Dine and dash: How trophic ecology and migration shape functional locomotory traits in Clupeiform fishes

Understanding how interactions between multiple selective forces influence traits at the macroevolutionary scale is key to understanding adaptive landscapes. Diadromy, an extreme form of migration between marine and freshwater environments, is thought to require locomotory traits conducive to long-distance migration. Yet, other selective forces, such as predator avoidance, habitat use, and prey acquisition, are also likely to shape locomotory adaptation in fishes. We examined how diadromy and trophic ecology together influenced locomotory trait diversity across Clupeiformes, a clade of fishes containing high trophic diversity and numerous transitions to diadromy. We found that both diadromy and trophic ecology influenced the pattern and pace of trait evolution. Diadromous taxa rapidly evolved traits characterized by high cruising efficiency, but the extent to which diadromous and non-diadromous taxa differed depended on their trophic ecology. Macropredators showed greater differences in locomotory traits between diadromous and non-diadromous taxa than phytodetritivores and micropredators, suggesting that traits conducive to migration might be most costly to consumers of evasive prey. This work shows that simultaneously characterizing the roles of multiple ecological or life-history factors in phenotypic evolution can bring the topography of adaptive landscapes into sharper focus and provide a more holistic view of the forces driving patterns of trait evolution.

Methods
Phylogenetic data comes from Egan et al. (in press).

Morphological data was collected for 131 taxa across Clupeiformes using museum specimens. We used a methodology first developed by Gerry et al. (2011) to collect functional locomotory trait data by obtaining the center of mass of a museum specimen. This then allowed us to calculate nine functional indices. For more information on the methods, see Finnegan et al. (2024).