Male Parental Investment Research Articles

Prospecting movements link phenotypic traits to female annual potential fitness in a nocturnal predator

Recent biologging technology reveals hidden life and breeding strategies of nocturnal animals. Combining animal movement patterns with individual characteristics and landscape features can uncover meaningful behaviours that directly influence fitness. Consequently, defining the proximate mechanisms and adaptive value of the identified behaviours is of paramount importance. Breeding female barn owls (Tyto alba), a colour-polymorphic species, recurrently visit other nest boxes at night. We described and quantified this behaviour for the first time, linking it with possible drivers, and individual fitness. We GPS-equipped 178 female barn owls and 122 male partners from 2016 to 2020 in western Switzerland during the chick rearing phase. We observed that 111 (65%) of the tracked breeding females were (re)visiting nest boxes while still carrying out their first brood. We modelled their prospecting parameters as a function of brood-, individual- and partner-related variables and found that female feather eumelanism predicted the emergence of prospecting behaviour (less melanic females are usually prospecting). More importantly we found that increasing male parental investment (e.g., feeding rate) increased female prospecting efforts. Ultimately, females would (re)visit a nest more often if they had used it in the past and were more likely to lay a second clutch afterwards, consequently having higher annual fecundity than non-prospecting females. Despite these apparent immediate benefits, they did not fledge more chicks. Through biologging and long-term field monitoring, we highlight how phenotypic traits (melanism and parental investment) can be related to movement patterns and the annual potential reproductive output (fecundity) of female barn owls.

Genetic Parent-Offspring Relationships Predict Sexual Differences in Contributions to Parental Care in the Eurasian Tree Sparrow

Negative relationships between the degree of parental investment and the presence of unrelated offspring in the nest due to extra-pair paternity (EPP) or conspecific brood parasitism (CBP) are predicted in monogamous species. This is because investing in unrelated offspring is costly to individual parents. However, such strategies may be adaptive for one social partner. Because parental investment changes in response to that by the social partner, the predicted relationship needs to be assessed empirically in wild animal populations, with consideration for male and female parental care. Furthermore, both EPP and CBP must be considered simultaneously in such a study. In this study, we tackled the issue using the semi-colonial Eurasian Tree Sparrow Passer montanus, in which both EPP and CBP were predicted to occur. We tested whether there is a negative relationship between the degree of parental care of both males and females and the presence of EPP or CBP, taking into consideration the parental investment of their social partners, using behavioral observations and parentage analyses based on seven microsatellite loci. The results revealed a moderately high frequency of EPP and CBP within a sparrow colony. A negative relationship between parental care by the social male parent and the presence of EPP was suggested, while this was possibly as a result of the increase in parental investment by their female partner. CBP was also inferred to be linked with male parental investment, while females may have compensated for the cost of CBP in their provisioning efforts by egg rejection. High frequencies of occurrence of both EPP and CBP allowed us to shed light on how parental investment is related to the presence of unrelated young in the complex social system of the Eurasian Tree Sparrow.

Paternity sharing in insects with female competition for nuptial gifts.

Male parental investment is expected to be associated with high confidence of paternity. Studies of species with exclusive male parental care have provided support for this hypothesis because mating typically co-occurs with each oviposition, allowing control over paternity and the allocation of care. However, in systems where males invest by feeding mates (typically arthropods), mating (and thus the investment) is separated from egg-laying, resulting in less control over insemination, as male ejaculates compete with rival sperm stored by females, and a greater risk of investing in unrelated offspring (cuckoldry). As strong selection on males to increase paternity would compromise the fitness of all a female's other mates that make costly nutrient contributions, paternity sharing (males not excluded from siring offspring) is an expected outcome of sperm competition. Using wild-caught females in an orthopteran and a dipteran species, in which sexually selected, ornamented females compete for male nuptial food gifts needed for successful reproduction, we examined paternity patterns and compared them with findings in other insects. We used microsatellite analysis of offspring (lifetime reproduction in the orthopteran) and stored sperm from wild-caught females in both study species. As predicted, there was evidence of shared paternity as few males failed to sire offspring. Further support for paternity sharing is the lack of last-male sperm precedence in our study species. Although paternity was not equal among sires, our estimates of paternity bias were similar to other insects with valuable nuptial gifts and contrasted with the finding that males are frequently excluded from siring offspring in species where males supply little more than sperm. This suggests paternity bias may be reduced in nuptial-gift systems and may help facilitate the evolution of these paternal investments.

Extra-pair paternity in a species with frequent extra-pair courtship feedings, few extra-pair copulations, and male-biased parental care

Patterns of extra pair paternity (EPP) and intraspecific brood parasitism (IBP) were studied in a Whiskered Tern Chlidonias hybrida population characterized by female brood desertion, a high level of extra pair courtship feedings (10%) and a low level of extra pair copulation (EPC; 0.6%). In this study, we used a set of microsatellite loci to analyse parentage in 56 Whiskered Tern families from southern Poland. Depending on the method, we detected that 1.4%–3.6% of chicks were sired by an extra-pair male, and extra-pair chicks were present in 3.6%–8.9% of broods. IBP was observed in 8.9%–14.3% of broods, corresponding to 3.6%–6.4% of the chicks. The low rate of EPP is in agreement with the hypothesis that in species with high male parental investment, females should avoid EPC. The low level of IBP indicates that intraspecific egg dumping is not a common female strategy in Whiskered Tern, similar to many other colonial waterbird species.

Hoopoe Upupa epops male feeding effort is related to female cosmetic egg colouration

Avian eggshell colouration might function as a post‐mating sexually selected signal of female quality, influencing male parental investment and, hence, reproductive success. This hypothesis has been tested for intrinsic eggshell pigments as biliverdin (blue‐green colouration) and/or protoporphyrin (brown coloured spots), but never for colourations applied post‐laying. Post‐laying staining colouration due to, for instance, uropygial secretion of the female could reflect its phenotypic properties and, thus, might be a cue for male investment in reproduction. In hoopoes, the uropygial gland of incubating females hosts symbiotic bacteria that are responsible for the brown colour of their uropygial secretion and of the eggshells, as they cover their bluish‐grey eggshells with gland secretion after laying. The secretion protects embryos from pathogenic trans‐shell infections and, thus, egg colouration may function as a cue or even as a post‐mating sexually selected signal of antimicrobial potential in hoopoes. In a wild hoopoe population breeding in nest boxes in Spain, we test this hypothesis by exploring whether egg colour predicts male parental investment. In accordance with the hypothesis, we found that the amount of food provided by males to incubating females was higher in nests with less saturated eggshell colours. This relationship was affected by female body condition. High quality females in terms of body condition and/or in secretion colour obtained better males in terms of provisioning effort during incubation. Given that eggshell saturation is negatively related to density of bacterial symbionts in uropygial secretions, one possibility is that males may regulate their parental investment in accordance to the expected characteristics of mutualistic bacteria hosted in uropygial glands and deposited on eggshells. We discuss alternative explanations for our results, concluding that the post‐mating sexual selection hypothesis is the most likely but experimental modification of egg colour is needed to test it further.

Compete then Care: Shifts in Male Reproductive Strategies Over the Life Course in a Polygynous Mammal

In polygynous species, there is often intense intra-sexual competition over access to females and high reproductive skew, and males invest more in mating effort than parenting effort. However, the benefits of investments in mating effort and parenting effort may change systematically over the course of males’ lives. In many polygynous mammalian species, there is an ∩-shaped relationship between age, condition, and resource holding power as middle-aged males that are in prime physical condition outcompete older and younger males. As males age, and their competitive abilities decline, males might benefit from reallocating investment from mating effort to parenting effort. We examined the effects of male age and paternity on the likelihood that male olive baboons, Papio anubis, would invest in parenting effort. Male baboons compete for high ranking positions in the group, and there is an ∩-shaped relationship between male age and dominance rank. High ranking males sire more infants than lower ranking males. Males and lactating females often form close ties (primary associates), and females’ primary associates are likely to be the sires of their infants. Males are attentive to their primary associates’ distress, support them in conflicts, and buffer their infants from rough handling and harassment. Here, we show that males are more likely to become the primary associates of lactating females as they age and their competitive abilities decline. These results suggest that fitness benefits derived from male parental investment may favor an extended post-reproductive lifespan in species in which males can identify their own offspring and positively affect their welfare.

Male parental investment reflects the level of partner contributions and brood value in tree swallows

Biparental care presents an interesting case of cooperation and conflict between unrelated individuals. Several models have been proposed to explain how parents should respond to changes in each other’s parental care to maximize their own fitness, predicting no change, partial compensation, or matching effort as a response. Here, we present an experiment in tree swallows (Tachycineta bicolor) in which we increased the offspring provisioning of females by presenting them, but not their mates, with additional nestling begging calls using automated playbacks. We performed this experiment in two populations differing in future breeding opportunities. We found that in response to a temporary increase in female parental effort, males in the northern population (with lower future breeding opportunities and thus higher brood value) matched the increased effort, whereas males in the southern population did not. We also found that increases in parental care during playbacks were driven by the females (i.e., females initiated the increased effort and their mates followed them) in the northern population but not the southern population. These results support the idea that with incomplete information about the brood value and need, cues or signals from the partner might become important in coordinating parental care. Male tree swallows increase parental effort when their mates need to work harder. Using an automated system, we broadcast playback of hungry nestling calls only when the female parent was visiting the nest. In a population where the value of the current brood was high, males significantly increased their provisioning rate, much more than their partners did. Since only the females could hear the playbacks, and the begging of the nestlings did not change in response to the treatment, we suggest that either the males used their partner’s feeding rate as a cue or the females may have communicated to their mates that they should work harder. These results suggest that cues or signals from the partner may be important in coordinating parental care.

Comparative studies need to rely both on sound natural history data and on excellent statistical analysis.

We certainly agree with Schradin [1] that comparative studies need to use the best information available—as well as clear definitions, up-to-date statistical techniques and common sense. We have divided our response into two sections: the first dealing with Schradin's critique of our 2017 paper and the classification of the social organization of shrews; the second dealing with three general issues that his commentary raises. The paper that Schradin is commenting on [2] asks whether cooperative breeders (which we define as species where non-breeding helpers assist breeders to raise their young) in mammals are more commonly found in arid environments than monogamous species (defined as species where breeding pairs of males and females remain together for more than one season) from which cooperative breeders appear to be derived [3]. It shows that, as in birds, cooperative breeders tend to live in relatively arid habitats compared to monogamous species. As we describe below, these conclusions are unaffected by differences between our classification of the social organization of shrews and the classification suggested by Schradin. Schradin's first criticism is that the categorizations of shrews that we have used in this analysis were based on one paper on a single species. This is incorrect, for our categorization of shrews was based on more than 70 separate sources (see electronic supplementary material, appendix S1). When we published our dataset [4], we were required to reduce the associated reference list by the editors of the journal and, to comply, we removed around 75% of our 2000+ sources, often listing a single reference per species or group of species, and frequently using generic reviews for particular groups where these were available: for example, for many rodent species, we simply listed Wolff and Sherman's Rodent Societies [5], and …

Adult sex ratio and social status predict mating and parenting strategies in Northern Ireland.

Evidence from animal species indicates that a male-biased adult sex ratio (ASR) can lead to higher levels of male parental investment and that there is heterogeneity in behavioural responses to mate scarcity depending on mate value. In humans, however, there is little consistent evidence of the effect of the ASR on pair-bond stability and parental investment and even less of how it varies by an individual's mate value. In this paper we use detailed census data from Northern Ireland to test the association between the ASR and pair-bond stability and parental investment by social status (education and social class) as a proxy for mate value. We find evidence that female, but not male, cohabitation is associated with the ASR. In female-biased areas women with low education are less likely to be in a stable pair-bond than highly educated women, but in male-biased areas women with the lowest education are as likely to be in a stable pair-bond as their most highly educated peers. For both sexes risk of separation is greater at female-biased sex ratios. Lastly, our data show a weak relationship between parental investment and the ASR that depends on social class. We discuss these results in the light of recent reformulations of parental investment theory.This article is part of the themed issue 'Adult sex ratios and reproductive decisions: a critical re-examination of sex differences in human and animal societies'.

Deadbeats or losers: Discretionary male parental investment can make females less choosy

Two of the most important reproductive decisions that animals face are how to choose mates and how to invest in offspring. In species where both males and females provide offspring care, these selection pressures will often be reciprocally intertwined: mate preferences may depend on parental investment patterns while parental investment patterns may depend on mate preferences. We describe and analyze a mathematical model of this interaction, in which females can choose amongst males who have high attractiveness or low attractiveness, while males can decide whether to provide offspring care. We compare the case where males decide whether to provide care to the cases where males always provide care and where they never provide care. For a wide range of parameter settings, we find that when males decide whether to provide care, females are selected to be less choosy. This reduction in female choosiness occurs even though discretionary male care leads to greater variation among males in their offspring output. This finding contrasts with previous theoretical studies, and is driven by our assumption that males can decide whether to help provide care after mating occurs. Our results show how the interdependencies between mate choice and parental care can generate outcomes that can only be understood by considering both processes simultaneously.

Religious Veiling as a Mate-Guarding Strategy: Effects of Environmental Pressures on Cultural Practices

Male parental investment can contribute to the fitness of both sexes through increased fertility and child survivorship. The level and intensity of parental investment are dependent upon ecological variations: in harsh and demanding environments, the need for biparental care increases. Moreover, when environmental pressures increase, uncertainty over paternity may lead to favoring stricter mate-guarding practices, thus directing males to invest more effort toward controlling and guarding their mates from infidelity. In this paper, we test the hypothesis that religious veiling, as a social and cultural practice which regulates and restricts sexuality, will be more important in harsher environments. Our results show that harsh and demanding environments are associated with the importance of religious veiling and the level of religiosity, providing a link between cultural practices such as religious veiling and ecological variation.

Edith Wharton in Washington, 2–4 June 2016

Edith Wharton in Washington, 2–4 June 2016

Salivary oxytocin increases concurrently with testosterone and time away from home among returning Tsimane' hunters.

Oxytocin, testosterone and cortisol can have opposing effects on social behaviour, yet few studies have examined their interactions. We measured changes in salivary oxytocin, testosterone and cortisol among Tsimane' men returning home after hunting, an ancient context of male status competition, parental investment and cooperation. Contra normal diurnal rhythm, oxytocin increased relative to baseline and this increase was positively associated with duration of the hunt and change in testosterone, but not cortisol, social context, hunting outcome or physical activity. The concurrent increase in endogenous peripheral oxytocin and testosterone is unexpected given their opposing independent effects on social cognition and behaviour, and has not been observed before. We discuss the potential significance of these effects for the biology of pair-bonding, parenting and social foraging in humans and other species.

Structure and function of the cassowary's casque and its implications for cassowary history, biology and evolution

Cassowaries (Casuarius) possess a cranial casque, sheathed by keratin and composed of modified cranial bones. We combine data and hypotheses on three areas of cassowary research. First, we present novel observations on casque anatomy. The bony core is fragile, incorporating a mass of trabeculae anteriorly and an empty space posteriorly. Secondly, we use these observations to evaluate hypotheses of casque function. Implications that the casque evolved within the context of activities involving percussive actions are unlikely and observations that might support these hypotheses are absent. It is most likely that the casque serves a sociosexual role and functions in visual and acoustic display. The similarity in casque form between males and females, combined with male parental investment, makes it plausible that the extravagant structures present in cassowaries evolved within the context of mutual sexual selection. Thirdly, we combine morphological, molecular and geological evidence to provide a new phylogenetic history for cassowaries. We suggest that cassowaries invaded New Guinea in at least two waves and provisionally regard crown–cassowaries as a geologically young, post-Pliocene clade. We provide these hypotheses as areas requiring discussion and urge other workers to test our ideas with new data on cassowary anatomy, behaviour and genetics.

Female economic dependence and the morality of promiscuity.

In environments in which female economic dependence on a male mate is higher, male parental investment is more essential. In such environments, therefore, both sexes should value paternity certainty more and thus object more to promiscuity (because promiscuity undermines paternity certainty). We tested this theory of anti-promiscuity morality in two studies (N = 656 and N = 4,626) using U.S. samples. In both, we examined whether opposition to promiscuity was higher among people who perceived greater female economic dependence in their social network. In Study 2, we also tested whether economic indicators of female economic dependence (e.g., female income, welfare availability) predicted anti-promiscuity morality at the state level. Results from both studies supported the proposed theory. At the individual level, perceived female economic dependence explained significant variance in anti-promiscuity morality, even after controlling for variance explained by age, sex, religiosity, political conservatism, and the anti-promiscuity views of geographical neighbors. At the state level, median female income was strongly negatively related to anti-promiscuity morality and this relationship was fully mediated by perceived female economic dependence. These results were consistent with the view that anti-promiscuity beliefs may function to promote paternity certainty in circumstances where male parental investment is particularly important.

Fathers are just as good as mothers at recognizing the cries of their baby

Previous investigations of parents' abilities to recognize the cries of their own babies have identified substantial and significant sex differences, with mothers showing greater correct recognition rates than fathers. Such sex differences in parenting abilities are common in non-human mammals and usually attributed to differential evolutionary pressures on male and female parental investment. However, in humans the traditional concept of 'maternal instinct' has received little empirical support and is incongruous given our evolutionary past as cooperative breeders. Here we use a controlled experimental design to show that both fathers and mothers can reliably and equally recognize their own baby from their cries, and that the only crucial factor affecting this ability is the amount of time spent by the parent with their own baby. These results highlight the importance of exposure and learning in the development of this ability, which may rely on shared auditory and cognitive abilities rather than sex-specific innate predispositions.

Does egg colouration signal female and egg quality in reed warbler (Acrocephalus scirpaceus)?

To explain the evolution of egg colouration in open cup nesting species, a number of functions have been suggested. Recent studies focus on the role of eggshell colour as a postmating sexually selected trait of females which manipulates male parental investment. A basic prediction of this hypothesis is that egg pigmentation reflects female quality. In this study we examine whether there is a relationship between eggshell colouration and either female quality or egg quality in reed warblers. This open cup nesting species has eggs that are heavily spotted with brownish marks on a bluish-green background. We used several parameters describing female and egg quality, and measured eggshell colouration at the blunt pole and the egg centre, deriving four colour variables from colour spectrometry. To determine egg quality parameters, the third egg of each clutch was sampled and analysed. To determine female quality, females were trapped shortly after egg laying, and several morphological and a single conditional variable were determined. Additionally, a blood sample was taken to determine blood parasites (avian malaria and Trypanosoma spp.) and a faecal sample to determine intestinal parasites (Isospora spp). Our results revealed that eggshell pigmentation appears to be independent of female condition and parasites, but reflects concentrations of egg compounds such as testosterone and lysozyme. Egg colouration is also related to yolk weight and egg size. Our results further suggested that the information about colour varies depending on the position on the egg (blunt pole or egg centre). The only relationship with females was between female size (tarsus length) and egg colouration, which suggests a genetic component. We discuss reasons for the absence of a relationship between egg colouration and female quality.

Parental care and UV coloration in blue tits: opposite correlations in males and females between provisioning rate and mate’s coloration

Parental investment and sexually‐selected signals can be intimately related, either because the signals indicate the amount of investment that an individual is prepared to make, and hence its value as a mate (the ‘good parent process’), or because individuals are selected to vary their own investment in relation to their mate’s signals (‘differential allocation’ or ‘reproductive compensation’). Correlations between parental investment and the sexually selected signals of both an individual and its mate are therefore of central interest in sexual selection. Blue tits Cyanistes caeruleus are an ideal study species to investigate such correlations because they provide substantial amounts of biparental care and possess sexually‐selected structural UV coloration that seems to signal attractiveness in both sexes. We investigated whether feeding rates of male and female blue tits were correlated with either their own or their mate’s UV coloration, and whether any such correlation was affected by the sex ratio of the brood. We also investigated whether any such correlations were reflected in offspring phenotype. Feeding rates were not correlated with either sex of parent’s own UV coloration. However, they were correlated with the mate’s UV coloration, but in opposite directions in males and females: females had higher feeding rates when mated to bright UV males, implying differential allocation, while males had lower feeding rates when mated to bright UV females, implying reproductive compensation. These relationships were unaffected by the sex ratio of the brood. In addition, fledgling tarsus length, but not mass, was related to male UV coloration, and to female UV coloration in interaction with male age. These results suggest that both male and female attractiveness influence parental investment of the mate, and that this in turn affects offspring phenotype. We found no evidence for differential sex allocation.

Religious cognition down-regulates sexually selected, characteristically male behaviors in men, but not in women

Men are typically stronger, riskier, “showier,” and more impulsive than women. According to sexual selection theory, such behaviors may have enhanced reproductive fitness for ancestral human males. However, such behaviors are facultative, and the mechanisms that cause them respond to social and environmental cues that indicate whether outlays of strength, risk-taking, showing off, or impulsivity are likely to lead to payoffs in any given instance. Recent research based on the Reproductive Religiosity Model suggests that, in contemporary Western societies, religious beliefs and institutions are differentially espoused and promulgated by restricted sexual strategists (whose reproductive strategies focus on high fertility, monogamy, and high parental care) to limit the exercise of unrestricted sexuality, which threatens the viability of restricted sexual strategies (e.g., by reducing paternity certainty and male parental investment). On this basis, we hypothesized that experimental manipulations of religious cognition would reduce men's impulsivity and motivation to demonstrate their physical prowess. Supporting this hypothesis, three experiments revealed that priming participants with religious concepts (i.e., participants wrote essays about religion, read an essay supporting the existence of an afterlife, or were implicitly exposed to religious words) reduced men's (but not women's) impulsivity with money and their physical endurance on a hand grip task. The primes affected men's behaviors irrespectively of men's scores on a self-report measure of religious commitment.

Mating by proxy: a novel perspective to donor conception

How single, partnered lesbian, and partnered heterosexual women undertaking donor insemination rate the importance of donor characteristics is explored in the context of Trivers's parental investment theory. Consistent with this theory, single women placed higher value on biographical traits reflective of the donor's level of potential resources (occupation, hobbies, age) and good character compared with either partnered lesbian or heterosexual women.