Kontiainen P, Brommer J E, Karell P, Pietiäinen H
Bird Ecology Unit, Department of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland.
J Evol Biol. 2008 Jan;21(1):88-96. doi: 10.1111/j.1420-9101.2007.01468.x. Epub 2007 Nov 22.
Avian egg size is highly variable on the population level, but is considered inflexible on the individual level. On the basis of 2969 measurements of individual eggs collected during 1981-2005, we analysed heritability, plasticity and selection on egg size in the Ural owl, a long-lived bird that preys on voles. Vole abundance varied in a 3-year cycle, creating varying food supply across the cycle's phases. Ural owl egg size is heritable (h(2) = 60%). Ural owls lay larger eggs in improved food conditions. On the basis of repeated breeding records of 59 females that bred in all vole cycle phases, we show that intra-individual adjustment (plasticity) explained 22.4% of the variation in egg size across phases. Egg size was under stabilizing selection. Extremely small and extremely large eggs had reduced hatchability, and individuals who laid either large or small eggs had lower lifetime fledgling production than the ones laying intermediately sized eggs. Our findings illustrate how maternal investment in egg size can both be heritable and highly responsive to variable environmental conditions, and suggest that variation in the investment in egg size across individuals is canalized.
鸟类蛋的大小在种群水平上具有高度变异性，但在个体水平上被认为是不可改变的。基于1981年至2005年期间收集的2969枚个体鸟蛋的测量数据，我们分析了长尾林鸮（一种以田鼠为食的长寿鸟类）蛋大小的遗传力、可塑性和选择情况。田鼠数量以三年为周期变化，在周期的不同阶段创造了不同的食物供应。长尾林鸮蛋的大小具有遗传性（h(2) = 60%）。长尾林鸮在食物条件改善时会产下更大的蛋。基于59只在田鼠数量周期的所有阶段都进行繁殖的雌性长尾林鸮的重复繁殖记录，我们发现个体内部的调整（可塑性）解释了不同阶段蛋大小变化的22.4%。蛋的大小受到稳定选择。极小和极大的蛋孵化率较低，产下大蛋或小蛋的个体一生的雏鸟产量低于产下中等大小蛋的个体。我们的研究结果说明了母体对蛋大小的投入如何既具有遗传性又对变化的环境条件高度敏感，并表明个体间蛋大小投入的差异是受限制的。
