04 February, 2015

Ananteris scorpions shed tail to escape predators

Last year I reported about a paper describing autotomy in the form of tail shedding in the scorpion Ananteris mauryi Lourenco, 1982 (Buthidae). I must admit I was a little skeptical about autotomy being an adaptive anti-predator strategy in scorpions based on the costs associated with such a dramatic event (loosing stinger and venom for defense and prey capture and loosing parts of the digestive system making defecation potentially impossible). Also, tail shedding has not been reported for any other scorpion genera.

Camilio Mattoni together with several other scorpion scientists have now published a very interesting paper showing that tail shedding is actually taking place in 14 species of Ananteris. The article concludes that metasomal detachment in Ananteris meets the criteria for defensive autotomy. Detachment is provoked by external stimuli and achieved by an intrinsic mechanism and the experiments suggest that the process is mediated and controlled by the nervous system. Tail shedding has serious costs (as mentioned in the first paragraph), but individuals were alive several weeks after shedding the tail, and some individuals survived for up to eight months.

The authors tested scorpions from several other South American genera, but autotomy was not seen in any of these. An interesting questions is why this special behavior has only developed in one genus.

Video showing the complete sequence of metasomal autotomy in a male Ananteris solimariae Botero-Trujillo & Flórez, 2011 scorpion

Autotomy, the voluntary shedding or detachment of a body part at a determined cleavage plane, is a common anti-predation defense mechanism in several animal taxa, including arthropods. Among arachnids, autotomy has been observed in harvestmen, mites, and spiders, always involving the loss of legs. Autotomy of the opisthosoma (abdomen) was recently reported in a single species of the Neotropical buthid scorpion genus Ananteris Thorell, 1891, but few details were revealed. Based on observations in the field and laboratory, examination of material in museum collections, and scanning electron microscopy, we document autotomy of the metasoma (the hind part of the opisthosoma, or ‘tail’) in fourteen species of Ananteris. Autotomy is more common in males than females, and has not been observed in juveniles. When the scorpion is held by the metasoma, it is voluntarily severed at the joints between metasomal segments I and II, II and III, or III and IV, allowing the scorpion to escape. After detachment, the severed metasoma moves (twitches) automatically, much like the severed tail of a lizard or the severed leg of a spider, and reacts to contact, even attempting to sting. The severed surface heals rapidly, scar tissue forming in five days. The lost metasomal segments and telson cannot be regenerated. Autotomy of the metasoma and telson results in permanent loss of the posterior part of the scorpion’s digestive system (the anus is situated posteriorly on metasomal segment V) and the ability to inject venom by stinging. After autotomy, scorpions do not defecate and can only capture small prey items. However, males can survive and mate successfully for up to eight months in the laboratory. In spite of diminished predation ability after autotomy, survival allows males to reproduce. Autotomy in Ananteris therefore appears to be an effective, adaptive, anti-predation escape mechanism.

Mattoni CI, García-Hernández S, Botero-Trujillo R, Ochoa JA, Ojanguren-Affilastro AA, Pinto-da-Rocha R, et al. Scorpion Sheds ‘Tail’ to Escape: Consequences and Implications of Autotomy in Scorpions (Buthidae: Ananteris). PLoS One. 2015;10(1):e0116639. [Open Access]

Thanks to Matt Simon for informing me about this article!

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