Abstract
Crustaceans release (autotomize) a limb grasped by a predator or conspecific, often as an escape tactic. However, there are potential fitness costs over the time needed to regenerate a missing limb. If anti-predatory defensive structures are lost, the individual risks further serious injury or death. The Caribbean spiny lobster, Panulirus argus, uses two long, armored, mobile, spinous antennae to defend against predators such as the gray triggerfish, Balistes capriscus. The loss of one or both antennae potentially leaves it highly vulnerable to attack unless the lobster has compensatory behavior to offset the weapon loss. I tested the ability of P. argus to defend itself against B. capriscus after loss of one and both antennae and evaluated how lobsters behaviorally compensated. Single sub-adult lobsters, both unrestrained and tethered, were pitted against adult triggerfish in large open seawater arenas. Triggerfish presented with a choice between intact lobsters and those missing an antenna strongly preferred to attack the latter. All lobsters with no antennae were quickly debilitated but those with one antenna were unexpectedly comparable to lobsters with both antennae in their ability to thwart triggerfish attack. That is, the differences in timing and frequencies of injury and mortality were not statistically significant, although the data suggest a trend for higher vulnerability after loss of one antenna. Additionally, the overall frequencies of particular defensive actions by lobsters missing an antenna closely resembled those of intact lobsters. The tail-flip escape action was infrequent and occurred mainly in the last part of trials in which a lobster was defeated. By comparison, successfully defending lobsters, with either one or two antennae, stood their ground and more consistently made effective, timely antennal counter actions in response to triggerfish predatory actions. Free ranging and tethered lobsters defended similarly and with similar success despite constraint of the former. Caribbean spiny lobsters with a single antenna can partially compensate for weapon loss potentially providing a survival advantage, thus allowing them to continue to move about over open terrain where this species commonly forages and migrates.
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