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.

Multiple approaches to understanding the taxonomic status of an enigmatic new scorpion species of the genus Tityus (Buthidae) from the biogeographic island of Paraje Tres Cerros (Argentina)

“…Molecular species delimitation analyses have proved to be a reliable tool to deal with closely related species of scorpions with difficult taxonomy, as those of genus Brachistosternus [31, 32]. This is the first time that this technique is applied in species of genus Tityus .…”

Discrete and morphometric traits reveal contrasting patterns and processes in the macroevolutionary history of a clade of scorpions

“…For example, a significant relationship is found when the morphometric PCO 2 is regressed on a psammophyly index ( F 1,37 = 15.45, Bonferroni adjusted P = 0.002), representing the degree of adaptation of each species for life on sandy substrates (calculated in Ojanguren‐Affilastro et al ., ; see Prendini, ). This increase in specialization has originated multiple independent times, either among individual species or pairs of species (Ojanguren‐Affilastro et al ., ), and may be one of the reasons why morphometric variables capture an increase in evolutionary rate towards the present. On the other hand, the discrete data set does contain a sizable proportion of autapomorphies (see Materials and methods).…”

“…Nonetheless, we believe that there is evidence suggesting that our results also capture biologically relevant phenomena. For example, a significant relationship is found when the morphometric PCO 2 is regressed on a psammophyly index (F 1,37 = 15.45, Bonferroni adjusted P = 0.002), representing the degree of adaptation of each species for life on sandy substrates (calculated in Ojanguren-Affilastro et al, 2016;see Prendini, 2001). This increase in specialization has originated multiple independent times, either among individual species or pairs of species , and may be one of the reasons why morphometric variables capture an increase in evolutionary rate towards the present.…”

“…) was obtained after pruning outgroups and species for which no morphological information could be gathered. Following previous analysis (Ceccarelli et al ., ; Ojanguren‐Affilastro et al ., ), the genus was subdivided into five clades that have radiated in different biogeographic regions (colour coded in Fig. ).…”

“…This clade, endemic to South America, is one of the region's best studied genera of scorpions and is composed of medium‐sized fossorial species that inhabit arid and semi‐arid environments (Kovařík & Ojanguren‐Affilastro, ). Several subclades have diversified in different biogeographic regions across the southern and eastern regions of the continent (Ojanguren‐Affilastro et al ., ), a process mostly driven by the uplift of the Andean mountain range (Ceccarelli et al ., ).…”