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.

Wasps up with parasite conservation in Britain?

I’m a few days late, but Happy Taxonomist Appreciation Day! Despite my tardiness, I am troubled by our global shortage of taxonomists, and I strongly support initiatives to (1) train more taxonomists, (2) provide them with livable and enjoyable career opportunities, and (3) find ways to integrate and value their important work amongst other science. I have mostly thought about this from a parasite conservation perspective, and I recently read an excellent paper that resonated with those thoughts. Below are some quotes (and my commentary) from Shaw and Hochberg (2001) that describe a parasite taxonomy crisis and some potential solutions:

Britain has a long history with natural history. For centuries, amateurs and professionals have been collecting and describing species from that relatively small land mass. In Britain, people probably don’t even seem like weirdos for gleefully wielding their custom-ordered extendable butterfly nets in public spaces. (Whatever, I’m not bitter, or anything.) Anyways, you might think that all of that enthusiasm for natural history has led to a complete inventory of Britain’s wildlife. But you’d be wrong.

“While the public may hold reasonably accurate perceptions that tropical ecosystems are teeming with unrecognized species, the average person in Britain is unaware that knowledge of the British biota – widely acknowledged as the best studied in the world – is also very limited.”

How could our taxonomic knowledge be so limited?! Parasites aren’t the only poorly known British taxa, but I’ll be talking about issues relevant to parasite taxonomy today. In particular, Shaw and Hochberg (2001) focused on a specific group of parasites: parasitoid wasps.

So how many parasitoid wasp species are there in Britain? When this paper was published in 2001, ~6000 species were known. To put that in perspective, that’s ~1/4 of the total known British insect biodiversity! To reiterate, without counting all of the other parasitic insects (e.g., fleas, lice), at least one quarter of the insect biodiversity is parasitic. I say “at least” because…

“…it seems likely that across parasitic Hymenoptera as a whole our knowledge of what is in the British fauna may be about 30-40% incorrect, or possibly even more…it strongly suggests that parasitic Hymenoptera will eventually turn out to be an even larger fraction of the total British insect fauna.”

Oh dear. We know that there must be many more parasitoid wasp species in the world (and Britain, specifically) than we currently know about for three reasons. First, whenever people conduct new field surveys or look at museum collections of parasitoids, they find that only a small fraction of the collected species have been described before. Second, many specimens are later found to be incorrectly identified, because morphological identification of parasitoid wasps is hard. And third, even when people think that they have nailed their morphological identifications, they might later find that the “species” that they are referring to is really a “morphospecies” representing 2 or 20 or even more cryptic species that are indistinguishable morphologically. For instance, here’s a quote from Smith et al. (2014) – an ambitious study matching morphological identifications to DNA barcodes for hundreds of parasitoid wasp species – regarding just one of the many cryptic species complexes that they uncovered:

“This minute black wasp with a distinctive white wing stigma was thought to parasitize 32 species of ACG hesperiid caterpillars, but barcoding revealed 36 provisional species, each attacking one or a very few closely related species of caterpillars.”

Yikes! When I read that, I thought, “Wow, if I ever need to do anything with parasitoid wasps, I’m going to need to find a collaborator who specializes in parasitoid wasp taxonomy.” So let’s say that I do need hypothetical help with an important biodiversity conservation project in Britain. Would I be able to find a parasitoid wasp expert to collaborate with? According to Shaw and Hochberg, in 2001, there were ~6 such experts – you know, approximately one expert for each thousand wasp species. (No, no, it’s fine, writing this isn’t giving me anxiety.) That seems like a tiny number of people who are responsible for ¼ of Britain’s insects! But at least there are some parasitoid wasp experts in Britain. The situation is likely worse in most other regions, where natural history is likely less popular and species diversity might be greater.

We must also remember that even if we can associate a DNA barcode or morphological description with a species name, we do not necessarily “know” that species. I brought this up a few weeks ago after reading John Lawton’s autecology and extinction crisis essay, and Shaw and Hochberg (2001) were clearly concerned about the biodiversity listicle phenomenon, too:

“Other insects are in a frame in which parasitic Hymenoptera are not, because parasitic wasps, with a low proportion of exceptions, are mostly just names.”

Are you having feelings about parasitoid wasps now?

Of course, it is worth asking why we need to know more about parasitoid wasps. Research and conservation funding are limited, so why prioritize research regarding parasitoid wasps? I’ll give three possible reasons, but others could be suggested:

(1) If we are conserving biodiversity for its intrinsic value and/or because we believe that the most biodiverse or species-rich ecosystems are the best (for any given criteria), then we should perhaps prioritize research on the most species-rich and neglected taxa. Until we understand the most biodiverse taxa, we probably can’t maximize biodiversity conservation.

(2) Parasitoid wasps can be beneficial for humans. For instance, because parasitoid wasps tend to be highly host specific, they can be used as targeted biocontrols for agricultural pests. We’re talking serious economic worth. And given their documented effectiveness with controlling pests, it is likely that they play important roles in controlling populations of many other insect species that we don’t currently consider ‘pests’, but which might become problematic if they lost their parasitoid overlords. So maybe we should prioritize learning more about parasitoid wasps and conserving them to prevent potential economic losses.

(3) Parasitoid wasps might be especially vulnerable to extinction or co-extinction, so we might need to prioritize their conservation to prevent rapid biodiversity loss. As Shaw and Hochberg (2001) point out:

“The brief statement in the Insect Red Data Book (Shaw in Shirt (1987): 257-8) on parasitic wasps is to the effect that they must be considered among the most threatened of British insects, but that attempting a listing of endangered species would be quite hopeless in view of our poor knowledge. The message in this has, however, generally been as totally ignored as the parasitic wasps themselves.”

And

“..our parasitic Hymenoptera fauna…must – without any real doubt, given their high trophic level and characterizing levels of specialization and dependence – be happening at a rate that would surely be considered alarming, if only it could be noticed.”

Worryingly, that decline has been noticed outside of Britain:

“Therion (1976; 1981) reporting on the Ichneumonidae… fauna of Belgium, found that of the 122 species formally present 32 (26%) could not be found in a period of intensive collecting between 1950 and 1974/1979, with at least 30 further species (25%) showing major declines.”

After making cogent arguments for prioritizing parasitoid wasp conservation, Shaw and Hochberg (2001) provided several suggestions for improving those conservation efforts. One suggestion – including parasitoid wasps in Species Action Plans for better-known host species, like endangered butterflies – is something that I’ll come back to in my next parasite conservation post. For today, I’d just like to emphasize their number one suggestion:

“Nothing would do as much for the conservation of parasitic Hymenoptera as the provision of properly funded, career-length posts for alpha-taxonomists in major collection-building research institutions.”

Thank you, existing parasitoid wasp taxonomists! You rock. And I hope we can make and support many more scientists like you in the near future.

References:

Shaw, M. R., and M. E. Hochberg. 2001. The Neglect of Parasitic Hymenoptera in Insect Conservation Strategies: The British Fauna as a Prime Example. Journal of Insect Conservation 5:253–263.

Smith, M. A., J. J. Rodriguez, J. B. Whitfield, A. R. Deans, D. H. Janzen, W. Hallwachs, and P. D. N. Hebert. 2008. Extreme diversity of tropical parasitoid wasps exposed by iterative integration of natural history, DNA barcoding, morphology, and collections. Proceedings of the National Academy of Sciences of the United States of America 105:12359–12364.