8) A case of co-evolution
Species evolve together, and in competition. Predators evolve ever deadlier weapons and skills to catch prey, which, as a result of Darwin’s canonical ‘struggle for existence’, become better at escaping them, and so the arms race continues. In 1973, evolutionary biologist Leigh Van Valen likened this to the Red Queen’s comment to Alice in Lewis Carroll’s Through the Looking Glass, “it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!” The ‘Red Queen’
hypothesis of co-evolution was born.
A problem with studying Red-Queen dynamics is that they can be seen only in the eternal present. Discovering their history is problematic, because evolution has generally obliterated all earlier stages.
Happily, Ellen Decaestecker from the Catholic University of Leuven in Belgium and her colleagues discovered a remarkable exception, in the co-evolutionary arms race between water fleas (Daphnia) and the microscopic parasites that infest them; their research was published in 2007. As the water fleas become better at evading parasitism, the parasites become better at infecting them. Both prey and predator in this system can persist in dormant stages for many years in the mud at the bottom of the lake they share. The sediments of the lake
can be dated to the year they were formed, and the buried predators and prey can be revived. Thus, their interactions can be tested, against one another, and against predators or prey from their relative pasts and futures.
Confirming theoretical expectations, the parasite adapted to its host over a period of only a few years. Its infectivity at any given time changed little, but its virulence and fitness rose steadily — matched at each stage by the ability of the water fleas to resist them.
This study provides an elegant example in which a high-resolution historical record of the co-evolutionary process has provided an affirmation of evolutionary theory, showing that the interaction of parasites and their hosts is not set in time but is instead the result of a dynamic arms race of adaptation and counter-adaptation, driven by natural selection, from generation to generation.
Reference
Decaestecker, E. et al. Nature 450, 870–873 (2007).
Additional resources
The Red Queen Hypothesis: http://en.wikipedia.org/wiki/Red_Queen
Van Valen, L. Evol. Theory 1, 1–30 (1973).
Author website
Ellen Decaestecker: http://bio.kuleuven.be/de/dea/people_detail.php?pass_id=u0003403
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