Over the past 2-3 years, I have become increasingly (and perhaps obsessively) interested in parasite extinctions and parasite conservation. I’ve blogged about parasite conservation a few times (here and here), but I’ve half-written about three times as many posts that I never published. Apparently, it’s quite difficult to distill topics near and dear to you into 500 word essays! But in celebration and preparation for an upcoming ESA organized oral session (yessssssss, we were accepted!), I’m going to power through and write a series of blog posts that try to encapsulate perspectives and theory regarding parasite conservation. I’m going to start easy today, though. Instead of asking which parasite species we should conserve (if any), I’m going to think about which parasite species scientists should study.
These thoughts require some backstory. Two weeks ago, I found out that all of John Lawton’s View from the Park essays from Oikos have been compiled into this list. I read a bunch of them, of course, and one of them really resonated with me. His essay, “On the behaviour of autecologists and the crisis of extinction”, is about birds and all other species, but it could easily be interpreted as an essay about the study of parasites. Here’s the first quote that made me think about parasites:
“One of the most repeated facts wheeled out in current discussions about biodiversity, be it in learned articles, newspaper reports or political debate, is that taxonomists have described approximately 1.7 million species, whilst the best current estimate for the total number of species on earth is 12.5 million. This is clearly a serious problem, and one that demands urgent attention (e.g. P. H. Raven and E. 0. Wilson (1992) Science 258, 1099).”
This idea – that we have named/described a tiny fraction of all existing species – is also popular in the parasite literature. People are still revising and debating estimates of the total number of parasite species in the world (e.g., here), but no matter what the current best-estimate is, we still haven’t described most of them. Therefore, everyone seems to agree that we have a (parasite) taxonomy crisis, that we desperately need more people naming/describing more (parasite) species, and that Taxonomist Appreciation Day should happen more than once per year.
But here’s a quote that hit me harder:
“Intriguingly, I have never seen anybody discuss what we actually know about the 1.7 million [species] that do have names. Overwhelmingly the answer will be nothing, except where they were collected, and what they look like…To use an analogy, not only do we have a hopelessly incomplete white pages telephone directory for the planet’s inhabitants, we have an even worse set of yellow pages.”
Ouch. As the author of the Parasite Ecology Blog, I’d love to tell you that we know tons about parasite ecology. Collectively, we do. But we know nothing about the ecology of most named/described parasite species. Why is that? Here are three reasons, which are neither mutually exclusive nor a complete list:
Potential reason 1: Parasites often have complex life cycles, where different ontogenetic stages occur in different host species (or the environment). For instance, when we find a new adult trematode in a bird host, name it, and describe it – which, coincidentally, requires much time/work – we’re still missing all the details about the rest of that parasite’s life cycle. Does it have one other host species? Two? 25? Which species? Etc.
This problem is relevant for some free-living species, too (e.g., which caterpillar turns into this butterfly?). But it’s a particularly common and difficult problem in the study of parasites.
Potential reason 2: Parasites often live inside their hosts, making it difficult for us to observe them in action, or to know if/when hosts became infected.
Potential reason 3: We lack the interest/incentive to dig into the ecology of most parasite species. I’ll come back to this in a second.
The Lawton essay goes on to ponder which species we should study in detail. He notes that we currently focus on specific taxa (e.g., vertebrates) in specific geographic regions (e.g., temperate areas), and argues that we should develop a stratified sampling method, instead – some kind of “major, coordinated effort by whole organism biologists to attempt a systematic sampling of the autecology and behaviour of the earth’s biota.”
Parasite ecologists also focus on specific taxa in specific regions. We’re highly motivated to study parasites that infect people and our domesticated species, especially in temperate regions. We also give much attention to parasites that have strong impacts on populations of important game species and some wildlife species. That isn’t to say that we don’t know anything about the ecology of parasite species from other host species. For instance, we know a lot about some of the cool parasites that manipulate their hosts’ behavior. But are we missing important basic ecological principles by focusing heavily on parasites in particularly important host species or particularly “cool” parasites?
You won’t be shocked to learn that I don’t have immediate answers to these questions. Lawton’s proposal to systematically sample more species for detailed ecological studies sounds awesome, but it also sounds highly difficult to organize and implement, even if we only consider parasites. But this is definitely something worth thinking about! Because as Lawton said:
“The problem has close parallels with the agonising debate over which species to conserve, assuming we have any choice at all in the matter.”
For parasites, there will be little to no support for conserving the parasite species that we know the most about: those that harm humans. (In fact, we’re actively trying to eradicate some of the most heavily studied parasites, like the Guinea worm.) How does one work towards conserving taxa whose best-known species are detrimental for people?