Hawaiian Nysius Insects Rely on an Obligate Symbiont with a Reduced Genome That Retains a Discrete Nutritional Profile to Match Their Plant Seed Diet.

Seed-feeding Nysius insects (Hemiptera: Lygaeidae) have a symbiotic association with distinct intracellular bacteria, "Candidatus Schneideria nysicola" (Gammaproteobacteria). Although many other hemipteran insect groups generally rely on bacterial symbionts that synthesize all ten essential amino acids lacking in their plant sap diets, the nutritional role of Schneideria in Nysius hosts that specialize on a more nutritionally complete seed-based diet has remained unknown. To determine the nutritional and functional capabilities of Schneideria, we sequenced the complete Schneideria genomes from three distantly related endemic Hawaiian Nysius seed bug species. The complete Schneideria genomes are highly conserved and perfectly syntenic among Hawaiian Nysius host species. Each circular chromosome is ∼0.57 Mb in size and encodes 537 protein-coding genes. They further exhibit a strong A + T nucleotide substitution bias with an average G + C nucleotide content of 29%. The predicted nutritional contribution of Schneideria includes four B vitamins and five of the ten essential amino acids that likely match its hosts' seed-based diet. Disrupted and degraded genes in Schneideria suggests that Hawaiian lineages are undergoing continued gene losses observed in the smaller genomes of the other more ancient hemipteran symbionts.

The Native Hawaiian Insect Microbiome Initiative: A Critical Perspective for Hawaiian Insect Evolution.

Insects associate with a diversity of microbes that can shape host ecology and diversity by providing essential biological and adaptive services. For most insect groups, the evolutionary implications of host-microbe interactions remain poorly understood. Geographically discrete areas with high biodiversity offer powerful, simplified model systems to better understand insect-microbe interactions. Hawaii boasts a diverse endemic insect fauna (~6000 species) characterized by spectacular adaptive radiations. Despite this, little is known about the role of bacteria in shaping this diversity. To address this knowledge gap, we inaugurate the Native Hawaiian Insect Microbiome Initiative (NHIMI). The NHIMI is an effort intended to develop a framework for informing evolutionary and biological studies in Hawaii. To initiate this effort, we have sequenced the bacterial microbiomes of thirteen species representing iconic, endemic Hawaiian insect groups. Our results show that native Hawaiian insects associate with a diversity of bacteria that exhibit a wide phylogenetic breadth. Several groups show predictable associations with obligate microbes that permit diet specialization. Others exhibit unique ecological transitions that are correlated with shifts in their microbiomes (e.g., transition to carrion feeding from plant-feeding in Nysius wekiuicola). Finally, some groups, such as the Hawaiian Drosophila, have relatively diverse microbiomes with a conserved core of bacterial taxa across multiple species and islands.