Authors:R. Szőllősi, A. Medvegy, E. Benyes, A. Németh and E. Mihalik
Brys, R. and Jacquemyn, H. (2010): Floral display size and spatial distribution of potential mates affect pollen deposition and female reproductivesuccess in distylous Pulmonaria officinalis (Boraginaceae). — Plant Biol. 12 : 597
The purpose of the study was to examine whether coresidence with parents affects the reproductive success of daughters in modern Japanese society. In Study 1, I tested whether women who were living with parents at the time of marriage would experience earlier first childbirth. In Study 2, I tested whether women who were living with parents when their firstborn child was young would experience earlier second childbirth. Cox regression models were used to estimate the relative risk of reproduction, taking into account several potential confounders. The results indicated that parents-in-law, especially mothers-in-law (i.e., the husband's mother), exerted the strong positive effects on the reproduction of daughters. These findings imply that, in a traditionally patrilocal country such as Japan, the relationship between mother- and daughter-in-law influences reproductive success more than that between biological mother and daughter. It is thus necessary to consider cultural context when testing the impact of grandparental investment in modern society.
The ‘generalized Trivers-Willard hypothesis’ (gTWH) proposes that heritable traits associated with reproductive success of one sex will be positively associated with a genetic tendency to produce offspring of that sex. However, unlike the original Trivers-Willard hypothesis, the predictions of gTWH are proposed to be borne out regardless of environmental conditions. This is a problem because it ignores the influence of the hypothetical genetic variance in offspring sex-ratio on population operational sex-ratio and thus offspring's likely success in finding a mate. Accordingly, there is a notable lack of evidence to support the existence of such heritable variation in offspring sex-ratio in humans or other mammals. The genetic tendency for all individuals within populations of birds and mammals to produce a male offspring with the same probability as one another is well-established. In fact it is a cornerstone of population sex-ratio theory, upon which is built hypotheses of facultative (environmental) sex-ratio adjustment, including the original Trivers-Willard hypothesis. I therefore suggest that any phenotypic correlations between offspring sex-ratio and traits that may be associated with the reproductive success of offspring of one sex are most likely to be environmental in origin.
Authors:T. Landete-Castillejos, A. Garcia, S. Langton, I. Inglis, L. Gallego and J. Garde
There are two main theories explaining offspring sex biases in polygynous mammals. Trivers and Willard (1973) argue that mothers with greater reproductive resources should invest in the sex with the greater variance in reproductive success, usually sons. In contrast, because daughters in many polygynous mammals stay with their mother and compete with her for food, Local Resource Competition theory (e.g. Clark, 1978; Silk, 1983) predicts that the mothers with the greatest reproductive resources should invest in daughters. We investigated the strategy of sex allocation of a captive, outdoor population of 139 mouflon mothers, Ovis musimon, kept in a game state. A complex picture emerged in which, despite weight and body condition being correlated with age in female mouflons, mothers lambed more daughters with increasing age but also, within a given age, gave birth to more sons with increasing weight. Results may be useful in game management aimed at increasing the recruitment or quality o f males in managed populations.
In the vast majority of mammalian species, including humans, males provide less direct care to their offspring than females do. However, the theory of sexual selection suggests that the expression of paternal investment involves trade-offs between mating and parental effort associated with reproductive and survival related costs and benefits. In this view, different social and biological factors can distribute males' reproductive investment across parenting and mating behavior. As for social factors, the quality of resources held by males is one of the primary determinants of males' reproductive success. As for biological factors, the physical attractiveness is also highly correlated with males' mating success through enhanced access to females. In the present study the effect of males' socioeconomic status and facial attractiveness on direct childcare was tested on a sample of 81 Hungarian families. The first prediction was that males who possess lower status tend to engage more in direct childcare than males with higher status. This prediction was partially supported in our results. Second, we predicted that males rated more attractive provide less amount of direct paternal effort. The results seem to support this view in the case of men with higher socioeconomic status.
Facial attractiveness strongly affects person perception, with attractive individuals judged more favourably than, and preferred to, their less attractive peers. But what makes a face attractive and where do our preferences come from? Are they shaped by Madison Avenue and the media or have they evolved over millennia to enhance reproductive success? Good candidates for evolved preferences include preferences for average faces, symmetric faces, and faces with extreme sex typical traits. I will focus here on our preference for average faces. I will present evidence that average faces are attractive, and then consider how such a preference could have evolved. Preferences can evolve for traits that signal mate quality, and preferences can emerge as by-products of more general information-processing mechanisms. I will present evidence that both mechanisms contribute to the preference for average faces. Finally, I consider the role of experience in shaping our preference for average faces. This is an important role, because what is average depends on the particular population of faces we experience. I will present recent results showing that what looks average, and therefore attractive, can be rapidly modified by exposure to consistently distorted faces. I conclude that our preference for average faces reflects the operation of evolved mechanisms, which are tuned by experience.
PÉRUSSE, D. (1993): Cultural and reproductivesuccess in industrial societies: Testing the relationship at the proximate and ultimate levels. Behavioral and Brain Sciences , 16 , 267-322.
Cultural and reproductivesuccess in