The relationship between water velocity and morphological complexity of stream dwellers

The effects of environmental factors have been considered important for the evolution of morphological complexity in organisms. The water flow exhibits constant disturbance on stream dwellers, independently of their taxonomic group. Thus, we assessed whether two different kinds of organisms (insects and algae) exhibit any ecological similarity by facing stream current. For this, we used several previous studies in order to relate the morphological complexity of insect gills and algal filaments to water velocity, in micro and mesohabitats. The results for micro-scale showed that complex body shape tends to favor taxa that colonize stream areas with lower velocity for both kind of organisms. However, mesohabitats exhibited no relationship between morphology and water velocity. We suggest that morphological complexity in organisms from different lineages (algae and insects) are similarly related to water velocity in stream habitats. Moreover, the methodology of stream samplings must be carefully designed to get more precisely the environmental factors that organisms experience.