Leave it all behind: a taxonomic perspective of autotomy in invertebrates

Abstract

Autotomy is defined herein as the shedding of a body part, where (1) the loss of the body part is defensive (autotomy helps prevent the whole animal from being compromised and is in response to external stimuli); (2) shearing occurs by an intrinsic mechanism along a breakage plane (there has been selection for certain body parts to be pulled off easily); and (3) the loss is controlled - the animal moves away from the trapped limb, the loss is under some form of central control (neural or hormonal), or the body part is detached quickly. Autotomy (under this defensive definition) has evolved independently for a diverse array of body parts in many taxa; we have summarised available information for over 200 invertebrate species. The advantages of autotomy include escape from entrapment, an effective form of attack, expulsion of an infected body part or in limiting wounding. We discuss how the incidence of autotomy may therefore be correlated with various traits such as limb function, sex differences, other defence mechanisms, habitat disturbance, and sociality. There are also costs associated with autotomy. Short-term costs include loss of a specialised appendage or organ, reduced speed and stability, or even death. Long-term costs include compromised foraging and feeding (often leading to reduced growth), altered anti-predator, competitive or reproductive behaviour, and even defective development. Regenerating lost appendages may also incur significant costs for the individual. We examine the costs and benefits of autotomy, and discuss the evolutionary selective pressures that contribute to the prevalence and effectiveness of autotomy in invertebrates.

Rapid regeneration of the major cheliped in relation to its function in male-male contests in the hermit crab Pagurus middendorffii

“…Crabs of many species can shed their appendages (autotomy; Juanes & Smith 1995, Maginnis 2006, Fleming et al 2007) when they escape from predatory interactions (Robinson et al 1970, Wasson et al 2002. Although autotomy of the cheliped is highly effective in immediate benefits for survival (Wasson et al 2002), the loss of the cheliped is known to have negative impacts on subsequent contests (Juanes & Smith 1995).…”

Tail autotomy and subsequent regeneration alter the mechanics of locomotion in lizards

“…Autotomy is a predator-escape strategy documented for a broad range of taxa (Fleming et al, 2007), including crabs (Bennett, 1973), spiders (Parry, 1957;Amaya et al, 2001), echinoderms (Emson and Wilkie, 1980), salamanders (Wake and Dresner, 1967), lizards (Congdon et al, 1974;Daniels, 1983;Arnold, 1984;Cooper and Vitt, 1985;Bateman and Fleming, 2009) and even some rodents (Sumner and Collins, 1918;Layne, 1972). Most commonly examined in lizards, this voluntary shedding of an appendage generally occurs in response to a predatory stimulus.…”

Cost of autotomy drives ontogenetic switching of anti-predator mechanisms under developmental constraints in a land snail

“…Autotomy is generally defined as a voluntary shedding of a body part along a breakage plane in response to external stimuli [23]. However, this strict definition cannot be used for body parts of animals without segments, because recognition of 'voluntary shedding' and 'breakage plane' in such animals is subjective.…”

“…However, autotomy subsequently imposes considerable costs usually (but not always) by regenerating the lost parts [19][20][21][22][23][24], in contrast to other permanent defensive devices such as shells of snails. Thus, other conditions being equal, snails may be expected to ontogenetically switch anti-predator responses from costly autotomy to less-costly structural defences upon maturity, being released from the developmental constraints of the shells.…”