title: Side-stepping secondary symbionts: widespread horizontal transfer across and beyond the Aphidoidea.
abstract: To elucidate the co-evolutionary relationships between phloem-feeding insects and their secondary, or facultative, bacterial symbionts, we explore the distributions of three such microbes--provisionally named the R-type (or PASS, or S-sym), T-type (or PABS), and U-type--across a number of aphid and psyllid hosts through the use of diagnostic molecular screening techniques and DNA sequencing. Although typically maternally transmitted, phylogenetic and pairwise divergence analyses reveal that these bacteria have been independently acquired by a variety of unrelated insect hosts, indicating that horizontal transfer has helped to shape their distributions. Based on the high genetic similarity between symbionts in different hosts, we argue that transfer events have occurred recently on an evolutionary timescale. In several instances, however, closely related symbionts associate with related hosts, suggesting that horizontal transfer between distant relatives may be rarer than transmission between close relatives. Our findings on the prevalence of these symbionts within many aphid taxa, along with published observations concerning their effects on host fitness, imply a significant role of facultative symbiosis in aphid ecology and evolution.
authors.affiliation: University of Arizona, Department of Ecology and Evolutionary Biology, Biological Sciences West, Tucson, Arizona 85721, USA. jarussel@u.arizona.edu
authors.forename: J A
authors.initials: JA
authors.lastname: Russell
authors.forename: A
authors.initials: A
authors.lastname: Latorre
authors.forename: B
authors.initials: B
authors.lastname: Sabater-Muñoz
authors.forename: A
authors.initials: A
authors.lastname: Moya
authors.forename: N A
authors.initials: NA
authors.lastname: Moran
mesh_terms: D000818:Animals; D001042:Aphids / Q000382:microbiology*; D001483:Base Sequence; D017931:DNA Primers; D004275:DNA, Ribosomal / Q000235:genetics; D020563:Gammaproteobacteria / Q000235:genetics* / Q000302:isolation & purification; D014644:Genetic Variation; D006430:Hemiptera / Q000382:microbiology*; D008969:Molecular Sequence Data; D010802:Phylogeny; D013559:Symbiosis
chemical_list: D017931:DNA Primers; D004275:DNA, Ribosomal