I have something to admit. Before starting my PhD researching the primate gut microbiome, I didn’t completely know the difference between the terms “monkey” and “primate”. Perhaps this is somewhat forgivable given that I was primarily a microbiologist, but I remember still feeling a sort of sneaky shame in googling the differences after I read the project title, like it was something I should definitely know.

This is a monkey (a Gibraltar macaque). Licensed under CC0 3.0.

As it turns out, the rules of what’s what in the primate tree are pretty simple once you know them. The evolutionary history of primates can be traced back to between 63 – 74 million years ago (MYA), and as they stand today can be divided into two main branches, named Strepsirrhini and Haplorrhini, which based on molecular studies are hypothesised to have branched away from each other around 64 MYA. Interestingly, the two groups are named after their noses, with Strepsirrhini meaning “wet-nosed” and Haplorrhini meaning “dry-nosed” and were called so by a French naturalist friend of Robert Grant, named Étienne Geoffroy Saint-Hilaire.

A simple primate evolutionary tree showing the major branchings. Strepsirrhini were formerly known colloquially as “prosimians”, although this is an outdated term now. Licensed under CC0 1.0.

Strepsirrhini primates (unsurprisingly) tend to have wet noses, as well as a more pointed, almost dog-like snout rather than the flatter faces of their Haplorrhini cousins, and are thought to be most similar in appearance to the first primates. The clades that make up the Strepsirrhini primates are the lemurs of Madagascar, the lorises from South East Asia and India, and the pottos and galagos (or bushbabies) of Africa. Until recently, tarsiers were also thought to belong to Strepsirrhini, however now they’ve been moved to the sister clade of Haplorrhini.

A selection of strepsirrhines spanning the clade. Licensed under CC0 3.0

If you’ve been wondering up to this point where the monkeys are, you need look no further than the Haplorrhines. In terms of number of species, this clade is almost entirely monkeys. The major two branches within this clade are between Catarrhini (meaning “down-nosed”), or Old World monkeys and apes found across Africa and Asia, and Platyrrhini (meaning “flat-nosed”), or New Wold monkeys found in Central and South America.

A map showing the distribution of monkeys across the globe, with Old World monkeys coloured in red and New World monkeys coloured in orange. Licensed under CC0 3.0

Within the catarrhines, the apes, or Hominoidea, comprise gibbons, orang-utans, gorillas, chimpanzees and, of course, us. Apes are thought to have formed their own distinct clade from Old World monkeys (or Cercopithecoidea) around 29MYA, so if you wanted to get really technical, and you were the kind of person who happily accepts birds as being modern day dinosaurs, it wouldn’t be entirely wrong to say that apes are actually monkeys too.

An orang-utan in Borneo, Malaysia. Licensed under CC0 3.0.

So, hopefully the next time you get stuck wondering whether the primate you’re looking at is a monkey or not, you’ll be a little more clued in.

As a biology PhD student, I’ll be the first to admit that there are some studies in science that, whilst interesting, can leave you questioning who comes up with these and why they (and we) should care so much.  If you, like me, are the kind of person who loves these kinds of things, the list of past Ig Nobel prize winners is a cornucopia of great examples.  Often, though, all it takes is delving a little deeper to find the importance in what seems like a pointless topic.  My PhD involves collecting primate poo samples to look at their gut bacteria, and so does occasionally elicit the classic and very valid question: “But what’s the point of it?” from people, so I thought for this week’s blog post I’d try and answer exactly that.

Primates are our closest relatives and, in fact, your closest relatives are also primates, as are you yourself.  We’ve known about the anatomical similarities between humans and other, non-human primates for hundreds of years.  The Grant Museum of Zoology plays host to what used to be a teaching collection for doctors studying at UCL, where the bones and structures of animals from non-human primates to fish would be studied to understand how our own bodies developed from the ancestors we shared with other organisms.  Then, in the 1980s, with the birth of molecular sequencing techniques, we gained the ability to study the DNA of animals.  From this we began to understand just how closely related to other primates we really are, leading us to the famous fact that we are 98% genetically identical to chimpanzees, our closest relative.

A juvenile chimpanzee skeleton from the Grant Museum of Zoology, accession number Z449

The next big step, in my (admittedly, probably biased) opinion, in our understanding of the human body and how it works has been our realisation that gut bacteria are hugely important to human health and disease.  We might tend to think of bacteria as harmful or infectious, but actually the bugs that live in your intestine are a normal part of a healthy human body.  They outnumber our own cells 10 to 1, making us 90% bacteria in terms of cell numbers alone (although our own cells are much larger, which is why by mass we’re still mostly human), break down parts of our food that we ourselves can’t digest and even provide us with many hormones (such as 90% of our serotonin, the “happiness” hormone).  In addition, gut bacteria has lately been linked to everything from keeping us lean or helping to make us obese, to maintaining normal bowel functions or exacerbating conditions such as irritable bowel syndrome.

So where do non-human primates come into this?  Well, as with the Grant Museum’s collection all those years ago, it’s nothing new to study our relatives in order to understand more about ourselves.  While understanding the gut bacteria of primates across the whole primate evolutionary tree lets us take a look at how gut bacteria have evolved alongside us to create a mutualistic relationship, primates in particular are a very interesting group of animals.  Within the Primate Order there is huge variation in the ways that these animals live their lives, and it is by considering these differences that we can begin to understand how the variations between different human lifestyles affect our gut bacteria and so our health.  For example, by comparing primates that eat mostly vegetation to species that eat fruit or meat or even gum like lorises, we can start to ask questions about how much our diet affects what bacteria can survive in the gut.  Looking at animals that are highly social, such as chimpanzees or baboons, vs. those that are mostly solitary creatures such as bushbabies can tell us how gut bacteria is spread and shared between individuals, communities and even between different species living in the same area (this is not as crazy as you think – humans have been found to share skin bacteria with their pet dogs).

Primate species, diet and social structure are all thought to be important in determining an animal’s gut bacteria. Licensed under Creative Commons CC0 1.0

But it’s not just ourselves that we can learn things about when we study non-human primates.  One large aspect of my PhD looks at how life in captivity affects the gut microbiomes of primates.  Whilst life in captivity is not ideal for any animal, raising them in zoos and centres can have benefits for endangered species.  Studying the gut bacteria has the potential to offer suggestions on how we might be able to enrich the diets of captive animals to ensure they maintain healthy gut bacteria whilst living in zoos.  Furthermore, by looking at what nutrients are necessary to keep a healthy set of bacteria, we might be able to start thinking about conservations issues such as which plants are highly important to conserve alongside these endangered animals.

So, I hope I’ve convinced you that gut bacteria are important, that my area of research has the potential to be of great help, and above all, that primate poo is a great thing to study.

As any lover of Attenborough will, I’m sure, understand, the idea that someone is not naturally interested in nature and zoology is something that I, as a researcher of primates (specifically, their gut bacteria), had never really considered before. Aware as I am that the fascinating but visually underwhelming (I’m sorry!) sea squirt might take a bit of effort to enthuse people I sort of assumed a general underlying love of at least all the four-legged, big-eyed, furry, woolly things of the world.

This wholly unreasonable assumption of mine was proven wrong during last week’s shift at the Grant Museum by one simple question from a very enthusiastic and lovely retired physicist:

“What would a group of physicists find interesting in a Zoology museum?”

What follow here are just two examples of nature seen through a different lens, which I hope go some way towards enthusing those not naturally curious about zoology.

All that glitters isn’t gold, all that shimmers isn’t green

Most of the green birds you see are pretenders.  Rather than truly being green, they’re a beautiful example of something called structural colouring.

When you use paint to colour a surface, what you are applying are coloured molecules, called pigments.  These produce colour through absorption of different wavelengths of light; to produce green, for example, red and blue light are absorbed whilst green light is reflected into your eyes.

The Green Honeycreeper, not a green bird. Photo credit: CC Image courtesy of Lip Kee on Flickr

First observed by Robert Hooke and Sir Isaac Newton and explained by Thomas Young a century later, structural colouring, however, is the production of colour through the interference of white light by microscopic surfaces, rather than absorption of certain wavelengths.  This can work in conjunction with pigments — for example, a peacock feather is pigmented brown, but microscopically structured so that they reflect blue and green light, and also making them iridescent, showing different colours depending on the angle from which you view them.

Structural colouring in animals, particularly birds, can be a big evolutionary advantage.  Creating pigments can be very energy-costly, and often requires rare elements that are difficult to extract from food during digestion, such as metals like cadmium, cobalt or chromium for green pigments.  Structural colouring is an ingenious way to create these brilliant colours through feather shape alone, hugely useful when trying to attract a mate or hide from predators in the trees.

Turacos are the interesting exception to these structural colourists.  Found in forests and woodlands in sub-Saharan Africa, these birds actually produce their own unique red and green pigments, called turacin and turacoverdin respectively, using an unusually high amount of copper.  Just why they make this pigment is still a mystery.  Their habitat coincides with the world’s richest copperbelt, leading some to speculate that this pigment production might’ve evolved to detoxify the large amount of copper these birds ingest through their food.  Whatever the reason, this unique ability to use copper in this way makes turacos some of the only truly green birds.

A truly green Angolan Turaco. Photo credit: CC Image courtesy of C. P. Ewing on Flickr

There are many examples of structural colouring in the Grant Museum, from the peacock’s feather to the wings of iridescent butterflies and the gold sheen of some beetles.  I highly recommend seeing how many you can spot next time you’re there.

A (constructal) theory of everything

It might not be the unified theory that Stephen Hawking is searching for, but the Constructal Law is a physics theory that can be used to explain the shapes of all the bones, limbs and preserved animal specimens that you see around you in the Grant Museum.

In its simplest form, Constructal Law states that systems naturally evolve over time to minimise energy waste.  Substitute the word “animals” for “systems”, and you have its application to zoology.  This seems like an obvious benefit; wasting less energy allows animals to get the most out of the food they eat, allowing them to flee from predators faster, spend less time gathering food and more time chatting each other up, and produce better-fed offspring. Where this rule becomes most interesting though is when you consider animal locomotion.

Even though running, flying and swimming have all evolved as separate methods of locomotion, they’re all linked by this simple physics principle.  Despite involving very different body mechanics, it turns out that there is a universal relationship between animals’ mass and speed, as well as the frequency and force of limb or tail movement, whether those are legs, wings or fins.  The relationship between a winged animal’s mass and the frequency of their wing beats shows the same relationship as between mass and rate of swimming in fish, as well as mass and stride frequency in running animals, and has all evolved to move the animal at optimal speed, reducing energy wastage whilst maintaining quick movement.  No other factors, such as type of creature, limb length, wingspan or otherwise, seem to factor in to this, only body mass and limb or tail movement.

Paddling and running on display at the Grant Museum. Photo credit: CC Image courtesy of Justin Pickard on Flickr

This principle helps determine how animals move around and is a brilliant example of how the great diversity of life still converges to fit fundamental physics principles.  Next time you’re in the Grant Museum, have a think about how all the animals around you have been shaped in part by this universal law.

The physicist I met got me to consider the animal specimens in the museum from a whole new angle, making me think about what different people would find interesting about zoology and, importantly, why, rather than just assuming everyone has an inbuilt love.  Just like the iridescent wings of certain animals, looking at a familiar collection from a different angle can offer a whole new view on zoology.  And seriously, give the sea squirt a chance.