Schtickzelle Nicolas, Fjerdingstad Else J, Chaine Alexis, Clobert Jean
Biodiversity Research Centre, Université catholique de Louvain, Croix du Sud 4, 1348 Louvain-la-Neuve, Belgium.
BMC Evol Biol. 2009 Oct 14;9:251. doi: 10.1186/1471-2148-9-251.
The evolution of social cooperation is favored by aggregative behavior to facilitate stable social structure and proximity among kin. High dispersal rates reduce group stability and kin cohesion, so it is generally assumed that there is a fundamental trade-off between cooperation and dispersal. However, empirical tests of this relationship are rare. We tested this assumption experimentally using ten genetically isolated strains of a ciliate, Tetrahymena thermophila.
The propensity for social aggregation was greater in strains with reduced cell quality and lower growth performance. While we found a trade-off between costly aggregation and local dispersal in phenotypic analyses, aggregative strains showed a dispersal polymorphism by producing either highly sedentary or long-distance dispersive cells, in contrast to less aggregative strains whose cells were monomorphic local dispersers.
High dispersal among aggregative strains may not destroy group stability in T. thermophila because the dispersal polymorphism allows social strains to more readily escape kin groups than less aggregative strains, yet still benefit from stable group membership among sedentary morphs. Such dispersal polymorphisms should be common in other social organisms, serving to alter the nature of the negative impact of dispersal on social evolution.
聚集行为有利于社会合作的进化，以促进稳定的社会结构和亲属之间的亲近。高扩散率会降低群体稳定性和亲属凝聚力，因此通常认为合作与扩散之间存在根本的权衡。然而，对这种关系的实证检验很少。我们使用十种遗传隔离的嗜热四膜虫菌株进行了实验来检验这一假设。
细胞质量降低和生长性能较低的菌株中社会聚集倾向更大。虽然我们在表型分析中发现了代价高昂的聚集与局部扩散之间的权衡，但聚集菌株通过产生高度定居或长距离扩散的细胞表现出扩散多态性，相比之下，较少聚集的菌株其细胞是单态的局部扩散者。
聚集菌株中的高扩散可能不会破坏嗜热四膜虫的群体稳定性，因为扩散多态性使社会菌株比聚集性较低的菌株更容易逃离亲属群体，但仍能从定居形态中的稳定群体成员身份中受益。这种扩散多态性在其他社会生物中应该很常见，有助于改变扩散对社会进化负面影响的性质。
