Contrasted host specificity of gut and endosymbiont bacterial communities in alpine grasshoppers and crickets

Bacteria colonize the body of macroorganisms to form associations ranging from parasitic to mutualistic. Endosymbiont and gut symbiont community are distinct microbiomes whose compositions are influenced by host ecology and evolution. Although the composition of horizontally acquired symbiont communities can correlate to host species identity (i.e., harbor host specificity) and host phylogeny (i.e., harbor phylosymbiosis), we hypothesize that the microbiota structure of vertically inherited symbionts (e.g., endosymbionts like Wolbachia) is more strongly associated with the host species identity and phylogeny than horizontally acquired symbionts (e.g., most gut symbionts). Here, using 16S metabarcoding on 336 guts from 24 orthopteran species (grasshoppers and crickets) in the Alps, we observed that microbiota correlated to host species identity, i.e., hosts from the same species had more similar microbiota than hosts from different species. This effect was ~5 times stronger for endosymbionts than for putative gut symbionts. While elevation correlated with microbiome composition, we did not detect phylosymbiosis for endosymbionts and putative gut symbionts: closely related host species did not harbor more similar microbiota than distantly related species. Our findings indicate that gut microbiota of studied orthopteran species is more correlated to host identity and habitat than to the host phylogeny. The higher specificity in endosymbionts corroborates the idea that -everything else being equal- vertically transmitted microbes harbor stronger specificity signal, but the absence of phylosymbiosis suggests that specificity changes quickly on evolutionary time scales.