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...

种间资源竞争（interspecific resource competition）被认为会选择资源利用的分化，减弱种间竞争相对于种内竞争（intraspecific competition）的强度，从而促进稳定共存（stable coexistence）。更广泛地说，由于种间竞争降低适合度（fitness），任何种间竞争机制都应产生选择压力，倾向于有利于减弱种间竞争的性状。然而，物种也可通过提高竞争能力来适应竞争，这可能破坏共存的稳定性。我们在红小豆（adzuki beans）和小扁豆（lentils）的混合物上，分别以异域分布（allopatry）和同域分布（sympatry）方式饲养了两种豆象（bean beetles）——专食性（specialist）四纹豆象（Callosobruchus maculatus）和广食性（generalist）绿豆象（C. chinensis），并在进化4代、8代和12代后测定了它们的相互入侵性（mutual invasibility）。与竞争者协同进化（coevolution）会减弱种间竞争的预期相反，同域分布与异域分布群体间的相互入侵率并无差异。相反，C. chinensis的入侵率（而非C...