In Search of Hot Mosquitofish


How do animals adapt to hot temperatures? What allows some animals to do well in hot conditions while others simply, well – die?

A natural thermal gradient - the hot bores of outback Queensland

A natural thermal gradient - the hot bores of outback Queensland

Seems like a pertinent question when one considers the world is getting hotter. And quickly.

My current ARC Discovery Project poses these very questions. I want to understand the mechanisms of adaptation to warmer temperatures and how this can shape a species' population dynamics and survival. It's not surprising then that my interest was piqued by rumours of an introduced species of freshwater fish (the ubiquitous mosquitofish) that can actually survive in the bath-hot bore drains of western Queensland.

Across the state's west, numerous deep bores tap into the rich underground water sources of the Great Artesian Basin. Water spews out of these pipes from depths of more than 1500m at temperatures in excess of 70°C, flowing into narrow drains and cooling – allowing livestock to persist in an environment that would be otherwise uninhabitable. Fish (well, so the rumours go) inhabit these open drains at year-round temperatures above 30°C and sometimes even greater than 40°C. The possibility of capturing and studying these fish was too tempting to ignore.

RA Skye Cameron + echidna

My RA and lab organising force Skye is used to my crazy, impetuous ideas, and she doesn't even seem surprised when my ideas are offered at stupidly short notice and without any respect for logistics. In this specific case, Skye laughed – and started packing – when I suggested we should head out west in search of some hot fish in just a few days’ time.

We would collect some fish from hot bores to study in the lab.

It was the prospect of teaming-up with some UQ colleagues that work out near Barcaldine (1200 km north-west of Brisbane) who know the local people, properties and bore-drain locations that lit a fire under my b-hind.

So - it was early on a Monday morning that Skye picked me up half-asleep (me, not her) and we set-off on our adventure with no guarantees of success (let's face it, little chance of success). By lunchtime on Tuesday we reached Barcaldine. We'd avoided suicidal kangaroos and emus playing chicken with every vehicle pelting along the highway, and we rendezvoused with Jeremy (RA) and Billie (Honours) – from my colleague Rod Fensham's lab group – at the local bakery. Incidentally, Rod and Jeremy work on the spring systems of Edgbaston - the site of Australia's most endangered freshwater fish, the red-finned blue-eye (more on this another time).

we had to stop driving at dusk as the emus and kangaroos made the roads dangerous

After the obligatory orientation tour of the town's pubs on Tuesday evening and a sampling (2 kgs) of the local beef (not by Skye), we set off in search of bores on Wednesday morning. It didn't take long before we found them.

The first property we visited had a bore flowing out at 55°C into a tiny, narrow drain. Over the course of 30 m, the water cooled down to temperatures of around 45°C, and as we walked along the drain we spotted our first hot candidates.

Little juvenile mosquito fish living at 42.8°C.

Holy be-jesus!! This temperature is higher than I thought possible for any mosquito fish to survive in.

It was incredible - fish living in water I found hot to the touch.

mosquitofish were found at temperatures as (naturally) hot as 42.8 degC

Walking along the drain revealed a beautiful temperature gradient that dropped down by around 1°C every 5 meters.

When we hit temperatures of around 35°C there was an absolute explosion of fish and the surface rippled with movement.

We'd found our hot fish – and in truly staggering numbers. The air temperature was just a little over 20°C – and it was dropping nightly to below 5°C – yet the fish were enjoying balmy water. These fish had found their stable, warm conditions and were clearly loving it.

kangaroos - as far as the eye could see

By the end of the next day, we'd collected mosquitofish from two more sites and were ready to head back to Brisbane with a troop-carrier full of bore water and thermophilic fish. All we had to do was avoid those roos and make it back for my daughter Nelle's birthday party by 11am Saturday (Happy Birthday Princess).

And we did. I was only 30 minutes late to the party …


The Grand Slam: How Hard Should You Hit?

Squirrels know what’s going down (or do they)? Image source: Wikimedia commons.

Squirrels know what’s going down (or do they)? Image source: Wikimedia commons.

The trade-off between performance and accuracy is a problem faced by a lot of different animals in a variety of situations. For example, consider a squirrel running along a bare branch to get from one tree to another; the faster it runs, the less time it spends exposed to predators. However, as the squirrel runs faster, it also increases its chances of mis-stepping and falling to its potential doom. 

So, to get the best of both worlds, the squirrel needs to optimise its running speed depending on its chance of slipping (the width of the branch) and the cost of falling off (the height from the ground).

These sort of performance/accuracy trade-offs are also commonplace in the human world. How fast should you smash out a text message to your supervisor asking him (politely) to email back your latest draft before the number of typos makes the whole thing unintelligible?  In particular, these trade-offs are of a great deal of interest in elite sports. An awesome example of a sport where this trade-off is of utmost importance is in singles tennis.

Serving hard: Heather Watson, Roger Federer and David Ferrer. Image source: Wikimedia commons.

In tennis, it’s pretty well accepted that if you serve really hard, it’s more difficult for your opponent to return the ball. But the harder you serve, the more likely it is that you’ll miss the service area and fault. So, players will usually belt it out on their first serve, but if they miss the first serve they’ll hedge their bets and serve softer the second time round to make sure they don’t double fault.

A/Prof Robbie WilsonDr Chris Brown and I have been testing this idea about performance trade-offs and optimal strategies using data from the men’s singles in the 2013 Australian Open. We’ve found this observation to be generally true: the probability of winning the point increases as the serve speed approaches its maximum, but the probability of faulting increases as well (for most players – some players are really consistent at getting it in regardless of how fast they serve). This was reflected in the frequency of high serve speeds in the first and second serves.

Jérémy Chardy, Andy Murray and Janko Tipsarevic. Image source: Wikimedia commons.

We’ve also constructed an optimality model which predicts the optimal serve speed taking into account the probability of faulting and the cost of a fault. An optimality model is, in essence, a mathematical model where you input the risks and rewards of a specific situation for a given individual, and it will tell you the optimal response for that individual if it wants to both minimise the risks and maximise the rewards. 

Optimality modelling is useful because it allows us to calculate the optimal response of specific individuals to any situation. We are looking at whether their opponent’s world ranking (ability to return a fast serve) and the point they’re going for or defending against (normal, game, set or match) affects their serve speed in relation to their optimum, but more on those results later.

Rafael Nadal, Caroline Wozniacki and Jérémy Chardy. Image source: Wikimedia commons.

We hope that our research can teach us more about how animals optimise their behaviour and physical efforts to improve their chances of successfully performing a given task. Depending on what we find, we might even be able to offer specific recommendations to tennis players wanting to improve their service game – who knows what the future might hold!

Andrew Hunter, a PhD student in our lab, is looking at performance/accuracy trade-offs in soccer. Will the results be similar between an individual and a team sport? We don’t know yet, but it will be interesting to find out.

Novak Djokovic, Agnieszka Radwańska and Venus Williams. Image source: Wikimedia commons.

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