Data from: Coevolution of competing Callosobruchus species does not stabilize coexistence

Interspecific resource competition is expected to select for divergence in resource use, weakening interspecific relative to intraspecific competition, thus promoting stable coexistence. More broadly, because interspecific competition reduces fitness, any mechanism of interspecific competition should generate selection favoring traits that weaken interspecific competition. However, species also can adapt to competition by increasing their competitive ability, potentially destabilizing coexistence. We reared two species of bean beetles, the specialist Callosobruchus maculatus and the generalist C. chinensis, in allopatry and sympatry on a mixture of adzuki beans and lentils, and assayed mutual invasibility after four, eight, and twelve generations of evolution. Contrary to the expectation that coevolution of competitors will weaken interspecific competition, the rate of mutual invasibility did not differ between sympatry and allopatry. Rather, the invasion rate of C. chinensis, but not C. maculatus, increased with duration of evolution, as C. chinensis adapted to lentils without experiencing reduced adaptation to adzuki beans, and regardless of the presence or absence of C. maculatus. Our results highlight that evolutionary responses to interspecific competition promote stable coexistence only under specific conditions that can be difficult to produce in practice.种间资源竞争通常会驱动物种在资源利用策略上产生分化，进而削弱种间竞争相较于种内竞争的强度，最终促进种群的稳定共存。更广泛地说，由于种间竞争会降低种群适合度，任何种间竞争相关的机制都应催生选择压力，青睐那些能够弱化种间竞争的性状。然而，物种也可通过提升自身竞争能力来适应种间竞争，这一过程可能反而破坏共存的稳定性。我们以两种豆象为实验材料：专食性的绿豆象（Callosobruchus maculatus）与广食性的四纹豆象（C. chinensis），分别在异域（单独饲养）和同域（混合饲养）条件下，于赤小豆与扁豆的混合基质中开展进化实验，并在进化至第4、8、12代时，检测二者的相互入侵能力。与“竞争者的协同进化会削弱种间竞争”的经典预期相悖，同域组与异域组的相互入侵速率并无显著差异。与之相反，仅四纹豆象（而非绿豆象）的入侵速率随进化时长的增加而提升：四纹豆象对扁豆的适应性显著增强，同时并未降低对赤小豆的适应性，且这一现象不受绿豆象是否存在的影响。我们的研究结果凸显：针对种间竞争的进化响应仅能在特定条件下促进稳定共存，而这类条件在实际操作中往往难以实现。