The hyper-diverse order Coleoptera comprises a staggering
~25% of known species on Earth. Despite recent
breakthroughs in next generation sequencing, there remains a limited
representation of beetle diversity in assembled genomes. Most notably,
the ground beetle family Carabidae, comprising more than 40,000
described species, has not been studied in a comparative genomics
framework using whole genome data. Here we generate a high-quality
genome assembly for Nebria riversi, to examine sources of novelty in the
genome evolution of beetles, as well as genetic changes associated with
specialization to high elevation alpine habitats. In particular, this
genome resource provides a foundation for expanding comparative
molecular research into mechanisms of insect cold adaptation. Comparison
to other beetles shows a strong signature of genome compaction, with N.
riversi possessing a relatively small genome (~147 Mb)
compared to other beetles, with associated reductions in repeat element
content and intron length. Small genome size is not, however, associated
with fewer protein-coding genes, and an analysis of gene family
diversity shows significant expansions of genes associated with cellular
membranes and membrane transport, as well as protein phosphorylation and
muscle filament structure. Finally, our genomic analyses show that these
high elevation beetles have endosymbiotic Spiroplasma, with several
metabolic pathways (e.g. propanoate biosynthesis) that might complement
N. riversi, although its role as a beneficial symbiont or as a
reproductive parasite remains equivocal.
Rapid Genome Evolution and Adaptation of Thlaspi arvense Mediated by Recurrent RNA-Based and Tandem Gene Duplications
