When Parasites Invade: Catching “The Boat”

I plan to typically blog about late-breaking parasite ecology research, but sometimes you just have to go back and highlight the really cool papers.  In this case, I’m writing about a 2010 Ecology Letters paper entitled “Parasites lost – do invaders miss the boat or drown on arrival?”

First, some terminology.  MacLeod et al. (2010) coined three phrases to describe potential ways that parasites might be lost from hosts when hosts invade new territory.  Parasites “miss the boat” if the hosts that invade the new territory don’t harbor the parasite.  They “sink with the boat” if they make it into the new territory with the host, but the hosts don’t successfully establish, so the parasites don’t either.  Finally, parasites are “lost overboard” if the hosts and parasites both make it to the new territory, but the parasites don’t successfully establish, even though the hosts do.  +10 points to Macleod et al. (2010) for using witty terminology!

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Three ways that parasites are “lost” when hosts invade new territories. Terminology coined by MacLeod et al. (2010).

Why should we care about the various ways that parasites are lost during a host’s range expansion?  One reason is that the “enemy release hypothesis” is currently one favorite hypothesis that explains why invasive species are so successful in their invaded range.  It suggests that invasive species leave behind the enemies (predators and parasites) that they coevolved with when they invade new places, so their populations are no longer regulated in a “top-down” fashion.  To understand how often enemy release actually happens, we need to know how often parasites are lost when hosts invade.

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“Na na na na naaa na! No one here can eat me!”
Lionfish photo from Smithsonian.com.

MacLeod et al. (2010) looked at historical records of introductions of birds and their ectoparasitic chewing lice to New Zealand.  They used the historical data to simulate probabilities that lice species missed the boat, sank with the boat, or were lost overboard.  I love how creative and simple (and elegant!) their experimental design was.

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Graphic of the experimental design that MacLeod et al. (2010) used to figure out the probabilities that parasites missed the boat, sank with the boat, or were lost overboard.

They found that about 12% of parasites species “missed the boat,” and about 20% of parasite species “released” their hosts from enemy pressure by being “lost overboard.”  Neat!  MacLeod et al. (2010) go on to talk about why parasites might be lost overboard, and I highly recommend reading the paper for more details.

What do you think?  Would these probabilities be different for endoparasites?

Reference:

MacLeod, C. J., A. M. Paterson, D. M. Tompkins, and R. P. Duncan. 2010. Parasites lost – do invaders miss the boat or drown on arrival? Ecology Letters 13(4): 516–27.

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