Meeting Abstract
Animal colouration has spurred some of the most active and controversial fields in evolutionary biology. Carotenoids are vital but limited resources in functions ranging from immunity to ornamentation. Parasite infection often correlates to intensity of carotenoid-based ornamentation and is believed to reflect an influence of parasites on host health. However, parasites can also shape host phenotype to their own advantage. Applying an extended phenotype approach to carotenoid distribution, we suggest the possibility that parasites affect this distribution depending on the host`s role in the parasites life cycle. Skin coloration (redness) and the ratio between skin and muscle coloration (red-red ratio) of sexually mature male Arctic charr (Salvelinus alpinus), is negatively correlated to infection intensities of the tapeworm Eubothrium salvelini that uses charr as a definitive host. Conversely, parasites that await trophic transmission are positively related to redness and red:red ratio. The positive association between Diplostomum sp. and redness/red:red ratio indicates parasite mediation not only related to immune function since they occupy the immune privileged eye. Thus, parasite mediation likely originates from more complex processes such as investment in reproduction. From the perspective of the parasite, promoting such investment could serve as an adaptation for trophic transmission. Conversely, opposing such investment could protect the final host from predation.
