de Heij Maaike E, van den Hout Piet J, Tinbergen Joost M
Animal Ecology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, 9750 AA Haren, The Netherlands.
Proc Biol Sci. 2006 Sep 22;273(1599):2353-61. doi: 10.1098/rspb.2006.3584.
Life-history theory predicts that parents produce the number of offspring that maximizes their fitness. In birds, natural selection on parental decisions regarding clutch size may act during egg laying, incubation or nestling phase. To study the fitness consequences of clutch size during the incubation phase, we manipulated the clutch sizes during this phase only in three breeding seasons and measured the fitness consequences on the short and the long term. Clutch enlargement did not affect the offspring fitness of the manipulated first clutches, but fledging probability of the subsequent clutch in the same season was reduced. Parents incubating enlarged first clutches provided adequate care for the offspring of their first clutches during the nestling phase, but paid the price when caring for the offspring of their second clutch. Parents that incubated enlarged first clutches had lower local survival in the 2 years when the population had a relatively high production of second clutches, but not in the third year when there was a very low production of second clutches. During these 2 years, the costs of incubation were strong enough to change positive selection, as established by brood size manipulations in this study population, into stabilizing selection through the negative effect of incubation on parental fitness.
生活史理论预测，父母会生育能使其适应性最大化的后代数量。在鸟类中，自然选择对父母关于窝卵数的决策的影响可能发生在产卵、孵化或育雏阶段。为了研究孵化阶段窝卵数对适应性的影响，我们仅在三个繁殖季节中对该阶段的窝卵数进行了操控，并测量了其对短期和长期适应性的影响。增加窝卵数并未影响被操控的第一窝雏鸟的适应性，但同一季节后续窝的出飞概率降低了。孵化第一窝增加窝卵数的父母在育雏阶段为第一窝的雏鸟提供了足够的照料，但在照料第二窝雏鸟时付出了代价。孵化第一窝增加窝卵数的父母，在种群第二窝产量相对较高的两年中，当地存活率较低，但在第二窝产量非常低的第三年并非如此。在这两年中，孵化成本足以将本研究种群中通过窝卵数操控所确立的正向选择，通过孵化对父母适应性的负面影响转变为稳定选择。
