Daily Archives for June 10, 2019

What does a koala’s nose know? A bit about food, and a lot about making friends


Ben Moore, Western Sydney University and Edward Narayan, Western Sydney University

The koala’s nose is distinctive – it’s a big black leathery rectangle in the middle of a round, grey face that’s surprisingly soft to the touch. And every koala nose is unique.

A study of 108 wild koalas found distinctive patterns of pigmentation around the nostrils allowed observers on the ground to reliably recognise individual animals, even when they’re in the trees.



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But more importantly for the koala, the nose is an important connection between this iconic marsupial and the world it lives in, from sniffing out toxins to saying hello.

And it starts right at birth. The tiny newborn koala, despite weighing only half a gram, already has the ability to smell and feel its way towards the milky scent of the pouch and its mother’s teats.

A koala’s nose knows how to sniff out toxins

Koalas, famously, spend most of their time sleeping or resting. When they’re not sleeping or resting, they are mostly feeding or moving between trees. In both of these activities – or in other words, for most of their waking hours – they follow their nose.

Koalas nearly always smell their food carefully before eating. So many koala experts were surprised to learn recently that koalas don’t have particularly many genes for olfactory receptors – the receptors found on nerve cells in the nasal cavity for detecting different smells.



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Koalas sniff out juicy leaves and break down eucalypt toxins – it’s in their genome

This matches up with anatomical observations that also suggest that among marsupials, the koala’s sense of smell is probably relatively poor, partly as a result of features associated with conserving water.

Gum leaves are chock full of natural plant toxins and other unpleasant chemicals, and koalas choose trees that minimise their exposure to the worst of these.

But most of the toxins that influence koala feeding are not volatile – they have no smell. It falls to the koala’s sense of taste (and genes for taste receptors are especially abundant in the koala genome) to make a final decision on whether a leaf is safe to eat.

Fortunately for the koala, the only-slightly-toxic compounds called terpenes (the invigorating scent of Eucalyptus oil) are highly volatile and offer a useful cue to the levels of other toxins in a leaf.

And one advantage of being a specialist feeder with a basic diet, is that there are relatively few odour cues to learn. It’s also fortunate the leaves koalas are checking out are right in front of their noses!

The koala’s nose might not only smell plant toxins, it may also play a minor role in detoxifying them.



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We know enzymes in our own noses can detoxify certain drugs, and in other specialist herbivores, such as woodrats, many of the same enzymes that detoxify natural plant toxins and drugs in the liver are also expressed in the lining of the nose.

These enzymes likely help stop the nose from becoming overwhelmed by odours and maintain sensitivity. Critically, they also protect the central nervous system, as nasal tissue is the only thing separating inhaled toxins from the brain.

A koala’s nose knows how to make friends

Sniffing out food is important, but it’s not the koala’s biggest forte. So why the big schnoz? The answer may lie with the importance of social communication.

Although the koala genome has relatively few olfactory receptors, it’s rich in vomeronasal receptors, which are expressed in cells in the nasal cavity that are sensitive to moisture-borne molecules like pheromones.

Koalas are generally solitary creatures, but that’s not to say they don’t know their neighbours. Along with the distinctive loud bellowing of male koalas during the breeding season, olfactory communication is what koalas use to find or avoid each other.

A male koala’s breeding season bellow. Video: Denise Dearing.

Koalas of both sexes often spend considerable time smelling the base and trunk of a tree before they decide whether to climb up or move on elsewhere. When they enter or leave a tree, koalas commonly dribble a stream of urine down the trunk, leaving a trail of chemicals that potentially reveal information about the koala’s sex, identity, dominance, relatedness to other koalas, readiness to mate, disease status and even what they’ve been eating.

But if koala urine is a book written in scent, the secretions of the male koala’s sternal gland are more like a barcode.

This gland is obvious as a yellow-brown stained patch of bare skin in the middle of male koalas’ chests, and offers a straightforward way to tell the sexes apart.

It secretes an oily mixture of fatty acids and other chemicals, which are then transformed into an even more complex chemical mixture by the unique bacterial community occupying each koala’s gland. The end result is a distinctive bouquet and an unmistakable badge of identity for each koala.

Nose kisses from a koala

Aside from these fascinating nasal abilities, there is one more thing that we love about the koala’s nose.

When wild koalas are brought into captivity, they continue to rely on their nose to learn about the strange new world around them – that includes their food and branches, but also the scientists and carers moving around them.



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They will pull anything of interest into smelling range, making them one of the few wild animals that will rub noses to say hello with humans and fellow koalas, even when barely acquainted!

But wild koalas are highly sensitive to human handling, which can generate sub-lethal stress through the stress hormone, cortisol.

Without question, the koala’s nose is fascinating and a marvel of evolution, but no matter how strong the temptation to touch it, please leave those koalas in peace!The Conversation

Ben Moore, Senior Lecturer in Ecology, Hawkesbury Institute for the Environment, Western Sydney University and Edward Narayan, Senior Lecturer in Animal Science, Western Sydney University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Climate sceptic or climate denier? It’s not that simple and here’s why



There’s a difference between not believing and denying the science on climate change.
Shutterstock/nito

Peter Ellerton, The University of Queensland

Climate change is now climate crisis and a climate sceptic now a climate denier, according to the recently updated style guide of The Guardian news organisation.

The extent to which the scientific community acknowledges climate change is very close to the extent to which it also sees it as a crisis. So the move from “change” to “crisis” recognises that both rest on the same scientific footing.

The Guardian’s editor-in-chief, Katharine Viner, said:

We want to ensure that we are being scientifically precise, while also communicating clearly with readers on this very important issue.

But the move from “sceptic” to “denier” is more interesting.



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Whose word should you respect in any debate on science?

Sceptics need to earn the name

Many people who do not accept the findings of climate science often mark themselves as “sceptics”. It is, in part, an attempt to portray themselves as champions of the Enlightenment: imagining that they refuse to believe something based solely on the word of others, and opt to seek the evidence themselves.

It is true that scepticism is an essential component of science – indeed, one of its most defining characteristics. The motto of the Royal Society, perhaps the world’s oldest scientific institution, is “nullius in verba” or “take nobody’s word for it”.

But scepticism has two imperatives, each buttressing the other. The first is the imperative to doubt, so nicely captured in the above motto. The second is the imperative to follow the evidence, and to give more credibility to claims that are well justified than those which are not.

In other words, it’s fine to ask questions, but you also have to listen to the answers.

Too often, so-called sceptics do not want to have their views challenged (let alone changed) and do not wish to engage with the science. Even worse, they may choose to adopt any number of justifications for rejecting science, not from their own free inquiry but from a ready-made selection provided by commercially or ideologically motivated industries.

This move away from “sceptic” might, therefore, be seen as simply an improvement in accuracy. But the move to “denier” might be seen as derogatory, especially as the term is associated with nefarious stances such as holocaust denial.

But is it, at least, accurate?

Three categories of climate science disbelief

Let’s consider three possible categories of people who do not accept the consensus and consilience of human-induced climate change:

  1. those who engage in scholarly disagreement through the literature

  2. those who are not engaged with the debate and have no clear view either way

  3. those who associate climate science with conspiracy, wilful ignorance or incompetence (or even see in it an unpalatable truth).

The first category is the rarest. Several papers with reliable methodology unchallenged in the literature show an enormous majority of climate scientists agree that the planet is warming and humans are largely responsible.

But contrary positions are not unknown. Some questions regarding the credibility of some aspects of climate models, for example, exist for some working academics.

While these scientists do not necessarily doubt all aspects of climate science, issues of reliability of methodology and validity of conclusions in some areas remain, for them, alive.

Whether they are correct or not (and many have been responded to in the literature), they are at least working within the broad norms of academia. We might call these people “climate sceptics”.

The second category is quite common. Many people are uninterested in science, including climate science, and have no real interest in the debate. This attitude is easy to criticise, but if there are pressing concerns regarding the availability and security of food, health and safety in your life, you may be preoccupied with these things and not marching for action on climate science.

Others may simply not spend much time thinking about it, nor care very much one way or the other — such is the nature of voluntarily participatory democracy. They might not believe in climate science, but that doesn’t mean they have rejected it. We might call these people “climate agnostics”.

The third category is the most problematic and arguably the most high-profile. It could be subdivided into:

  • people convinced of the incompetence of scientists and having a naïve view of their own analytical powers (or common sense)

  • folks motivated to reject climate science because of its implications for social or economic change, who consequently see climate science as a conspiracy of social or political engineering

  • those accepting of climate science but not caring about the consequences and seeking only to maximise their opportunities in any resulting crisis – which may include continuing existing business models based on fossil-fuel technologies (and hence encourage those who reject the science for social reasons).

Let’s call these subdivisions, in order: climate naives, climate conspiracists, and climate opportunists. Certain combinations of the above are also possible and are probably the norm.

The term “contrarian” is also a common one, but since it basically means only to go against public opinion, it seems a bit shallow in this analysis.

What is it to deny?

The definition of denialism is not uniform. In psychology it is to reject a widely accepted claim because the truth of it is psychologically discomforting (to that extent, there are many aspects of reality we all deny, ignore or minimise for the sake of our sanity).

In popular culture, including discussions of history and climate science, it is an active act of rebellion against the consensus and consilience of experts, often motivated by ideological factors. These are quite distinct and it may not pay any persuasive dividend to blur them together.

The latter definition does not seem appropriate for climate sceptics or for climate agnostics. But for the rest of the disbelievers, it does seem to resonate. So let’s try it here for a moment.



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This taxonomy of disbelief is not built on any psychological model, but is simply descriptive.

In summary, three categories of climate science disbelief are: sceptic, agnostic and denier. Three subdivisions of deniers are: naive, conspiracists and opportunists.

Is The Guardian right to use the blanket term “deniers” instead of any of the above? Arguably, they have a technical case in some instances, but I would say not in others.

What’s wrong with calling someone a climate agnostic instead of a climate denier, if that is a better description of their state of belief?

But for those who are deniers – and let’s be clear, the evidence is bearing down on all humans like a freight train – then a failure to act is more than negligence, it is a failure of moral courage. I would not want to be remembered as someone who denied that.The Conversation

Peter Ellerton, Lecturer in Critical Thinking; Curriculum Director, UQ Critical Thinking Project, The University of Queensland

This article is republished from The Conversation under a Creative Commons license. Read the original article.