22 November, 2018

Structure of venom molecules predicts phylogenetic relationships in scorpions

Scorpions are infamous because of their venom, which actually consist of a host of different toxins and molecules. Carlos E. Santibáñez-López and several co-workes have now published a study combining a mapping of the structure of venom molecules with the challenges and disagreements in scorpion higher-level systematics and phylogeny.

I must admit that most of the content of this article is above my head. I'm a humble animal behavior student. So I will let co-author Prashant Sharma sum up the main point of the article:

"The punchline is that we analyzed parametric analyses of the shape of venom proteins on the most comprehensive molecular phylogeny of scorpions. We found that venom shape  predicts phylogenetic relationships and provides synapomorphies for the two largest scorpion clades (Buthida and Iurida)." (Sharma personal communication 15.11.18)

As far as I understand, one important conclusion of this study is that "molecular morphology" can overcome the challenges of the traditional use of anatomical characters in scorpion higher-level systematics and phylogeny.

Scorpions have evolved a variety of toxins with a plethora of biological targets, but characterizing their evolution has been limited by the lack of a comprehensive phylogenetic hypothesis of scorpion relationships grounded in modern, genomescale datasets. Disagreements over scorpion higher-level systematics have also incurred challenges to previous interpretations of venom families as ancestral or derived. To redress these gaps, we assessed the phylogenomic relationships of scorpions using the most comprehensive taxonomic sampling to date. We surveyed genomic resources for the incidence of calcins (a type of calcium channel toxin), which were previously known only from 16 scorpion species. Here, we show that calcins are diverse, but phylogenetically restricted only to parvorder Iurida, one of the two basal branches of scorpions. The other branch of scorpions, Buthida, bear the related LKTx toxins (absent in Iurida), but lack calcins entirely. Analysis of sequences and molecular models demonstrates remarkable phylogenetic inertia within both calcins and LKTx genes. These results provide the first synapomorphies (shared derived traits) for the recently redefined clades Buthida and Iurida, constituting the only known case of such traits defined from the morphology of molecules.

Santibáñez-López CE, Kriebel R, Ballesteros JA, Rush N, Witter Z, Williams J, et al. Integration of phylogenomics and molecular modeling reveals lineage-specific diversification of toxins in scorpions. PeerJ. 2018;6:e5902. [Open Access]

A news report about the article

Thanks to Carlos E. Santibanez Lopez and Prashant Sharma for sending me their article and information!

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