Morphological plasticity in a caddisfly that co-occurs in lakes and streams

Abstract

Lake and stream fauna are frequently studied, yet surprisingly little is known about ecological and evolutionary dynamics of species that inhabit both lentic and lotic habitats. There are few examples of species co-occurring in different flow types, which raises questions about how co-occurrence may influence ability to adapt to changing climatic conditions. One such co-occurring species is the aquatic insect Limnephilus externus Hagen, 1861 (Trichoptera:Limnephilidae), a species known to be widely distributed in lakes of the Nearctic and Palearctic regions. Here, we test whether lake–stream populations of the caddisfly L. externus are evolutionarily or ecologically distinct. We examined larval body and case morphology, interspecies phoretic associations, and the mitochondrial DNA cytochrome c oxidase I gene among lake and stream populations of L. externus. We also explored potential morphological differences among distinct haplotypes. We observed differences between lake and stream populations in abundance, phenology, some aspects of body and case morphology, and abdominal mite presence, indicating that lakes and streams may yield distinct ecological phenotypes for this species. We also observed distinct regional differences in caddisfly body condition and case construction sturdiness and found distinct assemblages of microinvertebrates associated with the caddisfly’s body and cases. Lake–stream L. externus did not show genetic divergence; however, 3 potentially distinct haplotypes were present across the research sites as well as in sequences from North America and Canada. Limnephilus externus appears to exhibit wide geographic range and low geographic sequence structure, which could account for the species’ large variation in phenology and morphology at the lake–stream level. Combined life history and phylogenetic studies provide valuable insight into the ecological and evolutionary dynamics that influence the adaptability of aquatic fauna to climatic change.