Abstract
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.
Highlights
Autotomy is the process by which some animals voluntarily shed or detach a body part, usually as an anti-predator defense mechanism
Autotomy was not observed in A. solimariae specimens anesthetized with ice prior to manipulation, or when A. balzani and A. solimariae specimens were held by body parts other than the metasoma
Metasomal detachment in Ananteris meets the criteria for defensive autotomy [2, 3]
Summary
Autotomy is the process by which some animals voluntarily shed or detach a body part, usually as an anti-predator defense mechanism. In order to be considered autotomy, the process of shedding or detachment must be provoked by external stimuli, achieved by an intrinsic mechanism, and mediated by the nervous system [1,2,3]. Autotomy occurs along permanent sites of weakness, cleavage planes that permit a clean break when a body part is detached, with anatomical features that minimize trauma and promote rapid sealing of the fluid compartment, leading to swift closure and healing of the wound [2, 4]. The incidence of autotomy in natural populations may be determined by predation efficiency and intensity, anatomical mechanisms, microhabitat preference, sex and ontogenetic differences, intraspecific aggression and the use of other defense mechanisms [3, 8]
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