Flamingos (Phoenicopteridae) are well-known for being pink. And they are pink because they eat shrimp, brine shrimp to be exact (Artemia). These tiny crustaceans are only 8-10 millimetres long are best known for being the pet we all (accidentally) killed as a child: sea monkeys (mine went all over the floor if that makes you feel better).
These shrimps gather in dense clouds and are gobbled down by the hungry flamingo in the hundreds if not thousands and the more they eat the pinker they become, this pink colouration is a signal to other flamingos in the flock that it’s the most physically fit of the pack and the brightest birds will mate the most.
That appears to be the end of the story; the pinker the bird = the more sex, more than enough motivation for flamingos to eat shrimp till they burst. However, unseen to our eyes is a secret manipulator behind the whole plot: Flamingolepis liguloides. This parasite is a member of the cestode order and like all good villains they are masters of disguise and sneak up on our unsuspecting hero (in this case the flamingo) when they least expect it.
In a plot twist worthy of Agatha Christie, they were hidden in the shrimp all along! *Cue gasps from the audience*.
What the flamingo doesn’t know it’s that it’s the definitive host to this tape worm.
An infected shrimp will be influenced to seek out others to mate, despite the fact that is is now castrated, forcing them to gather into such an enormous mass (about 2 meters in length) that it’s easy pickings for the flamingo. In addition to this ability to corral it’s host it also causes the tissue of the shrimp to turn bright red by an increase of carotenoids (a pigmentation chemical) making them even more visible. Once inside the definitive host F. liguloides does its own mating and as the old adage goes; what goes in must come out and in time a whole new generation of tiny puppeteer’s is born.
With the exception of castration and possible death by flamingo F. liguloides infection has its upside. Their crustacean hosts may have less chance of survival if left uninfected. Infected shrimp can live in more toxic water due to a greater amount of lipids (fats) in their tissue, and a higher production of antioxidants. They were also able to survive in hotter water by an average of 4 degrees, as well as having longer life spans.
So perhaps this parasite isn’t a villain after all, but more of an anti-hero.
Sánchez, Marta I., et al. (2013) “High prevalence of cestodes in Artemia spp. throughout the annual cycle: relationship with abundance of avian final hosts.” Parasitology Research 112: 1913-1923.