Green A M, Mueller U G, Adams R M M
Section of Integrative Biology, University of Texas, Austin, TX 78712, USA.
Mol Ecol. 2002 Feb;11(2):191-5. doi: 10.1046/j.1365-294x.2002.01433.x.
Fungal cultivars of fungus-growing ants (Attini, Formicidae) are carried by dispersing queens from parent to offspring nest. This vertical cultivar transmission between generations is thought to result in long-term ant-fungus coevolution and selection for beneficial cultivar traits that maximize harvests and thus colony productivity. In contrast to this traditional view of vertical cultivar transmission, frequent horizontal cultivar transmission between ant species is implicated by a phylogenetic analysis of 72 cultivars propagated by two fungus-growing ant species coexisting sympatrically in central Panama. The two ant species are specialized on the same group of closely related cultivars, but in six of 12 cultivar clades identifiable within this group, cultivars from both ant species were united in the same clade. Five of these 'mixed' clades were supported by bootstrap values of about 90% or higher. In one instance, colonies from the two ant species cultivated the same, genetically identical, cultivar clone. These phylogenetic patterns indicate that: (i) cultivar exchanges between the two ant species occur routinely throughout ecological time; and that (ii) coevolutionary processes between ants and their fungi are more diffuse than previously assumed. Because the two ant species are specialized on a narrow group of closely related cultivars that they regularly exchange among each other, but not with other sympatric ant species, cultivar exchanges are constrained, most likely, by ant preferences for their own cultivar group or by stringent selection against transitions of ant lineages to distantly related cultivars.
切叶蚁（蚁科切叶蚁亚科）的真菌培养品种由扩散的蚁后从亲代巢穴携带到子代巢穴。这种世代间的垂直品种传播被认为会导致长期的蚂蚁 - 真菌共同进化，并选择有利于最大化收获从而提高蚁群生产力的品种特性。与这种传统的垂直品种传播观点相反，对在巴拿马中部同域共存的两种切叶蚁所繁殖的72个品种进行的系统发育分析表明，蚂蚁物种之间频繁发生水平品种传播。这两种蚂蚁专门针对同一组密切相关的品种，但在该组内可识别的12个品种分支中的6个中，来自两种蚂蚁的品种被归在同一分支中。其中五个“混合”分支得到了约90%或更高的自展值支持。在一个实例中，来自这两种蚂蚁的蚁群培养了相同的、基因相同的品种克隆。这些系统发育模式表明：（i）两种蚂蚁之间的品种交换在整个生态时间内经常发生；以及（ii）蚂蚁与其真菌之间的共同进化过程比以前假设的更为分散。由于这两种蚂蚁专门针对一组狭窄的密切相关品种，它们经常相互交换，但不与其他同域蚂蚁物种交换，品种交换很可能受到蚂蚁对自身品种组的偏好或对蚂蚁谱系向远缘品种转变的严格选择所限制。
