Mate attractiveness and primary resource allocation in the zebra finch

Abstract

Since egg production is nutritionally and energetically expensive, differential allocation theory predicts that females should allocate more resources at laying when mated to an attractive male. Females are also predicted to invest more in sons than in daughters under such conditions, because male offspring should have higher fitness returns than female offspring when fathered by an attractive male. We examined primary resource allocation in zebra finches, Taeniopygia guttata, when mated to both an attractive and an unattractive male. In the first breeding round, as predicted, females mated to attractive males laid heavier eggs, and there was a positive relation between female mass and egg mass. In contrast, for females mated to unattractive males there was no correlation between egg mass and body mass. Mate attractiveness did not affect clutch size or yolk androgen investment. Unexpectedly, in the second breeding round, in which the same females were paired with different males of opposite attractiveness to those in the first round, females did not alter their individual patterns of investment in egg mass. Therefore, we suggest there may be a physiological carryover effect and that females were primed by their first reproductive experience. In both rounds of breeding there was no difference in egg mass or yolk androgen concentration between male or female eggs in either treatment. Similarly, the primary sex ratio did not differ between treatments. This suggests that females do not differentially invest in male and female offspring in relation to the attractiveness of their mate in this species.