Phylogenetics, Trait Covariance Analysis, and the Evolution of Fin and Body Shape in the Surgeonfishes

Insights into ecomorphology are enriched when investigating evolutionary correlations between ecologically and functionally important traits. However, tools currently available to model patterns of shape covariation limit researchers to either assume that trait covariances between taxa are independent of, or completely described by, their shared evolutionary history. Using a novel Pagel's λ adjustment to incorporate phylogenetic signal in trait covariance analysis, we aim to solve this long-standing problem in phylogenetic comparative methods and investigate ecological associations and evolutionary shape covariation in the ecologically and morphologically diverse case study of surgeonfishes (Acanthuridae). By revising acanthurid phylogenetic relationships and analyzing the geometric morphometrics of their body, head, and fins, we found that head and body shape were significantly associated with dietary ecotype. Surgeonfishes showed a significant negative correlation between caudal fin and pectoral fin shape; high/low aspect ratio (AR) tails are associated with low/high AR pectoral fins, respectively, suggesting locomotor tradeoffs. With our new approach to estimate the influence of phylogeny on trait covariances between taxa, we found the caudal fin covaried with both the body and pectoral fin due to dietary and locomotor demands, respectively and exhibited the highest evolutionary variance along the primary axis of integration in all trait covariance comparisons.