Angiosperm to Gymnosperm host-plant switch entails shifts in microbiota of the Welwitschia bug, Probergrothius angolensis (Distant, 1902)

Adaptation of herbivorous insects to new host plants is key to their evolutionary success in diverse environments. Many insects are associated with mutualistic gut bacteria that contribute to the host's nutrition and can thereby facilitate dietary switching in polyphagous insects. However, how gut microbial communities differ between populations of the same species that feed on different host plants remains poorly understood. Most species of Pyrrhocoridae (Hemiptera: Heteroptera) are specialist seed-feeders on plants in the family Malvaceae, however populations of one species, Probergrothius angolensis, has switched to the very distantly related Welwitschia mirabilis plant in the Namib Desert. We first compared development and survival of laboratory populations of Pr. angolensis with two other pyrrhocorids on seeds of Welwitschia and found only Pr. angolensis capable of successfully completing its development. We then collected Pr. angolensis in Namibia from Malvaceae and Welwitschia host plants, respectively, to assess their bacterial and fungal community profiles using high-throughput amplicon sequencing. Comparison with long-term lab reared insects indicated stable associations of Pr. angolensis with core bacteria (Commensalibacter, Enterococcus, Bartonella, and Klebsiella), but not fungi or yeasts. Phylogenetic analyses of core bacteria revealed relationships to other insect-associated bacteria, but also found new taxa indicating potential host-specialized nutritional roles. Importantly, the microbial community profiles of bugs feeding on Welwitschia vs. Malvaceae revealed stark and consistent differences in the relative abundance of core bacterial taxa that correlate with the host-plant switch; a result we were able to recreate through feeding experiments. Thus, a dynamic gut microbiota may provide a means for insect adaptation to new host plants in new environments when food plants are extremely divergent.Funding provided by: Deutsche ForschungsgemeinschaftCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100001659Award Number: MA7282/1-1Quantitative PCR (qPCR) was performed on a RotorGene Q seed_qPCR.xlsx is qPCR performed on the insect seed diet qPCR_Pangolensis_DifferentDiets.xlsx is the qPCR performed on insects fed the different seed diets. Probergrothius angolensis gene alignments (MUSCLE) (untrimmed/unmasked) .phy files Genes: (Genbank MN542943 to MN543046) SCR Mitochondrial 16S ITS2 ITS1 dfd2 CytB CO1 CO2 abdA 18S Illumina MiSeq V3 Chemistry (Primers 515F-Y and 926R) 16S_AmpliconSequenceVariants_LabColony.xlsx is the ASV table for the analysis of the lab colony of P. angolensis. Qiime2_Analysis_Pipeline.txt is the analysis pipeline for the 62 P. angolensis samples from Namibia. negC-V4V5_S67.report.pdf is the report for the MiSeq negative control. 16S_AmpliconSequenceVariants_Namibia.xlsx is the ASV table for the analysis of the P. angolensis collected in Namibia. Firebug development assay Firebug_development_on_different_seeds.xlsx is the table containing survival, development, and fresh weight info for bugs fed the different seed diets