LAUSR

Ecologically relevant resource polymorphisms have received increased attention over the last two decades, yet marine examples are relatively rare and the evolutionary mechanisms that maintain them are not thoroughly understood. Here, we investigated trophic segregation associated with whole-body asymmetry direction within a polymorphic marine flatfish species, the starry flounder (Platichthys stellatus). Stable isotope ratios (15N/14N, 13C/12C) were determined for 213 fish from nine localities throughout the northeastern Pacific. Sinistral (left-eyed) flounder had slightly but significantly enriched δ15N over dextral (right-eyed) flounder, suggesting that sinistral flounder were targeting higher trophic level prey. Sinistral flounder had enriched δ13C in the southernmost samples only, suggesting that their prey was more marine derived than that of dextral fish in that region. A principal component composed of body depth and caudal peduncle depth was weakly associated with δ13C, suggesting that prey of flounder with decreased body and caudal depth were more freshwater derived. Gut contents revealed significantly greater trophic breadth of prey in sinistral flounder than dextral flounder. These data, combined with previous findings of differences between morphs in ecomorphology and prey strike behaviours in P. stellatus, and gut content differences in a congeneric (Platichthys flesus), provide evidence of trophic segregation associated with the direction of wholebody asymmetry within polymorphic flatfish species.