Sex investment ratios in eusocial Hymenoptera support inclusive fitness theory

Inclusive fitness theory predicts that sex investment ratios in eusocial Hymenoptera are a function of the relatedness asymmetry (relative relatedness to females and males) of the individuals controlling sex allocation. In monogynous ants (with one queen per colony), assuming worker control, the theory therefore predicts female-biased sex investment ratios, as found in natural populations. Recently, E.O. Wilson and M.A. Nowak criticized this explanation and presented an alternative hypothesis. The Wilson–Nowak sex ratio hypothesis proposes that, in monogynous ants, there is selection for a 1 : 1 numerical sex ratio to avoid males remaining unmated, which, given queens exceed males in size, results in a female-biased sex investment ratio. The hypothesis also asserts that, contrary to inclusive fitness theory, queens not workers control sex allocation and queen–worker conflict over sex allocation is absent. Here, I argue that the Wilson–Nowak sex ratio hypothesis is flawed because it contradicts Fisher’s sex ratio theory, which shows that selection on sex ratio does not maximize the number of mated offspring and that the sex ratio proposed by the hypothesis is not an equilibrium for the queen. In addition, the hypothesis is not supported by empirical evidence, as it fails to explain ‘split’ (bimodal) sex ratios or data showing queen and worker control and ongoing queen–worker conflict. By contrast, these phenomena match predictions of inclusive fitness theory. Hence, the Wilson–Nowak sex ratio hypothesis fails both as an alternative hypothesis for sex investment ratios in eusocial Hymenoptera and as a critique of inclusive fitness theory

Cadmium in newborns

Cadmium (Cd) is a well-known nephrotoxic environmental contaminant but there are indications that the developing nervous system might be even more sensitive to Cd than the kidneys in adults. Infants are exposed to Cd from various formulas and infant diets and the gastrointestinal Cd uptake is believed to be higher in newborns than in adults. Cd levels monitored in infant foods ranged between 0.74 and 27.0 µg/kg. Cow's milk formulas had the lowest levels and cereal-based formulas had up to 21 times higher mean levels. The mean weekly Cd exposure from the recommended formula intake was calculated to vary between 0.10 and 3.05 µg/kg body weight. Rat pups received an oral dose of 109Cd in water or four different formulas. The whole-body Cd retention was higher in the pups than previously reported in adult animals and highest in the water and in the cow's milk formula groups. The small intestinal Cd retention was high, even 9 days after exposure indicating a long absorption period in the newborns. Cd levels in kidney increased still 12 days after exposure in all diet groups. Piglets received low daily doses of Cd in water or wheat/oat/milk-based follow-up formula. The formula reduced Cd uptake in comparison to water, but the distribution of Cd to the kidneys was unexpectedly higher when Cd was given in formula than in water. Simulated infant digestion of infant foods resulted in lower solubility of Cd compared to adult digestion. In a human Caco-2 cell model, cellular Cd uptake and transport from five different infant food digests was approximately one order of magnitude lower than the solubility and varied between 4-6 % and 1-2 % of the dose, respectively. Binding of Cd to dietary fibres and phytic acid reduces intestinal Cd retention and probably explains the lower Cd bioavailability from cereal-based formulas compared to water or cow's milk formula. The exposure of Cd is higher from infant formulas than from breast milk and age-specific digestion conditions as well as composition of diets affect both the Cd solubility and bioavailability. The calculated Cd intake from recommended amount of infant formulas is below the established provisional tolerable weekly intake, which however, does not include a safety factor and is based on renal effects in adults

Parental Separation and Well-Being of Youths

This paper uses recent data for Germany and a new outcome variable to assess the consequences of parental separation on the well-being of youths. In particular, it is considered how subjective well-being, elicited from an ordinal 11-point general life satisfaction question, differs between youths living in intact and non-intact families, holding many other potential determinants of well-being constant using ordered probit regressions. The main finding of this study is that living in a non-intact family has not the hypothesised large negative effect on child well-being.child welfare, educational attainment, happiness, German Socio-Economic Panel

Family Structure Changes and Children´s Health, Behavior, and Educational Outcomes

More and more children do not grow up in traditional nuclear fam- ilies. Instead, they grow up in single-parent households or in fami- lies with a step-parent. Hence, it is important to improve our under- standing of the impact of "shocks" in family structure due to parental relationship dissolution on children. In this study I empirically test whether children are traumatized both in the short and the long run by shocks in the family structure during childhood. I focus on edu- cational, behavioral, and health outcomes. A population sample of Danish children born in January to May 1985 is used for the analysis. The empirical cross-sectional analysis indicates a negative relation be- tween the number of family structure changes and children’s health, behavior, and educational outcomes. These results are con…rmed by a di¤erences-in-di¤erences analysis of health outcomes. This suggests that there is not only a selection e¤ect, but also a causal e¤ect on children of shocks in the family structure.Family structure; child outcomes; health; crime; education

Secondary School Track Selection of Single-Parent Children – Evidence from the German Socio-Economic Panel

In present day Germany, one in seven children is raised in a single parent household. We investigate the effect of single parenthood on children’s educational attainment, measured by the school track at the age 14, using ordered probit models. We study whether the effect of living in single parenthood during early or late childhood differs. Finally, we ask whether the family effect operates through resources – fewer income and parental time available for the child –, or through adverse effects on psychological well-being. The data used in this study are a nationally representative sample of 14 year old children drawn from the German Socio-Economic Panel.school choice, educational attainment, ordered response model

Sperm mixing in the polyandrous leaf-cutting ant Acromyrmex echinatior

The insemination of queens by sperm from multiple males (polyandry) has evolved in a number of eusocial insect lineages despite the likely costs of the behavior. The selective advantages in terms of colony fitness must therefore also be significant and there is now good evidence that polyandry increases genetic variation among workers, thereby improving the efficiency of division of labor, resistance against disease, and diluting the impact of genetically incompatible matings. However, these advantages will only be maximized if the sperm of initially discrete ejaculates are mixed when stored in queen spermathecae and used for egg fertilization in a “fair raffle.” Remarkably, however, very few studies have addressed the level of sperm mixing in social insects. Here we analyzed sperm use over time in the highly polyandrous leaf-cutting ant Acromyrmex echinatior. We genotyped cohorts of workers produced either 2 months apart or up to over a year apart, and batches of eggs laid up to over 2 years apart, and tested whether fluctuations in patriline distributions deviated from random. We show that the representation of father males in both egg and worker cohorts does not change over time, consistent with obligatorily polyandrous queens maximizing their fitness when workers are as genetically diverse as possible

Single Motherhood and (Un)Equal EducationalOpportunities: Evidence for Germany

We examine the effect of single motherhood on children’s secondary school track choice using 12-year-old children drawn from the German Socio-Economic Panel. In line with previous studies for the U.S., the U.K. and Sweden, we find a negative correlation between single motherhood and children’s educational attainment. Looking for alternative explanations for this correlation, we use probit regression models to control for factors related to single motherhood such as higher educational background, lower household income and higher labor supply of the mother. Our evidence suggests that single motherhood reduces school attainment mainly because it is associated with lower resources (household income) available for the child.school choice, educational attainment, binary response model, German Socio-Economic Panel

Rationale for a Swedish cohort consortium

We herein outline the rationale for a Swedish cohort consortium, aiming to facilitate greater use of Swedish cohorts for world-class research. Coordination of all Swedish prospective population-based cohorts in a common infrastructure would enable more precise research findings and facilitate research on rare exposures and outcomes, leading to better utilization of study participants' data, better return of funders' investments, and higher benefit to patients and populations. We motivate the proposed infrastructure partly by lessons learned from a pilot study encompassing data from 21 cohorts. We envisage a standing Swedish cohort consortium that would drive development of epidemiological research methods and strengthen the Swedish as well as international epidemiological competence, community, and competitiveness.Peer reviewe

Sex-ratio dependent execution of queens in polygynous colonies of the ant Formica exsecta

Formica exsecta has become an important model system for studying intraspecific variation in sex ratios. Patterns of sex allocation in polygynous (multiple queen per nest) populations of F. exsecta are generally consistent with the queen-replenishment hypothesis. This hypothesis states that colonies produce gynes (reproductive females) in order to increase queen number and enhance colony survival and/or productivity when the number of resident queens is low. However, the small proportion of colonies that raise gynes produce more than necessary for simple queen replenishment. It has been hypothesized that excess production of gynes may occur to reduce the frequency of accepting foreign unrelated gynes into the colony when workers cannot distinguish nestmate from non-nestmate queens. This explanation for excess gynes requires weak or no aggression between non-nestmates and is expected to lead to the selective execution of new queens by colonies that do not invest in the production of gynes. Experimental studies where gynes were introduced into natal and foreign colonies indeed suggested that polygynous populations of F. exsecta have a poor nestmate recognition system. Although gynes were significantly more likely to be accepted in their parental colony compared to another foreign female-producing colony, the difference was small. Moreover, encounters between workers from different colonies within the population showed very little aggression and were no more aggressive than encounters between nestmates, again suggesting a weak capacity for nestmate recognition. Our experiment also showed that colonies that produced only males executed most of the gynes that were experimentally introduced into the colony, whereas female-producing colonies accepted most gynes. This is consistent with ants using a simple rule of thumb to decrease parasitism by unrelated queens, whereby colonies selectively destroy gynes whenever gynes are not produced in the colonies

Part-Time Jobs: What Women Want?

Part-time jobs are popular among partnered women in many countries. In the Netherlands the majority of partnered working women have a part-time job. Our paper investigates, from a supply-side perspective, if the current situation of abundant part-time work in the Netherlands is likely to be a transitional phase that will culminate in many women working full-time. We analyze the relationship between part-time work and life satisfaction, and between job satisfaction and preferred working hours using panel data on life and job satisfaction for a sample of partnered women and men. We also utilize time-use data to consider the distribution within the household of market work and housework, and discuss the work specialization hypothesis in this context. Our main results indicate that partnered women in part-time work have high levels of job satisfaction, a low desire to change their working hours, and live in partnerships in which household production is highly gendered. Taken together, our results suggest that part-time jobs are what most Dutch women want.part-time work, happiness, satisfaction, working hours, gender