CANNIBALISM AMONG DETRITIVOROUS CADDISFLY LARVAE IN SUBALPINEWETLANDS: FITNESS EFFECTS OF DIETARY SUPPLEMENTATION.

S.A.Wissinger,W.S.Brown, J.S. Alexander, J.A. Steinmetz, and S.M Kilby. AlleghenyCollege, Meadville, PA 16335 and Rocky Mountain Biological Lab, CrestedButte, CO 81224.

Larvae of the limnephilid caddisfly, Asynarchus nigriculus, are among the most abundant invertebrates in high-elevation, temporary wetlands in central Colorado. Although gut contents are dominated volumetrically by vascular plant detritus, they also contain fragments of animal material, including chitinous parts of conspecifics. Field and lab experiments indicated that cannibalism is common among late-instar Asynarchus larvae, even at low densities and with abundant detritus. The purpose of this study was to quantify the effects of varying the diet of this species on larval survival and development and on adult fitness correlates such as body size and fecundity. We conducted a field experiment in which larvae were reared in littoral cages with 1) ambient food (detritus + invertebrates, excluding caddisfly predators, 2) detritus with reduced invertebrates, and 3) ambient food + enhanced invertebrates and a protein-rich supplement (commercially prepared freeze-dried Tubifex). In a concomitant laboratory study we reared larvae individually with and without the protein-rich supplement. In the field, Asynarchus larvae grew faster, survived better, and pupated earlier, and adults emerged earlier in the protein-enhanced treatments than in the other treatments. Protein-enhancement had similar effects on growth and development in the lab, but survival was unaffected. Thus, the effect of food enhancement on survival in the field appears to be the result of reduced cannibalism rather than reduced starvation. In the field, only those larvae in the enhanced food treatments pupated and emerged by the time that temporary habitats used by this species had dried. Preliminary analyses suggest that protein enhancement also increased both the size and fecundity of adults. These results suggest that cannibalism, and carnivory in general, provide this detritivore with a protein/fat-rich dietary supplement that is important for the timely completion of development in these ephemeral, oligotrophic habitats.