Strassmann Joan E
Department of Biology, Washington University in St. Louis, CB1137, St. Louis, Missouri, 63130-4899.
J Eukaryot Microbiol. 2016 May;63(3):378-83. doi: 10.1111/jeu.12307. Epub 2016 Mar 11.
Evolved cooperation is stable only when the benefactor is compensated, either directly or through its relatives. Social amoebae cooperate by forming a mobile multicellular body in which, about 20% of participants ultimately die to form a stalk. This benefits the remaining individuals that become hardy spores at the top of the stalk, together making up the fruiting body. In studied species with stalked migration, P. violaceum, D. purpureum, and D. giganteum, sorting based on clone identity occurs in laboratory mixes, maintaining high relatedness within the fruiting bodies. D. discoideum has unstalked migration, where cell fate is not fixed until the slug forms a fruiting body. Laboratory mixes show some degree of both spatial and genotype-based sorting, yet most laboratory fruiting bodies remain chimeric. However, wild fruiting bodies are made up mostly of clonemates. A genetic mechanism for sorting is likely to be cell adhesion genes tgrB1 and tgrC1, which bind to each other. They are highly variable, as expected for a kin discrimination gene. It is a puzzle that these genes do not cause stronger discrimination between mixed wild clones, but laboratory conditions or strong sorting early in the social stage diminished by later slug fusion could be explanations.
只有当施惠者得到直接补偿或通过其亲属得到补偿时，进化而来的合作才是稳定的。社会性变形虫通过形成一个可移动的多细胞体来进行合作，在这个多细胞体中，约20%的参与者最终会死亡以形成一个柄。这对其余个体有利，它们会在柄的顶端形成耐寒的孢子，共同构成子实体。在已研究的有柄迁移物种中，如紫色盘基网柄菌、紫柄丝盖伞和巨大丝盖伞，在实验室混合培养中会基于克隆身份进行分选，从而在子实体内保持高度的亲缘关系。盘基网柄菌有无柄迁移，在蛞蝓状群体形成子实体之前，细胞命运并不固定。实验室混合培养显示出一定程度的基于空间和基因型的分选，但大多数实验室子实体仍然是嵌合体。然而，野生子实体大多由克隆体组成。分选的遗传机制可能是相互结合的细胞黏附基因tgrB1和tgrC1。正如亲缘识别基因所预期的那样，它们具有高度变异性。这些基因在混合野生克隆之间没有引起更强的区分，这是一个谜题，但实验室条件或社会阶段早期的强分选随后因蛞蝓状群体融合而减弱可能是解释原因。
