Williams T D
Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada.
Proc Biol Sci. 2001 Feb 22;268(1465):423-8. doi: 10.1098/rspb.2000.1374.
A negative relationship, or trade-off, between egg size and clutch size is a central and long-standing component of life-history theory, yet there is little empirical evidence for such a trade-off, especially at the intraspecific level. Here, I show that female zebra finches (Taeniopygia guttata) treated chronically during egg formation with the anti-oestrogen tamoxifen lay smaller eggs (by 8%) but produce larger clutches (on average two eggs more) than controls. Decreased egg mass in tamoxifen-treated females was associated with a 50% decrease in plasma levels of the two yolk precursors, vitellogenin and very-low-density lipoprotein. Although tamoxifen-treated females laid more, smaller eggs (and had a higher total expenditure in their clutch), they did not differ from controls in the number of chicks fledged, the mass or size of these chicks at fledging, or the chicks' egg-production performance at three months of age. However, tamoxifen-treated females had lower relative hatching success: they laid more eggs but hatched the same number of chicks. Among individual tamoxifen-treated females, birds that laid the smallest eggs early in their laying sequence laid the largest number of additional eggs, that is, there was a negative correlation, or trade-off, between egg size and clutch size.
卵大小与窝卵数之间的负相关关系，即权衡关系，是生活史理论的核心且长期存在的组成部分，然而，这种权衡关系的实证证据很少，尤其是在种内水平上。在这里，我表明，在产卵形成过程中用抗雌激素他莫昔芬长期处理的雌性斑胸草雀（Taeniopygia guttata）产下的卵较小（小8%），但比对照组产生的窝卵数更大（平均多两个卵）。他莫昔芬处理的雌性鸟卵质量下降与两种卵黄前体（卵黄蛋白原和极低密度脂蛋白）的血浆水平降低50%有关。虽然用他莫昔芬处理的雌性鸟产更多、更小的卵（并且其窝卵的总支出更高），但它们在出飞雏鸟的数量、这些雏鸟出飞时的质量或大小，或雏鸟三个月大时的产卵性能方面与对照组没有差异。然而，用他莫昔芬处理的雌性鸟的相对孵化成功率较低：它们产更多的卵，但孵出的雏鸟数量相同。在个体用他莫昔芬处理的雌性鸟中，在产卵序列早期产下最小卵的鸟产下的额外卵数量最多，也就是说，卵大小与窝卵数之间存在负相关关系，即权衡关系。
