception of predation risk in the nest and a sex‐specific sensitivity to the threat, which suggests a different perception of offspring reproductive value by parents. Finally, our results show that changes in parental behaviour in response to nest predation risk might have consequences for nestling fitness prospects.     

Reproductive ‘Surrogacy’ and Parental Licensing

A serious moral weakness of reproductive ‘surrogacy’ is that it can be harmful to the children who are created. This article presents a proposal for mitigating this weakness. Currently, the practice of commercial ‘surrogacy’ operates only in the interests of the adults involved (the gestator and the commissioning individuals who employ her), not in the interests of the child who is created. Whether ‘surrogacy’ is seen as the purchase of a baby, the purchase of parental rights, or the purchase of reproductive labor, all three views share the same significant flaws. They endorse the transfer, for a fee, of the infant from the woman who gestated it to those who commissioned it, but without justifying such a transfer; they fail to demonstrate that the commissioners have any entitlement to the infant, or, for that matter, suitability to be the infant's parents; and they fail to take any notice of the infant's needs, interests, and wellbeing. A mere genetic connection is not enough to establish that the commissioners are entitled to receive the baby or that they are competent to raise it. Their good intentions, however caring, are not enough. Therefore, just as in the practice of adoption, there should be a formal institutionalized system for screening and licensing the prospective social parents, which would make the infant's needs, interests, and wellbeing paramount. I reply to several potential objections to this proposal, including the objection that genetic parents who raise their own child are not screened and licensed.     

Flexible communication within bird families—The consequences of behavioral plasticity for parent–offspring coadaptation

Offspring are selected to demand more resources than what is optimal for their parents to provide, which results in a complex and dynamic interplay during parental care. Parent–offspring communication often involves conspicuous begging by the offspring which triggers a parental response, typically the transfer of food. So begging and parental provisioning reciprocally influence each other and are therefore expected to coevolve. There is indeed empirical evidence for covariation of offspring begging and parental provisioning at the phenotypic level. However, whether this reflects genetic correlations of mean levels of behaviors or a covariation of the slopes of offspring demand and parental supply functions (= behavioral plasticity) is not known. The latter has gone rather unnoticed—despite the obvious dynamics of parent–offspring communication. In this study, we measured parental provisioning and begging behavior at two different hunger levels using canaries (Serinus canaria) as a model species. This enabled us to simultaneously study the plastic responses of the parents and the offspring to changes in offspring need. We first tested whether parent and offspring behaviors covary phenotypically. Then, using a covariance partitioning approach, we estimated whether the covariance predominantly occurred at a between‐nest level (i.e., indicating a fixed strategy) or at a within‐nest level (i.e., reflecting a flexible strategy). We found positive phenotypic covariation of offspring begging and parental provisioning, confirming previous evidence. Yet, this phenotypic covariation was mainly driven by a covariance at the within‐nest level. That is parental and offspring behaviors covary because of a plastic behavioral coadjustment, indicating that behavioral plasticity could be a main driver of parent–offspring coadaptation.