Preservation of Parasites

Almost every species has its own unique species of parasite - so with every extinction we're losing at least one extra species, that may have never been properly studied. Andres Gomez, from the American Museum of Natural History in New York, argues that parasites need to be pushed up the agenda, not just in scientific research, but also in the teaching of conservation. Andres, thanks for joining us.  Firstly, why parasites?

Andres -   Parasites have very important roles in ecosystems.  They have shaped not only the evolutionary processes by which we observe biodiversity today, but they also have really important functional roles in maintaining ecosystems as we know them now.  They're also very important numerically.  We think that parasitism is the most common consumer strategy in the planet.  So if we want to conserve biodiversity, by necessity, we'll be conserving parasites.

Ben -   How well do we actually understand parasites?  Because of their impact on people, they've been a topic of quite a bit of research, but from a broader perspective, as part of their role in ecological systems, how well do you think we understand them?

Andres -   We are just beginning to understand their importance in ecosystems and things like food webs for example.  It's only in the last decade or so that we have done most of their research uncovers the functions that parasites carry out in ecosystems across the globe. So there's a lot to learn.

Ben -   Now, we've just been talking about the ecosystem services that oysters provide. Presumably, we're looking at similar things with parasites. There's something that they are doing that just wouldn't happen without their presence.

Andres -   Absolutely and there are many examples of that kind of process and we usually separate ecosystem services from functions and by services, we usually only mean things that benefit humans.  But there are a lot of ecosystem functions that are mediated by parasites that are incredibly important.  Parasites mediate things like competition, species co-existence, distribution and abundance of their hosts through ecosystems and a whole other suite of things that are happening in nature.

Ben -   We've also already mentioned the potential for genetic exploitation of microbes and this was a good argument for conserving things like bacteria and fungi.  Are we seeing the same things with parasites?  Is there something there that we can manipulate to get a benefit for people?

Andres -   I don't know that we would necessarily need to manipulate parasites genetically to get that kind of benefit.  We know that parasites produce a lot of biochemical substances out there that we can use for health and research for example.  We know that parasites are engaging their host's immune systems in very complex ways, and by learning about parasites, we can learn about our own physiology and anatomy.  We also know that parasites are doing things like absorbing heavy metals that they find in circulation in their hosts so, as much as they're hurting their host in one way or another, they could also be providing benefits to the host in some other ways.

Ben -   I mentioned earlier that we think that there's at least one species or parasite for every species if non-parasite.  Does this mean that in modern-day extinctions, they actually are the biggest losers?

Andres -   We believe so, yes.  We think that there are many more endangered parasites, than there hosts that we know are endangered.  There's a recent study that estimated that if we were to lose just 5 species of carnivores in North America, we would lose up to 56 species of parasites.  So, if you extrapolate that throughout the web of life, you could arrive at a number of threatened or extinct parasite species, that is a lot larger than those of the hosts that are usually the kinds of creatures that we care about.

Ben -   Presumably, parasites face all of the same threats that their hosts face.  So, looking at rhinos for example, if there is habitat loss that means that rhinos can't survive, that obviously immediately impacts on the parasites themselves.  Are there other risks and other pressures that parasites are facing that we aren't considering as part of conserving the larger animals?

Andres - Parasites are interesting because they are one of the few types of creatures out there for which we have dedicated extermination plans.  Invasive species being probably the only other one.  So when we carry out eradication efforts for parasites - for good reasons because they definitely cause human suffering and losses for the economic development and so forth - we may be affecting the survival of other related parasite species that were not the target of the eradication effort for example.  And there are other things that are happening - global processes like climate change that may benefit some parasites, but may definitely hurt others. 

Then there's one other thing about parasites is that it's critical and that is that we know that parasites will decline, will co-decline with their hosts.  So, as the population of the host declines, so will parasites, but the parasites will go extinct well before the hosts go extinct.  They need a threshold host population to maintain an efficient transmissional level.  So, we can have a situation which the host is still around but the parasites have gone already.

Ben -   So, what do we now need to start doing in order to tackle this?

Andres -   Well, we need to do several things. One of them is we need increase our research into parasites. We need to know what parasites are there, and in what kinds of conditions.  We need to know how they are transmitted and their ecological dynamics. If we don't know that, we can hardly develop a strategic plan to conserve them. We also need to educate biologists as to the importance of parasites in ecosystems and to evolutionary time.  And I think that we also need to do more things like what you're doing right now, making a case in the public that parasites are interesting, and they're charismatic in themselves, and that we probably wouldn't know biodiversity as we know it today without parasites.