26 November, 2018

The defense respons of scorpions to repeated attacks from a predator

Scorpions and other prey species are involved in a continuing arm race against their predators. The prey will get better in avoidance and defence and the predator tries to get better in overcoming the prey.

Mykola Rasko and co-workers have recently published a study investigating the sting use and venom expenditure during repeated attacks (simulated) in Hadurus arizonensis Ewin, 1928 (Caraboctonidae). Contrary to the projects expectations, the stinging behaviour, venom use and venom volume all decreased as the number of challenges increased. The scorpions defenses actually decreased during repeated attacks. This means that a predator of scorpions should use repeated attacks to overcome a scorpion, and this is also something that has been observed in some predators of scorpions.

Predatore-prey arms races ensure that a prey's defences are well matched with the predator's ability to overcome them. Scorpions have a formidable defensive capacity due to their venomous stinger. Mammalian and squamate scorpion predators overpower scorpions by making repeated attacks. We tested here how scorpions, Hadrurus arizonensis, apply their venom defensively during a simulated repeated attack, consisting of 10 consecutive challenges. Since the persistent repeated attack of a predator, even when stung in the process, seems to indicate its resolve, we expected defensive effort to increase with the number of challenges. We also expected that, owing to the life-and-death nature of a predatory attack, scorpions would be liberal in the use of their venom. We found, however, that stinging behaviour, venom use and venom volume all decreased as the number of challenges increased. Scorpions used only 7.8±9.6% (mean±SD) of their total venom volume during an attack consisting of 10 consecutive challenges. We conclude that a repeated attack seems an effective strategy for scorpion predators to reduce the defensive investment of scorpions.

Rasko M, Coelho P, Simone Y, van der Meijden A. How to attack a scorpion: venom metering during a repeated attack. Anim Behav. 2018;145:125-9. [Subscription required for full text]

22 November, 2018

Species composition and distribution in an arid ecosystem i Algeria

Salah Eddine Sadine and co-workers recently published an article looking into the diversity and distribution of scorpions in the region of Ouargla (Eastern Algerian Sahara).

The present work is a study of composition and structure of scorpion fauna in the region of Ouargla (Eastern Algerian Sahara), during a period of fourteen years from 2005 to 2018, we sampled from different biotopes more than 1550 adult specimens, divided into nine 9 species of scorpions: Androctonus amoreuxi, Androctonus australis, Buthacus arenicola, Buthacus samiae, Buthiscus bicalcaratus, Buthus saharicus, Buthus tunetanus, Orthochirus innesi, and Scorpio punicus. A. australis was the most abundant species with 47.36% of the total individuals captured. Other species such as S. punicus, B. arenicola and A. amoreuxi are ranked as accidental with rates less than 20%. Among the important results in this work is reporting for the first time the presence of B. bicalcaratus in Ouargla and the new records of B. samiae and B. saharicus in this area. The Shannon’s index was H’ = 2.05 and the evenness index was 0.65, showing a very important diversity of scorpions with more than 23.5% of scorpion species reported in Algeria; however, a poor balance between the number of sampled species with dominance of the thermophilic species that are the most adapted scorpions in this arid climate.

Sadine SE, Bissati S, Idder MA. Diversity and structure of scorpion fauna from arid ecosystem in Algerian Septentrional Sahara (2005-2018). Serket. 2018;16(2):51-9. [Open Access]

Thanks to Dr. Sadine for sending me his article!

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!