Invest in arms: behavioural and energetic implications of multiple autotomy in starfish (Asterias rubens)

The autotomy of body parts as a means of escaping predation or renewing dam aged tissues has evolved in a number of animal groups. Starfishes are uniqu e in that they can autotomise > 75% of their body mass and continue to surv ive. Presumably, multiple autotomy of tissue has energetic costs in terms o f potential fitness and may affect the allocation of energy reserves accord ingly. We investigated arm autotomy, predatory capabilities and subsequent regeneration in common starfish, Asterias rubens, that were induced to lose one, two or three arms. Initially, both regeneration of autotomised arms a nd the rate of growth of intact arms was slowest in animals that had lost t he most arms (i.e. three arms missing vs two arms missing vs one arm missin g). However, 8 months later, the growth of intact arms since the start of t he experiment was not significantly different between groups of starfish th at had autotomised different numbers of arms. However, the average dry weig ht per regnerating arm was significantly higher in starfish that had autoto mised the most arms. Arm loss decreased the ability of starfish to open mus sels and those that had autotomised two arms were significantly less likely to feed successfully on a mussel in a 24-h period than intact starfish. Ou r data suggest that proportionally more energy is allocated to arm regenera tion in starfish that have suffered multiple arm loss and this may compensa te a potential decrease in fitness that results from decreased feeding capa bility.