How many species are infected with Wolbachia? – a statistical analysis of current data

Abstract

Wolbachia are intracellular bacteria found in many species of arthropods and nematodes. They manipulate the reproduction of their arthropod hosts in various ways, may play a role in host speciation and have potential applications in biological pest control. Estimates suggest that at least 20% of all insect species are infected with Wolbachia. These estimates result from several Wolbachia screenings in which numerous species were tested for infection; however, tests were mostly performed on only one to two individuals per species. The actual percent of species infected will depend on the distribution of infection frequencies among species. We present a meta-analysis that estimates percentage of infected species based on data on the distribution of infection levels among species. We used a beta-binomial model that describes the distribution of infection frequencies of Wolbachia, shedding light on the overall infection rate as well as on the infection frequency within species. Our main findings are that (1) the proportion of Wolbachia-infected species is estimated to be 66%, and that (2) within species the infection frequency follows a ‘most-or-few’ infection pattern in a sense that the Wolbachia infection frequency within one species is typically either very high (>90%) or very low (<10%).

Incidence of Wolbachia in aquatic insects

“…Taken together, these results are similar to the previous estimates of incidence within all arthropods of 40%, 52%, and 66% (Hilgenboecker et al., 2008; Weinert et al., 2015; Zug & Hammerstein, 2012). Despite clear evolutionary and ecological separation between aquatic and terrestrial insects, it is now clear from these data that Wolbachia infection is potentially common in aquatic ecosystems.…”

“…Estimates from other surveys appear to mostly include aquatic insects only haphazardly during sampling of terrestrial insects (but see Sontowski et al., 2015). Of the aquatic insects tested in previous studies , most belonged to Odonata, Coleoptera, or Diptera (Hilgenboecker et al., 2008; Weinert et al., 2015; Zug & Hammerstein, 2012). As a result of this targeted collection, our estimates of incidence in Odonata, Coleoptera, and Diptera have less uncertainty than estimates from Ephemeroptera, Trichoptera, and Plecoptera.…”

“…This is consistent with previous literature (Hilgenboecker et al., 2008; Weinert et al., 2015; Zug & Hammerstein, 2012) and means that a species is considered infected if at least 1/1,000 individuals carry Wolbachia . The proportion of the area under the curve that is >0.001 is equivalent to the proportion of species infected with Wolbachia (Hilgenboecker et al., 2008; Weinert et al., 2015; Zug & Hammerstein, 2012). To ensure that our model specifications were correct, we attempted to recreate previously published estimates of symbiont incidence for all arthropods based on the database of Weinert et al.…”

“…For example, using data from a recent global meta‐analysis (Hilgenboecker et al., 2008), we estimate that less than 5% of tested insect species have aquatic stages in their life‐history. Those surveys appear to only include the winged stages of some aquatic insects found in terrestrial areas, sampled haphazardly as part of broader surveys focused on terrestrial arthropods.…”

“…They typically infect the reproductive tissues of insects where they can manipulate reproduction of their hosts to enhance the vertical transmission of Wolbachia from mother to offspring (Werren et al., 2008). Recent estimates for Wolbachia placed infection rates among arthropod species at 40%, 52%, and 66% (Hilgenboecker, Hammerstein, Schlattmann, Telschow, & Werren, 2008; Weinert, Araujo‐Jnr, Ahmed, & Welch, 2015; Zug & Hammerstein, 2012). These estimates show that Wolbachia is a common symbiont within arthropods, making it arguably the most abundant intracellular bacteria (Werren et al., 2008).…”