Food Resource Sharing of Alder Leaf Beetle Specialists (Coleoptera: Chrysomelidae) as Potential Insect–Plant Interface for Horizontal Transmission of Endosymbionts

Abstract

Recent studies suggest that endosymbionts of herbivore insects can be horizontally transferred to other herbivores feeding on the same host plants, whereby the plant acts as an intermediate stage in the chain of transmission. If this mechanism operates, it is also expected that insect communities sharing the same host plant will have higher chances to share their endosymbionts. In this study, we use a high-throughput 16S rRNA metabarcoding approach to investigate the presence, diversity, and potential sharing of endosymbionts in several species of leaf beetles (Coleoptera: Chrysomelidae) of a local community specialized on an alder diet in North America. Rickettsia and Wolbachia were predominant in the sample, with strong evidence for each species having their own dominant infection, of either or both types of bacteria. However, all species shared a much lower proportion of a particular Wolbachia type, compatible with the same strain dominant in one of the species of leaf beetles. Crucially, the same 16S rRNA haplotype of Wolbachia was found on alder leaf extracts. The combined evidence and the absence of this strain in a syntopic species of leaf beetle feeding on a different host plant support the hypothesis that at least the initial stages of the mechanism that would allow horizontal transmission of endosymbionts across species feeding on the same plant is possible. The accessibility and characteristics of endosymbiont associations of this system make it suitable for deeper analyses of their diversity and transmission in natural conditions.

Wolbachia infection and genetic diversity of Italian populations of Philaenus spumarius, the main vector of Xylella fastidiosa in Europe

“…Horizontal transmission may be a key factor in the infection dynamic and maintenance of heritable microbial symbionts, especially if they cause weak reproductive manipulations [ 143 , 147 ]. Acquisition and subsequent transmission of bacterial symbionts through feeding on plants may complement vertical transmission, favoring the spread and persistence of symbionts within the insect host populations [ 148 – 150 ]. In P .…”

“…Horizontal transmission may be a key factor in the infection dynamic and maintenance of heritable microbial symbionts, especially if they cause weak reproductive manipulations [143,147]. Acquisition and subsequent transmission of bacterial symbionts through feeding on plants may complement vertical transmission, favoring the spread and persistence of symbionts within the insect host populations [148][149][150]. In P. spumarius, intra-and inter-specific horizontal transmission via plant may be a rampant process contributing to the maintenance of Wolbachia within the infected populations of northern Italy, but probably not sufficient to compensate for the loss of infections, due to imperfect maternal transmission and environmental curing.…”

Multiple long-range host shifts of major Wolbachia supergroups infecting arthropods

“…Yet, in cell culture, Wolbachia can infect Wolbachia -free cells independently of cell contact through the culture medium 31 . Infection by Wolbachia , which is present in the haemolymph, can occur by contact with excretions or injuries of an infected host to an uninfected host 34 ; thus, shared food sources and feeding habits are plausible pathways for Wolbachia HS between different hosts 35 . Another factor contributing to Wolbachia HS is predation, where ingested larvae contaminate the uninfected host, crossing the digestive system epithelium and colonising the future ovarian stem cells 36 .…”

“…Even though Wolbachia may cause reduced host fitness, the opposite is also true, as Wolbachia may alter pathogen susceptibility conferring viral protection for its hosts 43 . Also, Wolbachia can survive for a limited time in an extracellular environment, albeit being an obligatory intracellular endosymbiont 12 , 35 .…”

Entomobacter blattae gen. nov., sp. nov., a new member of the Acetobacteraceae isolated from the gut of the cockroach Gromphadorhina portentosa

“…These results suggest that amplicon sequencing targeting the 16S rRNA V3–V4 regions, which is commonly used to examine the diversity of bacteria in a particular niche, may assign the genus Acetobacter to bacteria taxonomically closer to G55GP T . The genus Acetobacter is often identified by V3–V4 amplicon sequencing in insect guts, including beetles [41], fruit flies [42] and moths [43]. Although some fruit flies do actually harbour Acetobacter [44], it may well be that other insects carry bacteria more closely related to G55GP T .…”