Foster Kevin R, Shaulsky Gad, Strassmann Joan E, Queller David C, Thompson Chris R L
Ecology and Evolution, Rice University, Houston, Texas 77005, USA.
Nature. 2004 Oct 7;431(7009):693-6. doi: 10.1038/nature02894.
Most genes affect many traits. This phenomenon, known as pleiotropy, is a major constraint on evolution because adaptive change in one trait may be prevented because it would compromise other traits affected by the same genes. Here we show that pleiotropy can have an unexpected effect and benefit one of the most enigmatic of adaptations--cooperation. A spectacular act of cooperation occurs in the social amoeba Dictyostelium discoideum, in which some cells die to form a stalk that holds the other cells aloft as reproductive spores. We have identified a gene, dimA, in D. discoideum that has two contrasting effects. It is required to receive the signalling molecule DIF-1 that causes differentiation into prestalk cells. Ignoring DIF-1 and not becoming prestalk should allow cells to cheat by avoiding the stalk. However, we find that in aggregations containing the wild-type cells, lack of the dimA gene results in exclusion from spores. This pleiotropic linkage of stalk and spore formation limits the potential for cheating in D. discoideum because defecting on prestalk cell production results in an even greater reduction in spores. We propose that the evolution of pleiotropic links between cheating and personal costs can stabilize cooperative adaptations.
大多数基因会影响多种性状。这种现象被称为基因多效性，是进化的一个主要限制因素，因为一个性状的适应性变化可能会受到阻碍，因为它会损害受相同基因影响的其他性状。在这里，我们表明基因多效性可能会产生意想不到的效果，并有利于一种最神秘的适应性行为——合作。在社会变形虫盘基网柄菌中发生了一种惊人的合作行为，其中一些细胞死亡形成一个柄，将其他细胞作为生殖孢子高高举起。我们在盘基网柄菌中鉴定出一个基因dimA，它有两种截然不同的作用。它是接收导致分化为前柄细胞的信号分子DIF-1所必需的。忽略DIF-1而不变成前柄细胞应该会让细胞通过避开柄来作弊。然而，我们发现，在含有野生型细胞的聚集体中，缺乏dimA基因会导致被排除在孢子形成之外。柄和孢子形成的这种多效性联系限制了盘基网柄菌中作弊的可能性，因为在前柄细胞产生上的缺陷会导致孢子数量的更大减少。我们提出，作弊和个人代价之间的多效性联系的进化可以稳定合作适应性。
