Lessons in Monkey Studies, or, a Q&A with Anthony Di Fiore

Spider monkeys, sloth attacks, and a historic vote in Ecuador

Anthony Di Fiore is a professor of anthropology at UT Austin, where he’s a key member of the department’s biological anthropology faculty. In 2022 he was elected to the American Academy of Arts & Sciences for his contributions to that field, the latest in a long string of honors, but he’s been in the news most recently for sharing a video of an unusually active sloth.

Since then, Di Fiore’s been kind enough to provide a few more glimpses of life in the Ecuadorian rainforest, where he’s worked as a field primatologist for decades. For Extra Credit he shares more about his research and answers several burning questions, including “how can spider monkeys can help us understand human societies?” and “what do monkey droppings have to do with your genetics lab?” The icing on top? Even more monkey videos.

You’ve been doing field work in the same part of the Ecuadorian Amazon for almost 30 years. Can you give me a sense of what your time there looks like? Where are you and what are you doing?

The site that we work from, the Tiputini Biodiversity Station, is located in the largest national park in the Western Amazon. It's huge, and it's largely intact tropical forest. I mean, there's some petroleum exploration that goes on there, there are a number of Indigenous communities in the area, and there's some illegal extraction of wood that goes on and some hunting for subsistence and illegal markets, but for the most part you can walk around and you might see any of the apex species that you might imagine live in the Amazon. There are jaguar, harpy eagles, and pumas around, and lots of peccaries and deer. There’s 600 or 700 species of birds and 10 species of primate. It’s a forest, but the understory in most places isn't terrifically thick, so you can walk through it. And the monkeys, at least the ones that we follow most often, are staying in areas with a pretty tall canopy, so they’re way up high and we’re following them on the ground underneath.

Let's talk about the monkeys. You came to this topic from a biology background, and now you're in the anthropology department at UT Austin. I’m coming to this with no knowledge at all, but it seems like the first question is: What do monkeys have to do with anthropology?

Well, we humans are primates and they're primates. So there is that.

One of the historical reasons why, at least in the United States, much of primatology is done by folks that are affiliated with anthropology departments is because we know that you can learn something about the factors that influence human social behavior and human societies by studying those things in our primate relatives. It's not so much your traditional social anthropology as practiced in Europe, but anthropology in the U.S. is a very broad field. That’s one of the legacies of Franz Boas, the founder of modern anthropology in the U.S. — that understanding humans really requires triangulating from lots of different directions and using lots of different methods of inquiry and tools.

Now, studying primates in the Americas is a little further afield than studying primates in other parts of the world because primates in the Americas shared a common ancestor with humans some 35 to 40 million years ago. That’s ~80 million years of independent evolution once you go back to the common ancestor and then back up to humans along our evolutionary tree, so you don't expect to have primates from the Americas be as comparable or as informative about human behavior and human societies as, say, chimpanzees or gorillas. That said, there's a lot of variation in the primates from the Americas, and some of them, in particular woolly monkeys and spider monkeys and other members of the ateline primate family that I work with, share some features of their social systems with humans that are really interesting. One is the fact that both humans and these primates live in large social groups that contain many breeding age animals of both sexes, which isn't so common in primates. Another is that it’s females who typically leave the social group they’re born into and move to another group as they are approaching or reach sexual maturity. As a result, the male adults in a group tend to be relatives and the females are individuals that have moved in from outside. This is also true for chimpanzees and, we suspect, for the last common ancestry of chimps and humans. In many small-scale human societies, too, the social core is formed around a group of related males who are cooperative with one another and who are cooperatively antagonistic to males from other groups. Some of those are social system features you also see in the monkeys that we work with, particularly the spider monkeys, and that's a rationale for studying these species. If you can figure out what it is that a distantly related species has in common with humans and chimpanzees with respect to its ecology and how it makes its living, maybe you've elucidated what some of the ecological causative factors are for that kind of social system existing.

One of the ways you’re studying these primates is through camera traps. What are you looking for in these videos when you’re not filming sloths and ocelots?

We started the camera trap project in 2006 or 2007 because we found that spider monkeys were going to mineral licks — specific locations in the forest where a range of mammal ad bird species come to feed on soils or drink water — and we wanted to figure out how often that was happening. Spider monkeys spend an enormous amount of time in the area around a mineral lick, and it's a resource for them both nutritionally and socially. It's kind of like a café where you show up and you don't necessarily drink a coffee, but you're hanging out there and interacting with friends who come by. So, we wanted to know who was using the licks and for how long, and we were eventually able to use the camera traps to identify the individual spider monkeys that were coming down from the treetops to the licks. They all have names, they've all been genotyped, so we know a lot about them individually, and we can extract from the video trap records things like who's coming down, who's leading the way, who's coming down together, when during the annual cycle females have young kids, and when those young kids are coming down on the mom's back or not on their mom's back, i.e., how old they are when they start to move independently. So, there's a lot of indirect information that you can get from this data about the group composition and how they go to visit these mineral licks.  

On top of your work in the field, you also have a genetics lab on campus. Is it a common thing for field primatologists to have lab work as well? Can you tell me about what you do there?

It's more common than it used to be. More and more people are using genetic tools, but they often work with other people to do that. Maybe it's a little bit rare to do that stuff yourself.  

There's other kinds of labs besides genetics that other primatologists use, but I mostly work on genotyping the animals we’re studying, that is, basically, deriving their DNA fingerprint, which can be used to do things like assess paternity and maternity and infer how animals are related to one another. We’re also starting to do some environmental DNA work particularly around these mineral licks.

The genetic work we do is largely based on fecal samples, which we collect in the field and ship back to the lab in Austin. Then we extract DNA from those samples and use it to genotype or sequence DNA from each individual so that we can address questions about population structure, mating systems, and even some questions about movement and integration between groups.  

Is there a particularly exciting finding that’s come out of your lab work?

One of the most interesting things for me is studying which males in a group are responsible for parentage. A cool thing about these ateline primates is that the males don't really have a dominance hierarchy, unlike other primates you might be familiar with like baboons or chimpanzees, and their social relationships with their groupmates are very non-confrontational. When you watch chimpanzees, the males are going to be arguing with each other, displacing one another. Baboons, same thing. But with woolly monkeys and spider monkeys, you see very little of that within groups. In a situation like that, you might expect that parentage is going to be distributed among the males in a more egalitarian way as well. We’ve shown that that's mostly true in the atelines, and it's very different from the pattern that you see in other primates that live in multimale groups.

You’ve been in this field for more than 25 years now. What’s the greatest change been in that time?

Well, 25 years ago we didn't know anything about patterns of genetic parentage in wild primates, i.e., about who's actually having kids, and that was because it was hard to get DNA out of feces or other “low quality” samples at the time. It’s much more accessible now, to the point that I can do DNA extractions with students in one of my anthropology classes. There’s also a ton of interesting and publicly accessible genetic data that we use in teaching and research. For example, we can do things like direct students to go to GenBank, download DNA sequences, and have them assemble those DNA sequences and do an analysis. What might have been a Ph.D. project 30 years ago you can now do in a lab period in some undergraduate classes.

What about in the Amazon? Have you seen many changes in that pocket of the forest?

There are definitely changes that we can see, and it's reasonable to think that some of those may have to do with climate change over the past few decades. Even in the remote site where I work, I hear many fewer insects at night, and the dawn chorus of birds is a lot quieter. I'm no bird expert, and I don't know all the different species, but it seems like there's a lot fewer, and the ornithologists that work there have noticed the same thing. They’re seeing a lower diversity of birds too, but whether that’s due to climate change or some other factor is harder to say. The long-term temperature records there don’t exist to the same extent that we have them for more urban places or even many places in the U.S., but there’s definitely been years that are different climatically.

One exciting recent change is a really momentous vote that Ecuador just took on the future of the national park that I work in. Last month there was a referendum in which people in Ecuador voted to basically ban all petroleum extraction in one portion of the national park. Sixty percent or so of the population decided “we want to step back from an exploitative, petrocarbon-based economy,” so that’s amazing news for the national park but also for the environmental movement and the push for alternatives to fossil fuels for an energy future for Ecuador.