Female differential allocation in response to extrapair offspring and social mate attractiveness

Renewed debate over what benefits females might gain from producing extra‐pair offspring emphasizes the possibility that apparent differences in quality between within‐pair and extra‐pair offspring are confounded by greater maternal investment in extra‐pair offspring. Moreover, the attractiveness of a female''s social mate can also influence contributions of both partners to a reproductive attempt. Here, we explore the complexities involved in parental investment decisions in response to extra‐pair offspring and mate attractiveness with a focus on the female point of view. Adult zebra finches paired and reproduced in a colony setting. A male''s early‐life diet quality and his extra‐pair reproductive success were used as metrics of his mating attractiveness. Females paired with males that achieved extra‐pair success laid heavier eggs than other females and spent less time attending their nests than their mates or other females. Extra‐pair nestlings were fed more protein‐rich hen''s egg than within‐pair nestlings. Females producing extra‐pair offspring had more surviving sons than females producing only within‐pair offspring. Collectively, results show that females differentially allocate resources in response to offspring extra‐pair status and their social mate''s attractiveness. Females may also obtain fitness benefits through the production of extra‐pair offspring.     

The effects of female control of resources on sex-differentiated mate preferences

A number of sex differences in mate preferences have been reported across cultures. Women prefer partners who are older than them whereas men prefer partners who are younger than them. Women have stronger preferences for resource-acquisition characteristics whereas men have stronger preferences for physical attractiveness. Recently, studies have reported shifts in female preferences with increasing female empowerment and associated female attitudes. Other studies, however, report opposite effects of female wealth and income. In this study, we investigated the effects of female control of the resources necessary to raise offspring successfully on mate preferences. We developed measures of resource control at the level of the individual and investigated relationships between these and mate preferences using an internet survey. Resource control was associated with preferences for physical attractiveness over good financial prospects and greater maximum partner age tolerated. Resource control, however, was also associated with tolerance of younger partners. The results implicate the role of constraints on female access to and control of resources in sex-differentiated mate preferences and highlight differences between resource control and wealth.     

Combined effects of host quality and local mate competition on sex allocation inLariophagus distinguendus

Summary Many parasitoid wasps are known to adjust sex ratio in response to either local mate competition (LMC) or host quality. Nevertheless, few studies have investigated the combined effects of these two factors on sex allocation. The sex allocation pattern inLariophagus distinguendus, a parasitoid of granary weevil larvae, is contrasted to the expectations of Werren's (1984) model combining LMC and host quality. Several predictions of the model are confirmed, but others are not. Sex ratio on both large and small hosts declines with proportion of small hosts attacked in a manner consistent with the model. However, when only one host size is parasitized, sex ratio is not independent of that host size, as predicted by the model. Various possibilities for the deviation between expected and observed are discussed. A partial LMC/host quality model is developed which allows for some matings outside the natal patch, and predictions of this model conform more closely to the pattern observed inL. distinguendus. Finally, the application of parasitoid studies to basic questions in evolutionary ecology is briefly discussed.     

Female mate value at a glance: relationship of waist-to-hip ratio to health,fecundity and attractiveness

A fundamental assumption of adaptive explanations of female attractiveness is that bodily features that males judge as attractive reliably signal youthfulness, healthiness, and fertility or female mate value. One of the bodily features, waist-to-hip ratio (WHR), is a reliable indicator of a female's reproductive age, sex hormone profile, parity and risk for various diseases. Systematic variation in the size of WHR also systematically affects the judgment of female attractiveness, healthiness, and youthfulness. This article summarizes recent findings about the relationship between female's WHR and various factors affecting reproductive capability and risk for diseases. Research on the relationship between attractiveness and WHR is discussed in light of some methodological objections to previous research. Finally, cross-cultural and historical data are presented that suggest that the relationship between WHR and female attractiveness is not culture-specific and not inculcated by modern Western fashion dictates or media.     

The influence of developmental mortality on optimal sex allocation under local mate competition

In panmictic populations, optimal sex allocation is, under theassumptions of Fisher's model, not influenced by the probabilityof offspring developmental mortality, or by differences in mortalitybetween the sexes. In contrast, when mating opportunities areconfined to siblings, developmental mortality can influenceoptimal sex allocation. Many animal species have both localmating and developmental mortality. We show that when developmentalmortality is random for individual offspring, optimal sex allocationis influenced by mortality among males but not among females.Male mortality increases the allocation to males, but this shouldnever be male biased, even under extreme male mortality. Thisresult applies both when mothers are able to control the sexof individual offspring precisely, and when sex is allocatedwith binomial probability. The influence of mortality becomesprogressively larger when the variance of the distribution ofmortality over clutches diminishes. The reduction in fitnessis greater than the proportion of mortality, especially at smallclutch sizes, and mortality reduces the advantage of producingprecise sex ratios, and of local mate competition in general.     

The masculinity paradox: facial masculinity and beardedness interact to determine women's ratings of men's facial attractiveness

In many species, male secondary sexual traits have evolved via female choice as they confer indirect (i.e. genetic) benefits or direct benefits such as enhanced fertility or survival. In humans, the role of men's characteristically masculine androgen‐dependent facial traits in determining men's attractiveness has presented an enduring paradox in studies of human mate preferences. Male‐typical facial features such as a pronounced brow ridge and a more robust jawline may signal underlying health, whereas beards may signal men's age and masculine social dominance. However, masculine faces are judged as more attractive for short‐term relationships over less masculine faces, whereas beards are judged as more attractive than clean‐shaven faces for long‐term relationships. Why such divergent effects occur between preferences for two sexually dimorphic traits remains unresolved. In this study, we used computer graphic manipulation to morph male faces varying in facial hair from clean‐shaven, light stubble, heavy stubble and full beards to appear more (+25% and +50%) or less (?25% and ?50%) masculine. Women (N = 8520) were assigned to treatments wherein they rated these stimuli for physical attractiveness in general, for a short‐term liaison or a long‐term relationship. Results showed a significant interaction between beardedness and masculinity on attractiveness ratings. Masculinized and, to an even greater extent, feminized faces were less attractive than unmanipulated faces when all were clean‐shaven, and stubble and beards dampened the polarizing effects of extreme masculinity and femininity. Relationship context also had effects on ratings, with facial hair enhancing long‐term, and not short‐term, attractiveness. Effects of facial masculinization appear to have been due to small differences in the relative attractiveness of each masculinity level under the three treatment conditions and not to any change in the order of their attractiveness. Our findings suggest that beardedness may be attractive when judging long‐term relationships as a signal of intrasexual formidability and the potential to provide direct benefits to females. More generally, our results hint at a divergence of signalling function, which may result in a subtle trade‐off in women's preferences, for two highly sexually dimorphic androgen‐dependent facial traits.     

The adaptive value of humor and laughter

Most explanations for humor neglect important types of humor, such as tickling and word play; or raise difficult evolutionary theoretical problems, such as group selection, dubious fitness benefits, and excessive complexity of design; or ignore the data on humor and laughter. The present theory was based on the following observations. Tickling entails a mock attack at vulnerable body spots, and may provide youngsters with practice in defending themselves. The child's laughter is pleasant and encourages the tickler to persist. Similarly, juvenile primates including children encourage roughhousing by laughter and other emotional expressions. We also laugh at humorous content that provides striking counter-examples (incongruities), as in word play, or that informs us about fitness-relevant topics such as sexual, aggressive, and social poise scenarios. The present theory is that the pleasure of humor motivates us to seek out poignant, fitness- enhancing input of this sort. Laughter evolved to allow us to continue to recieve amusement. Laughter is a pleasant social signal that prompts the humorist to persist in providing this edifying stimulation. In response to true wit, laughter conveys appreciation and gratitude—an intention to reciprocate for having received a stimulating idea. Thus, humor benefits both humorist and laughter. This theory and others are evaluated in the light of evolutionary principles and relevant data.     

Polarity-dependent transcranial direct current stimulation effects on central auditory processing

Given the polarity dependent effects of transcranial direct current stimulation (tDCS) in facilitating or inhibiting neuronal processing, and tDCS effects on pitch perception, we tested the effects of tDCS on temporal aspects of auditory processing. We aimed to change baseline activity of the auditory cortex using tDCS as to modulate temporal aspects of auditory processing in healthy subjects without hearing impairment. Eleven subjects received 2mA bilateral anodal, cathodal and sham tDCS over auditory cortex in a randomized and counterbalanced order. Subjects were evaluated by the Random Gap Detection Test (RGDT), a test measuring temporal processing abilities in the auditory domain, before and during the stimulation. Statistical analysis revealed a significant interaction effect of time vs. tDCS condition for 4000 Hz and for clicks. Post-hoc tests showed significant differences according to stimulation polarity on RGDT performance: anodal improved 22.5% and cathodal decreased 54.5% subjects' performance, as compared to baseline. For clicks, anodal also increased performance in 29.4% when compared to baseline. tDCS presented polarity-dependent effects on the activity of the auditory cortex, which results in a positive or negative impact in a temporal resolution task performance. These results encourage further studies exploring tDCS in central auditory processing disorders.     

Energetic costs, underlying resource allocation patterns, and adaptive value of predator-induced life-history shifts

We studied costs and benefits of life history shifts of water fleas (genus Daphnia ) in response to infochemicals from planktivorous fish. We applied a dynamic energy budget model to investigate the resource allocation patterns underlying the observed life history shifts and their adaptive value under size selective predation in one coherent analysis. Using a published data set of life history shifts in response to fish infochemicals we show that Daphnia invests less energy in somatic growth in the fish treatment. This observation complies with theoretical predictions on optimal resource allocation. However, the observed patterns of phenotypic plasticity cannot be explained by changes in resource allocation patterns alone because our model-based analysis of the empirical data clearly identified additional bioenergetic costs in the fish treatments. Consequently, the response to fish kairomone only becomes adaptive if the intensity of size selective predation surpasses a certain critical level. We believe that this is the first study that puts resource allocation, energetic costs, and adaptive value of predator induced life-history shifts – using empirical data – into one theoretical framework.     

Impact of market value on human mate choice decisions

Mate choice strategies are a process of negotiation in which individuals make bids that are constrained by their status in the market place. Humans provide an unusual perspective on this because we can measure their explicitly expressed preferences before they are forced to make any choices. We use advertisements placed in newspaper personal columns to examine, first, the extent to which evolutionary considerations affect the level of competition (or market value) during the reproductively active period of people's lives and, second, the extent to which market value influences individual's willingness to make strong demands of prospective mates. We show that female market value is determined principally by women's fecundity (and, to a lesser extent, reproductive value), while male market value is determined by men's earning potential and the risk of future pairbond termination (the conjoint probability that the male will either die or divorce his partner during the next 20 years). We then show that these selection preferences strongly influence the levels of demands that men and women make of prospective partners (although older males tend to overestimate their market value).     

An effect of mate fertility on the attractiveness and oviposition rates of mated Drosophila melanogaster females

Mate fertility has a strong influence on the sexual receptivity of mated Drosophila melanogaster females, but an effect of mate fertility on the attractiveness of mated females has not previously been demonstrated. We compared the declines in attractiveness over the first 10 h after mating for females mated to fertile (XY) males and those mated to sterile (XO) males, and found a significant effect of mate fertility. A large and significant decrease in attractiveness, that is the same for both XY- and XO-mated females, is evident during the first 4 h after mating. However, a further decline in attractiveness occurs between 4 and 6 h after mating for XY-mated females, but not until between 6 and 10 h after mating for females with sterile mates. Thus, XY-mated females are significantly less attractive than XO-mated females at 6–8 h post-mating, but not at any other time. A sharp increase in oviposition rates for both types of mated females is associated with the decline in attractiveness that occurs between 4 and 10 h after mating.     

Learning to speciate: The biased learning of mate preferences promotes adaptive radiation

Bursts of rapid repeated speciation called adaptive radiations have generated much of Earth's biodiversity and fascinated biologists since Darwin, but we still do not know why some lineages radiate and others do not. Understanding what causes assortative mating to evolve rapidly and repeatedly in the same lineage is key to understanding adaptive radiation. Many species that have undergone adaptive radiations exhibit mate preference learning, where individuals acquire mate preferences by observing the phenotypes of other members of their populations. Mate preference learning can be biased if individuals also learn phenotypes to avoid in mates, and shift their preferences away from these avoided phenotypes. We used individual‐based computational simulations to study whether biased and unbiased mate preference learning promotes ecological speciation and adaptive radiation. We found that ecological speciation can be rapid and repeated when mate preferences are biased, but is inhibited when mate preferences are learned without bias. Our results suggest that biased mate preference learning may play an important role in generating animal biodiversity through adaptive radiation.     

Low fertility in contemporary humans and the mate value of their children: sex-specific effects on social status indicators

Evolutionary explanations of low fertility in modern affluent societies commonly state that low fertility is the outcome of high parental investments in the quality of their children. Although the empirical evidence that modern parents do face a quantity–quality trade-off is strong, two issues that are relevant from an evolutionary perspective have not received much attention. First, sex differences in the proximate aspects of quality have been largely ignored. Second, the relationship between the quantity of children and their reproductive success in contemporary low-fertility societies remains unclear. In this article, we study the quantity–quality trade-off as a trade-off between the number of children and the mate value and reproductive success of those children. We examine the trade-off in two steps. First, a lower number of children is expected to increase the mate value of these children. Second, greater mate value is expected to lead to greater reproductive success. Using sex-specific indicators of mate value, we test these hypotheses in a representative sample of the Dutch population aged 55–85 in 1992 (n=3229). This sample contains information on three successive generations in which the middle generation has completed fertility. We find support for the first hypothesis, but only partial support for the second hypothesis. A higher number of children is traded off against the mate value of the children, but not against their reproductive success. We conclude that the conditions under which the quantity of children is traded off against their reproductive success depend on the social environment.     

The adaptive value of phenotypic floral integration

Floral integration has been deemed an adaptation to increase the benefits of animal pollination, yet no attempts have been made to estimate its adaptive value under natural conditions. Here, the variation in the magnitude and pattern of phenotypic floral integration and the variance-covariance structure of floral traits in four species of Rosaceae were examined. The intensity of natural selection acting on floral phenotypic integration was also estimated and the available evidence regarding the magnitude of floral integration reviewed. The species studied had similar degrees of floral integration, although significant differences were observed in their variance-covariance structure. Selection acted on subsets of floral traits (i.e. selection on intrafloral integration) rather than on the integration of the whole flower. Average integration was 20% and similar to the estimated mean value of flowering plants. The review indicated that flowering plants present lower integration than expected by chance. Numerical simulations suggest that this pattern may result from selection favouring intrafloral integration. Phenotypic integration at the flower level seems to have a low adaptive value among the species surveyed. Moreover, it is proposed that pollinator-mediated selection promotes the evolution of intrafloral integration.     

The functional responses of adaptive consumers of two resources

This article investigates some aspects of the shape of the functional responses of consumers that utilize two resources. Adaptive variation in consumption behavior is shown to have a major effect on the relationship between amount of resource available and its rate of consumption by an average consumer individual. The effects of adaptive variation are dependent on the nutritional status of the two resources. If the resources are linearly substitutable, increases in the density of resource i will usually increase the quantity, functional response on i divided by density of i, and increases in the density of resource j will decrease this quantity. The result is that the functional response to resource i will generally decrease with the density of resource j, and will increase faster than it would otherwise have increased with the density of resource i. If resources are nonsubstitutable, an adaptive functional response to resource i will increase with the density of resource j, and it will increase more slowly with the density of resource i than it would have without adaptive change. If resources are both complementary and substitutable, the functional response will exhibit ranges of smooth change separated by rapid jumps between values, and different ranges of resource densities will result in a functional response with the characteristics of linearly substitutable or of non-substitutable resources. Adaptive functional response shape is dependent upon the tradeoff involved in raising each functional response. These results have implications for the types of indirect interactions that occur between resources as the result of a common consumer's functional response. They also suggest that the adaptive response of competing consumers to each other will differ depending on the nutritional status of the resources for which they are competing. Implications of these findings for consumer growth isocline shape and several other issues are explored.     

The economic value of the Earth's resources

Economics is the driving force of today's widespread environmental destruction. Markets undervalue the earth's resources and compound their overuse. Since World War II the world has used resources voraciously. The situation can be described as the industrial countries overconsuming resources, which are overextracted and exported by developing countries and traded at prices that are lower than the social costs. Resource-intensive patterns of growth and trade are Inefficient for the world economy, and lead to tragic maldistribution of the Earth's riches. They should be replaced by knowledge-intensive patterns of growth. Information technology and the environmental agenda are two of the most important trends in the world economy. Together they can lead to growth that is Intrinsically compatible with the environment.