Section of Integrative Biology, The University of Texas at Austin, Austin, Texas 78712, USA.
Evolution. 2010 Jul;64(7):2166-72. doi: 10.1111/j.1558-5646.2010.00959.x. Epub 2010 Jan 21.
Cooperation violates the view of "nature red in tooth and claw" that prevails in our understanding of evolution, yet examples of cooperation abound. Most work has focused on maintenance of cooperation within a single species through mechanisms such as kin selection. The factors necessary for the evolutionary origin of aiding unrelated individuals such as members of another species have not been experimentally tested. Here, I demonstrate that cooperation between species can be evolved in the laboratory if (1) there is preexisting reciprocation or feedback for cooperation, and (2) reciprocation is preferentially received by cooperative genotypes. I used a two species system involving Salmonella enterica ser. Typhimurium and an Escherichia coli mutant unable to synthesize an essential amino acid. In lactose media Salmonella consumes metabolic waste from E. coli, thus creating a mechanism of reciprocation for cooperation. Growth in a spatially structured environment assured that the benefits of cooperation were preferentially received by cooperative genotypes. Salmonella evolved to aid E. coli by excreting a costly amino acid, however this novel cooperation disappeared if the waste consumption or spatial structure were removed. This study builds on previous work to demonstrate an experimental origin of interspecific cooperation, and to test the factors necessary for such interactions to arise.
合作违反了我们对进化的理解中普遍存在的“弱肉强食”观点，但合作的例子比比皆是。大多数研究都集中在通过亲缘选择等机制来维持同一物种内的合作。然而，对于帮助与自身无关的个体（例如另一个物种的成员）的进化起源所需的因素，尚未经过实验测试。在这里，我证明如果存在（1）合作的预先存在的互惠或反馈，以及（2）合作的基因型更优先地获得互惠，那么物种之间的合作就可以在实验室中进化。我使用了涉及沙门氏菌血清型 Typhimurium和一种无法合成必需氨基酸的大肠杆菌突变体的两种物种系统。在乳糖培养基中，沙门氏菌消耗大肠杆菌的代谢废物，从而为合作创造了互惠的机制。在空间结构环境中生长确保了合作的好处更优先地被合作的基因型获得。沙门氏菌通过排泄昂贵的氨基酸来进化以帮助大肠杆菌，但是如果去除废物消耗或空间结构，这种新型合作就会消失。这项研究建立在以前的工作基础上，证明了种间合作的实验起源，并测试了这种相互作用出现所需的因素。
