Distribution, temperature, and trophic position as ecological drivers of body morphological divergence in cephalopods

Cephalopods exhibit diverse adaptations to environmental pressures, but previous studies often focus on single traits or few species, overlooking broader relationships between body geometry and ecology. This study quantifies phylogenetic correlations between ecological and morphological traits in cephalopods, testing whether body shape diversification was driven by ecology. Using nuclear and mitochondrial markers, we constructed a molecular phylogeny and examined body size in 680 species and shape in 383 species, exploring associations with distribution, temperature, and trophic level. Results showed that cephalopod body morphology exhibited moderate phylogenetic signals, whereas ecological traits displayed weaker phylogenetic patterns. Species with broader distributions, wider temperature tolerances, and higher trophic levels had larger mantle lengths. Similarly, wider-ranging and higher-trophic species evolved longer, broader fins. Larger cephalopods exhibited streamlined bodies with higher hydrodynamic efficiency, whereas smaller cephalopods showed smaller ecological traits and non-streamlined shape. Overall, cephalopod morphology is shaped by multiple factors, with body size and fin geometry reflecting adaptations to different marine niches. Streamlined large-bodied predators dominated open waters and higher trophic levels, while compact, non-streamlined shapes thrived in specialized habitats. These insights advance our understanding of cephalopod morphological divergence and provide empirical support for biogeographic principles and niche theory, while future phylogenetic topologies inferred from complete genomic data could further refine our results.