Phylogenetic, Spatial, and Species-Trait Patterns across Environmental Gradients: the Case of Hydropsyche (Trichoptera) along the Loire River
Résumé
When ILLIES published his concept on the longitudinal zonation of lotic invertebrates five decades ago (ILLIES, J., 1961: Internat. Rev. ges. Hydrobiol. 46: 205-213), he defined a research topic that currently interests many ecologists because he linked speciation and phylogeny with spatial distribution and trait adaptation to environmental conditions prevailing along rivers. We tested these ideas analyzing nine spe- cies of the caddisfly genus Hydropsyche from the Loire River (France). A morphology-based phylogeny illustrated that the oldest of our species occurred in the headwater and that specific phylogenetic distanc- es from the root location in the tree were significantly related to the specific longitudinal occurrences in the Loire. Furthermore, traits such as oxygen consumption, optimal velocity for filter-net-building, and larval size were significantly related to the specific phylogenetic distances, indicating meaningful, gradual adaptations to environmental gradients prevailing along European rivers (particularly in water temperature, near-bottom flow, sediment porosity). Thus, joining phylogeny, spatial distribution, and species traits provided insights into a central topic of contemporary ecology, the spatial patterns of speciation, taxonomic community structure (species distributions), and niche adaptation (traits).