Data from: Redder isn’t always better: cost of carotenoids in Chinook salmon eggs

Carotenoids provide animals with many fitness benefits through increased
mating success, immune function, gamete quality, and antioxidant capacity.
Despite these benefits, carotenoids are not utilized equally by all
animals, implying trade-offs associated with the pigments; although, few
studies have quantified fitness costs of carotenoid pigmentation. Salmon
are known for their conspicuous red coloration; however, amongst Chinook
salmon (Oncorhynchus tshawytscha), a natural genetic color polymorphism
exists (red and white morphs) which results in carotenoid-based color
differences in eggs and other tissues. Although the fitness benefit of egg
carotenoid content on egg incubation survival has been demonstrated,
carotenoid pigmentation also results in highly visible eggs vulnerable to
predation. Therefore, although white Chinook salmon eggs experience costs
in terms of viability, a potential benefit in terms of reduced predation
could help explain the maintenance of the polymorphism. Here, using red
and white eggs from wild Chinook salmon, we show that increased carotenoid
content of salmon eggs leads to greater predation risk. We found that 2
populations of wild-type rainbow trout (O. mykiss; an ecologically
relevant predator) showed a significant bias for red eggs over white eggs
under choice experiments, where red eggs were consumed first twice as
often and significantly faster than white eggs. Our study suggests that
trade-offs between red and white Chinook salmon during the egg stage
provide an evolutionary mechanism promoting the maintenance of the unique
Chinook salmon color polymorphism in nature, while also, for the first
time, demonstrating a direct fitness cost of carotenoids in salmon.