Bradshaw William E, Holzapfel Christina M
Department of Biology, University of Oregon, Eugene, Oregon, 97403-1210.
Evolution. 1996 Jun;50(3):1176-1181. doi: 10.1111/j.1558-5646.1996.tb02358.x.
Life-history theory relies heavily on the hypothesis that genetic tradeoffs among the components of fitness constrain their independent evolution and joint maximization. Herein we show that selection on preadult development time in the pitcher-plant mosquito, Wyeomyia smithii, leads to a correlated response in cohort mean generation time but no correlated response in survivorship, fecundity, or cohort replacement rate. Lines selected for fast development achieve a higher capacity for increase (r ) than lines selected for slow development, independently of larval density. These results imply that tradeoffs due to underlying antagonistic pleiotropy affecting growth, development, survivorship, and reproduction are not necessary constraints to life-history evolution. Previous work with W. smithii has shown a positive genetic correlation between development time and a general, genetically coordinated diapause syndrome. We propose that the observed nontradeoffs among the components of r may be subsumed into an even more fundamental tradeoff between performance during the summer generations and synchronization of development and reproduction with the changing seasons. Consequently, critical tests of genetic tradeoffs as a constraint to the independent evolution or simultaneous optimization of fitness components may need to consider the seasonal context.
生活史理论严重依赖于这样一种假说，即适合度各组成部分之间的基因权衡会限制它们的独立进化和共同最大化。在此我们表明，对猪笼草蚊（Wyeomyia smithii）成虫前期发育时间的选择会导致同组平均世代时间产生相关反应，但在存活率、繁殖力或同组更替率方面不会产生相关反应。与选择发育缓慢的品系相比，选择发育快速的品系具有更高的增长能力（r），且与幼虫密度无关。这些结果表明，由潜在的拮抗多效性影响生长、发育、存活和繁殖所导致的权衡并非生活史进化的必要限制。先前对猪笼草蚊的研究表明，发育时间与一种普遍的、基因协调的滞育综合征之间存在正遗传相关性。我们提出，观察到的r各组成部分之间的非权衡现象，可能包含在夏季世代的表现与发育和繁殖与季节变化同步之间更基本的权衡之中。因此，作为对适合度组成部分独立进化或同时优化的一种限制，对基因权衡的关键检验可能需要考虑季节背景。
