Why are salmonids pink?
Friday Seminar by Stig Omholt.
Pigmented flesh is a trait uniquely present in four of the ten genera of salmonid fishes, owing to their ubiquitous capacity for accumulating dietary carotenoids in the muscle. We have combined life-history reasoning with current knowledge of carotenoid metabolism to suggest a possible evolutionary scenario accounting for the emergence and maintenance of this phenotype. We claim that a basal carotenoid metabolism and a hormonally controlled targeted degradation of muscle tissue during maturation were established prior to the anadromous life style, and that these proximal features were concomitantly exploited by natural selection in an ancestral anadromous and nest making salmonid. Three different selection regimes are suggested to account for available empirical data concerning emergence as well as maintenance of the flesh pigmentation trait: a primary one driven by the need for enhanced somatic maintenance accompanying nest making under starving conditions, a secondary one driven by sexual selection, and a tertiary one driven by exposure to a meager carotenoid diet in non-anadromous fresh water populations.
The talk will also provide an update on our experimental and theoretical research programme associated with the above hypothesis.