Cestode parasites using brine shrimps Artemia as intermediate hosts and waterbirds as final hosts are known to change the colour of shrimps from pale pink to bright red owing to an increase in carotenoid pig- ments. In order to assess whether this coloration increases the chances of shrimp predation by the final host, we conducted an experiment in which 10 Calidris sandpipers were given a choice of 20 bright red and
20 pale pink shrimps. A strong preference for red, infected shrimps was recorded, suggesting that red colour is a manipulation by cestodes to increase transmission to its final hosts. The factors regulating access and functions of carotenoids in birds are under intense debate. For the first time, we show that access to carotenoid-rich foods in birds can have a cost derived from an increased exposure to parasites. To our knowledge, this is the first time that avian hosts have been shown to exert a colour- based preference for parasitized prey.Peer reviewe
