Department of Ecology and Evolutionary Biology, Rice University, 6100 Main Street, Houston, Texas 77005, USA.
Nature. 2011 Jan 20;469(7330):393-6. doi: 10.1038/nature09668.
Agriculture has been a large part of the ecological success of humans. A handful of animals, notably the fungus-growing ants, termites and ambrosia beetles, have advanced agriculture that involves dispersal and seeding of food propagules, cultivation of the crop and sustainable harvesting. More primitive examples, which could be called husbandry because they involve fewer adaptations, include marine snails farming intertidal fungi and damselfish farming algae. Recent work has shown that microorganisms are surprisingly like animals in having sophisticated behaviours such as cooperation, communication and recognition, as well as many kinds of symbiosis. Here we show that the social amoeba Dictyostelium discoideum has a primitive farming symbiosis that includes dispersal and prudent harvesting of the crop. About one-third of wild-collected clones engage in husbandry of bacteria. Instead of consuming all bacteria in their patch, they stop feeding early and incorporate bacteria into their fruiting bodies. They then carry bacteria during spore dispersal and can seed a new food crop, which is a major advantage if edible bacteria are lacking at the new site. However, if they arrive at sites already containing appropriate bacteria, the costs of early feeding cessation are not compensated for, which may account for the dichotomous nature of this farming symbiosis. The striking convergent evolution between bacterial husbandry in social amoebas and fungus farming in social insects makes sense because multigenerational benefits of farming go to already established kin groups.
农业一直是人类生态成功的重要组成部分。少数几种动物，特别是菌食性蚂蚁、白蚁和粉蠹，已经发展出了涉及食物传播和播种、作物种植和可持续收获的先进农业。更原始的例子可以被称为畜牧业，因为它们涉及的适应性较少，包括海洋蜗牛种植潮间带真菌和雀鲷养殖藻类。最近的研究表明，微生物在合作、交流和识别等复杂行为方面与动物惊人地相似，还有许多种共生关系。在这里，我们展示了社会变形虫盘基网柄菌具有一种原始的农耕共生关系，包括对作物的传播和谨慎收获。大约三分之一的野生采集克隆参与了对细菌的畜牧业。它们不会在其栖息地中消耗所有的细菌，而是会提前停止进食，并将细菌纳入其生殖体中。然后，它们在孢子传播过程中携带细菌，并可以播种新的食物作物，如果在新地点缺乏可食用的细菌，这是一个主要优势。然而，如果它们到达已经含有适当细菌的地点，提前停止进食的成本就得不到补偿，这可能解释了这种农耕共生关系的二分法性质。社会变形虫中的细菌畜牧业和社会性昆虫中的真菌农业之间引人注目的趋同进化是有道理的，因为农业的多代收益都流向了已经建立的亲缘群体。
