Data from: Differential maternal testosterone allocation among siblings benefits both mother and offspring in the Zebra Finch Taeniopygia guttata

Parents are selected to preferentially invest in the offspring with highest reproductive value. One mechanism to achieve this is the modification of competitive asymmetries between siblings by maternal hormones. In many organisms, offspring value varies according to birth position in the brood, which determines survival chances and competitive advantage over access to resources. In birds, variation in yolk androgen allocation over the laying sequence is thought to modulate dominance of senior chicks over junior brood mates. We tested this hypothesis in zebra finches, which show a natural decreasing pattern of within-clutch testosterone allocation. We abolished these within-clutch differences by experimentally elevating yolk testosterone levels in eggs 2-6 up to the level of the egg 1, and assessed fitness measures for junior (eggs 2-6) and senior (egg 1) offspring, and their mothers. T-injected eggs hatched later than control eggs. Junior but not senior chicks in T broods attained poorer phenotypic quality compared with control broods, which was not compensated by positive effects on seniors. Mothers were generally unaffected by clutch treatment. Thus, naturally decreasing within-clutch yolk testosterone allocation appears to benefit all family members, and does not generally enhance brood reduction by favoring senior chicks, in contrast to widely held assumption.

The data package contains one dataset:
-Boncoraglio et al database Dryad file
Original data collected in the lab. File created with Excel 2003. No abbreviations used for column headings.