The cost of travel: how dispersal ability limits local adaptation in host–parasite interactions (2020) Johnson et al., Journal of Evolutionary Biology. https://doi:10.1111/jeb.13754
There are countless parasites in nature, and many of them tend to have relatively short life-cycles. For example, ticks live for about two years, while may of their hosts (us included) live for much longer. Because there is such a disparity in lifespan, parasites are predicted to have a greater evolutionary potential than their hosts. In other words, parasites should evolve faster than their hosts, which theoretically means that parasites should be more fit on local hosts than they would be on non-local hosts, as they would have had more time to adapt (i.e., local adaption, see Did You Know?).
Despite these predictions, the evidence from experimental studies of parasite local adaptation is mixed at best. Some studies show the adaptation to local hosts we’d expect, but some studies don’t. One reason for the lack of consistent evidence is that parasite dispersal between habitats can limit the ability of parasites to adapt. To help explain that I’ll use a comparison to cooking. If you are cooking a dish and you want to make it spicier you add in more spice. But imagine that when you add in that spice, you are also adding a lot of cream. The dish could be spicy, because you are adding spice, but the cream is diluting the spice and masking any potential heat. That is what parasite dispersal does to local adaptation: parasites within a given habitat (the dish) may have the ability to adapt to their hosts (become spicier), but because parasites from other habitats (the cream) are coming into their habitat and diluting those adaptations it masks any overall adaptation to the host (never gets spicy). Today’s authors therefore wanted to test how parasite dispersal affected local adaptation to hosts.Read more