Yemisi Dare

Are dung beetles just as cool as elephants? Yemisi Dare, a parasitologist, says yes. Yemisi has dedicated her life to exploring how rarely appreciated organisms impact – and are impacted by – complex ecosystems. By email, she explained why understanding the genetic health of an ecosystem should start with an investigation of parasites – and why parasites have already achieved world domination.

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When it comes to biodiversity, we focus on charismatic megafauna. You’ve worked to study the lesser lights of our ecosystems. Why does the seemingly irrelevant matter?

My interest is in the discovery of creatures that often remain more mysterious, more surprising to discover, because they are not as obvious as larger creatures. Being small obscures the wonder from plain view, you have to come in closer, look more carefully. I hope that people do not equate small with irrelevant. I think of the Doozers in the Muppet show Fraggle Rock. A happy co-existence, but very little attention is paid by the Fraggles to the Doozers, except for the benefit that each derives from the other, unintentionally. I think instead that the challenge of valuing small sized creatures lies in the greater difficulty in observing their existence- and therefore seeing their connection to anything else. If you don’t know it’s there, how can you value it? But if we reframe the way we look at the world, we see so much more!

While you might find it hard to miss an elephant walking across a savanna in front of you, and marvel at this magnificent herbivore’s body and trunk that can change a landscape by trampling and pruning trees as it feeds, you may likely miss the tiny dung beetle, also walking along that same savanna ground, pushing a dung ball in front of it. I too am awed by elephants; I mean who doesn’t think they’re cool?! But it’s the discovery of a dung beetle that would cause that surprise and that “whoa, what’s THIS?!” reaction in me.

Dung beetles may have as much of an influence on their habitat as elephants, maybe even more. They aerate and fertilize the soil by mixing the dung into the soil which in turn creates a nutrient rich base for plants to grow. They provide ground burrows for other insect species when they dig their holes. They improve water retention in soils in very dry environments where water is so important for survival (I mean, this is the savanna after all). Thus, the beetles create and renew the habitat that the elephants and other large and small creatures need to survive. Of course, the dung beetles need the elephants and other larger animals to produce the dung, so there is an interdependency between the two. But unless you take a close look, you won’t see it. And frankly, a dung beetle pushing a ball along the ground is an incredibly cool thing to watch!

It just so happens that my passion is for animals that are obscure, very well hidden, often so small they require a magnifying glass or a microscope, and yet vital players in the configuration of ecological systems- the Doozers of nature. I have walked away from microscopes feeling like I’ve been let in on a special secret, that no one else that I know may ever learn about or see in their entire lives! This discovery does not happen only in a laboratory. One of my most favourite things to do is to kneel over an old puddle of water, bum up in the air, nose a couple of inches away from the water (the true and rightful posture of an aquatic invertebrate biologist), looking at all the tiny busy aquatic life; all the zipping and crawling and darting and wriggling…watching each tiny creature fastidiously carrying out its own distinct role in its environment. A whole universe in a puddle!

Okay, you may understand the dung beetle’s importance in landscaping a savanna, but why do small creatures matter if they only occupy a small puddle? Smaller creatures, because of their tiny size, can fill many more kinds of ecological spaces and perform many more functions in ecosystems than larger animals. And they are very well adapted to these varied niches. The huge range of diversity in adaptation blows me away. Yes, everyone knows that the Galapagos finches are a great demonstration of diversity in birds with the different beak types used for different kinds of food, but have you ever looked at the diversity of mouthparts in different aquatic crustaceans? In fact, the mouthparts of small marine crustaceans are so diverse and unique, that this is what is used to identify different species! There are entire identification keys made up of mouthparts and front legs! All of this variety allows these small creatures to exploit a huge range of food types, and therefore live in a wide range of niches, even within a small physical space. Aquatic crustaceans can be voracious carnivores or scavengers preying on even smaller creatures, while others are detritivores, eating dead stuff that’s lying around. Some catch prey swimming in water, others crawl around on the bottom substrate, others float near the surface, and yet others burrow for their food. Some species will filter water and clean it. Whales simply can’t do this. They are too big to occupy all these different strata.

But why do we care that there are so many different crustaceans with so many adaptations to feeding? Well, for one thing, many of these small crustaceans serve the very important function of nature’s garbage disposal and recycling system. Can you imagine what might happen if we didn’t have a waste disposal system for nature? How long do you think large creatures would survive without a cleaning system? There are so many different adaptions among these crustaceans that ensure that this vital cleaning and recycling service is done quickly and efficiently, with specially adapted mouth and body parts for tearing apart a large or small carcass that falls in the water or chomping down bits of rotting vegetation. As if that isn’t enough, all of these creatures are important sources of food for bigger creatures. Now multiply what happens in one small puddle, across all puddles in all landscapes – now you can see that they can have a big effect!

This happens on land too. Tiny creatures that you need to look closely at or you might miss them are hard at work, remodeling the landscape by breaking down plant and animal material, recycling nutrients into the soil, burrowing and creating new habitat for other species, pollinating flowering plants, and providing a vital and abundant food source for a wide range of other, larger species.

My all-time favourite group of animals are parasites. I think these are the most fascinating and diverse group of organisms on the planet, often in plain sight, occupying every known ecosystem – in abundance – yet hidden from view by their small size and their many elegant adaptations that make them hard to notice. They affect virtually all aspects of the lives of their hosts by influencing and manipulating behavior, altering feeding habits and food choice, reproduction, metabolism, and the ability to fight off infection. In fact, they are vital enough that they can be used to measure how healthy a population is, or how resilient an ecosystem is. I joke with my friends that parasites have already achieved world domination, we just don’t know it.

Are small creatures canaries in the coal mine for threats to biodiversity?

I think it’s important to not separate small creatures from everything else, since size is not what determines a creature’s inclusion in a whole ecosystem’s biodiversity – they are part of the biodiversity. However, you might ask if smaller sized species are indicators of an ecosystem’s vulnerability. In which case, I would say they certainly can be.

Smaller creatures tend be to lower on the food chain and have many predators higher along this chain. This is simply because being a smaller size makes them easy for many other larger species to fit them in their mouths! So, if something happens to these small species, it could potentially affect a lot of other species that depend on them for food. Species that have disproportionately large effect over other species in an ecosystem are called keystone species. Thus, if you have an idea of the health status of keystone species, it gives you an idea of how other species in an ecosystem might be doing too.

Take for example, the tiny shrimp-like Corophium that lives in the mudflats of the Bay of Fundy. If you’ve ever walked along these red mudflats at low tide, you would have noticed all the tiny holes dotting every foot of the mudflats. These burrows house immense numbers of these little “mudshrimp” that serve as a high nutrient source of food for a range of shore bird species, like Sandpipers and Plovers, as well as a wide range of fish. In particular, birds that are on a migratory path up north to the arctic use these mudflats for fueling stopovers where they feast on the Corophium before heading to their wintering grounds. Now imagine if something happened to the mudflats and this species was wiped out. What would happen to all the different bird and fish species that depend on them? Climate change, changes in the mudflats as a habitat (for example, the commercial harvest of bloodworms found in the flats has caused large areas of mud to be churned up, destroying the mudshrimp burrows), man-made toxic chemicals that have washed into the intertidal zones, and parasitic disease can all affect these Corophium. This in turn threatens the survival of the many species that depend on the mudshrimp. Thus, by monitoring the robustness of these keystone species, you can get an idea of the vulnerability of the biodiversity of an ecosystem.

People are often surprised to learn that parasites can also be good indicators of biodiversity of ecosystems and identifiers of threats to these systems. How could the presence of parasites be an indicator of the number of species in an ecosystem? Well, some parasites have complex lifecycles, meaning that they need to move through more than one species of host in order to complete their lifecycles. One group of parasites in particular that has the most fascinating and incredibly complex lifecycles are the trematodes. Trematodes complete different developmental and reproductive stages of the lifecycles in completely different host species. Another interesting thing about trematodes, is that they generally tend to move from one host species to the next through food chains and they can be quite specific about which host species they can survive in. Thus, one host species (let’s say a bullfrog) eats another infected host species (let’s say a dragonfly). The frog is then eaten by a duck. The infected duck then passes parasite eggs into pond water along with its feces and an aquatic snail comes along and eats the feces. The parasite larvae are then released from the snail into the water and dragonfly larvae swimming in the water become infected with the parasite. Thus, the parasite is transferred along this complicated food chain from the dragonfly to the snail and develops into a different lifestage along the way in each of these hosts. Host specificity of these parasites make them even more fascinating: using the above example, the parasites cannot just pass through any frog species, it would have to be the American bullfrog (Lithobates catesbeianus), and it couldn’t just be any duck, it would have to be a wood duck (Aix sponsa), the snail would have to be Stagnicola elodes and so on. Thus, by identifying a species of parasite, you could determine a number of other species in that habitat.

You can imagine that it might be tricky to figure out the path of these lifecycles, especially when many of them have three or more hosts in the cycle! There are estimated between 18,000 and 24,000 species of trematodes! Parasitologists have spent a lot of time trying to figure out the different lifecycles, identifying which host species a particular parasite species might pass through. So, what does this have to do with biodiversity indicators? Well, once you have a lifecycle figured out for one parasite species, you know that if you find this species in one host species, there likely are other host species along the food chain in the same ecosystem, otherwise that parasite could not exist. Using the example above, if you found the trematode species in wood ducks, there’s a good chance that there are also American bullfrogs, Green darners and Stagnicola elodes in that habitat. If you found more than one parasite species in the wood ducks, and you would know which other species are likely present because of the specificity of the other trematode species in their respective hosts. If there are many trematodes species found in a habitat, there likely are lots of different host species in that habitat. Lots of parasites often means lots of biodiversity! Now this is a rough estimate and does not account for movement of hosts between habitats. Also as mentioned above, there is often at least one stage of the lifecycles of trematodes that’s outside of the host, that is, the eggs shed into water via host feces. These eggs hatch and the larval stage (called miracidia) swim around in the water until they come across the next appropriate host species. This stage is particularly sensitive to the physical conditions of the water, including temperature, pH, current and light. Thus, elements like habitat disturbance, warmer water temperatures, concentrations of chemicals (like fertilizers and pesticides) all influence the survival of this stage of the parasite. If you found few parasites, there might be cause for concern about the general health of that ecosystem.

These tiny organisms therefore serve as good indicators of biodiversity and environmental conditions of an ecosystem.

We now know corridors are critical to the survival of large creatures. But they also matter to, say, salamanders. Why?

Corridors are particularly important for animals that migrate or routinely travel distances between feeding, breeding and overwintering habitats. Being able to move among these different habitats is critical for the survival of populations and high mortality during travel can significantly impact a population. Providing safe causeways for travel is not only important for large animals, but also for small animals that move among habitats.

Here’s an example that I hope will illustrate why corridors matter to a number of non-charismatic (ie non-mammal) species.

For my PhD, I was interested in looking at large-scale patterns of parasitism in leopard frogs (Lithobates pipiens). I was interested in taking a cross-section of a natural population and looking at things like age and sex as factors that could influence vulnerability to infection. Well, to examine parasites, you most often have to look inside a specimen, but I didn’t want to go out and kill off a significant proportion of a population just to see what was inside! So. Where does a biology student get lots of wild frogs to study without killing them? The answer came from an understanding of the behavior of these frogs.

Each year, at the end of summer, leopard frogs migrate from their breeding and feeding grounds to other ponds where they overwinter and, in the spring, they migrate back to the same ponds that they came from. They can cover distances of a few kilometers in this bi-annual trek. They tend to travel under the perfect conditions of temperature and moisture, mostly at night. These conditions are specific enough that the move happens over a very short period of time, less than a week. They also move in cohorts, so adult males will move on mass one night, then adult females will travel another night. The juveniles will go at another time. Now many people have observed these movements, probably not realizing what they were seeing. You’re driving on a highway one night and you notice that there are a ton of frogs hoping around on the roads that night. This is actually a population that is on the move. What may once have been a continuous area of marshland, now has a giant highway running through it. However, the frogs have evolved to follow exactly the same route year after year and they continue to try to cross the highways. What results is an annual massacre of populations of frogs as they are squashed by cars that wipe out a significant proportion of a cohort in a single night.

I decided that I would use roadkill for my study, knowing that it would make the examination of the frogs significantly more difficult, but I felt that while I could not stop the massacre, I could try to use the carcasses for something useful, something to better inform on this already vulnerable population. Because of the separation of the ages and sexes, I didn’t need to sort a great deal through mixed samples, I just decided to collect on different nights.

My first night out saw me with a headlight and a bucket on the side of a highway that ran through this marshland, absolutely appalled at the decimation. Cars raced down this road, oblivious to the hundreds of dead frogs in their wakes. Bucket in hand, I walked up the road for about a 1km stretch scraping up bits of carcasses. By the time I turned around and walked back, the road was again covered in dead animals. In an hour, I had enough carcasses to make up a robust sample. This repeated for the next couple of nights. I could not imagine how this population could possibly withstand this level of mortality for more than a few years at most. Naturalists have since reported significant reduction in population sizes for this area.

The obvious solution would be to stop all road traffic for the 2-3 days these animals are crossing a highway. Barring that, build a corridor. But there have been growing pains with these and original efforts have not been very successful. That’s because while larger animals will find and choose to use a built corridor, amphibians and reptiles, tend to follow more random crossing patterns. They may not cross at the same spot year in and out, thus the frogs described above may be found crossing at a location 2 km away from where they crossed the year before. A corridor built in one location may not be relevant the following year. Newer designs of corridors account for these behavioural differences and

This is one example of a single population of Leopard frogs, but this happens every year with many species.

You’ve learned a lot through your journey. What’s the one thing you know now, that you wish you knew at 15?

Do the right thing. It won’t make your life easier, it will rarely be rewarded with any conventional definition of success, and in many ways it will make your life harder, because it will often not be popular. But it will bring significance to your existence on this planet, ensure your relationships are authentic and meaningful, will help you to be of service to others, and you will learn your true nature as you do the right thing often against dismal odds. As for what the right thing is….listen for that inner voice, it is never wrong.