Sockman K W, Schwabl H, Sharp P J
School of Biological Sciences, Washington State University, Pullman, Washington 99164-4236, USA.
Horm Behav. 2000 Nov;38(3):168-76. doi: 10.1006/hbeh.2000.1616.
In most bird species, the timing of incubation onset may influence the degree of hatching asynchrony, which, together with variation in clutch size, affects reproductive success. In some domesticated species that usually show no hatching asynchrony, plasma prolactin concentrations in females rise with the onset of incubation and the end of laying, and this rise enhances incubation behavior and may terminate laying. To investigate whether a rise in prolactin during laying is involved in the regulation of clutch size and incubation onset in a species with hatching asynchrony, we measured plasma concentrations of immunoreactive prolactin (ir-prolactin) in laying American kestrels, Falco sparverius, and quantified clutch size and incubation behavior. In a separate study, we administered one of three concentrations of ovine prolactin (o-prolactin) via osmotic pumps implanted in females when egg 2 of a clutch was laid. ir-Prolactin concentrations during laying were higher in small than in large clutches and increased in parallel with the development of incubation behavior. o-Prolactin treatment enhanced incubation behavior, but did not affect clutch size, possibly because the manipulation was performed after clutch size had already been determined. Consistent with studies on domesticated species that show synchronous hatching, our results indicate that rising prolactin during laying enhances the expression of incubation behavior in a species that shows hatching asynchrony. Further studies are necessary to determine whether the relationship between prolactin and clutch size in the American kestrel is one of causation or of mere association.
在大多数鸟类中，开始孵化的时间可能会影响孵化异步的程度，而孵化异步与窝卵数的变化共同影响繁殖成功率。在一些通常不表现出孵化异步的家养物种中，雌性的血浆催乳素浓度会随着孵化开始和产卵结束而升高，这种升高会增强孵化行为并可能终止产卵。为了研究在具有孵化异步的物种中，产卵期间催乳素的升高是否参与窝卵数和孵化开始的调节，我们测量了正在产卵的美洲隼（Falco sparverius）血浆中免疫反应性催乳素（ir-催乳素）的浓度，并对窝卵数和孵化行为进行了量化。在另一项研究中，当一窝卵产下第二枚时，我们通过植入雌性体内的渗透泵给予三种浓度的羊催乳素（o-催乳素）之一。产卵期间，小窝卵的ir-催乳素浓度高于大窝卵，并且与孵化行为的发展同步增加。o-催乳素处理增强了孵化行为，但不影响窝卵数，这可能是因为该操作是在窝卵数已经确定之后进行的。与关于表现出同步孵化的家养物种的研究一致，我们的结果表明，产卵期间催乳素的升高会增强在表现出孵化异步的物种中孵化行为的表达。有必要进一步研究以确定美洲隼中催乳素与窝卵数之间的关系是因果关系还是仅仅是关联关系。
