Time flies during field season! I apologize for falling a bit behind in my weekly post schedule. I could tell you exciting field stories about killer bees and torrential downpours, or less exciting stories about endless rows of snails waiting to be dissected, but instead, let’s talk about climate change and parasites.
There has been a lot of talk about potential shifts in the ranges of parasites/pathogens as the global climate changes. For instance, will we see increases in range sizes of tropical parasites/pathogen as they move into warming temperate regions? I tend to think about a 2009 paper by Kevin Lafferty when I think about range changes of parasites/pathogens, where he argued that for a given parasite, certain regions may become favorable, but others will also become unfavorable. Therefore, we might expect range shifts, rather than range expansions.
I also blogged about a 2012 Ecology Letters paper that I liked where Mordecai et al. (2013) showed that transmission of malaria via mosquitoes should have a unimodal relationship with temperature. That is, as Lafferty (2009) suggested, some places where malaria is currently endemic should become too hot for malaria as the global temperature increases.
And now, for a new paper! This one is open access, so you can check out here if you’re interested. As I’ve blogged about before, many parasites are “ontogenetic niche specialists.” That is, because of their complex life cycles, parasites end up occupying multiple specific niches during one ‘generation.’ This makes parasites vulnerable to secondary extinction, because if one host goes extinct in an area, the parasite cannot complete the life cycle. Pickles et al. (2013) explored this concept as it relates to climate change. That is, if the ranges of the hosts change with the climate, what happens to the range of the parasite? Each host might increase the size of its range, but if the hosts’ ranges don’t overlap, the parasite might actually lose some of its range. Pickles et al. (2013) call this an “ecological mismatch.”
Awesome things about this paper:
- The first author’s last name is Pickles. I personally don’t like pickles, but that last name deserves bonus points.
- COOL PARASITE SYSTEM! The adult meningeal worm (Parelaphostrongylus tenuis) infects white-tailed deer as a definitive host, free-living parasite larvae are shed in the deer feces, slugs or snails eat the parasites and become infected (L2 and L3 larvae), and then deer later eat the gastropods and become infected with the adult worms. How often do deer accidentally eat gastropods?
- They used a site that I hadn’t heard of for data collection. www.mammalparasites.org has the distributions of known mammal parasites! Check it out!
Pickles et al. (2013) modeled range shifts of the hosts and P. tenuis under a few different climate scenarios. In general, the model predicted expansion of the ranges of all of the hosts. However, the range of P. tenuis shifted without expanding by much. In some places, like the increasingly dry Great Plains, they predicted that P. tenuis may be extirpated. And in other places, like the warming Alberta, they predicted that P. tenius may invade with the white-tailed deer. This seems to work well with Lafferty’s (2009) predictions about range shifts as opposed to range expansion.
Finally, Pickles et al. (2013) pointed out that this may be a big deal for other ungulates, like elk and caribou. P. tenuis can infect several ungulates besides white-tailed deer, but can’t successfully reproduce in those ungulates. However, P. tenuis infection causes morbidity and mortality in those other species, whereas the parasite is relatively benign in white-tailed deer. So, ungulates in these currently P. tenuis-free regions may be in for a rude surprise. Maybe as ecological mismatch between deer and P. tenuis increases, we’ll see co-evolution between P. tenuis and other ungulates? Dun, dun, dun!
Pickles, R.S.A, D. Thornton, R. Feldman, A. Marques, and D. L. Murray. 2013. Predicting shifts in parasite distribution with climate change: a multitrophic level approach. Global Change Biology, 19: 2645-2654.