Molecular systematics of aphids and their primary endosymbionts

Aphids constitute a monophyletic group within the order Homoptera (i.e., su perfamily Aphidoidea). The Aphidoidea originated in the Jurassic about 150 my ago from some aphidiform ancestor whose origin can be traced back to abo ut 250 my ago. They exhibit a mutualistic association with intracellular ba cteria (Buchnera sp.) related to Escherichia coli. Buchnera is usually cons idered the aphids' primary endosymbiont. The association is obligate for bo th partners. The 16S rDNA-based phylogeny of Buchnera from four aphid famil ies showed complete concordance with the morphology-based phylogeny of thei r aphid hosts, which pointed to a single original infection in a common anc estor of aphids some 100-250 my ago followed cospeciation of aphids and Buc hnera. This study concentrated on the molecular phylogeny of both th aphids and their primary endosymbionts of five aphid families including for the f irst time representatives of the family Lachnidae. We discuss results based on two Buchnera genes (16S rDNA and the beta subunit of the F-ATPase compl ex) and on one host mitochondrial gene (the subunit 6 of the F-ATPase compl ex). Although our data do not allow definitive evolutionary relationships t o be established among the different aphid families, some traditionally acc epted groupings are put into question from both bacterial and insect data. In particular, the Lachnidae and the Aphididae, which from morphological da ta are considered recently evolved sister groups, do not seem to be as clos ely related as is usually accepted. Finally, we discuss our results in the light of the proposed parallel evolution of aphids and their endosymbionts. (C) 2001 Academic PressAphids constitute a monophyletic group within the o rder Homoptera (i.e., superfamily Aphidoidea). The Aphidoidea originated in the Jurassic about 150 my ago from some aphidiform ancestor whose origin c an be traced back to about 250 my ago. They exhibit a mutualistic associati on with intracellular bacteria (Buchnera sp.) related to Escherichia coli. Buchnera is usually considered the aphids'primary endosymbiont. The associa tion is obligate for both partners. The 16S rDNA-based phylogeny of Buchner a from four aphid families showed complete concordance with the morphology- based phylogeny of their aphid hosts, which pointed to a single original in fection in a common ancestor of aphids some 100 - 250 my ago followed cospe ciation of aphids and Buchnera. This study concentrated on the molecular ph ylogeny of both th aphids and their primary endosymbionts of five aphid fam ilies including for the first time representatives of the family Lachnidae. We discuss results based on two Buchnera genes (16S rDNA and the 13 subuni t of the F-ATPase complex) and on one host mitochondrial gene (the subunit 6 of the F-ATPase complex). Although our data do not allow definitive evolu tionary relationships to be established among the different aphid families, some traditionally accepted groupings are put into question from both bact erial and insect data. In particular, the Lachnidae and the Aphididae, whic h from morphological data are considered recently evolved sister groups, do not seem to be as closely related as is usually accepted. Finally, we disc uss our results in the light of the proposed parallel evolution of aphids a nd their endosymbionts. (C) 2001 Academic Press.