The draft genome of the big-eyed arboreal ant, Pseudomyrmex gracilis

We present the genome sequence of the ant Pseudomyrmex gracilis. While a number of ant genomes have recently been sequenced, the subfamily to which P. gracilis belongs, Pseudomyrmecinae, has been previously unexplored. This subfamily includes many arboreal ants and the genus Pseudomyrmex is rich in plant-ant mutualisms. The completed genome sequence of P. gracilis is therefore an important step in studying the genomic evolution of plant-ant mutualistic behavior. A large proportion of the P. gracilis genome is estimated to be composed of repetitive elements including 80 Mb from 1,488 distinct repeat families and eight Mb of simple repeats. Previous reports indicate that the genome size of P. gracilis is 387 Mb but we assemble 282 Mb, likely as a result of the high degree of repetitive sequence. Despite the 100 Mb of apparently missing sequence, the genome assembly appears to be relatively complete with regard to coding sequence; nearly all (99%) of core eukaryotic genes are present in a single copy in the assembled sequence. Included in the repetitive sequence is a large amount of nuclear mitochondrial DNA. We find evidence for over 50 distinct nuclear copies of several sequences similar to mitochondrial genes, suggesting widespread transposition from the mitochondrial genome. In addition to showing interesting aspects of genome evolution on its own, the P. gracilis genome will also help shed light on the evolution of ant arboreality and plant-ant mutualism.