Microbial transfer through fecal strings on eggs affect leaf beetle microbiome dynamics

Background Gut microbiomes of holometabolous insects can be strongly affected by the metamorphosis. Previous studies suggest that microbiome colonization and community development often rely on specialized transmission routes between host life stages, but there is a lack of comparative studies of microbial community dynamics due to different transmission mechanisms. Results We compared the gut microbial community dynamics across life stages for five Galerucella species that differ in a potential microbial transfer mechanism by sequencing amplicons of the 16S rRNA gene. Females of three of the studied species place a fecal string on top of the egg, which may improve the transfer of gut microbes, whereas females of the two other species do not place such a fecal string. We found that the α-diversity was more stable between life stages in fecal string placer-species compared with the non-fecal string placer-species. Moreover, there were also consistent differences in the microbiome between species, where we identified multiple taxa in each species that consistently appeared in all life stages. Conclusions Fecal strings placed on eggs seem to play an important role in the diversity and dynamic of gut bacteria in Galerucella species, and the vertical transfer of gut bacteria between host insect generations. Alternative, but less efficient, transmission routes seem to occur in non-fecal string placer-species.