Population Divergences Of Representative Aphis Species And Their Relationships With Host Plants

Aphids are worldwide pests that inflicts serious damage to crops.They also have extraordinary abilities to transmit many serious plant viruses.The complexity of aphid–plant interactions is important to understanding the evolutionary mechanisms responsible for most of the diverse plant-feeding insects.Based on a worldwide comprehensive dataset of aphid species and their host plant records,this thesis investigated the macroevolutionary patterns between aphids and host plants.Furthermore,two mitochondrial markers(COI and Cytb),one nuclear marker(EF-1α)and an endosymbiont gene(gnd)were used to investigate the population divergence mechanisms of two representative Aphis species.The main results and conclusions are as follows.1.The main macroevolution relationship between aphids and host plant are followed:(1)we found a significant correlation between host plant diversity and aphid species richness.(2)the patterns of host plant utilization were different among aphid subfamilies.We found a mixed system with congruent associations between aphid subfamilies and its’ host plant(Adelgidae,Mindarinae,Aphidinae and Eriosomatinae),but aslo numerous random associations.(3)the phylogenetic pattern of several aphid subfamilies were similar with their host plant orders(Adelgidae,Phylloxerinae and Phylloxerininae),but most of the rest of aphid subfamilies does not show in this pattern.2.Based on COI gene,both population divergence of Aphis spiraecola and A.gossypii were obtained in high level,the maximum genetic distance within species reached 2.39% and 2.59% respectively,which far exceed the 2% DNA barcode threshold proposed by previous peers.Two distinct clades of A.spiraecola and A.gossypii were obtained in phylogenetic analysis with high bootstrap value.Furthermore,the phylogenetic trees of other genes were support the topological structure of COI gene.In the A.spiraecola haplotype network,we found that the haplotype of Rosaceae and Compositae displayed high genetic divergence,which accordance with the genetic distance analysis.The haplotype network of A.gossypii showed that the haplotype of Commelinaceae had high genetic divergence.We speculated that the population divergence of A.spiraecola and A.gossypii were tightly tied to host plant.By analyzing the relationship between aphids and host plants from both macroevolutionary and microevolutionary perspectives,this thesis indicates that host plants may play an important role in the divergence of aphids and lead to the formation of aphid species diversity.