如果說自然選擇既是普遍的又是無情的，那么群體中的差異又是如何維持的呢,？
演化生物學中這一迫切需要回答的問題,，由Kimberly Hughes及同事在對虹鳉(孔雀魚)所做的一項研究中得到了回答。
虹鳉是一個特別有用的模型系統(tǒng),，因為雄性虹鳉的顏色是已知遺傳變異性最大的生物性狀之一,。以前的研究表明，在一個由顏色鮮艷的虹鳉組成的種群中,，出乎意料的是,，具有罕見顏色圖案的雄性往往比較興旺。
Hughes等人利用精心控制的野生種群發(fā)現(xiàn),，不僅雌性虹鳉喜歡與這些罕見雄性交配,，而且這些雄性也比那些身上條紋比較普通的雄性能生出更多后代。
這一現(xiàn)象（被稱為“負頻率依賴性選擇”）表明與眾不同是有價可循的,，同時也為種群中差異性的維持提供了一個機制,。（生物谷Bioon.com）
生物谷推薦的英文摘要
Nature doi:10.1038/nature12717
Mating advantage for rare males in wild guppy populations
Kimberly A. Hughes，Anne E. Houde,，Anna C. Price& F. Helen Rodd
To understand the processes that maintain genetic diversity is a long-standing challenge in evolutionary biology,， with implications for predicting disease resistance， response to environmental change,， and population persistence1,， 2， 3. Simple population genetic models are not sufficient to explain the high levels of genetic diversity sometimes observed in ecologically important traits2. In guppies (Poecilia reticulata)， male colour pattern is both diverse and heritable,， and is arguably one of the most extreme examples of morphological polymorphism known4,， 5. Negative frequency-dependent selection (NFDS)， a form of selection in which genotypes are favoured when they are rare6,， can potentially maintain such extensive polymorphism,， but few experimental studies have confirmed its operation in nature7， 8. Here we use highly replicated experimental manipulations of natural populations to show that males with rare colour patterns have higher reproductive fitness,， demonstrating NFDS mediated by sexual selection. Rare males acquired more mates and sired more offspring compared to common males and,， as previously reported， had higher rates of survival8. Orange colour,， implicated in other studies of sexual selection in guppies,， did predict male reproductive success， but only in one of three populations. These data support the hypothesis that NFDS maintains diversity in the colour patterns of male guppies through two selective agents,， mates and predators. Similar field-based manipulations of genotype frequencies could provide a powerful approach to reveal the underlying ecological and behavioural mechanisms that maintain genetic and phenotypic diversity.
