Sandpipers Select Red Brine Shrimps Rich in Both Carotenoids and Parasites

Trophically transmitted parasites often manipulate the behaviour of their intermediate host, which is assumed to increase the vulnerability to predation by the final host (for a review, see Moore 2002). However, the adaptive value of behavioural changes associated with infections is difficult to demonstrate. Increased predation by the final host is the main criterion supporting adaptive manipulation by parasites (Poulin 1994), yet this has rarely been shown because most studies of trophically transmitted parasites concentrate on their interactions with intermediate hosts. Old World brine shrimps Artemia spp. (Crustacea, Branchiopoda, Anostraca) are intermediate hosts for several species of avian cestodes whose transmission depends on predation by shorebirds (Anomotaenia tringae, A. microphallos, Euricestus avoceti), flamingos (Flamingolepis liguloides, F. flamingo, Gynandrotaenia stammeri), grebes (Confluaria podicipina) and gulls (Wardium stellorae) (Georgiev et al. 2005). Natural populations of Artemia show a continuous distribution of coloration ranging from very pale individuals to intensely red coloured ones. Artemia recorded near the water surface, where birds feed, tend to be red and infected with cestodes, whereas those close to the bottom tend to be pale pink and parasite free (Gabrion et al. 1982; Sánchez et al. 2007a). Red colour is likely to be an indirect consequence of parasite-induced surface behaviour (Gabrion et al. 1982; Sánchez et al. 2006). To avoid damage by solar radiation, Artemia possess pigments with photoprotective functions (all-trans-canthaxanthins) (Nelis et al. 1988), which confer a pink coloration at high concentrations. Thus red coloration in Artemia is carotenoid based, and infected individuals are especially rich in carotenes and lipids (Amat et al. 1991; Sánchez et al. 2006, 2008). Many shorebirds are visual predators that regularly consume Artemia (e.g. Verkuil et al. 2003; Sánchez et al. 2007b). Red Artemia are a main source of carotenoids which are essential pigments for birds (Hill & McGraw 2006). Strong preference for orange, Correspondence Marta I. Sánchez, Equipe Génétique et Dynamique des Populations, CEFE, UMR 5175, CNRS, 1919 Route de Mende, 34293 Montpellier, France. E-mail: [email protected]