Slagsvold Tore
Zoological Museum, University of Oslo, Sarsgate 1, N-0562, Oslo 5, NORWAY.
Evolution. 1990 Jul;44(4):1009-1017. doi: 10.1111/j.1558-5646.1990.tb03821.x.
I present the hypothesis that asynchronous hatching is a means of ensuring an equal degree of parental investment in the progeny of each sex in altricial species of birds that are sexually dimorphic in size. In a comparative analysis of bird species of Africa and the Western Palearctic, I find a positive relationship between hatching asynchrony and sexual size dimorphism, in support of the hypothesis. The relation is significant for species in which males are larger than females, and in species in which females are larger than males. In addition, it holds even if allometric effects of body size are controlled for. No such relationship is found in species with self-feeding young. Alternative hypotheses to explain asynchronous hatching in altricial birds are discussed. The results of the comparative study are also consistent with some of these hypotheses. For instance, asynchronous hatching may be a mechanism used by parents of dimorphic species to deal with unpredictable primary sex ratios; it may be a way of avoiding simultaneous peak food demands by the young; or it may be a way of advancing the time of hatching so that the division of labor between the parents is optimized.
在体型上具有两性差异的晚成雏鸟类中，异步孵化是确保亲代对每种性别的后代进行同等程度投资的一种方式。在对非洲和西古北区鸟类物种的比较分析中，我发现孵化异步性与两性体型差异之间存在正相关关系，这支持了该假说。这种关系在雄性比雌性大的物种以及雌性比雄性大的物种中都很显著。此外，即使控制了体型的异速生长效应，这种关系仍然成立。在幼雏能自行觅食的物种中未发现这种关系。文中还讨论了解释晚成雏鸟类异步孵化的其他假说。比较研究的结果也与其中一些假说相符。例如，异步孵化可能是两性异形物种的亲代用来应对不可预测的初级性别比例的一种机制；它可能是避免幼雏同时出现食物需求高峰的一种方式；或者它可能是提前孵化时间的一种方式，以便优化亲代之间的分工。
