“Resist globally, infect locally: a trans-continental test of adaptation by stickleback and their tapeworm parasite”

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Jesse N. Weber, Martin Kalbe, Kum Chuan Shim, Noémie I. Erin, Natalie C. Steinel, Lei Ma, and Daniel I. Bolnick

Resist globally, infect locally: ecology and evolution of a fish and tapeworm across two continents

More than twenty tapeworms extracted from a wild threespine stickleback from Echo Lake, Vancouver Island, Canada.
(Credit: Daniel Bolnick)

Hosts and parasites are engaged in an evolutionary arms race. Each evolves strategies to ensure its own success, to the detriment of its antagonist. This one-upmanship leads to a finely tuned balance between parasite offense and host defense. But what happens when parasites or hosts encounter an unfamiliar, foreign foe? A new paper in The American Naturalist shows that hosts can evolve defenses against parasites they have never even encountered. In collaboration between scientists from the University of Texas at Austin and the Max Planck Institute of Evolutionary Biology in Plön, Germany, researchers exposed a small fish (the threespine stickleback, Gasterosteus aculeatus) from either western Canada or northern Europe, to tapeworm parasites (Schistocephalus solidus) from either continent. On both continents, marine stickleback recently colonized freshwater lakes, where they evolved greater resistance to the tapeworm. Fish from different lakes have different levels of resistance, but it is not clear what drives this variation; it is not cleanly connected to either the presence or absence of infections in those lakes. Although in each case, resistance evolved in response to local parasites, these defenses also happen to be effective against foreign tapeworms from halfway around the world. In fact, the fish are even better at resisting foreign parasites, because the local tapeworms have evolved strategies to better-infect their familiar hosts. This is exactly the opposite of a common assumption, that hosts are particularly vulnerable to unfamiliar parasites. Read the Article