Evolutionary genetics of fitness and gender

两性被选择为不同的功能，但共享相同的基因库。这一观察结果对女性和男性如何进化有着深远的影响，并表明冲突可能是他们进化互动的重要组成部分。如果两性在生殖控制权上发生冲突，可能会导致推动快速进化变化的军备竞赛。这种两性间的“红皇后”过程挑战了传统的性选择观点，并表明仅仅是繁殖方面的冲突就足以推动新物种的形成。我们对果蝇模型遗传系统的研究表明，军备竞赛在这个物种中是快节奏的。当我们通过实验阻止一种性别（雌性）进化出限制雄性基因表达的独特遗传技巧时，我们发现雄性通过行为、生化信号和直接胁迫，在短短几十代的时间里迅速进化出优势。如果同一基因在两性中表达，但其功能选择不同，那么结果可能是一场“拔河比赛”。第二种形式的冲突是可以解决的：通过各种遗传机制，许多基因只在女性或男性中表达。然而，我们的工作表明，存在着相当高水平的未解决冲突。我们发现，男性健康水平的提高伴随着女性健康水平的相应下降，反之亦然。帮助雌性生存或繁殖的基因对雄性也有有害的影响。在许多暗示中，低适应性基因在人群中很常见，通过配偶选择获得的潜在收益将受到性冲突的有害影响的限制。我们的研究表明，X染色体是这种冲突的主要来源，它加剧了择偶问题，因为X染色体上的雄性优势基因总是遗传给女儿。如果雄性把它们的X基因传给儿子，这个问题就会得到缓解，就像鸟类或蝴蝶那样。这也许可以解释为什么鸟类和蝴蝶有如此明亮的色彩和戏剧性的求爱表演。总的来说，性冲突似乎是进化变化的关键驱动力，并且可以解释为什么导致不育的病理在有性物种中很常见，包括我们自己。

The two sexes are selected for different functions yet share the same gene pool. This observation has profound implications for how females and males are expected to evolve, and suggests that conflict may be an important part of their evolutionary interaction. If the sexes are in conflict over control of reproduction, arms races that drive rapid evolutionary change may result. This intersexual 'Red Queen' process challenges traditional views of sexual selection, and suggests that conflict over reproduction alone may be enough to drive the formation of new species. Our research in the Drosophila model genetic system shows that the arms race is fast-paced in this species. When we experimentally prevent one sex (females) from evolving with unique genetic tricks that limit gene expression to males, we see that males quickly evolve to take advantage - through behaviour, through biochemical signals and through direct coercion - over mere dozens of generations. If the same gene is expressed in both sexes, but its function is selected divergently, then a 'tug-of-war' may be the outcome. This second form of conflict can be resolved: many genes are only expressed in females or in males, through a variety of genetic mechanisms. However, our work demonstrates that remarkably high levels of unresolved conflict exist. We find that increases in male fitness are accompanied by matching declines in female fitness, and vice versa. The same genes that help a female survive or reproduce have a harming impact on males. Among the many implications are that low fitness genes are common in populations, and potential gains made via mate choice will be limited by the harming effects of sexual conflict. Our work shows that the X chromosome is the major source of this conflict, worsening the problem of mate choice because male-benefit genes on the X always go to daughters. This problem is alleviated if males transmit their X to sons, as occurs in birds or butterflies. This may account for why birds and butterflies have such bright colouration and dramatic courtship displays. Overall, sexual conflict appears to be a key driver of evolutionary change, and may explain why pathologies causing infertility are common in sexual species, including our own.