Fitness traits and underlying genetic variation related to host plant specialization in the aphid Sitobion avenae

Sitobion avenae (F.) is an important cereal pest worldwide that can survive on various plants in the Poaceae, but divergent selection on different host plants should promote the evolution of specialized genotypes or host races. In order to evaluate their resource use strategies, clones of S. avenae were collected from oat and barley. Host-transfer experiments for these clones were conducted in the laboratory to compare their fitness traits. Our results demonstrated that barley clones had significantly lower fecundity and tended to have longer developmental times when transferred from barley to oat. However, oat clones developed faster after they were transferred to barley. Clones from oat and barley had diverged to a certain extent in terms of fecundity and developmental time of the nymphs. The separation of barley clones and oat clones of S. avenae was also evident in a principal component analysis. Barley clones tended to have higher broad-sense heritabilities for fitness traits than oat clones, indicating the genetic basis of differentiation between them. Barley clones showed significantly higher extent of specialization compared to oat clones from two measures of specialization (i.e., Xsp and Ysp). Therefore, barley clones were specialized to a certain extent, but oat clones appeared to be generalized. The fitness of S. avenae clones tended to increase with higher extent of specialization. The evolution toward ecological specialization in S. avenae clones, as well as the underlying genetic basis, was discussed.