Svensson Erik
Department of Animal Ecology, Ecology Building, S-223 62, Lund, Sweden.
Evolution. 1997 Aug;51(4):1276-1283. doi: 10.1111/j.1558-5646.1997.tb03974.x.
Natural selection on breeding time through postfledgling survival was investigated in a population of blue tits, Parus caeruleus, between 1993 and 1996. In particular, selection acting through large brood sizes among early breeders (fecundity-dependent selection) was separated from selection acting through fitness benefits unrelated to the numerical benefits of large brood sizes (fecundity-independent selection). There was evidence that natural selection favored early breeding in 1993 and 1995 (significantly so in 1993), whereas in 1994 there was a tendency for selection to be stabilizing. Analyses of selection gradients further showed that there was direct selection for both early breeding and large brood sizes in 1993. Experimentally delayed pairs produced a lower proportion of surviving young among their fledglings compared to early pairs, indicating that the seasonal fitness trend is a causal one and not caused by differences between early and late breeders in territory or individual quality. There was no evidence for significant heritability for four reproductive traits (clutch sizes, laying dates, hatching dates, and brood size at fledging) although repeatability values ranged from 0.26 to 0.53. The importance of year-specific selective regimes in the evolution of avian breedings times are discussed and a role for population density in this context is proposed.
1993年至1996年间，在青山雀（Parus caeruleus）种群中研究了通过雏鸟出飞后的存活率对繁殖时间进行的自然选择。具体而言，将早期繁殖者中通过大窝雏数起作用的选择（与繁殖力相关的选择）与通过与大窝雏数的数量效益无关的适合度效益起作用的选择（与繁殖力无关的选择）区分开来。有证据表明，自然选择在1993年和1995年有利于早期繁殖（1993年显著），而在1994年，选择有稳定化的趋势。选择梯度分析进一步表明，1993年对早期繁殖和大窝雏数都有直接选择。与早期配对相比，实验性延迟配对的雏鸟中存活幼鸟的比例较低，这表明季节性适合度趋势是因果性的，而非由早期和晚期繁殖者在领地或个体质量上的差异导致。虽然四个繁殖性状（窝卵数、产卵日期、孵化日期和出飞时的窝雏数）的遗传力不显著，但重复率值在0.26至0.53之间。讨论了特定年份选择机制在鸟类繁殖时间进化中的重要性，并提出了种群密度在此背景下的作用。
