The role of particle surface texture on case material selection and silk lining in caddis flies

Many organisms construct external structures to increase their fitness. However, there is a considerable energetic cost for construction that often involves a trade-off with other physical or behavioral traits or construction processes. Cylindrical case-bearing caddis fly larvae need a smooth interior case wall, presumably to undulate their abdomen for respiration. We studied 5 species of caddis fly that build cases with sand grains. Experiments were conducted to force these species to reconstruct or repair their cases using 20 paired combinations from 11 types of artificial materials with different surface textures. Surface roughness was determined by confocal laser scanning microscopy. Among the 4 species that display voluntary undulation behavior for respiration, 2 species (Goera japonica and Apatania sp.) that make their case wall smooth by secreting silk showed only moderate preference for smooth particles. The other 2 species (Psilotreta kisoensis and Perissoneura paradoxa; Odontoceridae), which do not line their cases with silk, showed a strong preference for smoother particles. The results suggest that these 2 types of case bearers employ antithetical strategies that being a trade-off between costs for secreting silk and selecting smoother particles to make a smooth case wall. The fifth species (Glossosoma ussuricum), which does not display voluntary undulation behavior or interior silk lining, was nonselective for surface roughness of the case-building particles. It is indicated that these differences are related to both the conformation of cases and respiration behavior. Copyright 2010, Oxford University Press.