Scorpions from Mexico: From Species Diversity to Venom Complexity

Scorpions are among the oldest terrestrial arthropods, which are distributed worldwide, except for Antarctica and some Pacific islands. Scorpion envenomation represents a public health problem in several parts of the world. Mexico harbors the highest diversity of scorpions in the world, including some of the world's medically important scorpion species. The systematics and diversity of Mexican scorpion fauna has not been revised in the past decade; and due to recent and exhaustive collection efforts as part of different ongoing major revisionary systematic projects, our understanding of this diversity has changed compared with previous assessments. Given the presence of several medically important scorpion species, the study of their venom in the country is also important. In the present contribution, the diversity of scorpion species in Mexico is revised and updated based on several new systematic contributions; 281 different species are recorded. Commentaries on recent venomic, ecological and behavioral studies of Mexican scorpions are also provided. A list containing the most important peptides identified from 16 different species is included. A graphical representation of the different types of components found in these venoms is also revised. A map with hotspots showing the current knowledge on scorpion distribution and areas explored in Mexico is also provided.

Systematic revision of Brachypelma red-kneed tarantulas (Araneae : Theraphosidae), and the use of DNA barcodes to assist in the identification and conservation of CITES-listed species

Mexican red-kneed tarantulas of the genus Brachypelma are regarded as some of the most desirable invertebrate pets, and although bred in captivity, they continue to be smuggled out of the wild in large numbers. Species are often difficult to identify based solely on morphology, therefore prompt and accurate identification is required for adequate protection. Thus, we explored the applicability of using COI-based DNA barcoding as a complementary identification tool. Brachypelma smithi (F. O. Pickard-Cambridge, 1897) and Brachypelma hamorii Tesmongt, Cleton & Verdez, 1997 are redescribed, and their morphological differences defined. Brachypelma annitha is proposed as a new synonym of B. smithi. The current distribution of red-kneed tarantulas shows that the Balsas River basin may act as a geographical barrier. Morphological and molecular evidence are concordant and together provide robust hypotheses for delimiting Mexican red-kneed tarantula species. DNA barcoding of these tarantulas is further shown to be useful for species-level identification and for potentially preventing black market trade in these spiders. As a Convention on International Trade in Endangered Species (CITES) listing does not protect habitat, or control wildlife management or human interactions with organisms, it is important to support environmental conservation activities to provide an alternative income for local communities and to avoid damage to wildlife populations.

Shining a light into the world’s deepest caves: phylogenetic systematics of the troglobiotic scorpion genus Alacran Francke, 1982 (Typhlochactidae : Alacraninae)

The scorpion genus Alacran Francke, 1982, endemic to eastern Mexico, was created to accommodate Alacran tartarus Francke, 1982. This remarkable troglobiotic species is adapted for life in some of the world’s deepest caves, 720–916 m below the surface in the Sistema Huautla of the state of Oaxaca (the deepest records at which a scorpion has been found). A second species, Alacran chamuco Francke, 2009, was later described from Te Cimutaá, also in Oaxaca. In the present contribution, we describe a third species, Alacran triquimera, sp. nov., recently discovered in a cave system in the state of Puebla, and test the monophyly and internal relationships of Alacran, based on a cladistic analysis of 10 terminal taxa (including seven species representing all four genera of Typhlochactidae) and 151 informative morphological characters, building on a previously published matrix. The single most parsimonious tree obtained, supports the monophyly of Alacran and the following relationships among its component species: (A. chamuco (A. tartarus + A. triquimera, sp. nov.)). The phylogenetic relationships among the three species of Alacran are consistent with the biogeographical history of the caves they inhabit. Based on the geological history of the Sierra Madre del Sur and the likely similar speleogenesis of the Tres Quimeras, Sistema Huautla and Te Cimutaá caves, we propose a vicariance hypothesis to account for the disjunct distribution of the three species of Alacran, whereby an initially more widespread, panmictic ancestral population speciated into three geographically isolated taxa following fragmentation of the southern Sierra Madre del Sur.

Taxonomic revision of the genus Mayazomus Reddell & Cokendolpher, 1995 (Schizomida: Hubbardiidae), with description of five new species from Chiapas, Mexico

The genus Mayazomus currently contains two species from southeastern Mexico. It was originally characterized by a strongly elongated pedipalp trochanter, united in its entire width to the femur; the patella strongly curved; the tibia with a large mesal apophysis opposable to tarsus; the spermathecae with two pairs of thin lobes subequal in length; and the presence of four or more setae on tergite II. In the present contribution, the species of the genus Mayazomus are revised and new diagnostic characters for the genus are proposed, including the correction that the female flagellum bears three rather than two annuli. The two known species are redescribed based on examination of the holotypes, plus newly acquired material representing both sexes (female previously unknown for one). Five new species from the Mexican state of Chiapas are described, based on adult males and females: Mayazomus tzotzil new species, Mayazomus aluxe new species, Mayazomus kaamuul new species, Mayazomus yaax new species, and Mayazomus loobil new species. Dimorphism in male pedipalps is reported for the first time for the genus. A dichotomous key is provided for identification of the seven species in the genus; and a distribution map is included. 

New Fossil Scorpion from the Chiapas Amber Lagerstätte

A new species of scorpion is described based on a rare entire adult male preserved in a cloudy amber from Miocene rocks in the Chiapas Highlands, south of Mexico. The amber-bearing beds in Chiapas constitute a Conservation Lagerstätte with outstanding organic preservation inside plant resin. The new species is diagnosed as having putative characters that largely correspond with the genus Tityus Koch, 1836 (Scorpiones, Buthidae). Accordingly, it is now referred to as Tityus apozonalli sp. nov. Its previously unclear phylogenetic relationship among fossil taxa of the family Buthidae from both Dominican and Mexican amber is also examined herein. Preliminarily results indicate a basal condition of T. apozonalli regarding to Tityus geratus Santiago-Blay and Poinar, 1988, Tityus (Brazilotityus) hartkorni Lourenço, 2009, and Tityus azari Lourenço, 2013 from Dominican amber, as was Tityus (Brazilotityus) knodeli Lourenço, 2014 from Mexican amber. Its close relationships with extant Neotropic Tityus-like subclades such as 'Tityus clathratus' and the subgenus Tityus (Archaeotityus) are also discussed. This new taxon adds to the knowledge of New World scorpions from the Miocene that are rarely found trapped in amber.

Five new cave-dwelling species of Hemirrhagus Simon 1903 (Araneae, Theraphosidae, Theraphosinae), with notes on the generic distribution and novel morphological features

The suborder Mygalomorphae is generally poorly represented in the cave faunas of the world. The genus Hemirrhagus is endemic to Mexico and has 22 described species. It is the only one with epigean, troglophile and troglobitic species. Lack of urticating setae, loss of eye pigmentation and ocular reduction are interpreted as evolutionary reversals related to their troglobitic habits. From five troglobitic species in the genus, only the male of Hemirrhagus stygius is known. Five new troglobitic species are described with both sexes: Hemirrhagus akheronteus sp. nov., Hemirrhagus billsteelei sp. nov., Hemirrhaugus diablo sp. nov., Hemirrhagus kalebi sp. nov. and Hemirrhagus sprousei sp. nov. The female of Hemirrhagus chilango is described for the first time. Hemirrhagus akheronteus sp. nov. has a group of spinose setae on the opisthosoma; this setal modification was never reported in any other theraphosid spiders. Females of Hemirrhagus kalebi sp. nov. and Hemirrhagus sprousei sp. nov. lay fixed hammock egg sacs, which is an unusual behavior among species in Theraphosinae. Two stridulating setae previously reported only in epigean species are present on some of the new troglobites.

Total evidence phylogeny of the North American harvestman family Stygnopsidae (Opiliones : Laniatores : Grassatores) reveals hidden diversity

Systematic relationships among Laniatores have received considerable attention during the past few years. Many significant taxonomic changes have been proposed, particularly in the superfamily Gonyleptoidea. As part of this superfamily, the basalmost Stygnopsidae is the least known family. In order to propose the first total evidence phylogeny of the family, we produced four datasets: three molecular markers – partial nuclear 28S, mitochondrial ribosomal 16S, mitochondrial protein-encoding cytochrome c oxidase subunit I; and 72 morphological characters. With these data, we performed three different phylogenetic analyses: (1) Bayesian Inference with molecular data, and (2) Bayesian Inference and (3) Maximum Likelihood using combined data. Our results are congruent: a monophyletic Stygnopsidae subdivided into two major clades: Stygnopsinae and Karosinae, subfam. nov. The following genera are redefined: Stygnopsis, Hoplobunus and Serrobunus stat. rev. The following taxa are described: Iztlina venefica, gen. nov., sp. nov. and Tonalteca, gen. nov. Additionally, the following changes are proposed: Serrobunus queretarius (Šilhavý, 1974), comb. nov., Stygnopsis apoalensis (Goodnight & Goodnight, 1973), comb. nov., Stygnopsis mexicana (Roewer, 1915), comb. nov., Stygnopsis oaxacensis (Goodnight & Goodnight, 1973), comb. nov., and Tonalteca spinooculorum (Goodnight & Goodnight, 1973), comb. nov. We also discuss the status of the genera Isaeus stat. rev. and Mexotroglinus. Finally, we discuss the evolution of male genitalia and convergence of selected homoplastic diagnostic characters.

Two new species of ricinuleids of the genus Pseudocellus (Arachnida: Ricinulei: Ricinoididae) from southern Mexico

Two new species of ricinuleids of the genus Pseudocellus are described from Mexico: Pseudocellus cruzlopezi sp. nov. from Oaxaca, and Pseudocellus monjarazi sp. nov. from Chiapas. Both species are described from adult males and females. The first species is epigean and edaphomorphic, whereas the second is cavernicolous and troglomorphic. The number of known species of the genus Pseudocellus increases to 25, and Mexican species to 16, indicating that Mexico has the highest diversity of ricinuleids in the world. An updated identification key to adult males of the 16 described species found in Mexico and southern USA is provided.

Integrative systematics untangles the evolutionary history of Stenochrus (Schizomida: Hubbardiidae), a neglected junkyard genus of North American short-tailed whipscorpions

Until recently, the Nearctic short-tailed whipscorpion genus, StenochrusChamberlin, 1922, included 27 species distributed primarily in Mexico, the USA and Central America. Morphological disparity among its species, associated with their adaptation to diverse habitats, raised the question as to whether Stenochrus was monophyletic. The phylogenetic relationships among short-tailed whipscorpions have only recently begun to be explored, and the monophyly of Stenochrus had never been tested. The present contribution provides the first phylogeny of Stenochrus and related genera, based on 61 morphological characters and 2991 aligned DNA nucleotides from two nuclear and two mitochondrial gene markers, for 73 terminal taxa. Separate and simultaneous analyses of the morphological and molecular data sets were conducted with Bayesian Inference, Maximum Likelihood, and parsimony with equal and implied weighting. Terminals represented only by morphological data (‘orphans’) were included in some analyses for evaluation of their phylogenetic positions. As previously defined, Stenochrus sensuReddell & Cokendolpher (1991, 1995) was consistently polyphyletic and comprised eight monophyletic clades, justifying its reclassification into eight genera including Heteroschizomus Rowland, 1973, revalidated from synonymy with Stenochrus by Monjaraz-Ruedas et al. (2019). Rowland & Reddell’s (1980)mexicanus and pecki species groups were consistently paraphyletic. Orphans grouped with the most morphologically similar taxa.