Differential effects of steroid hormones on levels of genetic variance in a wild bird: possible mechanism of maternal-effects x genetic variance interaction?

Genetic variation is one of the key concepts in evolutionary biology and an important prerequisite of evolutionary change. Still, we know very little about processes that modulate its levels in wild populations. In particular – we still are to understand why genetic variances often depend on environmental conditions. One of possible environment-sensitive modulators of observed levels of genetic variance are maternal effects. In this study we attempt to experimentally test the hypothesis that maternally-transmitted agents (e.g. hormones) may influence the expression of genetic variance in quantitative traits in the offspring. We manipulated the levels of steroid hormones (testosterone and corticosterone) in eggs laid by blue tits in a wild population. Our experimental setup allowed for full crossing of genetic and rearing effects with the experimental manipulation. We observed, that birds treated with corticosterone exhibited a significant decrease in genetic variance of tarsus length. We also observed less pronounced, marginally significant effects of hormonal administration on the patterns of genetic correlations between traits expressed under varying pre-hatching hormonal conditions. Our study indicates, that maternally transmitted substances such as hormones may have measurable impact on the levels of genetic variance – and hence, on the evolutionary potential of quantitative traits.

Cross-generational transmission from drug abuse in parents to attention-deficit/hyperactivity disorder in children

BackgroundAttention-deficit/hyperactivity disorder (ADHD) predisposes to drug abuse (DA) and twin studies suggest shared genetic effects. We here seek to determine, using adoption and adoption-like samples, the magnitude of the cross-generational transmission from DA in parents to ADHD in their children and clarify the degree to which this arises from genetic v. rearing effects.MethodWe ascertained ADHD and DA from multiple Swedish registries. Statistical analysis was performed by Cox and path models.ResultsRisk for ADHD was significantly and similarly increased in the offspring of biological mothers and fathers with DA who did v. did not rear their offspring. Risk for ADHD was not elevated in the offspring of adoptive or step-parents with DA.ConclusionsCross-generational transmission was observed from DA in parents to ADHD in their children. An analysis of adoptive and adoptive-like parent–offspring relationships suggested that this transmission results from genetic and not from rearing effects.

Floor versus cage rearing: effects on production, egg quality and physical condition of laying hens housed in furnished cages

The influences of floor- and cage-rearing on egg production, egg quality and physical condition were investigated in laying hens housed in furnished cages. Two groups of 180 Isa Brown commercial layer pullets were reared in cages (CR) or floor pens (FR) and transferred to furnished cages, where their production, egg quality and physical condition was observed throughout the laying period (18-78wks of age). At 17 weeks of age, hens were placed in one of 36 furnished cages with 10 birds in each cage, each containing a nest box, perches, a dust bath, and abrasive strips. From 19 to 78 weeks of age, egg production data were collected daily. Commercial egg quality was assessed monthly. At, 19 and 78 weeks of age, claw length and feather cover were visually assessed using a four-point scale in a sample (10%) of hens. Production variables were above breeders’ standards and not significantly affected by rearing system. Dirty eggs and cracked eggs were more frequent in FR birds. Meat spots were significantly more frequent in FR hens at middle lay, but less frequently at the end of the laying period. Rearing system did not influence egg and yolk weight or unit Haugh and shell colour. Among FR hens, eggshell density, thickness and mass were significantly lower at the end of the laying period. Rearing system did not affect claw length, but the plumage of FR hens was negatively affected at the end of production cycle.

Applicability of Baumrind's parent typology to collective cultures: Analysis of cultural explanations of parent socialization effects

This article reviews studies that have examined whether Baumrind's parenting styles are related to child outcomes similarly in cultures where independence is said to be emphasized versus cultures where interdependence is said to be emphasized. I present evidence showing that Baumrind's parenting styles have similar function in both collectivist and individualist cultures. Based on these studies, I argue against the claim of some researchers that authoritarian parenting is not detrimental or authoritative parenting beneficial to the development of young people in cultures that are said to emphasize interdependence. However, more research is needed before conclusions can be reached about the extent to which the culture construct explains child-rearing effects on child development. Future directions for research, which include the importance of identifying diverse forms of parenting within interdependent cultures so as to distinguish the influence of functional and dysfunctional forms of parenting on child outcomes, are suggested.