Abstract
Scorpion toxins are thought to have originated from ancestral housekeeping genes that underwent diversification and neofunctionalization, as a result of positive selection. Our understanding of the evolutionary origin of these peptides is hindered by the patchiness of existing taxonomic sampling. While recent studies have shown phylogenetic inertia in some scorpion toxins at higher systematic levels, evolutionary dynamics of toxins among closely related taxa remain unexplored. In this study, we used new and previously published transcriptomic resources to assess evolutionary relationships of closely related scorpions from the family Hadruridae and their toxins. In addition, we surveyed the incidence of scorpine-like peptides (SLP, a type of potassium channel toxin), which were previously known from 21 scorpion species. We demonstrate that scorpine-like peptides exhibit gene duplications. Our molecular analyses demonstrate that only eight sites of two SLP copies found in scorpions are evolving under positive selection, with more sites evolving under negative selection, in contrast to previous findings. These results show evolutionary conservation in toxin diversity at shallow taxonomic scale.
Highlights
Animal venoms are outstanding evolutionary innovations used to subdue and digest prey, with other important functions, such as self-defense or intraspecific conflicts [1,2,3,4,5]
We focused on five hadrurid species: Hadrurus arizonensis, Hadrurus spadix, Hadrurus concolorous, Hoffmannihadrurus aztecus, and Hoffmannihadrurus gertschi
Maximum likelihood (ML) analysis and species tree reconciliation of a 1982-locus matrix (727,571 amino acid sites, 35.6% missing data) yielded a topology that was largely congruent with phylogenomic trees previously published by us [27,36]
Summary
Animal venoms are outstanding evolutionary innovations used to subdue and digest prey, with other important functions, such as self-defense or intraspecific conflicts [1,2,3,4,5]. Venoms are secretions consisting of organic and inorganic components that alter cellular processes in the target organism. Several arthropod groups are well known for their venoms, such as bees and wasps [6,7], centipedes [8,9,10], remipedes [11], and arachnids (e.g., see [12,13]). Our knowledge of scorpion toxins has benefitted from high-throughput sequencing technologies, though taxonomically, sampling favors the diverse scorpion family Buthidae. Transcriptomic analyses have expanded beyond the Buthidae to the other 19 scorpion families
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