Evolutionary and ecological signals in Wolbachia-beetle relationships: A review

Abstract

Intracellular bacteria of the genus Wolbachia are the most abundant endosymbionts infecting many arthropods, with Coleoptera being the most diverse hosts in terms of taxonomy and ecology. There has been great progress in studies on the relations between Wolbachia and beetles, however, only some of the research details the consequences of infection. In this review, I summarise the knowledge on the evolutionary relations or ecological associations between Wolbachia and its beetle hosts. These bacteria often cause cytoplasmic incompatibility in the infected hosts and are responsible for a selective sweep of the mitochondrial genomes in some beetles. Wolbachia can manipulate the sex ratio or reproduction of some species of beetles, however, it does not induce parthenogenesis, with the possible rare exception of some Naupactini. Proof of the co-evolution of Wolbachia with beetles is missing, but some aquatic groups seem to be prone to co-speciation, unlike terrestrial taxa. On the other hand, there is a growing number of studies indicating or proving horizontal transmission of Wolbachia among beetle hosts, mostly via common host plants or the foraging substrate (such as dung). Wolbachia is not alone in infecting beetles as other endosymbiotic bacteria occur in beetles (Rickettsia, Spiroplasma, Cardinium, Arsenophorus), which have often been reported as interchangeable, suggesting the infection by various bacteria is dynamic. Nonetheless, there are still many issues associated with Wolbachia that are not yet been described in beetles (like the provision of nutrition or protection against pathogens) and high-throughput sequencing should be used to improve our understanding of Wolbachia-Coleoptera relations.