Geological variation in particle surface-roughness preference in the case-bearing caddisflies

Abstract

Optimality modeling suggests that the choice of resources often represents the best achievable balance of costs and benefits. However, there is no empirical data describing the effect of resource availability on the development of the material choice behavior during construction of a biological structure. Cylindrical case-bearing caddisfly larvae prefer smooth-surface particles to allow construction of a smooth interior case wall. We evaluated the relationship between case material preference and the local availability of sand particle species in 7 distant populations of 2 odontocerid species, Psilotreta kisoensis and Perissoneura paradoxa. The field survey revealed that all populations selectively used the smooth particles from the surrounding sediment to construct their cases. However, when comparing among populations, the larvae originating from areas with relatively few smooth particles constructed cases using rougher particles. We then forced the larvae to choose from a mixture of equal amounts of 2 artificial particles that had different textures (rough and smooth). The preference for smooth artificial particles was lower in populations that naturally incorporated rougher particles in their cases. Our results are consistent with the predictions of optimal foraging theory as the populations living in areas with abundant smooth particles had a stronger preference for smoothness than those in areas where such particles were rare. The abundance of smooth particles in the sediment depended on its mineralogical/ petrological origin. Thus, we suggest that material preference is influenced by local geology. Our results provide important insight into the mechanisms controlling construction behavior. Key words: construction behavior, decision making, optimality theory, sediment geology, surface roughness, Trichoptera. [Behav Ecol]