Why run and hide when you can divide? Evidence for larval cloning and reduced larval size as an adaptive inducible defense

Abstract

Predator-induced cloning (asexual reproduction), with reduced size as consequence of cloning, suggests a novel adaptation to the threat of predation. Although cloning is a common reproductive strategy of many plants and animals, cloning in response to stimuli from predators has, at present, been documented only in the larvae (plutei) of the sand dollar, Dendraster excentricus. Other studies report larval cloning in echinoderms under optimal conditions of food and temperature. A burst of asexuality should be favored when environmental conditions are conducive to growth, but it is less clear that cloning is advantageous when conditions indicate risk from predators. This study tested the hypothesis that the small size of predator-induced clones reduces vulnerability during encounters with planktivorous fish. Successful cloning was inferred from an increase in larval density, a reduction in larval size and stage, and some direct observations of budding. All clones were smaller than uncloned sibling larvae, suggesting an advantage against visual predators. Pair-wise predation trials demonstrated that planktivorous fish ate more uncloned sibling plutei than small clones. These results offer a new ecological context for asexual reproduction: rapid size reduction as a defense. If the identifiable cues for cloning in echinoderm larvae (food and predators) are linked in nature, then larval cloning may be a response to a single ecological scenario rather than two separate and unrelated conditions.