Molecular data do not support the traditional morphology-based groupings in the scorpion family Buthidae (Arachnida: Scorpiones)

Body size prediction in scorpions: a phylogenetic comparative examination of linear measurements of individual body parts

Body size has always been the focus of several ecological studies due to its undeniable influence on other life-history traits. The conventional representation of body size in arthropods typically relies on linear measures, such as total body length, or the length of specific body parts that can be used to represent body size. While these measures offer simplicity over more complicated alternatives (e.g., dry mass), technical problems persist for arthropods with complex body structures, as is the case for scorpions. In these animals, accurate measurements often require extensive handling, including the stretching of body parts. In light of the difficulties associated with directly measuring total length and carapace length in scorpions (two prevalent proxies for body size in the group), this study evaluates the ability of seven simple linear measurements in predicting length measures of boy size in scorpions under a phylogenetic framework. Predictive equations derived from phylogenetic mixed linear models fitted under Bayesian framework were implemented in custom R functions that can be applied for size prediction in a wide range of scorpions. Overall, accurate predictions of total length and carapace length could be achieved using any of the studied traits as single predictors. However, the most accurate predictions for total length were obtained using the length of metasomal segment V, while the best predictions for carapace length were achieved using telson length. The addition of a secondary predictor had low impact on the quality of the size predictions, indicating that increasing model complexity by incorporating additional predictors is not necessary to achieve accurate size estimates. Technical advantages and limitations associated with each linear measurement are discussed. In conclusion, this study broadens the repertoire of methods available for accurately estimating body size in scorpions, particularly in instances where body size information can only be obtained indirectly through allometric relationships.

Venomics of Scorpion Ananteris platnicki (Lourenço, 1993), a New World Buthid That Inhabits Costa Rica and Panama

Ananteris is a scorpion genus that inhabits dry and seasonal areas of South and Central America. It is located in a distinctive morpho-group of Buthids, the 'Ananteris group', which also includes species distributed in the Old World. Because of the lack of information on venom composition, the study of Ananteris species could have biological and medical relevance. We conducted a venomics analysis of Ananteris platnicki, a tiny scorpion that inhabits Panama and Costa Rica, which shows the presence of putative toxins targeting ion channels, as well as proteins with similarity to hyaluronidases, proteinases, phospholipases A2, members of the CAP-domain family, and hemocyanins, among others. Venom proteolytic and hyaluronidase activities were corroborated. The determination of the primary sequences carried out by mass spectrometry evidences that several peptides are similar to the toxins present in venoms from Old World scorpion genera such as Mesobuthus, Lychas, and Isometrus, but others present in Tityus and Centruroides toxins. Even when this venom displays the characteristic protein families found in all Buthids, with a predominance of putative Na+-channel toxins and proteinases, some identified partial sequences are not common in venoms of the New World species, suggesting its differentiation into a distinctive group separated from other Buthids.

Proteomic analysis and lethality of the venom of Aegaeobuthus nigrocinctus, a scorpion of medical significance in the Middle East

The scorpion Aegaeobuthus nigrocinctus inhabits areas in Turkey and the Levant region of the Middle East where severe/lethal envenomings have been reported. Previous research indicated its extreme venom lethality to vertebrates and distinct envenomation syndrome. We report on the composition of A. nigrocinctus venom from Lebanese specimens using nESI-MS/MS, MALDI-TOF MS, SDS-PAGE and RP-HPLC. Venom lethality in mice was also assessed (LD50 = 1.05 (0.19-1.91) mg/kg, i.p), confirming A. nigrocinctus venom toxicity from Levantine populations. Forty-seven peaks were resolved using RP-HPLC, 25 of which eluted between 20 and 40 % acetonitrile. In reducing SDS-PAGE, most predominant components were <10 kDa, with minor components at higher molecular masses of 19.6, 26.1, 46.3 and 57.7 kDa. MALDI-TOF venom fingerprinting detected 20 components within the 1,000-12,000 m/z range. Whole venom 'shotgun' bottom-up nLC-MS/MS approach, combined with in-gel tryptic digestion of SDS-PAGE bands, identified at least 67 different components belonging to 15 venom families, with ion channel-active components (K+ toxins (23); Na+ toxins (20); Cl- toxins (2)) being predominant. The sequence of a peptide (named α-KTx9.13) ortholog to Leiurus hebraeus putative α-KTx9.3 toxin was fully determined, which exhibited 81-96 % identity to other members of the α-KTx9 subfamily targeting Kv1.x and Ca2+-activated K+ channels. Chlorotoxin-like peptides were also identified. Our study underscores the medical significance of A. nigrocinctus in the region and reveals the potential value of its venom components as lead templates for biomedical applications. Future work should address whether available antivenoms in the Middle East are effective against A. nigrocinctus envenoming in the Levant area.

Congruence between ultraconserved element-based matrices and phylotranscriptomic datasets in the scorpion Tree of Life

Scorpions are ancient and historically renowned for their potent venom. Traditionally, the systematics of this group of arthropods was supported by morphological characters, until recent phylogenomic analyses (using RNAseq data) revealed most of the higher-level taxa to be non-monophyletic. While these phylogenomic hypotheses are stable for almost all lineages, some nodes have been hard to resolve due to minimal taxonomic sampling (e.g. family Chactidae). In the same line, it has been shown that some nodes in the Arachnid Tree of Life show disagreement between hypotheses generated using transcritptomes and other genomic sources such as the ultraconserved elements (UCEs). Here, we compared the phylogenetic signal of transcriptomes vs. UCEs by retrieving UCEs from new and previously published scorpion transcriptomes and genomes, and reconstructed phylogenies using both datasets independently. We reexamined the monophyly and phylogenetic placement of Chactidae, sampling an additional chactid species using both datasets. Our results showed that both sets of genome-scale datasets recovered highly similar topologies, with Chactidae rendered paraphyletic owing to the placement of Nullibrotheas allenii. As a first step toward redressing the systematics of Chactidae, we establish the family Anuroctonidae (new family) to accommodate the genus Anuroctonus.

Tracking the trends of karyotype differentiation in the phylogenetic context of Gint, a scorpion genus endemic to the Horn of Africa (Scorpiones: Buthidae)

To determine the mechanisms of karyotype differentiation in scorpions of the genus Gint, we employed an integrative approach, combining cytogenetic data and sequence-based phylogeny. We cytogenetically examined six species with emphasis on multivalent meiotic configurations, 18S rDNA and (TTAGG)n distribution and compared chromosomal data with genetic divergence based on analysis of 16S rRNA and COI gene markers. Our results show that Gint species exhibit substantial karyotype diversity (2n = 18–45) and a high incidence of chromosome heterozygosity. Meiotic chromosome chains formed by up to six elements were found in 85% of analysed individuals, causing intraspecific chromosome variation in three species. Fluorescence in situ hybridization revealed that the 18S rDNA distribution pattern differed in Gint species, including at the intrapopulation level, but the chromosomal localization of (TTAGG)n motif was stable across species. Conspicuous interspecific differences in chromosome counts broadly corresponded with genetic divergence among Gint species. Our findings indicate that Gint karyotypes have undergone dynamic reorganization through independent fusions, fissions and reciprocal translocations. Owing to present chromosomal polymorphism, such structural changes shaping the genome architecture appear to be still ongoing in the populations of some Gint species.