Autotomy as a prelude to regeneration in echinoderms

Abstract

'Autotomy' refers to the adaptive detachment of animal body parts where this serves a defensive function, is achieved by an intrinsic mechanism, and is nervously mediated. With regard to each echinoderm class, this article itemises those structures that are autotomous, evaluates the extent to which autotomy precedes regeneration in natural populations, reviews current knowledge of the morphology of autotomy planes and mechanisms that effect fracture at autotomy, and comments on autotomy-related issues arising from studies of the cellular events of regeneration. Each autotomy plane can be regarded as an assemblage of breakage zones traversing the individual anatomical components of the autotomous structure. In any one autotomy plane some breakage zones are permanent sites of weakness that are fractured by external forces and some are potential sites of weakness that undergo a loss of tensile strength only at the time of autotomy. The latter occur predominantly in mutable collagenous structures, although there are a few examples of muscles that undergo an endogenous rupturing process. Available evidence indicates that autotomy is by far the commonest proximate cause of structural loss in echinoderms. Most echinoderm regeneration is therefore necessitated by autotomy and proceeds from the retained side of a fractured autotomy plane. Due to a lack of relevant research there is as yet little evidence for or against the presence of specific regeneration-promoting adaptations at autotomy planes, although it is argued that an autotomy plane designed primarily to effect rapid detachment would by itself increase regenerative efficiency.

Survival and arm abscission are linked to regional heterothermy in an intertidal sea star

“…However, arm abscission was delayed following exposure to thermal stress and was usually observed >2days after the treatment. In general, in echinoderms (including asteroids), autotomy involves rapid (within at most a few minutes) abscission of a body part mediated by the nervous system, followed by a long regeneration process (Mladenov et al, 1989;Marrs et al, 2000;Wilkie, 2001). Indeed, the incidence of arm loss in nature is rather infrequent in P. ochraceus (Lawrence, 1992), although regenerating individuals can be found in every population.…”

Eco-mechanics of lamellar autotomy in larval damselflies

“…Appendages that are not essential for survival, but that are frequently a target of attack, may reduce the costs of autotomy (Fleming et al, 2007). Adaptive autotomy is expected to be a consequence of underlying functional morphological traits that permit selfamputation at a fracture plane, such as a joint, when an external force is applied (Wilkie, 2001;Fleming et al, 2007). However, the relationship between form and function is generally incompletely…”

Mechanical adaptability of a sponge extracellular matrix: evidence for cellular control of mesohyl stiffness inChondrosia reniformisNardo

“…The fact that morphological studies of C. reniformis had not revealed the presence of potentially contractile cells in a quantity or disposition sufficient to account for this phenomenon (Bonasoro et al, 2001) (F. Bonasoro, unpublished observations), raised the possibility that the mechanical properties of the mesohyl itself are under physiological control. A precedent for this is provided by the 'mutable' collagenous tissue of echinoderms, the variable tensility of which is neurally modulated and which is involved throughout the phylum in the energy-sparing maintenance of posture and in the rapid detachment of anatomical structures at autotomy (Trotter et al, 2000;Wilkie, 2001;Wilkie, 2005). The main aim of this investigation was to test the hypothesis that the passive mechanical properties of the mesohyl of C. reniformis are under direct cellular control by determining the effect on the flexural stiffness of the mesohyl of a range of agents that influence cellular activities in other animals.…”