Lethal and sublethal costs of autotomy and predator presence in damselfly larvae

We studied the costs of lamellae autotomy with respect to growth and surviv al of Lestes sponsa damselfly larvae in field experiments. We manipulated p redation risk by Aeshna cyanea dragonfly larvae and lamellae status of L. s ponsa larvae in field enclosures and compared differences in numbers, size and mass of survivors among treatments. In the absence of a free-ranging A. cyanea larva, about 29% of the L. sponsa larvae died. This was probably du e to cannibalism. The presence of a free-ranging A. cyanea reduced larval s urvival by 68% compared to treatments in which it was absent or not permitt ed to forage on L. sponsa damselflies. Across all predator treatments, lame llae autotomy reduced survival by about 20%. The mean head width and mass o f survivors was lower in the enclosures with a free-ranging A. cyanea compa red to the other two predator treatments. This suggested that larvae grew l ess in the presence of a free-ranging predator, indicating that increased a ntipredator behaviours were more important in shaping growth responses than reduced population density. Mass, but not head width, of survivors was als o reduced after autotomy. The fitness consequences of these effects for the adults may be pronounced. In general, these field data strongly suggest th at lamellae autotomy affects population regulation of damselflies.