Costs and economy of autotomy for tail movement and running speed in the skink Trachylepis maculilabris

Economy of autotomy (shedding less than complete tails) is advantageous via retention of ability to autotomize and reduction of costs, including lipid loss, regeneration, and decreased social status. We studied its effects on predator-distracting tail movements and running speed in the speckle-lipped mabuya ( Trachylepis maculilabris (Boettger, 1913)) by removing fractions of the autotomizable portion. Distance moved was shorter for autotomized tail segments one third of the total tail length than for longer segments. Movement duration did not vary with proportion removed. Longer movement suggests that shedding longer segments improves ability to distract predators, enhances difficulty of capturing a tail, and may require longer handling time. Tails were difficult to break in regenerated sections and did not move when broken. The lack of movement of regenerated portions after separation suggests permanent loss of capacity to distract predators. Decreased speed was confirmed as a cost of autotomy in lizards that lost at least two thirds of their tail. In lizards that lost one third of tails speed was intermediate to that of intact lizards and those that lost more. Graded decrease in speed as proportional loss increases is consistent with progressive loss of a counterweight that reduces lateral motion while running. Economy of autotomy entails trade-offs between immediate and long-term escape ability.