تأثیر ترجیحات همسر و سفارش تخمگذاری در تخصیص مادر در گونه های طوطی تک همسری با ناهمزمان افراطی جوجه ریزی

It is well established that in many avian species, prenatal maternal resource allocation varies both between and within clutches and may affect offspring fitness. Differential allocation of maternal resources, in terms of egg weight and yolk composition, may therefore allow the female to adjust brood reduction and to fine-tune reproductive investment in accordance with the expected fitness returns. The adaptive value of such maternal resource allocation is thought to be context-dependent as well as species-specific. We investigated the effects of female preference for her mate on the allocation of prenatal maternal resources in the budgerigar, Melopsittacus undulatus, a monogamous species of parrot that shows an extreme hatching asynchrony. We assessed mate preferences in a two-way preference test and allowed females two breeding rounds: one with the preferred and one with the non-preferred partner. We found no effect of preference on either latency to lay or clutch size, but females mated with the preferred partner laid eggs that contained significantly more yolk. Their eggs also contained significantly more androstenedione but not testosterone. Our results suggest that in this species, female preference may influence maternal resource allocation, and that the functional roles of each androgen in the yolk should be considered separately. In addition, we found a significant effect of laying order on egg and yolk weight as well as on yolk testosterone and androstenedione levels. These measures, however, did not change linearly with the laying order and render it unlikely that female budgerigars compensate for the extreme hatching asynchrony by adjusting within-clutch allocation of prenatal maternal resources.

Early maternal allocation of resources provides a non-genetic mechanism for the female to modify the phenotype of the offspring in accordance with the environmental conditions that she experiences and that her offspring are likely to face after hatching (Mousseau and Fox, 1998). In oviparous animals, such as birds, the egg provides a sealed system in which the embryo develops and once the egg is laid, investment in the offspring through maternal resources is restricted. Birds are therefore excellent subjects for studying the causes and consequences of differential maternal allocation during the prenatal phase.