Studies On Divergence Of Sitobion Avenae Populations From Both Sides Of The Qingling Mountains

Sitobion avenae (F.) is a cosmopolitan cereal pest, but geographic barriers like theQinling Mountains in Shaanxi Province of China may lead to isolation among its populations,thus causing allopatric speciation. We sampled S. avenae populations from areas north andsouth of the Qinling Mountains. First, we tested them at20OC in common gardenexperiments. The results showed that northern populations had reduced developmental timefor first instar nymphs, but prolonged for third and fourth instar nymphs compared to southernpopulations. The post-reproductive time and total lifespan of adults from southern populationswere longer than those from northern populations, but no significant differences were foundin reproductive time or age at first reproduction. Southern populations showed higher lifetimeand daily fecundities than northern ones. Significant differences were found in correlation oflife-history traits between northern and southern populations. Principal component analyses(PCA) of S. avenae’s vital life-history traits showed separation of populations from threesouthern locations, indicating their local adaptation. The clustering patterns generated by PCAalso showed divergence between northern and southern populations. Alatae of S. avenaeseemed to be able to disperse across the Qinling Mountains, which was indicated by theclustering together of some individuals from one side of the mountains with those from theother side. Second, we investigated genetic differences between populations of S. avenae,using seven microsatellite loci. The results showed that there were significant differencesbetween southern and northern populations, but the genetic differentiation among them at themolecular level was low. The level of genetic differentiation among southern populations washigher than that of northern populations. The impacts of the Qinling Mountains on thedivergence and gene flow among S. avenae populations, as well as the potential of allopatricspeciation for this species, are discussed.