Sex-specific effects of yolk-androgens on growth of nestling American kestrels

Maternally derived androgen hormones concentrate in avian egg yolks as the yolks grow on the female’s ovary, possibly forming a basis for important maternal effects in birds. In the American kestrel (Falco sparverius), experimental elevation of yolk androgens in the first-laid egg of a clutch (a-egg) to the concentrations found naturally in a clutch’s later-laid eggs reduces the growth rate of a-egg nestlings compared to controls. These findings, together with discoveries from other species that the effects of yolk androgens on growth of female nestlings may differ from their effects on growth of male nestlings, raise the hypothesis that natural changes in yolk-androgen concentrations with laying order are ultimately due to a difference between the sexes in their yolk-androgen sensitivity and between early- and late-laid eggs in their sex ratio. By re-analyzing previously published data and adding to the analysis data from previously unanalyzed blood samples used for sex determination, we investigated possible sex-specific effects of yolk-androgens in the context of a potential sex-biased laying order in free-living American kestrels. We used a multi-level, mixed model with a Gompertz function to analyze growth of nestlings hatching from a-eggs that were control-treated or in which we experimentally elevated yolk-androgen concentrations shortly after laying to the higher concentrations naturally found in later-laid eggs. We discovered that male nestlings were more susceptible than female nestlings to growth inhibition by yolk-androgen elevation but did not find a bias in sex ratio with respect to laying order. Together, these findings do not support the above hypothesis. However, they are consistent with the hypothesis that sex differences in yolk-androgen sensitivity enable mothers to economically tune reproductive effort to an individual offspring’s reproductive value, which can vary more for one sex than the other.     

Chlorobiphenyl contaminants at Pladda and Garroch Head in the Firth of Clyde following the cessation of sewage sludge dumping

Sewage sludge dumping at Garroch Head in the Firth of Clyde ceased on 31 December 1998. Eighteen of the 209 chlorinated biphenyls (CBs) were measured in plaice livers, collected in 1999 and 2000, from the former Garroch Head dump site. Samples were also obtained from Pladda, a site reasonably remote from the former dump site but also in the Clyde, in 1999 only. These results were compared to the CB concentrations in plaice livers collected between 1992 and 1998 from Garroch Head and Pladda. Additional samples were also taken from a clean reference site, close to Colonsay. Concentrations of the congeners in the livers of fish caught at the former Garroch Head dump site in 1999 were marginally higher than those from Pladda, with a mean CB concentration of 1861 microg kg(-1) lipid in the Garroch Head plaice livers and 1725 microg kg(-1) lipid for the sample from Pladda. The mean CB concentration in the 2000 Garroch Head samples was 2253 microg kg(-1) lipid. CB concentration in plaice livers from Colonsay were lower than both the Pladda and Garroch Head fish, with plaice livers from Colonsay giving a mean CB concentration of 1076 microg kg(-1) lipid in 1999 and 345.1 microg kg(-1) lipid in 2000. The data was evaluated using principal component analysis (PCA). Pattern analysis was undertaken by normalising to the recalcitrant CB 153. There was an indication that the CB pattern has changed since the cessation of dumping with the proportion of tri- and tetra-chlorinated CBs being lower in plaice from Garroch Head than in previous years.     

Critical factors in assessing exposure to PBDEs via house dust

Assessment of indoor exposure to polybrominated diphenyl ethers (PBDEs) requires a critical examination of methods that may influence exposure estimates and comparisons between studies. We measured PBDEs in residential dust collected from 20 homes in Boston, MA, to examine 5 key questions: 1) Does the choice of dust exposure metric-e.g., concentration (ng/g) or dust loading (ng/m2)-affect analysis and results? 2) To what degree do dust concentrations change over time? 3) Do dust concentrations vary between rooms? 4) Is the home vacuum bag an acceptable surrogate for researcher-collected dust? 5) Are air and dust concentrations correlated for the same room? We used linear mixed-effects models to analyze the data while accounting for within-home and within-room correlations. We found that PBDE dust concentration and surface loading were highly correlated (r=0.86-0.95, p<0.001). Average dust concentrations did not significantly differ over an 8-month period, possibly because home furnishings changed little over this time. We observed significant differences between rooms in the same home: PBDE concentrations in the main living area were 97% higher than the bedroom for decaBDE (p=0.02) and 72% higher for pentaBDE (p=0.05). Home vacuum bag dust concentrations were significantly lower than researcher-collected dust and not strongly correlated. Air (vapor and particulate phase) and dust concentrations were correlated for pentaBDE (p=0.62, p<0.01), but not for decaBDE (p=0.25). In addition, potential markers of BDE 209 debromination (BDE 202 and the BDE197:BDE201 ratio) were also observed in household dust samples. One vacuum bag sample contained the highest concentrations of BDE 209 (527,000 ng/g) and total PBDEs (544,000 ng/g) that have been reported in house dust.