Ilmonen Petteri, Taarna Terho, Hasselquist Dennis
Section of Ecology, Department of Biology, University of Turku, 20014, Turku, Finland.
Department of Animal Ecology, Ecology Building, 22362, Lund, Sweden.
Oecologia. 2002 Jan;130(2):199-204. doi: 10.1007/s004420100804. Epub 2002 Jan 1.
Although clutch size variation has been a key target for studies of avian life history theory, most empirical work has only focused on the ability of parents to raise their altricial young. In this study, we test the hypothesis that costs incurred during incubation may be an additional factor constraining clutch size in altricial birds. In the pied flycatcher (Ficedula hypoleuca), we manipulated the incubation effort of the female by enlarging and reducing clutch sizes. To manipulate incubation effort only, the original clutch sizes were restored shortly after hatching. We found that fledging success was lower among broods whose clutches were enlarged during incubation. There was, however, no effect of manipulation on female body condition or on their ability to mount a humoral immune response to diphtheria or tetanus toxoid during the incubation or nestling provisioning period. Instead, we found that the original clutch size was related to the immune response so that females with seven eggs had significantly lower primary antibody responses against tetanus compared to those with six eggs. Our results suggest that incubating females are not willing to jeopardise their own condition and immune function, but instead pay the costs of incubating a larger clutch by lower offspring production. The results support the view that costs of producing and incubating eggs may be substantial and hence that these costs are likely to contribute to shaping the optimal clutch size in altricial birds.
尽管窝卵数的变化一直是鸟类生活史理论研究的关键目标，但大多数实证研究仅关注亲鸟养育晚成雏的能力。在本研究中，我们检验了一个假设，即孵化过程中产生的代价可能是限制晚成鸟窝卵数的另一个因素。在斑姬鹟（Ficedula hypoleuca）中，我们通过增加和减少窝卵数来操纵雌鸟的孵化投入。为了仅操纵孵化投入，在孵化后不久将原始窝卵数恢复。我们发现，在孵化期间窝卵数增加的巢中，雏鸟的出飞成功率较低。然而，在孵化期或育雏期，操纵对雌鸟的身体状况或其对白喉或破伤风类毒素产生体液免疫反应的能力没有影响。相反，我们发现原始窝卵数与免疫反应有关，因此与产6枚卵的雌鸟相比，产7枚卵的雌鸟对破伤风的初次抗体反应显著较低。我们的结果表明，正在孵化的雌鸟不愿意危及自身状况和免疫功能，而是通过降低后代产量来承担孵化更大窝卵数的代价。这些结果支持了这样一种观点，即产卵和孵化的代价可能很大，因此这些代价可能有助于塑造晚成鸟的最佳窝卵数。
