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

Abstract

We studied the costs of lamellae autotomy with respect to growth and survival of Lestes sponsa damselfly larvae in field experiments. We manipulated predation risk by Aeshna cyanea dragonfly larvae and lamellae status of L. sponsa 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 due to cannibalism. The presence of a free-ranging A. cyanea reduced larval survival by 68% compared to treatments in which it was absent or not permitted to forage on L. sponsa damselflies. Across all predator treatments, lamellae autotomy reduced survival by about 20%. The mean head width and mass of survivors was lower in the enclosures with a free-ranging A. cyanea compared to the other two predator treatments. This suggested that larvae grew less in the presence of a free-ranging predator, indicating that increased antipredator behaviours were more important in shaping growth responses than reduced population density. Mass, but not head width, of survivors was also reduced after autotomy. The fitness consequences of these effects for the adults may be pronounced. In general, these field data strongly suggest that lamellae autotomy affects population regulation of damselflies.

Effects of predator-induced thinning and activity changes on life history in a damselfly

“…Studies on damselflies have found no effect of thinning but an effect related to reduction in feeding behaviour, which caused a reduced growth effect (McPeek 1990(McPeek , 1998Stoks et al 1999). These studies differ from ours in two respects.…”

Food stress and predator-induced stress shape developmental performance in a damselfly

“…The presence of a caged predator had similar life history effects as a low food level. Such predator-induced effects have previously been demonstrated in this study species (Stoks et al 1999a(Stoks et al , 1999b and in many other taxa (e.g. Skelly and Werner 1990;Feltmate and Williams 1991;Peckarsky et al 1993;Ball and Baker 1996;McPeek 1998).…”

“…Directly after their moult into instar F-1, larvae were placed under the experimental conditions. I exposed the damselflies to the presence of Aeshna cyanea dragonfly larvae because they are important predators of L. sponsa (Stoks et al 1999a(Stoks et al , 1999b. Dragonfly larvae (instar F-2) were collected from the same pond and housed separately in the laboratory under the same conditions as the L. sponsa larvae and fed ad libitum with Chironomus larvae.…”

Autotomy reduces immune function and antioxidant defence

“…Given its cytotoxicity, activated PO loses its activity rapidly, and to maintain constant levels there is a need for continuous production (Sugumaran 2002 (Stoks 1999(Stoks , 2001Stoks et al 1999). The decreased PO activity after 24 hours was not due to a decrease in overall protein synthesis rate as lamellae autotomy did not affect RNA/DNA ratios (see appendix in the electronic supplementary material).…”

“…When larvae reached the final instar, we removed all three lamellae from one random half of the larvae by gently pulling them with two fingers until the animals autotomized these appendages at the specialized breaking joints (as in Stoks 1999;Stoks et al 1999). The other half of the larvae underwent a sham operation without removing the lamellae.…”