Fig. 1: Reed beetle symbionts show strongly reduced and perfectly syntenic genomes.

a–c Representative images of Donaciinae beetles, a Donacia thalassina, b Plateumaris braccata, c Donacia versicolorea (picture kindly provided by Rebekka Janke). d Localization of symbiotic organs (white arrowhead) at the midgut/hindgut junction. Scale bar 0.5 mm. e Fluorescence in situ hybridization micrograph showing a cross-section of the symbiotic organs of a female Donacia vulgaris. Fluorescently labeled symbionts (yellow) are visible in the cells and the lumen of the enlarged Malpighian tubules. General DNA counterstaining was done with DAPI (blue). Scale bar 40 µm. f Genome of “Candidatus Macropleicola muticae”, the symbiont of Macroplea mutica. Picture of M. mutica kindly provided by Lech Borowiec. g Hive plot depicting perfect synteny across the symbiont genomes of five representative Donaciinae spanning the phylogenetic diversity of the subfamily. Coloring of genes in f and g: environmental information processing (green); genetic information processing (violet); metabolism (peach); RNA (yellow); cysteine and methionine metabolism (blue); phenylalanine, tyrosine, and tryptophan metabolism (pink); other amino acids metabolism (brown); other (gray).