The adaptation of bumblebees to extremely high elevation associated with their gut microbiota.

Bumblebees are among the most abundant and important pollinators for sub-alpine and alpine flowering plant species in the Northern Hemisphere, but little is known about their adaptations to high elevations. In this article, we focused on two bumblebee species, Bombus friseanus and Bombus prshewalskyi, and their respective gut microbiota. The two species, distributed through the Hengduan Mountains of southwestern China, show species replacement at different elevations. We performed genome sequencing based on 20 worker bee samples of each species. Applying evolutionary population genetics and metagenomic approaches, we detected genes under selection and analyzed functional pathways between bumblebees and their gut microbes. We found clear genetic differentiation between the two host species and significant differences in their microbiota. Species replacement occurred in both hosts and their bacteria (Snodgrassella) with an increase in elevation. These extremely high-elevation bumblebees show evidence of positive selection related to diverse biological processes. Positively selected genes involved in host immune systems probably contributed to gut microbiota changes, while the butyrate generated by gut microbiota may influence both host energy metabolism and immune systems. This suggests a close association between the genomes of the host species and their microbiomes based on some degree of natural selection.IMPORTANCETwo closely related and dominant bumblebee species, distributed at different elevations through the Hengduan Mountains of southwestern China, showed a clear genomic signature of adaptation to elevation at the molecular level and significant differences in their respective microbiota. Species replacement occurred in both hosts and their bacteria (Snodgrassella) with an increase in elevation. Bumblebees' adaptations to higher elevations are closely associated with their gut microbiota through two biological processes: energy metabolism and immune response. Information allowing us to understand the adaptive mechanisms of species to extreme conditions is implicit if we are to conserve them as their environments change.

Homologs of eukaryotic Ras superfamily proteins in prokaryotes and their novel phylogenetic correlation with their eukaryotic analogs.

Ras superfamily proteins are key regulators in a wide variety of cellular processes. Previously, they were considered to be specific to eukaryotes, and MglA, a group of obviously different prokaryotic proteins, were recognized as their only prokaryotic analogs or even ancestors. Here, taking advantage of quite a current accumulation of prokaryotic genomic databases, we have investigated the existence and taxonomic distribution of Ras superfamily protein homologs in a much wider prokaryotic range, and analyzed their phylogenetic correlation with their eukaryotic analogs. Thirteen unambiguous prokaryotic homologs, which possess the GDP/GTP-binding domain with all the five characteristic motifs of their eukaryotic analogs, were identified in 12 eubacteria and one archaebacterium, respectively. In some other archaebacteria, including four methanogenic archaebacteria and three Thermoplasmales, homologs were also found, but with the GDP/GTP-binding domains not containing all the five characteristic motifs. Many more MglA orthologs were identified than in previous studies mainly in delta-proteobacteria, and all were shown to have common unique features distinct from the Ras superfamily proteins. Our phylogenetic analysis indicated eukaryotic Rab, Ran, Ras, and Rho families have the closest phylogenetic correlation with the 13 unambiguous prokaryotic homologs, whereas the other three eukaryotic protein families (SRbeta, Sar1, and Arf) branch separately from them, but have a relatively close relationship with the methanogenic archaebacterial homologs and MglA. Although homologs were identified in a relative minority of prokaryotes with genomic databases, their presence in a relatively wide variety of lineages, their unique sequence characters distinct from those of eukaryotic analogs, and the topology of our phylogenetic tree altogether do not support their origin from eukaryotes as a result of lateral gene transfer. Therefore, we argue that Ras superfamily proteins might have already emerged at least in some prokaryotic lineages, and that the seven eukaryotic protein families of the Ras superfamily may have two independent prokaryotic origins, probably reflecting the 'fusion' evolutionary history of the eukaryotic cell.