Host phylogeny and ecological associations best explain Wolbachia host
shifts in scale insects Running title: Wolbachia host shifts
Abstract
Wolbachia are among the most prevalent and widespread endosymbiotic
bacteria on earth. Wolbachia’s success in infecting an enormous number
of arthropod species is attributed to two features: the range of
phenotypes they induce in their hosts, and their ability to switch
between host species. Whilst much progress has been made in elucidating
their induced phenotypes, our understanding of Wolbachia host shifting
is still very limited: we lack answers to even fundamental questions
concerning Wolbachia’s routes of transfer and the importance of factors
influencing host shifts. Here, we investigate the diversity and
host-shift patterns of Wolbachia in scale insects, a group of arthropods
with intimate associations with other insects that make them well-suited
to studying host shifts. Using Illumina multi-target amplicon sequencing
of Wolbachia-infected scale insects and their direct associates we
determined the identity of all Wolbachia strains. We then fitted a
Generalised Additive Mixed Model (GAMM) to our data to estimate the
influence of host phylogeny and the geographic distribution on Wolbachia
strain sharing among scale insect species. The model predicts no
significant contribution of host geography but strong effects of host
phylogeny, with high rates of Wolbachia sharing among closely related
species and a sudden drop-off in sharing with increasing phylogenetic
distance. We also detected the same Wolbachia strain in scale insects
and several intimately associated species (ants, wasps, beetles, and
flies). This indicates putative host shifts and potential routes of
transfers via these associates and highlights the importance of
ecological connectivity in Wolbachia host-shifting.