A Global Plan for Parasite Conservation

Why should we conserve parasites?

If you’re a long-time follower, you probably already know why we should conserve parasites. But for those of you who are new, welcome, and please enjoy this short journey into posts from the past!

Parasitism is a common consumer strategy in the natural world; so much so that 40-50% of all animals might be parasites! That’s perhaps millions of parasitic animal species spread across 15 phyla, including animals as diverse as ticks, intestinal worms, and bot flies. There are also parasitic plants and fungi. Parasites might have especially high extinction risks, because they are at risk from both primary extinction pressures, like the direct effects of climate change, and secondary extinction, or co-extinction, when their host species decline or disappear. If conservation efforts are supposed to conserve all species based on their intrinsic value, then parasite species should be a large target for conservation activities.

But maybe you’re more of a utilitarian, and you want to know what parasites do for ecosystems and for us. The short answer? A lot, and probably a lot more than we know. We know the most about parasite species that harm people, harm our domestic species, and threaten wildlife species, but those parasite species are just drop in the bucket of global parasite biodiversity. We haven’t discovered and described most of those other, relatively benign parasite species, even in groups that we know provide important ecosystem services, like the parasitoid wasps that provide pest control. And some parasite species have already gone extinct due to human activities—science didn’t even give them a name before we didn’t have them any moa. All of this is to say that we do not know everything about parasites, so we do not know exactly what a world without parasites would look like.

But we do know that parasites play important roles in ecosystems. For example, parasite biomass is a large and important part of food webs. Within food webs, parasites link many species together in ways that we might not even expect, like the nematomorphs that cause crickets to jump into streams, where the crickets are eaten by endangered Japanese trout. Every non-parasitic species that you can think of evolved with parasites and interacts with parasites, which is why sex and immune systems evolved. In humans, immune systems might totally freak out in the absence of parasites, leading to auto-immune disorders. While no one wants to conserve detrimental human parasites, a few relatively benign parasites might be good for people and other species, too. Parasites are so central to the biology and ecology of non-parasitic species that some question whether we can even conserve hosts without their parasites: if we brought back mammoths from extinction, but couldn’t bring back mammoth parasites, would we really have brought back mammoths?      

What steps do we need to take to conserve parasites?

There are strong arguments for conserving parasites, but unfortunately, we are not conserving parasites yet. In fact, in some cases, we are driving parasites to extinction when we try to conserve other species, like when we delouse or deworm host species brought into captivity. Given how little we know about most parasite species and how little we are currently doing to conserve them, what immediate steps can we take to conserve parasite biodiversity?

We suggest that 12 steps should be taken in the next decade to conserve parasite biodiversity. Some of these steps will appeal most to researchers interested in fundamental science and people who want to participate in community science programs, because they involve data collection and synthesis. For instance, we need more research about how parasite biodiversity responds to changes in host biodiversity. Other steps are geared more towards practitioners, because they involve risk assessment and prioritization and conservation practice, like creating ways to assess parasites’ extinction risks and building red lists of threatened parasite species. And everyone can enjoy and be involved with the steps related to education and outreach, like including parasite-themed lessons in K-12 and college education.

If you’re interested in learning more about the 12 steps in The Global Parasite Conservation Plan, check out our recently published paper! This was a wonderful group effort from an international team of researchers, many of whom you might have seen at our ESA Organized Oral Session in 2018. And for a bunch of new papers about parasite conservation, check out our whole “Parasite Conservation in a Changing World” special issue that was just published in Biological Conservation!

This was, of course, a shameless plug for my own research, but it was for a good cause. Let’s save the parasites.

Invasive parasitic flies may cause extinction of Darwin’s finches

Welcome to the middle of a post series about parasite-induced host extinction! Today I’m blogging about one particular example of a parasite that might drive a host species extinct, and next week I’ll move on to the more conceptual/review-type stuff. So, if you haven’t yet, take a guess at this question to help me prepare for next week: In our current mass extinction, what percentage of species extinctions do you think have been caused (extinct species) or nearly-caused (endangered species) by parasites, pathogens, or viruses? Round your answer to the nearest 10%.

Around 1997, a parasitic nest fly (Philornis downsi) was found in the nests of several species of Galapagos bird species. The fly larvae feed on the blood of nestlings, and this can have profound effects on nestling survival for some bird species. In some years, the fly larvae can even reduce the probably of nestling survival to zero! So, Koop et al. (2016) created a population projection model to explore what impacts the introduced nest fly may have on the long-term survival of medium ground finches on Santa Cruz.

Koop et al. (2016) parameterized their model using five years of data regarding nestling survival in the presence and absence of parasitic nest flies. This was complicated by the fact that the impact of parasitic nest flies on nestling survival varied by year. So Koop et al. (2016) treated the “fly effect” stochastically, where each year of their simulations was given a “fly effect size” from one of the five observed years, and observed years were either weighted evenly or weighted towards “good” (small fly effect) or “bad” (big fly effect) years. Here’s the bad news: when weighting evenly or towards bad years, simulated medium ground finch populations went extinct within a century.

The good news is that the probability of long-term finch population viability could be greatly increased by reducing the proportion of nests that have the parasitic nest fly. At this point, it isn’t clear what methods would be best for reducing the proportion of nests that have the parasitic nest fly, but Koop et al. (2016) talk about some possible management activities. My favorite one was providing a source of permethrin-treated cotton that finch parents could incorporate into their nests.

Reference:

Koop, J.A.H., P.S. Kim, S.A. Knutie, F. Adler, and D.H. Clayton. 2016. An introduced parasitic fly may lead to local extinction of Darwin’s finch populations. Journal of Applied Ecology 53: 511–518.