In Search of Hot Mosquitofish

A natural thermal gradient - the hot bores of outback Queensland

- by Robbie Wilson

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

The Grand Slam: How Hard Should You Hit?

Today on the blog we're happy to have former Wilson Honour's student, Rebecca Wheatley, who describes her thesis work on gecko personality. Rebecca's currently working as a research associate in the Wilson lab, and plans to start a PhD next year. You can find out more about Rebecca on her science blog, The Adventures of the Integrative Ecologist. 

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).

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

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 Wilson, Dr 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.

Can water dragons actually run on water?

Today's guest poster is Dr Christofer Clemente. After postdoctoral stints at Cambridge and Harvard, Chris obtained an ARC DECRA and joined the Wilson lab at UQ. You can keep up with Chris's adventures on his science blog, Biomechanics Downunder.

I have long been impressed with the ability of the South American Basilisk lizard to run on water. There are plenty of videos of it on youtube, for example a short one here. 

It's pretty amazing. Looking at this video alone shows 2 important aspects of its locomotion: 

1. it's able to lift the whole body out of the water, and 
2. it's able to do so for quite long distances (around 10-15m). 

Some lizards' ability to run on water has been documented quite well by a series of papers by a group at Harvard University, particularly Tonia Hsieh. They've done some great work, including describing how smaller lizards are better able to support their body weight than are larger lizards, modelling 3D forces and recording 3D kinematics of the lizards' stride. Below is a gif showing some of the detailed kinematics of the lizard stride from George Lauders lab webpage. 

(NOTE: just click on the gifs if they are not running)

One other important point reported in these papers, based on the description given in Hsieh (2003), is it seems the lizards' kinematics change when running on water, such that the limb moves behind the hip, rather than being both in front and behind the hip.   

This is shown quite well in the gif above. So given this information on how Basilisk runs on water, we can then ask the question,  

Can the water dragon (Intellagama lesueurii) also run on water? 

I was led to believe it may be able to from two dominate and convincing lines of logic. 

1. they are water dragons! - it might behoove them to be able to do so and 
2. I heard reports of the juvenile lizard being observed doing so from a fellow researcher. 

So I modified the lizard racetrack which I have here at the University of Queensland, by placing a short, water-filled aquarium across the water dragons' path which they must cross to get to the other side. Then I sat back and filmed them using the fastec high speed camera system. And this is a typical (read: absolutely best) result below

Well the first thing I noticed is that they are no basilisk lizards. The body is not held out of the water and progress is significantly slowed. The first step seems hardly effective at all, and the second step is much deeper, and seems like a breaking step, with the foot held flat. However, the following step seem to have some similarity to those of the basilisk. From steps 3 onwards, the foot does not appear to be pushed as far forward, and much of the stroke seems to be posterior of the hip, as in basilisk. Secondly the trapped air bubbles on the foot are interesting, and these are also observed for basilisk, where they are thought to be the result of tiny fringes along the toes of the south american lizard. Such fringes however, are not obvious in the water dragons. Below is a snapshot of the bubble being dragged down on the trailing edge of the foot. 

So I'm unsure what to make of this all. It does look like they are capable of some run/swim locomotion, but it certainly falls short of the amazing prowess of the basilisk.

Here are some less impressive runs. Though notice that the right hind foot is actually brought out of the water - suggesting they could be using surface effects to give more downward force. 

And this one below shows a similar stroke. 

So that's as far as I've got. Let me know whether you think it is sufficiently interesting to warrant detailed kinematic analysis, or whether you think water dragons are just a little impaired when it comes to running on water. 

Finally, I leave you with what happens after several trials and the dragons know the water is coming up. It led me to believe, that for water dragons, they sure do not like water! 

The boldest gecko: personality in a reptile

Today on the blog we're happy to have former Wilson Honour's student, Rebecca Wheatley, who describes her thesis work on gecko personality. Rebecca's currently working as a research associate in the Wilson lab, and plans to start a PhD next year. You can find out more about Rebecca on her science blog, The Adventures of the Integrative Ecologist.

Animal behaviour is a big field - and it's constantly expanding as research reveals gaps in our understanding of why animals do the things they do. One topic in animal behaviour that holds a great deal of interest for me is that of animal personality. This is a relatively new concept and, frankly, it's a little bit controversial. 

The word "personality" conjures up a variety of mental images, most of which pertain to one animal in particular: us. It goes without saying that people have different personalities; we experience it every day. But do other animals have personalities as well?

Great tit (Parus major), beadlet sea anemone (Actinia equina) and pumpkinseed sunfish (Lepomis gibbosus); three species that display animal personality, from very different groups. Image source: Wikimedia commons.

In animal behaviour, the term "personality" is defined as consistent differences in behaviour displayed by individuals. An example of a personality trait is how an individual responds to a threatening situation, termed boldness or shyness. Bold individuals are undaunted by threatening situations and will approach the stimulus, while shy individuals will stay away or hide.

There are heaps of different personality traits that have been studied, including boldness, exploratory behaviour and aggression, amongst many others. Individuals' "personalities" are thought to range along a proactive-reactive continuum, where proactive individuals are aggressive and bold while reactive individuals are more passive and shy (sound familiar? It's not unlike a simplified version of the extroverted/introverted behaviour displayed by people).

There's growing evidence that "personality" is present within many groups of animals. Despite this, we don't really know much about what determines an animal's place along the proactive-reactive continuum or why this variation exists.

My study species: the Asian house gecko (Hemidactylus frenatus). Image credit: Wikimedia Commons (1 & 3) and Rebecca Wheatley (2).

During my honours project, I investigated "personality" in male Asian house geckos (Hemidactylus frenatus). I measured the anti-predator behaviour (a proxy for boldness) of 100 geckos by filming each gecko for one hour and then by calculating the proportion of time it spent inside the shelter in its terraruim. 

Each gecko was measured under three different treatments:

1. "empty terrarium": where nothing (aside from the shelter) was added to the terrarium, to give me a measure of each gecko’s normal amount of anti-predator behaviour
2. "terrarium with novel object": where I added a novel object to the terrarium, to see what happened to their anti-predator behaviour when something new was added to the environment
3. "terrarium with threatening stimulus": where I added a threatening stimulus, to see how their anti-predator behaviour changed when something scary was added to their environment

I found that different individuals reacted to the treatments in different ways, but the overall trend looked like this:

 

We can see that when a novel object was added to the environment, the geckos' anti-predator behaviour generally decreased when compared to their standard level of anti-predator behaviour. This might be because they wanted to check out the new object to make sure it wasn't food or some other valuable resource. 

However, when I added a threatening stimulus, their anti-predator behaviour jumped back up again to around the same as its standard level. So it seems that the threatening stimulus effectively cancelled out the novel object effect.

How do we know if these behaviours constitute as "personality"? Well, I found that while different individuals displayed consistent anti-predator behaviour within treatments, they also responded to the treatments in different ways. Some displayed more anti-predator behaviour when the environment was altered (were "shyer"), while others displayed less (were "bolder").  Therefore, from our definition, we can see that their anti-predator behaviour is a personality trait: they display consistent differences in behaviour that are context-specific.

Checking on my gecko housing set-up. Image credit: Amanda Niehaus.

But why do individuals have different personalities? Previous research has found that a few things can be associated with an animals' boldness or shyness. A large body mass is often associated with a bold personality, which is probably because heavier individuals are usually larger and more likely to win in a fight (so they have a good reason to be bold). Similarly, individuals with a hard bite force, a strong claw pinch or any other performance trait which would give them an advantage in a contest are usually bolder as well.  

The possession of traits that might make it easier for them to escape from a predator in a pinch, like fast running speed, have also been associated with boldness. In addition, resting (or "standard" for reptiles) metabolic rate has been linked to animal personality; it's thought that bolder, more aggressive individuals need a higher metabolic rate to keep up with their energetic demands.

I investigated how some of these traits interact to effect boldness in my geckos. I measured each gecko's mass, standard metabolic rate, maximum running speed and maximum bite force and analysed their interactive effects on anti-predator behaviour. Contrary to what I expected (and to what the literature would lead us to predict), I found that none of these traits affected anti-predator behaviour. This could be due to a few different things: one possibility is that boldness and shyness in Asian house geckos has a hormonal basis. It could also be that "personality" in geckos develops based on experiences rather than any specific physiological or performance trait. To discover the answer to this question, further research into the interactive effects of such traits on personality needs to be done.

One of my geckos in his metabolic chamber. I did all my metabolic tests during the day (when they are least active, being nocturnal animals) so I could get an accurate estimate of their resting (standard) metabolic rate. Image credit: Amanda Niehaus.

Anyway, why does it all matter – why does "personality" even exist? The fact is there are costs and benefits to being both proactive and reactive. Proactive individuals are bolder and more aggressive, so they are usually better at holding territories and getting laid – but they're also a lot more conspicuous to predators, so they tend to "live hard, die young". Reactive individuals, on the other hand, might not have the best real estate or as many mates at any given time, but their shy behaviour means they usually live longer. So, if we imagine an ecosystem where predation is low, it's better to be proactive and reap the benefits without the risk of being eaten. But if the ecosystem changes (for example, a bunch of predators move into the neighbourhood) and all the proactive guys die off – who is left? This is the most popular theory as to why different personalities exist; so that if conditions change quickly, some individuals survive and the population continues.

Although extremely interesting, these personality experiments were only one small aspect of my honours project, which aimed to answer questions about fighting ability (resource-holding potential) and fighting strategies. More on that later!

- by Rebecca Wheatley

Bit of a teaser for the rest of my project. Image credit: Amanda Niehaus.

What Determines Gecko Fighting Performance | An Honours Project by Rebecca Wheatley

This is Rebecca. She just submitted her Honours thesis, and is probably chilling with a vodka lemonade on a beach somewhere. | Or else she's wishing she was. |

A couple months ago, I asked Bec to describe her thesis - and to show me the experiments she had running. Here's what she said:

My research is using Asian house geckos as a model to answer questions about how morphology, performance, metabolic rate and personality interact to affect fighting ability in animals.

Gecko housing project

Rebecca's work is exciting because few studies have evaluated how morphology (or body size | shape), physiology, and personality work together to determine animal performance.

And can animals really have personalities? Of course, but not like you and I do. In the non-human world, personality can refer to repeatable differences in behaviour among individuals. For example, some individuals consistently tend to be shy, and others tend to be bold. Boldness | shyness is important for animals, as it can determine the likelihood of obtaining food or mates, or getting captured by predators.

When I caught up with Rebecca, she was measuring geckos' metabolism in purpose-designed jars, which were hooked up to specialised equipment that measures oxygen consumption. Oxygen consumption is one way that scientists assess metabolic rate in animals in the lab.

collecting data on gecko metabolism

Rebecca was also video recording interactions between randomised pairs of geckos. Asian house geckos are aggressive little lizards, and will sort out dominance via displays of their open mouths, biting, and | or chasing. In her thesis, Rebecca looked at which animals were likely to be dominant, and whether that depended on their metabolism, morphology, and | or personality. 

collecting data on gecko fighting

And what did she find? The oversimplified version is that bite force, body mass, and running speed were most important in determining gecko dominance. Big, fast, hard-biting geckos were likely to be winners. The surprising thing was that metabolism and boldness didn't seem related to fighting performance.

There's a lot more to Rebecca's research: she used all the information she collected on morphology | physiology | behaviour to test important ecological theories about how individuals should interact (known as game theories). But we'll talk more about that another time - we don't want to give away everything just yet.

Thank you Rebecca, for taking the time to share your honours work with us, and for being such a wonderful labmate!

written and photographed by Amanda Niehaus, PhD

Welcome to Our Newest PhD Students

The lab is getting bigger! Andrew Hunter {Chopper} and Ami Fadhillah Amir have just joined the lab to do their PhDs - Chopper on performance and Ami on conservation. Ami acquired a prestigious Malaysian scholarship for her work, so we don't know for sure if the following is applicable for her ... but for Chopper, at least, post-doc Sean Fitzgibbon put together a financial plan for his upcoming years of servitude:

"Chop, I have just looked at the conditions of your award and spoken with your accountant.

We offer the following:
Stipend $23,728 per annum (Tax-free) = $461/wk

Committed expenditure:
Mortgage $380/wk remainder $81
Utilities $28/wk remainder $53
Football subs $17/wk remainder $36
Groceries $23/wk remainder $13
Home brew $8/wk remainder $5

We suggest that you set-up a trust savings account to invest your weekly surplus income of $5. Based on my calculations, after your PhD you should be able to live off your savings (and interest - based conservatively on 6.2%) for approx. 2.1 days. This should really take the heat off when you are searching for a job post-hand-in

Welcome to the familia! Let me know if we can be of further assistance*." - S.F.

*this post is not meant to replace real financial planning and new PhD students should always consult a bona fide accountant for advice on saving vs. spending their income. If they can afford one.

Fieldwork, Groote Eylandt, NT

It was only a week ago we got back from Groote Eylandt. What a special place. Wild, and raw, and special. An island of contrasts, between a traditional culture and a modern mining industry. An island with a lot of crocodiles.

the GEMCO manganese mine

It was my first trip up, and Nelle came along. We met the Rangers and friends and family and Gavin and Kerry and the rest of the team and Alex-from-Stanford. We drank tea on the deck at the Ranger station, and packed up everything {but petrol} for a quoll-catching venture to the east side of the island. {Former labmate} Billy was appointed Ranger Coordinator. We learned our first Anindilyakwan words. We entertained Nelle, and learned the value of ABC for Kids downloads {and PhD students}.

On the deck with Jennifer and her niece; with Chopper; with MacBook Pro

We drove east to Umbakumba then headed into the bush on sandy tracks. We set up tents on top of a berm, feeling {relatively} safe from water-borne crocs and collected firewood from the beach. We watched a heavy moon pull itself up into the sky.

Picnic Beach, Groote Eylandt

Under Jaime's guidance, we set out traps for quolls, hoping to catch at least a few to obtain measurements and hair samples.

Jaime and Eddie set out, bait, and mark quoll traps

We caught 4. Plus a few bandicoots. It was good enough for Jaime to get her samples, and good enough for me - these were the first wild quolls I'd seen.

A quoll curled up in its very own, custom-made pillowcase

We were almost as successful catching fish ... the ocean here teems with them {apparently} but we didn't have much luck. Three fish only made it into our bellies.

That's ok. We had plenty of patience ... 

and potatoes. 

fishing for dinner

- written by Amanda Niehaus

Groote Eylandt, August 2012

Leaving Darwin, the propellers outside hummed loudly (reassuringly). We pressed our noses to the windows, looked out on the wild top coast of Australia. The fires lit by thousands of years of tradition. And then, we were there. Over the mines, into the red dirt.

Groote Eylandt.

Crabs will fake it to avoid a fight

Crabs will fake it to avoid a fight, research finds

Dr Robbie Wilson, Head of the Performance Lab at UQ, where this study was conducted, said the research identified more than just some crabby behaviour.

“This study is important because it reveals the general principles behind how liars and cheats are controlled and encouraged in nature.

“Whether it's a soccer player diving to fool a referee or a crab trying to intimidate a rival with weak claws, our lab has shown that individuals cheat more when their deception is likely to go undetected,” Dr Wilson said.

Ms Candice Bywater who is finishing her PhD on fiddler crabs, said that she found that more males bluff their way through fights when they are less likely to get caught.

photo by D. Hancox

“When there are lots of crabs living in one area, there is lots of competition for resources like females and food. High competition means there is a greater chance of males having to fight each other to win resources compared to when there are not many crabs about. Those crabs might not have to fight at all,” Ms Bywater said.

“Crabs that have strong claws will generally win fights. Producing large and strong claws is important to their survival.

“Where crabs are likely to have to fight a lot, the crabs are producing large, strong, reliable claws. We found that when there are not many other male crabs in a population (low competition), males produce large but relatively weak claws (unreliable), as they don't have to fight as often and ultimately because can get away with it."

In nature, signals may be behavioural, as in growling or posturing, but are often structural, including the antlers of a deer, and the enlarged fore-claw of many crustaceans.

A male that overstates his quality could improve his ability to gain food or mates, but surprisingly, most signals are honest reflections of a male's prowess.

Media contact: Dr Robbie Wilson, School of Biological Sciences, E: r.wilson@uq.edu.au, mobile: 0458 204 962; Performance Lab: http://www.wilsonperformancelab.com/ 

Bywater, C & Wilson RS. 2012. Is honesty the best policy? Testing signal reliability in fiddler crabs when receiver-dependent costs are high. Functional Ecology.

David GK, Condon CK, Bywater CL, Ortiz-Barrientos D & Wilson RS. 2011. Receivers limit the prevalence of deception in humans: Evidence from diving behaviour in humans. PLoS ONE 6(10): e26017 http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0026017

Written by UQ Media

How to fight dirty

If you're a crayfish, your best bet is probably to grow an intimidatingly-large claw ...

but pack the muscle (i.e. punch) into the other claw.

Many animals - like crayfish - signal their fighting prowess by displaying specialized limbs, musculature, or weaponry to others. In signaling, bigger is often better; but in a fight, rivals could gain advantage by concealing their real strength in less conspicuous limbs.  

Cryptic asymmetry occurs when differences in limb strength are unrelated to differences in limb size, and was previously considered only in primates; however, we found asymmetric strength in males of the slender crayfish, which use their claws in display and combat. 

In a paper just published in Biology Letters, Robbie and collaborator Mike Angilletta suggest that asymmetric strength could be used to confuse rivals and influence the outcome of fights.

(look over here ... look over here ... )

 WHAM.

Big News at the Moment - Feb 2012

1. Robbie got his 69th publication, and for some reason thought that was funny.

2. Candice returned from the US, jet-lagged and culture-shocked. We've missed her.

3. Billy's still ... somewhere?

4. Jaime's officially started her PhD, and taken up the last desk in the Fun Zone.

5. Another of Candice's PhD papers just got accepted for publication! This one's:
Bywater, C & Wilson RS. 2012. Is honesty the best policy? Testing signal reliability in fiddler crabs when receiver-dependent costs are high. Functional Ecology (in press Feb 2012)

6.  Robbie decided it was time to get married. To me.

And that's February, 2012!

The Scent of a Predator (Well, Kind of)

The following article is adapted from a talk presented by Jaime Heiniger at SICB 2012, along with coauthors Billy Van Uitregt and Robbie Wilson. The original talk was called: "Fine tuning anti-predator responses: are the costs of inducible predator defences proportional to the magnitude of the responses?"

***

For amphibians, it's a mad, mad world. And - importantly - an unpredictable one. Natal pools might contain predators, or not; competitors, or not; food, or not; and conditions can change every day. As a result of all this unpredictability, many amphibians can alter their appearance and behaviour in ways that increase their likelihood of survival. But these defensive strategies usually come at a cost - slower growth, higher metabolic requirements, and smaller size at maturation are just a few common outcomes.

toadlets in the lab

To maximise the benefits and minimise the costs associated with predator defense, it's predicted that the magnitude of the defensive response should reflect the magnitude of the threat. Thus, more threat = more phenotypic change; and less threat = less phenotypic change. This is known as the threat-sensitive predator avoidance hypothesis (TSPAH), and although it's known that prey can fine-tune their responses to the degree of predation risk, it's unclear if the magnitude of threat-sensitive defensive responses relate to their associated costs.

{Jaime} tested this idea by examining the effects of increases in perceived predation risk on the expression of defences and their associated costs in larvae of the toad, Bufo marinus. She reared tadpoles in varying concentrations of predation cue* and quantified their growth, morphology and development, as well as metamorphic size, locomotor performance and oxygen consumption.

*for those curious, predation cue is actually water from around deceased tadpoles. Tadpoles are sensitive to the smell of their dead mates. (Aren't we all?)

taddies in the lab

{Jaime} found that tadpoles responded to increases in perceived predation risk by gradually decreasing their activity.

As a consequence of their more-sedentary lifestyle, individuals metamorphosed later, smaller and with reduced endurance. Toads that emerged from the different treatments didn't vary in maximum jumping distance but those from 'high predation' treatments metamorphosed with longer relative hind limbs - meaning they could jump farther for their body size.

jaime's metamorph habitats

 These are interesting results, because they show that
a) toads produce defenses that are proportional to the perceived threat
b) defensive behaviour is costly
c) the costs are in proportion to the amount of defense
d) but phenotypes produced in response to predation threat may aid the individual.

Cool stuff, Jaime!

Why Be Fake? Because Honesty is Too Expensive ...

In earlier posts, we've talked about the life of a crab ... and about the predisposition for some crabs to fake how strong they are. At SICB in January, Candice presented a talk detailing why exactly it pays to be weak.

image by Dan Hancox

Here's my recap on Candice's talk ...
Crustaceans are violent types, posturing and fighting for territories, mating partners, and resources. Because claws are such excellent weapons, fights are often decided by the individuals merely checking each others' claws out. Bigger claws = dominance. This ameliorates the risks associated with claw-battle, while still deciding dominance.

But Candice has found that the size of the claw is not always indicative of its strength - namely, some individuals are fakers. You see, claw muscles - which are used to clamp and tear in a fight situation - are hidden inside the chitinous claw. So a big-clawed crustacean might just lack big muscles underneath, meaning it's more likely to lose if the interaction escalates into a fight.

So why wouldn't a crustacean just grow the muscle? This is what Candice wondered. She noticed that crabs with re-generated claws tended to have wimpy claws, relative to their claw size. So, she measured the energy needed to maintain claw muscles in fiddler crabs with strong, original claws as well as crabs with weak, regenerated claws.

 

Candice believes that dishonesty in fiddler crabs is related to metabolic costs - namely, how much energy is required to keep that muscle active. Crabs with strong, original claws spent ~22% of their metabolic energy budget on their claw muscle - pretty close to the amount of metabolic energy humans use to support our large glucose-hungry brains.

In contrast, crabs with weak, re-generated claws used only ~12% of their daily energy on claw muscle.

That constitutes a massive energetic savings for fakers, unless they get caught ...