Diversity and phylogenetic relationships of Wolbachia in Drosophila and other native Hawaiian insects

Abstract

Wolbachia is a genus of parasitic alphaproteobacteria found in arthropods and nematodes, and represents on of the most common, widespread endosymbionts known. Wolbachia affects a variety of reproductive functions in its host (e.g., male killing, cytoplasmic incompatibility, parthenogenesis), which have the potential to dramatically impact host evolution and species formation. Here, we present the first broad-scale study to screen natural populations of native Hawaiian insects for Wolbachia, focusing on the endemic Diptera. Results indicate that Wolbachia infects native Hawaiian taxa, with alleles spanning phylogenetic supergroups, A and B. The overall frequency of Wolbachia incidene in Hawaiian insects was 14%. The incidence of infection in native Hawaiian Diptera was 11% for individuals and 12% for all species screened. Wolbachia was not detected in two large, widespread Hawaiian dipteran families-Dolichopodidae (44 spp screened) and Limoniidae (12 spp screened). Incidence of infection within endemic Hawaiian lineages that carry Wolbachia was 18% in Drosophilidae species, 25% in Caliphoridae species, > 90% in Nesophrosyne species, 20% in Drosophila dasycnemia and 100% in Nesophrosyne craterigena. Twenty unique alleles were recovered in this study, of which 18 are newly recorded. Screening of endemic populations of D. dasycnemia across Hawaii Island revealed 4 unique alleles. Phylogenetic relationships and allele diversity provide evidence for horizontal transfer of Wolbachia among Hawaiian arthropod lineages.

Figure 1. Maximum-likelihood phylogeny of 284 Wolbachia isolates for surface protein gene wsp conducted using RAxML-HPC2 v7.2.7.^, Phylogeny is mid-point rooted, and color-coded according to the (A) (red) and (B) (blue) supergroup systematic classifications. Inset numbers correspond to bootstrap support values. Numbers 1–6 demarcate subsections of the phylogeny containing Wolbachia sequenced from Hawaiian insects in this study. Symbols α and β indicate groups that contain endemic Hawaiian taxa and those that do not, respectively. Hawaiian subsections are enlarged to show relationships and endemicity of constituent taxa in Figures 2–4.

Figure 4. Hawaiian Wolbachia subgroups 3 and 5 (supergroup A). See Figure 2 legend for explanation and interpretation of species abbreviations, branch support, DNA barcodes and other symbols.

Figure 2. Hawaiian Wolbachia subgroup 1 (supergroup B) from the maximum-likelihood phylogenetic reconstruction presented in Figure 1. The gray box delineates Hawaiian sequences, with endemic taxa starred. Hawaiian genera abbreviations are as follow: Dr. = Drosophila (Diptera: Drosophilidae), Dy. = Dyscritomyia (Diptera: Calliphoridae), S. = Scaptomyza (Diptera: Drosophilidae), and N. = Nesophrosyne (Hemiptera Cicadellidae). Branch numbers correspond to bootstrap values (BS < 50 not shown). Names correspond to the taxonomic placement of the host species and unique allele name (e.g., wGiff); parenthetical three-digit barcode corresponds to Table S1.

Figure 3. Hawaiian Wolbachia subgroup 2 (supergroup B). See Figure 2 legend for explanation and interpretation of species abbreviations, branch support, DNA barcodes and other symbols.