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Presented at the NABS Annual meeting, Vancouver, British Columbia, 2004
in Population Ecology 2
Seasonal time constraints and the development-size trade-off: pond drying delays development in a wetland caddisfly (Limnephilus externus)
J.E. Jannot1,3 and S.A. Wissinger2,3. 1Department of Biological Sciences, Purdue University, West Lafayette, IN USA 47907, 2Departments of Biological and Environmental Sciences, Allegheny College, Meadville, PA USA 16335, 3Rocky Mountain Biological Laboratory, Gothic, CO USA 81224
Organisms often face a trade-off between juvenile developmental time and adult size. This trade-off is especially likely when developmental time constraints exist such as pond drying that limit the time to metamorphosis. Few studies have examined the influence of pond drying on aquatic insects. We examined how the development-size trade-off changes when caddisfly larval resources interact with drying. We predicted that larvae in ephemeral habitats should emerge earlier and at smaller sizes than individuals in longer hydroperiod habitats, and that increased larval resources should increase growth rate and accelerate development, facilitating early metamorphosis and reducing negative effects of drying. Limnephilus externus larvae use ponds that vary in hydroperiod. We exposed forty larvae per replicate to two hydroperiods (drying, permanent) and two diets (protein supplement, no supplement) in 16 outdoor mesocosms with natural substrates. Contrary to predictions, time spent as a larva was longer and female adults were smaller in drying than permanent treatments (p < 0.01). Diet had no effect on either development or adult body size. Delaying metamorphosis under drying conditions suggests a life history constraint in L. externus. Warm temperatures experienced in rapidly drying ponds also may induce a high metabolic cost, jeopardizing completion of the life cycle.
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