Putative carotenoid-binding proteins from the hemolymph of endemic Lake Baikal amphipod Eulimnogammarus cyaneus and E. vittatus

Color is an important trait in nature, playing a role in selection and speciation. The most important colorants in crustaceans are carotenoids, which in complexes with carotenoid-binding proteins provide an astonishing variety of colors from red to violet. Over 350 species and subspecies of amphipods (Crustacea: Amphipoda) endemic to Lake Baikal exhibit an impressive variability of colors and coloration patterns. However, the mechanisms forming this diversity are underexplored. In this work, we analyze the coloration of two species of endemic Lake Baikal amphipods, Eulimnogammarus cyaneus and E. vittatus. These species are brightly colored and, even more importantly, characterized by intraspecific color variability. We showed that the color of either species strongly correlated with the abundance of two putative carotenoid-binding proteins (the relative abundance of these proteins was higher in blue or teal-colored animals than in the orange- or yellow-colored ones.). With LC-MS/MS, we were able to identifiy these proteins, which turned out to be similar to the pheromone/odorant-binding protein family.