Social and genetic benefits of parental investment suggest sex differences in selection pressures

Provisioning behavior in altricial birds is often used to measure parental investment and is assumed to have fitness consequences to the parents providing it, with the benefits outweighing the costs. Here we investigate the fitness costs and benefits (parent survival and offspring recruitment) of provisioning behavior in wild house sparrows Passer domesticus, using long‐term data from a pedigreed isolated population. We disentangled the long‐term fitness consequences in terms of number of recruits, of provisioning behavior from those of other parental investments and individual quality through a cross‐foster design. We accounted for extra‐pair offspring in all analyses. Provisioning behavior confers social fitness benefits in terms of the number of recruits to both parents. Only in females we detected an influence individual quality: female sparrows with high provisioning frequencies were associated with more genetic recruits than those who provided food less frequently to their young, even though foster parents reared the offspring. We detected a relationship between annual survival probability and provisioning behavior only in males, but not in females. This finding, together with indirect benefits differing by sex, indicates that different selection pressures are acting on the sexes. Our study can show that it is justified to use provisioning behavior as a form of parental investment sensu Trivers, since we show that this behavior is costly to parents and that the genetic fitness benefits exceed the costs.     

Early puberty in adopted children

Early puberty is frequently observed in adopted children. In various studies, early puberty has been associated with decreased final height. In Europe, studies were undertaken to treat early puberty in adopted children with GnRH agonist. This article reviews the current understanding of early puberty in adopted children, including prevalence, background and treatment options. Data from the European studies are briefly described. Besides auxological aspects, psychological items are addressed as well. Studies on the psychological effect of early puberty in adopted children are reported. Future issues include further study in the mechanism of early puberty in adopted children, evaluation of final height results of the growth studies and quality of life assessments in this specific group of children.     

Preferential parental investment in daughters over sons

Female-biased parental investment is unusual but not unknown in human societies. Relevant explanatory models include Fisher’s principle, the Trivers-Willard model, local mate and resource competition and enhancement, and economic rational actor models. Possible evidence of female-biased parental investment includes sex ratios, mortality rates, parents’ stated preferences for offspring of one sex, and direct and indirect measurements of actual parental behavior. Possible examples of female-biased parental investment include the Mukogodo of Kenya, the Ifalukese of Micronesia, the Cheyenne of North America, the Herero of southern Africa, the Kanjar of south Asia, the Mundugumor of New Guinea, contemporary North America, and historical Germany, Portugal, and the United States. Lee Cronk is Assistant Professor of Anthropology at Texas A&M University, College Station, Texas. His main research interests are in human behavioral ecology, reproductive strategies, and East African hunter-gatherers and pastoralists.     

Historical perspectives on parental investment and childbearing

This article provides some historical perspectives on parental investment and childbearing. Scholars are debating whether parents always loved and nurtured their children. The historical record provides some support for both sides. Parents who abandoned their children often did so with the hope that someone else would be able to raise them. But others, like the ancient Carthagians, sacrificed their own children to appease the gods. Colonial Americans appear to have been particularly solicitous of the well-being of their children. The paper then traces the changes in the role of women in facilitating the process of childbirth in America. Scholars are cautioned not to idealize the childbirth experiences of women in the past as they experienced considerable pain and fear.     

An asymmetric parental investment conflict with continuous strategy sets

In the parental investment conflict each of the sexes decides how much to invest in its brood, where its decision influences both sexes' fitness. In nature, each species is usually characterized by a common parental care pattern, male-only care, female-only care or biparental care. A possible way for understanding the factors that have led each species to adopt its unique parental care pattern is to analyse a male's and a female's decision process using a game-theoretical model. This paper suggests a two-stage game-theoretical model with two types of players, male and female. During the game each parent makes three decisions. The interval between the beginning of the game, i.e. after mating and having offspring, and the moment a parent starts to care for them is a random variable. Thus, in the first stage a parent chooses the cumulative probability distribution of this interval, and its amount of parental care. In the second stage the other parent chooses its probability for cooperation. It is assumed that as long as parental care is not provided the offspring are at risk, and that parental caring accrues a different cost for each sex. We compute the Evolutionary Stable Strategies (ESS) under payoff-relevant asymmetry, and show that uniparental and biparental care are possible ESS. We also characterize cases where the sex having the lower cost "forces" the sex having the higher cost to care and vice versa.     

Accurate partition of individuals into full-sib families from genetic data without parental information.

Two Markov chain Monte Carlo algorithms are proposed that allow the partitioning of individuals into full-sib groups using single-locus genetic marker data when no parental information is available. These algorithms present a method of moving through the sibship configuration space and locating the configuration that maximizes an overall score on the basis of pairwise likelihood ratios of being full-sib or unrelated or maximizes the full joint likelihood of the proposed family structure. Using these methods, up to 757 out of 759 Atlantic salmon were correctly classified into 12 full-sib families of unequal size using four microsatellite markers. Large-scale simulations were performed to assess the sensitivity of the procedures to the number of loci and number of alleles per locus, the allelic distribution type, the distribution of families, and the independent knowledge of population allelic frequencies. The number of loci and the number of alleles per locus had the most impact on accuracy. Very good accuracy can be obtained with as few as four loci when they have at least eight alleles. Accuracy decreases when using allelic frequencies estimated in small target samples with skewed family distributions with the pairwise likelihood approach. We present an iterative approach that partly corrects that problem. The full likelihood approach is less sensitive to the precision of allelic frequencies estimates but did not perform as well with the large data set or when little information was available (e.g., four loci with four alleles).     

Molecular analysis of the parental origin of trisomy in two families with two children having regular trisomy 21

In order to investigate the parental origin of the trisomy in two families with two free trisomy 21 affected siblings, cytogenetic and molecular analyses were performed. In each case the parental origin was the same for both patients. In one of the families an association between the concordance of the paternal origin of the trisomy and the existence of mosaicism in the blood was established. The various etiologies which may account for recurrence are discussed.     

Nest building, sexual selection and parental investment

Avian nest building has traditionally been viewed as resulting in natural selection advantages, but it is also been associated with courtship and pair formation. We hypothesize that nest-building activity could be used as a sexually selected display, allowing each sex to obtain reliable information on the condition of the other. In this paper, we test the ‘good parent’ process in a scenario where nest size is a sexually selected trait. Thus, individuals with more extreme displays (larger nests) might obtain benefits in terms of either parental investment or differential parental investment by the partner. We predicted that: (1) species in which both sexes contribute to nest building have larger nests than those in which the nest is built only by one sex, because both sexes are using the nest-building process as a signal of their quality; (2) species in which both sexes work together in the nest-building process invest more in reproduction, because each can assess the other more reliably than in species where only one sex participates in nest building; and (3) in light of the two preceding predictions, nest size should be positively related to investment in parental care. A comparative analysis of 76 passerine species confirmed that nest size, relative to the species' body size, is larger when both sexes build the nest and that species with a larger nest relative to their body size invest more in reproduction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Intrafamilial conflict and parental investment: a synthesis

We outline and develop current theory on how inherent genetic conflicts of interest between the various family members can affect the flow of parental investment from parents to offspring, and discuss the problems for empirical testing that this generates. The parental investment pattern realized in nature reflects the simultaneous resolution of all the conflicts between the family players. This depends on the genetic mechanism, the mating system and reproductive constraints, on whether extra demand by progeny affects current or future sibs, and particularly on the behavioural mechanisms underlying demand (begging or solicitation) and supply (provision of parental investment by parents). The direction of deviation from the optimal parental investment for the parent(s) depends on the slope of what we term the 'effect of supply on demand', the mechanism that determines how changes in food supply affect begging levels. If increasing food increases begging (positive slope), less parental investment is supplied than the parental optimum and if increasing food decreases begging (negative slope), more parental investment is supplied. The magnitude of deviation depends on both the 'effect of supply on demand' and on the 'effect of demand on supply' (the mechanism determining how changes in begging affect food supply, which always has a positive slope). We conclude that it will often be impossible to deduce the extent of underlying conflict by establishing the amount of parental investment given relative to the ideal optimum for the parent. Some possible directions for future research are discussed.     

Estimating relative parental investment in sons versus daughters

Fisher proposed that natural selection would adjust the population sex ratio so that parental expenditure on sons equals expenditure on daughters. Thus if two daughters can be produced for every son, the Fisherian equilibrium is ? sons and ? daughters. The relative cost of a son versus a daughter is necessarily manifested in the trade-off between family size and sex ratio, and we offer a method to estimate this trade-off from data on family compositions. Simulation studies indicate that the method works well in some cases but not others. Application of the method to data on a polychaete suggests that sons are much costlier than daughters; the observed sex ratio in fact significantly favored daughters, but not to the extreme predicted by our measure of differential cost.     

Basal metabolic rate is positively correlated with parental investment in laboratory mice

The assimilation capacity (AC) hypothesis for the evolution of endothermy predicts that the maternal basal metabolic rate (BMR) should be positively correlated with the capacity for parental investment. In this study, we provide a unique test of the AC model based on mice from a long-term selection experiment designed to produce divergent levels of BMR. By constructing experimental families with cross-fostered litters, we were able to control for the effect of the mother as well as the type of pup based on the selected lines. We found that mothers with genetically determined high levels of BMR were characterized by higher parental investment capacity, measured as the offspring growth rate. We also found higher food consumption and heavier visceral organs in the females with high BMR. These findings suggested that the high-BMR females have higher energy acquisition abilities. When the effect of the line type of a foster mother was controlled, the pup line type significantly affected the growth rate only in the first week of life, with young from the high-BMR line type growing more rapidly. Our results support the predictions of the AC model.     

Similarities between parents and their adopted children

As shown in 7,230 parent-child pairs (6,726 biological and 504 adoptive), adoptive parents and their adopted children tend to resemble each other in height, weight and fatfolds to an extent paralleling height, weight and fatfold resemblances of natural (biological) parents and their children. Accordingly, the magnitudes of parent-child resemblances commonly given may not be indicative of the extent of heritability of stature, weight and subcutaneous fat.     

Cues of parental investment as a factor in attractiveness

One prediction derived from parental investment theory is that women will be more attentive than men are to cues of a prospective mate's dispositions to invest in children. Research with 1793 Internet participants, representing a diverse population sample, found that (a) women tend to be generally more critical than men are in their evaluations of potential mates, but not potential friends or neighbors, and (b) cues of a positive disposition towards parental investment (DPI) have a positive influence on female evaluations of the attractiveness of males. This latter effect, however, is less domain-specific than previous research [La Cerra, M. M. (1995). Evolved mate preferences in women: Psychological adaptations for assessing a man's willingness to invest in offspring (doctoral dissertation, University of California, Santa Barbara). Dissertation Abstracts International: Section B: the Sciences & Engineering Mar, 55(9-B), 4149] indicated; it is not limited to mating contexts and to cues focusing on parental investment. In fact, much of the sex difference appears to be due to indifference by males towards cues of female DPI. A second study further clarified that the previous findings were not due solely to the Internet methodology or the immediate accessibility of images being evaluated.     

Within-brood competition and the optimal partitioning of parental investment

In this article, we introduce a simple within-brood competitive growth model that maximizes parental fitness in unpredictable food conditions in species that exhibit parental care, progressive provisioning, and an initial brood overproduction. We argue that competition between siblings may provide a proximate mechanism for parents to adjust the number of surviving offspring or the social organization of the group in social species to food conditions.     

An increase in parental investment during the breeding season

The intensity of nest-defence aggression by female redwinged black birds (Agelaius phoeniceus) with eggs decreased late in the breeding season, while aggression at this time increased amongst females defending broods. High predation pressure late in the breeding season decreased the probability of survival of the late nesting attempts, so that females with young had a much greater chance of success than females with eggs at this time. The observed changes in aggressive responses are predicted by the theory of parental investment.     

Health care support issues for internationally adopted children: a qualitative approach to the needs and expectations of families

Background

Families of internationally adopted children may face specific problems with which general practitioners (GPs) may not be familiar. The aim of the study was to explore problems faced by families before, during and after the arrival of their internationally adopted child and to assess the usefulness of a specific medical structure for internationally adopted children, which could be a resource for the GP.

Methodology/Principal Findings

We conducted a qualitative study using individual semistructured guided conversations and interviewed 21 families that had adopted a total of 26 children internationally in the Puy de Dome department, France, in 2003. Quantitative data were used to describe the pathologies diagnosed and the investigations performed.Our study showed that the history of these families, from the start of the adoption project to its achievement, is complex and warrants careful analysis. Health-care providers should not only consider the medical aspects of adoption, but should also be interested in the histories of these families, which may play a role in the forming of attachments between the adoptee and their adoptive parents and prevent further trouble during the development of the child. We also showed that adoptive parents have similar fears or transient difficulties that may be resolved quickly by listening and reassurance. Most such families would support the existence of a specific medical structure for internationally adopted children, which could be a resource for the general practitioner. However, the health-care providers interviewed were divided on the subject and expressed their fear that a special consultation could be stigmatizing to children and families.

Conclusions/Significance

A specific consultation with well-trained and experienced practitioners acting in close collaboration with GPs and paediatricians may be of help in better understanding and supporting adopted children and their families.     

The parental investment model and minimum mate choice criteria in humans

Trivers' parental investment model states that individuals facinghigher levels of parental investment will become increasinglychoosy in their choice of mates. For humans, this leads to twopredictions. First, both males and females will be choosierin relationships more likely to lead to the production of children.Second, females will be choosier than are males, because theirminimum risk of parental investment is higher. Previous studiesof human mate choice found support for these predictions, withone curious exception: male choosiness was lower for short-termsexual relationships involving no relationship commitment (one-nightstands) than for short-term relationships involving no sexualactivity (single dates). Because the risk of parental investmentwould be higher in a one-night stand, this suggests that truerisk of parental investment was not the underlying factor governingchoosiness levels, either because study subjects assigned differentlevels of sexual activity to the relationships than were intendedby the investigators of the study or because perceived riskis more important in human mate choice than real risk. To confirmthat male/female differences in choosiness criteria exist inhumans, and to evaluate the effect that different expected levelsof real or perceived parental investment may have on choosiness,we studied mate choosiness in the context of five types of relationshipsthat reflected explicitly defined, increasing levels of riskof parental investment for both males and females. The subjectswere 468 undergraduate students, mostly between the ages of18–24. By using questionnaires, male and female participantsrated their minimum requirements in a potential mate for 29personal characteristics with respect to level of relationship.Our results confirm the major predictions of the parental investmentmodel for humans but suggest that sex differences in choosinessare better explained by perceived rather than real risk of parentalinvestment.     

Testing models of parental investment strategy and offspring size in ants

Parental investment strategies can be fixed or flexible. A fixed strategy predicts making all offspring a single ‘optimal’ size. Dynamic models predict flexible strategies with more than one optimal size of offspring. Patterns in the distribution of offspring sizes may thus reveal the investment strategy. Static strategies should produce normal distributions. Dynamic strategies should often result in non-normal distributions. Furthermore, variance in morphological traits should be positively correlated with the length of developmental time the traits are exposed to environmental influences. Finally, the type of deviation from normality (i.e., skewed left or right, or platykurtic) should be correlated with the average offspring size. To test the latter prediction, we used simulations to detect significant departures from normality and categorize distribution types. Data from three species of ants strongly support the predicted patterns for dynamic parental investment. Offspring size distributions are often significantly non-normal. Traits fixed earlier in development, such as head width, are less variable than final body weight. The type of distribution observed correlates with mean female dry weight. The overall support for a dynamic parental investment model has implications for life history theory. Predicted conflicts over parental effort, sex investment ratios, and reproductive skew in cooperative breeders follow from assumptions of static parental investment strategies and omnipresent resource limitations. By contrast, with flexible investment strategies such conflicts can be either absent or maladaptive. Electronic Supplementary Material Supplementary material is available for this article at