Examining the links between hormones and behaviour in siamang

Hormones can tell us so much about our mood and behaviour – from the motivating dopamine to the bonding hormone oxytocin. You may have heard about this in humans, but it’s true of other primates too!

We’re a wildlife conservation science organisation - and in any given month our Zoo is a hub for zoologists, researchers and university students carrying out research projects and contributing to the scientific knowledge that’s available.

All research involving animals goes through an ethics approval process – with applications reviewed by a dedicated Animal Ethics Committee composed of animal welfare experts. This includes applications from our animal care and conservation teams, zoo interns as part of our annual internship programme, NGOs interested in developing products that benefit wildlife and the environment, or by students carrying out their postgraduate study in New Zealand.

A current piece of research examining the links between hormones and behaviour in siamang is being carried out by Auckland University PhD student Holly Steiner. Siamang were chosen as they are one of only two ape families that form long lasting ‘monogamous pair bonds’ – with the other being humans!

“We know that pair bonding behaviour and romantic relationships are essentially linked to hormones like oxytocin, serotonin and dopamine - or ‘good brain chemicals.’ This study is about whether or not we can see any links between pair bonding behaviours, such as female proceptive or receptive behaviours (initiating or responding to sexual advances) and the male response to it, at a hormonal level,” explains Holly.

Holly’s background is in biological anthropology, which is the study of human biological variation and evolution. When carrying out her under-graduate degree she became interested in human behaviour, and took a paper in primatology (a recognised sub discipline). In mid-2020 for her Master’s thesis research, she initiated a study into how the Zoo’s orangutans and siamang gibbons used the High Canopy – a brand-new cutting-edge habitat that these apes had only recently been introduced to.  

“When I started observing Auckland Zoo’s siamang pair Kera and Intan I realised they use the space exactly the same – and would follow one another. This observation really sparked an interest for me in what the physiological drivers of this could be. This is when I stumbled into behavioural endocrinology - a really interesting field of research.

It’s amazing to think about how every single behaviour, every single thing that you do, is driven by a hormonal interaction inside your body. It's not just neurochemicals, but all of your other more stable bodily hormones are interacting as well. I thank my lucky stars that Amy (Auckland Zoo’s Deputy Curator of Mammals) was keen to support me to go further with my research project.”

Gibbons are known for their booming calls. The vast majority of gibbons – 18 out of 20 species - engage in a behaviour known as duetting where a bonded pair will create a call specific to them. Siamang have a large inflatable throat sac that amplifies these deep calls, and they can be heard up to three kilometres away.  This behaviour happens daily in the wild, and it's partly territorial. At the Zoo we see the same behaviour (which visitors of Auckland Zoo can attest to!), which confirms it's also helping to reaffirm their bond.

“There’s a possibility that there could be changes in the frequency or length of duet behaviour around, let’s say, ovulation. Sometimes I've had whole sampling periods that have just been 18 minutes of duet behaviour and nothing else!”

Research shows that siamang spend more time in physical contact with one another when compared to other gibbon species as well. In Holly’s research, the behavioural data she is looking for includes who initiates interactions and who breaks off these interactions first. This applies to behaviours like touching, grooming, resting and any bouts of agonistic (behaviours related to fighting – including threats) or aggressive behaviour.

“You don’t tend to see agonistic behaviours with these two as it’s apparent they are really closely bonded with one another. The only behaviour that could be seen to be agonistic is when there’s food present. Kera eats slowly and when Intan has finished eating he might try to reach for or grab a favoured food item from her. Usually she is not interested in letting him take the food. Yet if she does the same behaviour he usually lets it go and there’s no agonistic response. This could be because he is particularly docile, or because of his relationship with her. So any instances of that kind of interaction is noted.”

Holly’s study also looks at who solicitates grooming. “Sometimes you'll see Kera move over to Intan and lie down. That’s her saying I want to be groomed – and around 60-70% of the time it works. There are grooming bouts that start without this solicitation, so I note that as well. In my research I’d like to calculate and characterise the hormonal cycle and relate it to the behaviour. Does it follow the same trends, or is it completely unrelated?

In total I have 200 hours of observational data (which equates to around 100 per individual). There’s a helpful quote that says for 100 hours of data, you can see 1% of the full behavioural spectrum, and you need upwards of 10,000 hours of behavioural data to know everything that an animal does.”

To compare these behavioural observations with hormone markers, the Zoo’s primate team collected three faecal samples from both Kera and Intan per week, over an eight-month period. These 5ml samples were stored in a 50ml Falcon tube with 30mls of ethanol, and frozen. At the end of each 4-week period, Holly brought the samples to the University of Auckland for processing and analysis.

Samples are freeze dried and pulverised into powder which is mixed with a methanol solution, centrifuged, and the hormone extracted. At the end of this process a tiny tube of liquid is produced. To measure the amount of hormone present, Holly uses an ELISA plate – which is a technique that quantifies the amount of target substance (eg: hormones or antibodies) in the sample by measuring the rate of binding to the antiserum on the plate. This technique is used in medical tests for diagnosing infections or confirming pregnancy. The sample and plate are then prepared with reagents and placed into a reader. This device will read what concentration of the target hormone is in each individual sample, and from there Holly can calculate the cycle.

The three hormones targeted for the study are testosterone, progesterone and oestrogen.

Holly sees this study as preliminary research that she, or other researchers, can use as a base and choose to dive more deeply into. She’s excited to be in this field as growing up she was interested in animals and at one point aspired to be a veterinarian.

“Now I get to do both. I get to do behavioural research I’m really interested in, and get exposed to conservation work, like the work of Auckland Zoo.”

Now that the behavioural data-gathering has wrapped up at our Zoo, Holly is busy processing and analysing samples in the lab and intends to start on the next lot of research with a siamang pair at Hamilton Zoo soon. Once the data is analysed, it will be shared with us to give us more information about Intan and Kera, and their interactions.

It’s important as a good modern zoo to support research like this that can add to the collective knowledge about species in the Zoo and in the wild, and lead to greater advancements in animal welfare, husbandry and conservation.