Costs of Reproduction in Breeding Female Mallards: Predation Risk during Incubation Drives Annual Mortality

The effort expended on reproduction may entail future costs, such as reduced survival or fecundity, and these costs can have an important influence on life-history optimization. For birds with precocial offspring, hypothesized costs of reproduction have typically emphasized nutritional and energetic investments in egg formation and incubation. We measured seasonal survival of 3856 radio-marked female Mallards (Anas platyrhynchos) from arrival on the breeding grounds through brood-rearing or cessation of breeding. There was a 2.5-fold direct increase in mortality risk associated with incubating nests in terrestrial habitats, whereas during brood-rearing when breeding females occupy aquatic habitats, mortality risk reached seasonal lows. Mortality risk also varied with calendar date and was highest during periods when large numbers of Mallards were nesting, suggesting that prey-switching behaviors by common predators may exacerbate risks to adults in all breeding stages. Although prior investments in egg laying and incubation affected mortality risk, most relationships were not consistent with the cost of reproduction hypothesis; birds with extensive prior investments in egg production or incubation typically survived better, suggesting that variation in individual quality drove both relationships. We conclude that for breeding female Mallards, the primary cost of reproduction is a fixed cost associated with placing oneself at risk to predators while incubating nests in terrestrial habitats.

Recorded quadrant incidence of female breast cancer in Great Britain suggests a disproportionate increase in the upper outer quadrant of the breast

Background: The upper outer quadrant (UOQ) of the breast is the most frequent site for incidence of breast cancel; but the reported disproportionate incidence in this quadrant appears to rise with year of publication. Materials and Methods: In order to determine whether this increasing incidence in the UOQ is an artifact of different study populations or is chronological, data have been analysed for annual quadrant incidence of female breast cancer recorded nationally in England and Wales between 1979 and 2000 and in Scotland between 1980 and 2001. Results: In England and Wales, the recorded incidence of female breast cancer in the UOQ rose front 47.9% in 1979 to 53.3% in 2000, and has done so linearly over tune with a con-elation coefficient R of +/- 0.71 +/- SD 0.01 (p < 0.001). Analysis of independent data front Scotland showed a similar trend in that recorded female breast cancer had also increased in the UOQ from 38.3% in 1980 to 54.7% in 2001, with a con-elation coefficient R for the linear annual increase of +0.80 +/- SD 0.03 (p < 0.001). Conclusion: These results are inconsistent with current views that the high level of UOQ breast cancer is due solely to a greater amount of target epithelial tissue in that region. Identification of the reasons for such a disproportionate site-specific increase could provide clues as to causative factors in breast cancer.