From conservatism to lability: Phylogenetic signal and evolutionary models decode macrobenthos functional trait...

The macrobenthic communities play crucial ecological roles in Arctic fjords. This study integrates mitochondrial cytochrome c oxidase subunit I (mtCOI)-based phylogenies with functional trait data for 50 species from Kongsfjorden-Krossfjorden, Svalbard to investigate evolutionary constraints shaping trait variation. Phylogenetic signal (PS) was quantified across 21 traits using Pagel's λ, Blomberg's K, Moran's I, and Abouheif's C_mean. Most traits exhibited strong PS (Pagel's λ ≥ 1.0, p = 0.001), indicating pronounced evolutionary conservatism among Arctic macrobenthos. Tube-dwelling (C_mean = 0.310, p = 0.002) and burrowing (Moran's I = 0.053, p = 0.004) traits exhibited the highest autocorrelation, which reflects adaptation to extreme Arctic fjord conditions. Feeding and environmental position traits showed strong PS and autocorrelation, while reproductive traits were evolutionarily labile. Phylogenetic correlograms revealed hierarchical evolutionary constraints with strong conservatism in living habitat, intermediate constraint in feeding habits, and high lability in reproductive strategies across Arctic macrobenthic assemblages. Phylogenetic principal component analysis highlighted major axes of trait variation structured by shared ancestry. Evolutionary model fitting identified Early Burst (EB) as the best model for overall trait evolution, suggesting rapid initial diversification followed by evolutionary deceleration. Univariate traits showed mixed patterns, with environmental position following EB, while body size and motility evolving gradually under Brownian Motion model. These findings provide novel insights into complex evolutionary dynamics where deep phylogenetic constraints coexist with functional flexibility.