Tag Archives: bacteria

Changing With the Times

High parasite diversity accelerates host adaptation and diversification (2018) Betts et al., Science. https://doi:10.1126/science.aam9974

Image Credit: Dr. Graham Beards, CC BY-SA 3.0

The Crux

Host-parasite relationships are often thought of or depicted in a pairwise structure. That is, one host is attacked by one parasite, without an acknowledgement or consideration of how complex the relationship can be. For example, hosts are often attacked by more than one type of parasite, and the parasites themselves have to compete with one another for resources from the host. Because parasites are costly for a host, the hosts benefit from evolving resistance to the parasites. It follows that the more parasites a host is attacked by, the higher the benefit of evolving resistance, so we’d expect to see more resistance in hosts that are attacked more often. This should then result in differential evolutionary rates among hosts, which would then result in greater evolutionary divergence (see Did You Know?)

To test this idea, the authors of today’s study used a bacterium (Pseudomonas aeruginosa) and five lytic viral parasites (hereafter bacteriophages). These bacteriophages reproduce within host cells until they eventually cause the host to burst, killing the host (think of the chestburster in Alien, but a LOT of them). Because their reproduction results in the death of the host, lytic parasites impose a very strong selection pressure on hosts, making this a perfect host-parasite system to test the above prediction.

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