Low Parental Investment Research Articles

Early-life conditions and age at first pregnancy in British women

There is growing evidence that the reproductive schedules of female mammals can be affected by conditions experienced during early development, with low parental investment leading to accelerated life-history strategies in the offspring. In humans, the relationships between early-life conditions and timing of puberty are well studied, but much less attention has been paid to reproductive behaviour. Here, we investigate associations between early-life conditions and age at first pregnancy (AFP) in a large, longitudinally studied cohort of British women (n = 4553). Low birthweight for gestational age, short duration of breastfeeding, separation from mother in childhood, frequent family residential moves and lack of paternal involvement are all independently associated with earlier first pregnancy. Apart from that of birthweight, the effects are robust to adjustment for family socioeconomic position (SEP) and the cohort member's mother's age at her birth. The association between childhood SEP and AFP is partially mediated by early-life conditions, and the association between early-life conditions and AFP is partially mediated by emotional and behavioural problems in childhood. The overall relationship between early-life adversities and AFP appears to be approximately additive.

Development of Social Variation in Reproductive Schedules: A Study from an English Urban Area

BackgroundThere is striking social variation in the timing of the onset of childbearing in contemporary England, with the mean age at first motherhood about 8 years earlier in the most deprived compared to the least deprived neighbourhoods. However, relatively little is known about how these social differences in reproductive schedule develop in childhood.Methodology/Principal FindingsWe studied the development of differences in reproductive schedules, using a cross-sectional survey over 1000 school students aged 9–15 in the metropolitan borough of North Tyneside. Students from more deprived neighbourhoods had earlier ideal ages for parenthood than those from more affluent ones, and these differences were fully apparent by age 11. We found evidence consistent with three mechanisms playing a role in maintaining the socioeconomic gradient. These were: vertical intergenerational transmission (students whose own parents were younger at their birth wanted children younger); oblique intergenerational transmission (students in neighbourhoods where parents were younger in general wanted children earlier); and low parental investment (students who did not feel emotionally supported by their own parents wanted children at a younger age).Conclusions/SignificanceOur results shed some light on the proximate factors which may be involved in maintaining early childbearing in disadvantaged communities. They help understand why educational initiatives aimed at adolescents tend to have no effect, whereas improving the well-being of poor families with young children may do so. Our results also suggest that there will be considerable intergenerational inertia in the response of reproductive schedules to changing socioecological conditions.

Lower parental investment in stepchildren: The case of the Israeli "Great Journey."

Lower parental investment in stepchildren: The case of the Israeli "Great Journey."

SEXUAL SELECTION DETERMINES PARENTAL CARE PATTERNS IN CICHLID FISHES

Despite a massive research effort, our understanding of why, in most vertebrates, males compete for mates and females care for offspring remains incomplete. Two alternative hypotheses have been proposed to explain the direction of causality between parental care and sexual selection. Traditionally, sexual selection has been explained as a consequence of relative parental investment, where the sex investing less will compete for the sex investing more. However, a more recent model suggests that parental care patterns result from sexual selection acting on one sex favoring mating competition and lower parental investment. Using species-level comparative analyses on Tanganyikan cichlid fishes we tested these alternative hypotheses employing a proxy of sexual selection based on mating system, sexual dichromatism, and dimorphism data. First, while controlling for female reproductive investment, we found that species with intense sexual selection were associated with female-only care whereas species with moderate sexual selection were associated with biparental care. Second, using contingency analyses, we found that, contrary to the traditional view, evolutionary changes in parental care type are dependent on the intensity of sexual selection. Hence, our results support the hypothesis that sexual selection determines parental care patterns in Tanganyikan cichlid fishes.

Sex differences in response to cues of parental investment: An evolutionary social psychological perspective.

Past research on human mating behaviors has operationalized parental investment (PI) in terms of sex differences – with females reflecting high parental investment (and resultant long-term mating strategies) and males demonstrating low parental investment (and resultant short-term mating strategies). The present research draws on methods adopted from social psychology to operationalize parental investment in terms of conscious and non-conscious attitudinal indices. In a sample of young heterosexual adults, we examined sex differences in two measures of attitudes toward one’s ability/willingness to invest in parenting. One measure was a self-report index while the other was based on autonomic nervous system (ANS) responses. No sex difference was obtained regarding self-report responses to PI. However, males showed significantly larger increases in heart rate than females when presented with PI-relevant (compared with PI-neutral) stimuli. The findings are consistent with past research suggesting that males are less prepared to confront issues associated with parenting than are females. Further, the findings suggest that males are somewhat unaware of their own perceived lack of parental preparedness. The incongruity between males’ self-reports and their ANS responses is discussed with regard to Error Management Theory (EMT; Haselton & Buss, 2000). We also discuss more generally how this research may serve as a model for using the subjectivist tradition in social psychology to expand our study of objective variables derived from the evolutionary perspective.

RESEARCH: Parental Global Religiousness, Sanctification of Parenting, and Positive and Negative Religious Coping as Predictors of Parental and Child Functioning

Conducted with an economically and ethnically diverse sample of 149 parents of preschoolers, this study tested the degree to which parental global religiousness, sanctificationof parenting, and positive and negative religious coping predicted three measures of parental functioning (investment, satisfaction, and efficacy) and three measuresof child functioning (coping competence, inattentive/hyperactive symptoms, and oppositional defiant symptoms). Hierarchical regression analyses that controlledfor sociodemographic and family variables showed that parental and child functioning were better predicted by the manner in which parents saw God involved in theirparenting than by their global religiousness or the extent to which they sanctified parenting. Specifically, (a) positive facets of family functioning were associated withlower levels of negative religious coping and, to a lesser extent, with some evidence of positive religious coping, and (b) negative facets of functioning—especially low parentalinvestment and satisfaction, and high child opposition—were linked to higher

Terminal Investment Strategies and Male Mate choice: Extreme Tests of Bateman

Bateman's principle predicts the intensity of sexual selection depends on rates of increase of fecundity with mating success for each sex (Bateman slopes). The sex with the steeper increase (usually males) is under more intense sexual selection and is expected to compete for access to the sex under less intense sexual selection (usually females). Under Bateman and modern refinements of his ideas, differences in parental investment are key to defining Bateman slopes and thus sex roles. Other theories predict sex differences in mating investment, or any expenditures that reduce male potential reproductive rate, can also control sex roles. We focus on sexual behaviour in systems where males have low paternal investment but frequently mate only once in their lifetimes, after which they are often killed by the female. Mating effort (=terminal investment) is high for these males, and many forms of investment theory might predict sex role reversal. We find no qualitative evidence for sex role reversal in a sample of spiders that show this extreme male investment pattern. We also present new data for terminally-investing redback spiders (Latrodectus hasselti). Bateman slopes are relatively steep for male redbacks, and, as predicted by Bateman, there is little evidence for role reversal. Instead, males are competitive and show limited choosiness despite wide variation in female reproductive value. This study supports the proposal that high male mating investment coupled with low parental investment may predispose males to choosiness but will not lead to role reversal. We support the utility of using Bateman slopes to predict sex roles, even in systems with extreme male mating investment.

Selection for birth date in North Sea haddock and its relation to maternal age

Summary Birth date can be important to lifetime reproductive success. However, selection for birth date has rarely been addressed in fish, despite the opportunity provided by otolith microstructure. This study examined the relationship between maternal age, spawning time and early survivorship in the North Sea haddock stock. Temporal changes in egg production were compared with the birth date distribution of progeny surviving to the demersal phase in 1994, 1996 and 1999, when the age structure of the spawning stock differed. Estimates of intra‐annual variation in stock egg production indicated that first‐time spawning 2‐year‐olds began spawning much later than older age‐classes. The form and magnitude of selection on birth date varied between years, indicating that the production of multiple batches of eggs over an extended period has some adaptive significance to progeny survival. Survivorship was consistently poor from the late spawning period when age 2 females contributed most to stock egg production. This persistent selection against late hatched offspring could reflect either low parental investment, as age 2 females produce smaller eggs, or the short length of the growing season prior to settlement. Variability in birth date selection, particularly with respect to first vs. subsequent years of spawning, implies a strong selection pressure for a long reproductive lifespan. As such, reproductive potential in this and other exploited fish species with a similar reproductive trait may have been affected adversely by the general decline in repeat spawning females in recent years.

Male nest site fidelity and female serial polyandry in lingcod (Ophiodon elongatus, Hexagrammidae)

Nest site fidelity and serial polyandry were examined in lingcod, Ophiodon elongatus, a teleost fish in which the nest-guarding male parent invests more heavily in parental care than the elusive female parent. Lingcod parental and progeny genotypes were established for fish spawning on a 200 m(2) section of Snake Island reef, British Columbia in two successive years to evaluate male and female mate choice (monogamy or polygamy) and nest site reuse by the same parents (nest site fidelity) and/or different parents (nest site affinity). Thirteen nests (egg masses) guarded by nine males and 14 nests guarded by seven males were observed in 2002 and 2003, respectively. No female laid more than one nest per season or spawned in the study area in both years. In contrast, at least six (86%) and possibly all seven (100%) of the 2003 guardian males had been guardian or auxiliary males in 2002. Both nest site affinity and extreme male nest site fidelity were observed, with at least four males reusing the exact same nest site. Serial polyandry resulting from the high male and low female nest site fidelity is consistent with predictions based on a low female parental investment and high rate of progeny loss to predation and cannibalism. Male polygyny, achieved primarily by cuckoldry within seasons, was enhanced by the lack of female fidelity between seasons. Polygamy in both sexes of nest-tending marine fish may minimize reproductive skew and maximize genetic diversity within populations.

Reproductive consequences for males of paternal vs territorial strategies in the polygynous spotless starling under variable ecological

Abstract The males' trade-off between caring for the offspring or investing in attracting additional mates is well established in the theory of mating systems. The reproductive consequences for males of alternative strategies adopted by them in response to these conflicting demands should depend on several ecological and social factors that may strongly vary among years. This variation, however, has been rarely addressed in field studies despite it being essential to understand the evolution of parental care in facultatively polygynous species. In the present paper, we examine the reproductive consequences of paternal vs. territorial strategies in the polygynous spotless starling (Sturnus unicolor) during four consecutive breeding seasons (1996-1999) in which the number of male defending nest boxes and several population variables such as nestling starvation rates, nest predation rates and fledgling production varied markedly. In 1996 we manipulated the propensity of males to feed their offspring by means of androgens and antiadrogens, and examined the consequences of male behaviour on reproductive success during the subsequent four breeding seasons. Males implanted in1996 with the antiandrogen cyproterone acetate (Cy-males) fed more frequently than males implanted with testosterone (T-males) or control males (C-males) both during the season in which they were implanted and in the next season. The number of nest boxes defended influenced total breeding success mainly in the years when male feeding frequency was less important for breeding success per nest. A lower proportion of Cy-males than T- or C-males still held at least a nest box in 1999, three years after they were implanted. As a result, the number of fledglings produced over the four years studied was smaller for Cy-males than for T- or C-males. These results suggest that the oscillating selective forces acting on breeding male starlings seem to operate more frequently against the development of parental care strategies, while the polygynous strategy seems to be favoured under a wide array of ecological conditions. Although increased density of potential breeders may constrain territorial expansion and polygyny, the high cost of losing a minimum breeding site may select for the maintenance of aggressive behaviour and low parental investment.

Beyond the "Cinderella effect" : Life history theory and child maltreatment.

A central thesis of this paper is that understanding the nature of child maltreatment is so complex that no one disciplinary specialty is likely to be sufficient for the task. Although life history theory is the guiding principle for our analysis, we argue that an evolutionary explanation adds precision by incorporating empirical findings originating from the fields of anthropology; clinical, developmental, and social psychology; and sociology. Although evolutionary accounts of child maltreatment have been largely limited to the role of the coefficient of relatedness, the prospective reproductive value of a child, and the residual reproductive potential of parents, a case is made for expanding this basic application. An explanatory model is presented that describes how ecological conditions as well as parental and child traits interact to influence the degree of parental investment. As shown in the model, these various "marker variables" alter parental perceptions of the benefits and costs associated with child care and promote low-investment parenting, which leads to disrupted family management practices and to a downward-spiraling, self-perpetuating system of coercive family interaction, increased parental rejection of the child, and even lower parental investment. Child maltreatment is the ultimate outcome of this downward trajectory of family relations.

Sexual selection and intra-femalecompetition in the green poison-dart frog, Dendrobates auratus

Observations on the mating and parental behaviour of the green poison-dart frog were used to test two hypotheses for the function of female-female competition in this species. The hypothesis that females compete to monopolize as many mates as possible was not supported because: (1) male territoriality was associated with competition for females; (2) intra-female competition for mates was not more common or intense than intra-male competition; (3) females were more selective about mating than were males; (4) estimated offspring production by individual females did not exceed the parental capacity of a single male. The hypothesis that females compete to monopolize the parental care of particular males was consistent with observations that: (1) females competed for males, but were more selective about mating than were males; (2) females remained near particular males and attempted to keep other females from mating with those males; (3) females may have used courtship to prevent males from mating with other females. Both hypotheses were consistent with evidence that: (1) females are large compared with males in D. auratus, relative to closely related species with low male parental investment; (2) females destroyed the eggs of other females when they located them.

Parental care of Tilapia mariae in the field and in aquaria

Parental care of Tilapia mariae was observed in nature (Ethiop River, Nigeria) and in aquaria with or without intruders present. In the field, 25–30% of nests are guarded by one parent, normally the female. It is assumed that most missing males have deserted. Males who participate in brood care exhibit both close brood guarding and brood defence at a lower level than females, and hence seem to invest less than females. Broods were guarded under three distinct types: (1) female at the brood, male in surroundings, (2) parents take turns, or (3) parents stay together at the brood. Each pair used predominantly one type until the young swam freely, thereafter type 3. Females defended most in type 3, but male attack rate did not differ among the types. Type 3 seems related to increased risk of brood predation and type 2 to the female's foraging needs, being more common when she is small and the mates do not differ much in size. The unequal guarding times of type 1 indicate rather a low parental investment by the male (and thus risk of desertion) than specialization in roles on equal investment basis. Parental behaviour exhibited in aquaria differed in many ways from that in nature. The role types were indistinct and there were more signs of motivational conflict between the mates. Isolated pairs avoided joint guarding in the embryo period and while switching, female turns were much longer than male turns, unlike in nature. When intruders were added, males attacked them more than did females.

Male body size and mating success in swarms of the mayfly Epeorus longimanus

Epeorus longimanus is a widely distributed mayfly in the western United States that forms relatively large mating swarms. The operational sex ratio of swarms is highly male biased and males are potentially polygynous, suggesting that male‐male competition over mates may be intense. We investigated whether body size influenced male mating success in E. longimanus, as evidence of sexual selection. Males collected as mating pairs had significantly greater body lengths compared with males collected randomly from the swarm on each of six sampling dates examined, and had significantly greater head widths than males from random collections on two dates. There was no indication that large males occupied preferred positions within the swarm, and we suspect that the large male advantage may be due to greater success in pursuing females. We found no evidence of size‐assortative mating in E. longimanus indicating that males attempt to male with every female encountered, consistent with the brief copulatory period in mayflies and overall low parental investment of males.

Dominance and reproduction in a parthenogenetic lizard

Summary. In most vertebrates, males and females are believed to differ in terms of their investment in offspring. Dominance theory suggests that one way individuals of the sex with lower parental investment can increase reproductive success would be to dominate others of the same sex. The dominant competitors are thought to achieve preferred access to mates, and thus, have greater reproductive success than subordinates. Reproduction in parthenogenetic Cnemidophorus uniparens normally proceeds without males, but individuals exhibit mounting behaviors in captivity that are typical of closely related Cnemidophorus species that reproduce sexually. Thus, these animals provide an unusual opportunity to study the effects of behavior on reproduction apart from copulation and fertilization. In this study relationships between dominance and reproduction were investigated in the unisexual lizard species, C. uniparens. Dominance hierarchies were rapidly established and maintained in the laboratory by agonistic encounters among individuals. The number of times an individual charged its cagemates was positively correlated with the number of clutches and eggs laid. Also, dominant animals who charged their cagemates were likely to win agonistic encounters; recipients of charges usually fled. Hierarchies based on different behaviors were not all related to reproduction. Charges as a predictor of dominance was unrelated to body length, percent increase in body length and time spent in the basking site. However, individuals with a high percent increase in body length spent more time basking. This is likely a result of the increased energy demands of growth in addition to reproduction. Physiological stress as measured by plasma corticosterone titers was unrelated to dominance. We suggest that dominance is an important factor affecting reproduction in C. uniparens.

Parental care and EGG size in salamanders: An examination of the safe harbor hypothesis

SummaryThe safe harbor hypothesis includes the suggestion that parental care causes the embryonic stage to be the safest harbor, and, therefore, egg size will increase in populations with parental care to decrease the duration of subsequent, higher risk stages. Neither the safe habor hypothesis nor r and K theory seem adequate to explain the correlation between egg size and the presence/absence of parental care among salamanders, a group in which there is a further correlation between the larval (hatchling) habitat and egg size/parental care. Pond‐breeding salamanders generally have small eggs and lack parental care, and stream‐breeding salamanders generally have large eggs and parental care. I argue that the fundamental difference in the food available to hatchling salamanders between lentic (plankton‐rich) and lotic (plankton‐poor) environments selects for relatively lower parental investment in the lentic environment. From the standpoint of parental fitness, small (more numerous) hatchlings have a greater payoff where the available food is mall and dense (zooplankton in lentic environments), and large hatchlings are selectively advantageous where the food is of large size and less dense (benthic invertebrates in lotic environments). Selection for larger hatchlings in lotic environments results in longer embryonic periods and, ceteris paribus, greater total embryonic mortality. Embryo hiding and guarding have evolved among lotic‐breeding salamanders as compensatory mechanisms to reduce the rate of embryonic mortality. In this view, parental care is a consequence of selection for larger egg size and not an umbrella that allows egg size to increase, contrary to the safe harbor hypothesis.The relationship between variance in parental investment and food available to offspring, developed here for salamanders, may be of general significance. YosiakiItô, a critic of r and K theory, independently arrived at a similar conclusion from a broader data base.

Intersexual aggression and male sexual activity in captive rhesus macaques

Rape has been posited to be an outgrowth of male reproductive strategies. Forced copulations may have evolved as a consequence of the low parental investment made by males in producing and raising offspring. We designed a laboratory experiment which paired rhesus macaque males with females in order to assess the influence of intersexual aggression on male sexual activity. Younger and older adult males had comparable levels of sexual behavior, but younger males were more aggressive towards females than were older males. In addition, females threatened younger males more than older males. Male attacks on females did not result in sexual intercourse. On the contrary, a negative correlation existed between male aggression towards females and male success at achieving intromissions. Female aggression towards males appeared to be an effective tactic which reduced the chances of sexual intercourse. We conclude that intersexual aggression acts either as a mechanism of dominance assertion or as a means to increase spatial distance between individuals. These data do not support the idea that rape in humans has an evolutionary foundation derived from male reproductive strategies.

Sex Ratio in Umbonia crassicornis Amyot and Serville (Homoptera: Membracidae)

Mean sex ratio of Umbonia crassicornis Amyot and Serville offspring is biased toward females. Clutch size, but not the proportion of female offspring in the clutch, is related to female size. Survival of nymphs is, however, related to deviation from an equal sex ratio. We argue that nutrient quality received by offspring from the plant, rather than manipulation by the mother, influences sex ratio and the condition of offspring. INTRODUCTION Sex ratios favoring females are considered a major factor in the development of eusociality in insects, particularly the haplo-diploid eusocial Hymenoptera (Hamilton, 1964; Wilson, 1975; Trivers and Hare, 1976; but see Alexander, 1974; Alexander and Sherman, 1977). However, the basis for skewed sex ratios in diploid animals is poorly understood. Trivers and Willard (1973) suggest that sex ratio bias in mammals with low male parental investment could be influenced by the nutritional status of parent females at the time of reproduction. Control of sex ratios should occur in species where the reproductive success of males is highly variable compared to that of females. Since females in good condition are likely to produce strong progeny, they should bias their offspring toward sons which may experience greater reproductive success than their sisters. Conversely, a female in less than optimum nutritional condition should bias her offspring toward daughters since number of females is usually limiting and even weak daughters will find mates. This model (Trivers and Willard, 1973) is based on the following assumptions: (1) the condition of offspring is correlated to that of the parent; (2) the condition of offspring is maintained throughout adulthood, and (3) slight advantages in the adult male condition enhance reproductive success more than in females. Although this hypothesis has been explored for some mammals, there is no supporting evidence from insect studies (Thornhill, 1979). We examine if sex ratios in the presocial insect Umbonia crassicornis Amyot and Serville (Homoptera: Membracidae) support this hypothesis. Unlike other homopterans, females of some membracid species care for offspring (Wood, 1974, 1976a and b, 1977, 1978). Parent females of Umbonia crassicornis remain on eggs, make slits in the bark of the host plant to facilitate feeding by nymphs, maintain offspring aggregations and ward off potential predators. Maternal care is strongly correlated with nymphal survival, as the absence of parent females during the first three instars results in almost certain mortality of offspring (Wood, 1974, 1976a). Females do not desert offspring nor do aggregations of offspring move from the branch where eggs were deposited. Males make no investment in offspring except for gametes. Females mate only once while males mate several times. Most females are semelparous, but a small minority may deposit a second clutch.

Father Absence and Reproductive Strategy: An Evolutionary Perspective

Explanations offered by social scientists for the effects of father absence on children are reviewed; certain aspects of these interpretations are found wanting. Another explanation using theory from evolutionary biology is suggested: children show evolved, sensitive-period learning in early childhood which is linked to mother's pair-bond status or to mother's attitude toward males. As a result of children's perceptions a developmental track is established, which influences expression of reproductive strategy in adulthood. Male children born into matrifocal households exhibit at adolescence a complex of aggression, competition, low male parental investment, and derogation of females and feminity, while females show early expression of sexual interest and assumption of sexual activity, negative attitudes toward males, and poor ability to establish long-term relationships with one male. Male children reared in father-present or nuclear households show less interest in competitive dominance with other males and more interest in manipulation of nonhuman aspects of the environment, while females show delayed sexual interest and activity and a mating strategy directed at locating a male who will invest in her and her offspring.

Mating Behavior in the Streptocephalus Fairy Shrimps (Crustacea: Anostraca)

Mating behavior in the Streptocephalus fairy shrimps consists of the following behavior patterns: detection and orientation, station taking, clasping, intromission, and disengagement. Since males have low parental investment in their offspring and since males must compete for receptive females, sexual selection should favor males which mate with undiscrimi- nating eagerness. While observations reported here generally support this prediction, males discriminate against clearly unsuitable mates both before and during station-taking. Females should choose their mates carefully, based on some quality related to male fitness, since each clutch of eggs represents a large parental investment, but the criteria used by females in mate choice remain obscure. Bateman (1948), in an important discussion of sexual selection in Drosophila, speculated that if males have low parental investment compared to females, males should mate with undiscriminating eagerness while females should mate with discriminating passivity. He reasoned that the reproductive success of a male is limited by the number of females he inseminates and not by the amount of sperm produced. Males, then, should try to mate with as many females as possible. Since the fitness of a female is likely to be limited by egg production, females might be expected to maximize their reproductive investment by choosing their mates with respect to some genetic quality related to the male's fitness. Bateman's predictions serve to focus the present study of sexual behavior of the Streptocephalus fairy shrimps. These animals inhabit temporary ponds, primarily in arid and semi-arid regions. Pond duration, which is sometimes very brief, imposes an element of urgency in the reproductive strategy of fairy shrimps; that is, they must reproduce quickly and often. This aspect of their biology makes them convenient animals for studies of sexual behavior. A review of the available literature on fairy shrimp mating behavior can be found in Moore and Ogren (1962), and it includes no reference to studies of Streptocephalus behavior. Consequently this paper includes a description of the sequence of behavior patterns in Streptocephalus courtship. METHODS. Laboratory populations of Streptocephalus fairy shrimps were established from many eggs taken in soil samples from temporary pond habitats during the dry stage. Soil samples were placed in 4-liter jars and flooded with aerated, distilled water. The fairy shrimps which hatched under these conditions were fed daily with either cultured green algae or with a suspension of baker's yeast. The animals generally reached reproductive maturity within 2 weeks and continued to