From Lability to Conservatism: Evolutionary Patterns in the Traits of Stream Trichoptera

ABSTRACT The ability to predict biodiversity responses to ongoing environmental change depends on understanding the extent to which traits are conserved across evolutionary history. Examining the relationship between traits and phylogeny provides key insights into how evolutionary history constrains and structures the traits. We quantify the strength of the phylogenetic signal (PS) in Trichoptera traits, as an indicator of evolutionary patterns from phylogenetic conservatism to evolutionary lability. We hypothesised that construction behaviour, feeding group, respiration, locomotion, and body flexibility would exhibit strong PS, consistent with phylogenetic conservatism. In contrast, we hypothesised that body size, body shape, and voltinism would exhibit weak PS, consistent with evolutionary lability. We compiled data on Brazilian genera of Trichoptera from the Taxonomic Catalogue of the Fauna of Brazil and data on eight traits distributed across 28 categories associated with these genera. We reconstructed a phylogenetic tree of Brazilian Trichoptera genera based on a published hypothesis. We estimated the PS in traits of Trichoptera using K mult statistics. Voltinism, body size, and body shape exhibited more evolutionary lability than construction behaviour, body flexibility, locomotion, respiration, and feeding group traits, with families and suborders overlapping in their trait composition. We concluded that Trichoptera traits span a continuum from phylogenetic conservatism to evolutionary lability, and that recognizing the strength of evolutionary constraints on these traits could inform prediction of their responses to ongoing environmental change. By integrating phylogenetic and trait‐based perspectives, this study reveals that the strength of evolutionary constraints can vary markedly even within a single insect order. This underscores the importance of evolutionary history for understanding trait distributions and predicting how freshwater assemblages may respond to environmental changes.