Institute for Integrative Biology, ETH Zürich, Zürich, Switzerland
Institute of Biology, Leiden University, Leiden, The Netherlands.
Proc Biol Sci. 2018 Mar 28;285(1875). doi: 10.1098/rspb.2018.0054.
Microbial genotypes with similarly high proficiency at a cooperative behaviour in genetically pure groups often exhibit fitness inequalities caused by social interaction in mixed groups. Winning competitors in this scenario have been referred to as 'cheaters' in some studies. Such interaction-specific fitness inequalities, as well as social exploitation (in which interaction between genotypes increases absolute fitness), might evolve due to selection for competitiveness at the focal behaviour or might arise non-adaptively due to pleiotropy, hitchhiking or genetic drift. The bacterium sporulates during cooperative development of multicellular fruiting bodies. Using lineages that underwent experimental evolution in allopatry without selection on sporulation, we demonstrate that interaction-specific fitness inequalities and facultative social exploitation during development readily evolved indirectly among descendant lineages. Fitness inequalities between evolved genotypes were not caused by divergence in developmental speed, as faster-developing strains were not over-represented among competition winners. In competitions between ancestors and several evolved strains, all evolved genotypes produced more spores than the ancestors, including losers of evolved-versus-evolved competitions, indicating that adaptation in non-developmental contexts pleiotropically increased competitiveness for spore production. Overall, our results suggest that fitness inequalities caused by social interaction during cooperative processes may often evolve non-adaptively in natural populations.
在遗传纯合群体中，具有高度合作行为能力的微生物基因型通常会因混合群体中的社会相互作用而表现出适应度不平等。在这种情况下，获胜的竞争者在一些研究中被称为“骗子”。这种特定于相互作用的适应度不平等，以及社会剥削（即基因型之间的相互作用会增加绝对适应度），可能是由于对焦点行为的竞争力的选择而进化的，也可能是非适应性进化的，例如多效性、 hitchhiking 或遗传漂变。细菌在多细胞生殖体的合作发育过程中形成孢子。使用在没有孢子形成选择的异域进行实验进化的谱系，我们证明了在发育过程中，特定于相互作用的适应度不平等和兼性社会剥削很容易在后代谱系中间接进化。进化基因型之间的适应度不平等不是由发育速度的差异引起的，因为较快发育的菌株在竞争胜利者中并不占优势。在祖先和几个进化菌株之间的竞争中，所有进化的基因型产生的孢子都比祖先多，包括在进化对进化的竞争中失败的菌株，这表明在非发育环境中的适应会多效性地增加对孢子产生的竞争力。总的来说，我们的结果表明，在合作过程中由社会相互作用引起的适应度不平等可能经常在自然种群中以非适应性的方式进化。
