Most red, orange and yellow coloration in vertebrate animals is the result of carotenoid pigments. Vertebrates cannot synthesize carotenoids and instead must obtain them from their diet, but carotenoids also play important roles in reducing oxidative stress and supporting the immune system. The carotenoid trade-off hypothesis predicts that when dietary carotenoids are limited, animals must sacrifice coloration or immunity. Many published studies of the carotenoid trade-off hypothesis cite the assumption that dietary carotenoids are limiting, but this statement is largely untested. Likewise, little is known about carotenoid trade-offs in females of species with reversed sexual dichromatism, i.e. species in which females are more brightly colored than males. Females have an additional competing need for carotenoids, namely that the pigments can be incorporated into egg yolk and passed on to their offspring. This proposal seeks to use a combination of laboratory and field studies to understand the complex relationship between carotenoid absorption, sexual coloration, and somatic maintenance in pigmented females by developing a statistical model to predict carotenoid availability and allocation in the wild. The proposed study will address these questions using the convict cichlid (Amatitlania nigrofasciata), a well-studied Central American fish in which females have carotenoid-based ventral coloration. The proposed study would use field work to design a simultaneous equations model on which to base future laboratory studies of the interaction between environmental carotenoid availability and the food matrix in carotenoid-pigmented species. Development of a statistical model for carotenoid absorption will allow other researchers to place their work on the carotenoid trade-off hypothesis into a theoretical context, in addition to having implications for fish health in ornamental and food fish farming, both multi-million dollar industries in the United States.
Carotenoids are orange, red, and yellow pigments found in fruits and vegetables. Vertebrates cannot synthesize carotenoids, and instead must obtain them from their diet. Vertebrates with carotenoid-based body color may be forced to trade off carotenoids for pigmentation against other physiological demands for carotenoids, including defense against parasites and pathogens. Increased dietary access to carotenoids is often cited as the primary factor responsible for body carotenoid levels, but rarely are carotenoid concentrations in the natural diet tested directly. We conducted a field survey to determine the level of carotenoid availability in the natural environment of a carotenoid-ornamented fish, the convict cichlid Amatitlania siquia. We found that carotenoids in the stomachs of wild convict cichlids did not vary significantly with parasite infection or between sampling sites. We also identified for the first time a zoonotic, pathogenic bacterium, Edwardsiella spp., in this wild population of A. siquia. In the laboratory, convict cichlids were fed diets varying in their carotenoid content, which were based on the findings from the field study. These fish did not differ in their response to Edwardsiella bacteria, suggesting that carotenoids are not limiting in nature. This research contributes to our understanding of the evolution of animal coloration, particularly carotenoid-based pigmentation.
