Body-shape variation of Acroneuria lycorias (Plecoptera:Perlidae) nymphs across magnitude and frequency stream flows

Morphological variation across environmental gradients can indicate an organismal phenotypic response to the surrounding environment. The interaction of body shape and water movement creates physical forces that can affect the ecology and evolution of benthic organisms in stream systems. Magnitude and frequency components of flow regimes have been linked to morphological variation in body shape of fish and macrophytes, but very few attempts have been made to evaluate similar relationships in stream insects. The aim of our study was to evaluate body-shape variation in large nymphs of an insect species and to test for a correlation with natural streamflow fluctuations in a regional geographic space. We sampled Acroneuria lycorias (Plecoptera:Perlidae) populations at 9 stream sites (8 systems) with an associated US Geological Survey stream gage. We calculated ecological flow statistics from daily discharge data, and we used 2-dimensional geometric morphometrics to describe variation in A. lycorias body shape. Multivariate analysis showed correlation of A. lycorias body shape with flow attributes. After correction for allometry, A. lycorias nymphs from streams with relatively high discharge and stable flow had an elongated streamlined body plan. Acroneuria lycorias nymphs from streams with relatively low discharge and flash flow had a short and wide (stout) body plan. Stream flows are under continuous natural and human-induced fluctuations, and our study provides information to help understand biological responses to hydrologic conditions.