生物谷报道:进化论认为,物种进化永远是朝着“最优基因”的目标前进。不过,一项最新的研究表明,动物雌雄两性在进化中可能无法“皆大欢喜”,对雄性有利的基因往往会阻碍雌性同类相关的适应性。相关论文发表在6月28日的《自然》杂志上。
英国爱丁堡大学(University of Edinburgh)的Katharina Foerster和同事分析了1971年至2005年收集的一种苏格兰马鹿的相关数据,并且利用每只马鹿对种群个体数量的贡献来衡量它们的适应性。研究人员通过统计发现,如果一只雄性的适应性(指生存能力和繁殖数量)强,那么它的雌性亲属的适应性往往低于平均水平。这一现象表明,两性在进化过程中存在着一种竞争,即基因的性别对抗性选择(sexually antagonistic selection)。
Foerster表示,“对一个物种的雌雄性个体而言,最优基因存在着一种平衡。”所谓的最优基因是与性别紧密相关的。
尽管此前对黑腹果蝇的实验室研究得到过类似的结论,但这是科学家第一次真正的“自然”选择研究。不过,科学家并没有发现对应的结论,即雌性马鹿的高产会影响雄性亲属的繁殖能力。研究人员表示,这可能是由于母亲对雌雄后代的早期影响比较类似,从而补偿了雄性遗传上的不利条件。
同样地,研究人员也没有发现雄性马鹿的适应性与其雄性后代有任何关联。她们推测,雄性无法将自身的适应性特征传达给雄性后代,很可能是因为这类性别对抗基因位于X染色体上。
加拿大皇后大学的Adam Chippindale对该项研究给予了高度的评价。他表示,研究基因选择中的性别差异并不容易。“首先,衡量适应性就是一项极为困难的工作,更不用说几代之间的不同性别差异性的传递……即使在实验室中也很难得到类似的数据,研究人员对马鹿进行了长达几十年的关注,所得到的结论也是十分出色的。”
Chippindale认为,如果能够收集到更多理想的数据,研究人员很可能会最终发现,这一与性别相关的基因选择是普遍存在的。“最优基因只有在合适的性别环境中才是最优的,”他说。(引自科学网)
原始出处:
Nature 447, 1107-1110 (28 June 2007) | doi:10.1038/nature05912; Received 11 December 2006; Accepted 11 May 2007
Sexually antagonistic genetic variation for fitness in red deer
Katharina Foerster1, Tim Coulson2, Ben C. Sheldon3, Josephine M. Pemberton1, Tim H. Clutton-Brock4 & Loeske E. B. Kruuk1
Institute of Evolutionary Biology, University of Edinburgh, Edinburgh EH9 3JT, UK
Division of Biology and Centre for Population Biology, Imperial College, Silwood Park, Ascot, Berkshire SL5 7PY, UK
Edward Grey Institute, Department of Zoology, University of Oxford, Oxford OX1 3PS, UK
Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK
Correspondence to: Katharina Foerster1Loeske E. B. Kruuk1 Correspondence and requests for materials should be addressed to K.F. (Email: foerster@orn.mpg.de) or L.E.B.K. (Email: loeske.kruuk@ed.ac.uk).
Evolutionary theory predicts the depletion of genetic variation in natural populations as a result of the effects of selection, but genetic variation is nevertheless abundant for many traits that are under directional or stabilizing selection1. Evolutionary geneticists commonly try to explain this paradox with mechanisms that lead to a balance between mutation and selection2. However, theoretical predictions of equilibrium genetic variance under mutation–selection balance are usually lower than the observed values, and the reason for this is unknown3. The potential role of sexually antagonistic selection in maintaining genetic variation has received little attention in this debate, surprisingly given its potential ubiquity in dioecious organisms. At fitness-related loci, a given genotype may be selected in opposite directions in the two sexes. Such sexually antagonistic selection will reduce the otherwise-expected positive genetic correlation between male and female fitness4. Both theory5, 6, 7 and experimental data8, 9, 10, 11, 12 suggest that males and females of the same species may have divergent genetic optima, but supporting data from wild populations are still scarce13, 14, 15. Here we present evidence for sexually antagonistic fitness variation in a natural population, using data from a long-term study of red deer (Cervus elaphus). We show that male red deer with relatively high fitness fathered, on average, daughters with relatively low fitness. This was due to a negative genetic correlation between estimates of fitness in males and females. In particular, we show that selection favours males that carry low breeding values for female fitness. Our results demonstrate that sexually antagonistic selection can lead to a trade-off between the optimal genotypes for males and females; this mechanism will have profound effects on the operation of selection and the maintenance of genetic variation in natural populations.