Phylogeny, species delimitation and convergence in the South American bothriurid scorpion genus Brachistosternus Pocock 1893: Integrating morphology, nuclear and mitochondrial DNA

Abstract

A phylogenetic analysis of the scorpion genus Brachistosternus Pocock, 1893 (Bothriuridae Simon, 1880) is presented, based on a dataset including 41 of the 43 described species and five outgroups, 116 morphological characters and more than 4150 base-pairs of DNA sequence from the nuclear 18S rDNA and 28S rDNA gene loci, and the mitochondrial 12S rDNA, 16S rDNA, and Cytochrome c Oxidase Subunit I gene loci. Analyses conducted using parsimony, Maximum Likelihood and Bayesian Inference were largely congruent with high support for most clades. The results confirmed the monophyly of Brachistosternus, the nominal subgenus, and subgenus Ministernus Francke, 1985, as in previous analyses based only on morphology, but differed in several other respects. Species from the plains of the Atacama Desert diverged basally whereas the high altitude Andean species radiated from a more derived ancestor, presumably as a consequence of Andean uplift and associated changes in climate. Species limits were assessed among species that contain intraspecific variation (e.g., different morphs), are difficult to separate morphologically, and/or exhibit widespread or disjunct distributions. The extent of convergence in morphological adaptation to life on sandy substrata (psammophily) and the complexity of the male genitalia, or hemispermatophores, was investigated. Psammophily evolved on at least four independent occasions. The lobe regions of the hemispermatophore increased in complexity on three independent occasions, and decreased in complexity on another three independent occasions.