New Zealand tree and Giant Weta (Orthoptera) transcriptomics reveal divergent selection patterns in metabolic loci

Abstract

Exposure to low temperatures requires an organism to overcome physiological challenges. New Zealand weta belonging to the genera Hemideina and Deinacrida are found across awide range of thermal environments and therefore subject to varying selective pressures. Herewe assess the selection pressures across theweta phylogeny,with a particular emphasis on identifying genes under positiveordiversifying selection.We usedRNA-seqtogenerate transcriptomes for all 18Deinacrida andHemideina species.Atotal of 755 orthologous genes were identified using a bidirectional best-hit approach, with the resulting gene set encompassing a diverse range of functional classes. Analysis of ortholog ratios of synonymous to nonsynonymous amino acid changes found 83 genes that are under positive selection for at least one codon.Awide variety ofGeneOntology terms, enzymes, andKEGG(Kyoto Encyclopedia ofGenes andGenomes)pathways are representedamongthesegenes. In particular, enzymes involved in oxidative phosphorylation, melanin synthesis, and free-radical scavenging are represented, consistent with physiological and metabolic changes that are associated with adaptation to alpine environments. Structural alignment of the transcripts with the most codons under positive selection revealed that themajority of sites are surface residues, and therefore have the potential to influence the thermostability of the enzyme, with the exception of prophenoloxidase where two residues near the active site are under selection. These proteins provide interesting candidates for further analysis of protein evolution.