Published February 2, 2021
They sleep during the day and forage at night. They can’t jump, but they’re excellent climbers. They have huge round eyes. And — unique among primates — they have a venomous bite.
Meet slow lorises. These arboreal animals, found in forested regions across Southeast Asia, include several species that comprise the genus Nycticebus.
Slow lorises occupy an intriguing spot on the genetic tree of life. They belong to a suborder of primates that diverged early on from all other primates, so studying them can shed light on the evolutionary history of primates, and what makes various primates, including humans, unique.
And yet, relatively little is known about slow lorises, says Stephanie Poindexter, assistant professor of anthropology, College of Arts and Sciences. That’s one reason she decided to build her research program around the animals, using field, lab and computational techniques to understand how the critters navigate and use their habitats.
“One thing that’s interesting is how little we know about them relative to other primates,” Poindexter says. “It’s not a complete black hole, but if you compare it to baboons or chimpanzees, there’s just not a whole lot of information about what they get up to and why they do what they do. They’re nocturnal — it’s not like people have ignored them for the fun of it. They’re hard to study.”
Her team is exploring a number of questions relating to the movement, behavior and sensory system of slow lorises, and how these traits evolved. Current projects span a variety of topics, ranging from a comparative look at primate dispersal patterns to features of the nasal cavity that may impact the sense of smell in slow lorises and other primates in the same suborder (strepsirrhines). Past publications have covered topics such as where they sleep and whether they exhibit a preference for using a certain hand.
In a paper published online on Jan. 22 in the journal Animal Behaviour, researchers including Poindexter and UB PhD student Keely Maynard investigate how Javan slow lorises learn to secure food in the wild.
The species’ diet includes insects, liquid gums that seep out from trees and floral nectars.
To get the gum, the animals wrap themselves around the trunks of trees, use their teeth to gouge holes, wait a while, and return later to eat the fluids that the trees produce while healing. Obtaining nectar also requires some work, with the slow lorises climbing to the terminal branches of trees to lick flowers.
The study’s conclusion: It takes time — about 600 days — for Javan slow lorises to develop an adult diet, which may help to explain why they stay with their mothers for so long. The project was led by Anna Nekaris, professor of anthropology at Oxford Brookes University, with Maynard as first author.
“Javan slow lorises have an extended adolescence period, where the animals are adult-sized and sexually mature, but they’re remaining with their natal group,” Maynard says. “This extended period of development could be used to learn to forage on these difficult food items.”
“When they’re young, they’re feeding in proximity to adults. They’re not just on their own,” says Poindexter, Maynard’s PhD adviser. “We think it takes time to learn how to eat certain food types. Young slow lorises show a lot of variability in their diet. And then around 600 days or so, there’s less variability, and their diet starts to reflect more of an adult diet, with fewer insects. The insects are easier to get. It’s grab and go.”
Poindexter and Maynard conducted the research while working with Nekaris at Oxford Brookes. To obtain the data, the scientists — like the slow lorises — stay up at night.
“Different teams go out, so the slow lorises get observed throughout the night,” Poindexter says. “The data we used was from a long-term dataset, so there have been many hands involved in collecting this data over many years.”
Poindexter’s work has included co-authoring two listings for two slow loris species in the International Union for Conservation of Nature Red List of Threatened Species: Nycticebus coucang, the greater slow loris, and Nycticebus hilleri, the Sumatran slow loris. Both are considered endangered.
The animals face a number of threats to their survival, including the wildlife trade and habitat loss caused by deforestation.
“I went to Oxford Brookes for a master's in primate conservation, and the plan was to study captive ape welfare, but when I got there, I learned about the welfare and conservation issues slow lorises were facing,” Poindexter says. “At that point, I decided enough people were working on chimpanzees and that the slow lorises deserved just as much effort and attention.
“During my master’s, I also got interested in how odd the slow loris was relative to other primates. I wanted to know how and why they evolved some of the unique morphologies and behaviors I had observed.”
Maynard also comments on the marvels of the slow loris, noting that, “Slow lorises are fascinating. They’re venomous, they live in family groups, they engage in social monogamy, and they’re just really interesting.
“I joined Dr. Poindexter’s lab because her research is really aligned with my interests. We’re both interested in movement ecology and habitat usage, and how slow lorises interact with their environment. I think it’s important to understand what roles all animals play in our ecosystems. If we lose that animal, it could have a lot of ramifications.”