Carlos E. Santibáñez-López

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.

Overview of the Knottin scorpion toxin-like peptides in scorpion venoms: Insights on their classification and evolution.

Scorpion venoms include several compounds with different pharmacological activities. Within these compounds, toxins affecting ion channels are among the most studied. They are all peptides that have been classified based on their 3D structure, chain size and function. Usually, they show a spatial arrangement characterized by the presence of a cysteine-stabilized alpha beta motif; most of them affect Na(+) and K(+) ion-channels. These features have been revised in several occasions before, but a complete phylogenetic analysis of the disulfide containing peptides is not been done. In the present contribution, two databases (Pfam and InterPro) including more than 800 toxins from different scorpions were analyzed. Pfam database included toxins from several organisms other than scorpions such as insects and plants, while InterPro included only scorpion toxins. Our results suggest that Na(+) toxins have evolved independently from those of K(+) toxins no matter the length of the peptidic chains. These preliminary results suggest that current classification needs a more detailed revision, in order to have better characterized toxin families, so the new peptides obtained from transcriptomic analyses would be properly classified.

New and poorly known species of the mexicanus group of the genus Vaejovis (Scorpiones: Vaejovidae) from Oaxaca, Mexico

Abstract Four new species belonging to the mexicanus group of the genus Vaejovis C.L. Koch 1836 from Oaxaca, Mexico are described. The number of species of this group for the state is raised to seven. The males of V. franckei and V. setosus are described for the first time. A key to Oaxacan species of the mexicanus group is provided.

Venom gland transcriptomic and venom proteomic analyses of the scorpion Megacormus gertschi Díaz-Najera, 1966 (Scorpiones: Euscorpiidae: Megacorminae)

Abstract The soluble venom from the Mexican scorpion Megacormus gertschi of the family Euscorpiidae was obtained and its biological effects were tested in several animal models. This venom is not toxic to mice at doses of 100 &mgr;g per 20 g of mouse weight, while being lethal to arthropods (insects and crustaceans), at doses of 20 &mgr;g (for crickets) and 100 &mgr;g (for shrimps) per animal. Samples of the venom were separated by high performance liquid chromatography and circa 80 distinct chromatographic fractions were obtained from which 67 components have had their molecular weights determined by mass spectrometry analysis. The N‐terminal amino acid sequence of seven protein/peptides were obtained by Edman degradation and are reported. Among the high molecular weight components there are enzymes with experimentally‐confirmed phospholipase activity. A pair of telsons from this scorpion species was dissected, from which total RNA was extracted and used for cDNA library construction. Massive sequencing by the Illumina protocol, followed by de novo assembly, resulted in a total of 110,528 transcripts. From those, we were able to annotate 182, which putatively code for peptides/proteins with sequence similarity to previously‐reported venom components available from different protein databases. Transcripts seemingly coding for enzymes showed the richest diversity, with 52 sequences putatively coding for proteases, 20 for phospholipases, 8 for lipases and 5 for hyaluronidases. The number of different transcripts potentially coding for peptides with sequence similarity to those that affect ion channels was 19, for putative antimicrobial peptides 19, and for protease inhibitor‐like peptides, 18. Transcripts seemingly coding for other venom components were identified and described. The LC/MS analysis of a trypsin‐digested venom aliquot resulted in 23 matches with the translated transcriptome database, which validates the transcriptome. The proteomic and transcriptomic analyses reported here constitute the first approach to study the venom components from a scorpion species belonging to the family Euscorpiidae. The data certainly show that this venom is different from all the ones described thus far in the literature. HighlightsResults of proteome analysis of venom and transcriptome analysis of venom gland from M. gertschi scorpion are reported.This venom is not toxic to mammals but is lethal to arthropods (crickets and shrimps) at the doses assayed.HPLC separation permitted identification of 67 components, from which 30 distinct protein/peptide components were found.Sequences found are: enzymes, toxins, non‐disulfide bridged peptides, scorpines, La1‐like peptides and other components.Over 50% of the whole soluble venom is made of low molecular weight non‐peptide/protein components, of unknown function.

A new genus and a new species of scorpion (Scorpiones: Buthidae) from southeastern Mexico

Abstract Chaneke fogoso gen. nov. et sp. nov., are described based on specimens collected near the coast in southeastern Guerrero, Mexico. The genus is characterized by the peculiar rhomboidal shape of the subaculear tubercle, and the lack of at least one trichobothrium on the femur, patella and chela of the pedipalp, which make it the second known buthid genus with decreasing neobothriotaxy on those three pedipalpal segments, together with Alayotityus Armas 1973. Tityopsis aliciae Armas & Martin-Frias 1998, from Oaxaca, Mexico, is transferred to the new genus, resulting in Chaneke aliciae (Armas & Martin-Frias 1998), comb. nov. A cladistic analysis including all other New World “microbuthids” with decreasing neobothriotaxy, with 30 morphological characters, indicates that Chaneke is monophyletic, clearly distinct from Alayotityus Armas 1973 (from eastern Cuba) and Tityopsis Armas 1974 (from western Cuba).

Systematics of the keyserlingii Group of Diplocentrus Peters, 1861 (Scorpiones: Diplocentridae), with Descriptions of Three New Species from Oaxaca, Mexico

ABSTRACT The scorpion genus Diplocentrus Peters, 1861, comprising more than 50 species, most of which are endemic to Mexico, is the most diverse in the family Diplocentridae Karsch, 1880 (Santibáñez-López et al., 2011). Hoffmann (1931) divided the Mexican species into two groups, the whitei group and the keyserlingi group, based largely on differences in size and coloration. Francke (1977) redefined these groups. The whitei group, renamed the mexicanus group because it included the type species of the genus, comprised species with short cheliceral fingers and the pedipalp femur wider than high. The keyserlingii group comprised species with long cheliceral fingers and the pedipalp femur higher than wide. Several new species of Diplocentrus were since described, but no attempt was made to synthesize the taxonomy of the species assigned to either group or further clarify the validity of the groups. In the present contribution, the species of Diplocentrus with the pedipalp femur higher than wide are reviewed. An operational diagnosis is provided for the keyserlingii group. Diplocentrus formosus Armas and Martín-Frías, 2003, previously synonymized with Diplocentrus tehuano Francke, 1977, is reinstated. Revised, updated diagnoses are provided for all previously described species and three new species, Diplocentrus kraepelini, n. sp., Diplocentrus sagittipalpus, n. sp., and Diplocentrus sissomi, n. sp., are described. The female of Diplocentrus mitlae Francke, 1977, is described for the first time. A dichotomous key is provided for identification of the 10 species in the keyserlingii group.

An Insight into the Triabin Protein Family of American Hematophagous Reduviids: Functional, Structural and Phylogenetic Analysis

A transcriptomic analysis of the saliva of T. pallidipennis together with a short proteomic analysis were carried out to reveal novel primary structures of the lipocalin/triabin protein families in this reduviid. Although triabins share some structural characteristics to lipocalins and they are classified as in the calcyn/lipocalin superfamily, triabins differ from lipocalins in the direction of β-strands in the general conformation of the β-barrel. The triabin protein family encompasses a wide variety of proteins, which disrupt the hemostasis of warm-blooded animals. Likewise, the function of proteins classified as triabins includes proteins that are carriers of small molecules, protease inhibitors, binders of specific cell-surface receptors as well as proteins that form complexes with other macromolecules. For example, triabin and pallidipin from the saliva of T. pallidipennis are thrombin and platelet aggregation inhibitors, respectively; triplatin from T. infestans binds to thromboxane A2; and nitrophorin from Rhodnius prolixus carries nitric oxide. Therefore, based on 42 new transcriptome sequences of triabins from the salivary glands of T. pallidipennis reported at present, and on triabin sequences of other American hematophagous reduviids already reported in the literature, subfamilies of triabins were proposed following phylogenetic analyses and functional characterization of triabin members. Eight subfamilies of proteins were recognized with known functions, which were the nitrophorin and amine binding proteins, Rhodnius prolixus aggregation inhibitor, triafestin, triatin, dipetalodipin and pallidipin, triplatin and infestilin, dimiconin and triabin, and procalin subfamilies. Interestingly, 70% of the analyzed sequences came from these eight subfamilies because there was no biological function associated with them, implying the existence of a vast number of proteins with potential novel biological activities.

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

Abstract. 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.

Variation in the spiniform macrosetae pattern on the basitarsi of Diplocentrus tehuacanus (Scorpiones: Diplocentridae): new characters to diagnose species within the genus

Abstract Spiniform macrosetae have been useful as a taxonomic trait in the genus Diplocentrus, such as the telotarsal spiniform macrosetae formula widely used to separate species. Basitarsal spiniform macrosetae have been studied in the family Scorpionidae but not in its sister family (Diplocentridae). In this study, we analyzed the variation in the position and number of spiniform macrosetae on the basitarsus of one species of the genus Diplocentrus. We found minimal ontogenetic, intersexual and geographical variation within the species. We also compare the pattern found in Diplocentrus tehuacanus Hoffmann 1931 to those of two morphologically similar species, and found that the basitarsal macrosetal pattern is also a good, reliable taxonomic character at the interspecific level.

Updating knowledge on new medically important scorpion species in Mexico

&NA; The increment in the number of scorpion envenoming cases in Mexico is mainly associated to the rapid growth of the urban areas, and consequently, to the invasion of natural habitats of these arachnids. On the other hand, there is a great diversity of scorpion species, so it is indispensable to identify those of medical importance, which we now know are many more than the 7–8 previously reported as dangerous to humans. Because different LD50 values have been reported for the venom of the same species, probably due to variations in the experimental conditions used, in this work we determined the LD50 values for the venoms of 13 different species of scorpions using simple but systematic procedures. This information constitutes a referent on the level of toxicity of medically important scorpion species from Mexico and establishes the bases for a more comprehensive assessment of the neutralizing capacity of current and developing antivenoms. HighlightsThe total diversity of Mexican toxic scorpions has not been determined.We demonstrated that there are at least 13 medically important species.Systematic determination of venom LD50 revealed different levels of toxicity.These results will help to develop new anti‐venoms.