Towards unravelling Wolbachia global exchange: a contribution from the Bicyclus and Mylothris butterflies in the Afrotropics

Abstract

Background Phylogenetically closely related strains of maternally inherited endosymbiotic bacteria are often found in phylogenetically divergent, and geographically distant insect host species. The interspecies transfer of the symbiont Wolbachia has been thought to have occurred repeatedly, facilitating its observed global pandemic. Few ecological interactions have been proposed as potential routes for the horizontal transfer of Wolbachia within natural insect communities. These routes are however likely to act only at the local scale, but how they may support the global distribution of some Wolbachia strains remains unclear. Results Here, we characterize the Wolbachia diversity in butterflies from the tropical forest regions of central Africa to discuss transfer at both local and global scales. We show that numerous species from both the Mylothris (family Pieridae) and Bicyclus (family Nymphalidae) butterfly genera are infected with similar Wolbachia strains, despite only minor interclade contacts across the life cycles of the species within their partially overlapping ecological niches. The phylogenetic distance and differences in resource use between these genera rule out the role of ancestry, hybridization, and shared host-plants in the interspecies transfer of the symbiont. Furthermore, we could not identify any shared ecological factors to explain the presence of the strains in other arthropod species from other habitats, or even ecoregions. Conclusion Only the systematic surveys of the Wolbachia strains from entire species communities may offer the material currently lacking for understanding how Wolbachia may transfer between highly different and unrelated hosts, as well as across environmental scales.

A prevalence survey of Wolbachia in butterflies from southern China

“…Most of the Wolbachia STs detected in butterflies in this study (14 species, 88%) belonged to supergroup B, whereas those found in Ypthima praenubila Leech and Ypthima spec. (Nymphalidae) belonged to supergroup A, similar to previous studies (e.g., Ahmed et al, 2016;Ilinsky & Kosterin, 2017;Duplouy et al, 2020).…”

“…The infection incidence in our collection was lower than reported elsewhere (Tagami & Miura, 2004;Salunke et al, 2012;Ilinsky & Kosterin, 2017;Duplouy et al, 2020). Possibly, the actual percentage of Wolbachia infection is higher than estimated, due to the relatively small sample size for some butterfly species and populations.…”

“…For Mylothris spp. and Bicyclus spp., some congeneric species also carry similar Wolbachia strains, but the mechanisms of transmission remain unclear (Duplouy et al, 2020). Therefore, it is still necessary to determine which of the aforementioned routes might be responsible for the spread of Wolbachia strains among congeneric species.…”

“…The actual mechanisms that drive horizontal transmission in field populations of butterflies generally remain unclear (Ahmed et al, 2016;Duplouy et al, 2020). The successful transfer of an endosymbiont between species depends on the ability of the microbe to first enter and then survive in a novel host environment, followed by successful migration to the host germline to ensure propagation.…”

“…and in 46% of 21 Bicyclus spp. (Duplouy et al, 2020), and in 29% of 24 Acraea spp. (Jiggins et al, 2001) in Africa.…”