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Presented at the NABS Annual meeting, La Crosse, Wisconsin, 2001
CADDISFLY CANNIBALISM IN SUBALPINE TEMPORARY WETLANDS: PROXIMATE MECHANISMS AND LIFE HISTORY
S. A. Wissinger1,3 and E. E. Bilger2,3. 1Biology Department, Allegheny College, Meadville, PA 16335 USA, 2Department of Entomology, University of Georgia, Athens, GA, 30602 USA, 3Rocky Mountain Biological Laboratory, P. O. Box 519, Crested Butte, CO 81224 USA
The caddisfly, Asynarchus nigriculus (Limnephilidae) is ubiquitous in temporary, subalpine wetlands in the central Rockies. Larvae develop rapidly, are extremely aggressive, and frequently form cannibalistic mobs. We conducted a variety of experiments to elucidate the proximate mechanisms that facilitate/deter cannibalism in this species. In microcosms, aggression between same-sized larvae rarely resulted in one-on-one cannibalism. One-on-one cannibalism increased with disparity in body size, but these disparities are never realized in nature because of synchronous development. Starved animals were no more vulnerable than fed animals, but were more aggressive and spent the most time grazing on the case silk of conspecifics. Case grazing led to escalated fights and to mob formation when individuals were injured. Case removal increased vulnerability to cannibalism dramatically. Individuals from habitats with low nutrients were no more aggressive than those with high nutrients. These data suggest that 1) avoidance of cannibalism could explain the remarkable level of developmental synchrony in this species; 2) cases could be as important for protection from cannibals as from other predators, and 3) selection for rapid development in temporary habitats is a more likely explanation for cannibalism in this species than low nutrients per se.
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