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.

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

Trade-offs in Gecko Design

Sounds glam, right? Gecko design?

At the 2012 SICB in Charleston, Skye presented research that shows how traits that improve bite force in geckos have negative impacts on the gecko's sprint speed. Meaning that males who are better fighters might also be less adept at escaping predators ...

Costly design indeed.

Let's learn more by having a look at Skye's abstract, with {comments in brackets from me}.

Trade-offs and compensatory traits: bite force and sprint speed pose conflicting demands on the design of male geckos (Hemidactylus frenatus)
by Skye Cameron, Melissa Wynn and Robbie Wilson

The evolution of exaggerated ornaments and armaments is driven by the benefits accrued to reproductive success and by the costs imposed on viability. {This means that} when traits are required to perform multiple functions that are important to both reproduction and viability, trade-offs can result in a compromised phenotype.

{Imagine, for example, a species of bird in which females are more likely to mate with males that have larger tails; but males with larger tails are more likely to be captured by predators. Both reproductive potential and survival are important to the male - so evolutionarily, the bird may end up compromising on tail length to make sure he both reproduces and survives.}


{Intuitively, we expect that exaggerated male traits (like super-long tails) would decrease locomotor capacity, resulting in lower survival rates due to predation.} Despite only mixed empirical support for such locomotor costs, recent studies suggest these costs may be masked as a result of the evolution of compensatory mechanisms that offset any detrimental effects.

{What are compensatory mechanisms? Imagine if that bird with the long tail-feathers developed longer wings, that enhanced its flying abilities. It might offset some of the survival costs of the long tail.}

In this study, {Skye} provides a comprehensive assessment of the importance of potential locomotor costs that are associated with improved male-male competitive ability by simultaneously testing for locomotor trade-offs and compensatory mechanisms. For males of the Asian house gecko (Hemidactylus frenatus), both fighting capacity and escape performance are likely to place conflicting demands on an individual’s phenotype.

Males that are highly territorial and aggressive are more likely to require greater investment in jaw size/strength in order to compete with rival males; {Skye} found that males with larger heads had stronger bites and showed greater prey-capture and fighting capacity. This performance trade-off was amplified for male geckoes with larger heads when {they were} sprinting up inclines.

{So, what does this mean? Geckoes with large heads are better at fighting and better at capturing prey, but may be worse at evading predators themselves. A compensatory mechanism would be something - like longer legs - that would enhance their ability to avoid predation.} {However, Skye} found little evidence for compensatory mechanisms that off-set the functional trade-off between bite force and sprint speed.

Ongoing work in this area includes testing the survival of male geckoes with different sized heads in controlled-but-natural conditions.

Bigger *is* Better: Phallus size and male physical performance across temperatures

The second presentation we'll discuss is Robbie's. Robbie's talk - though sadly fraught with technological difficulties - conveyed to the audience the answer to that age-old question:
does a bigger phallus actually mean the male is better?

I won't give away the ending just yet, (or maybe I will ... ) - in mosquitofish, anyway - the answer seems to be yes.

Bigger is Better in all environments: temperature-induced variation in phallus size is a reliable indicator of male physical performance and gamete quality

Males of many organisms possess elaborated structures that are used to engage in fights with other males and/or to attract females during courtship. The size and elaboration of these secondary sexual traits can be affected by the environment via its influence on the condition of an individual male. This link between male condition and the elaboration of male sexual signals is one of the most important mechanisms maintaining the reliability of these traits as signals of male quality.

male elk use extravagant antlers to battle for females

The role temperature plays in mediating the condition of individual males and the size and elaboration of their sexually selected traits is currently unknown. Males of the eastern mosquitofish (Gambusia holbrooki) possess a modified anal-fin phallus (gonopodium) that is used as both a signal of dominance and a stabbing weapon during male-male competitive bouts {as well as to fertilise females}.


{Robbie} examined the effect of temperature on the size of this putative sexual signal (phallus size) by chronically exposing males to either 20° or 30°C for four weeks. {He} also tested the influence of these thermal environments on various measures of male quality; including male territorial performance, swim speed and gamete function.

Males chronically exposed to 30°C possessed longer phalluses, greater ejaculate sizes, larger testes and faster sperm swimming speeds than those exposed to 20°C. This is the first study to show that environmental variation in phallus size can be a reliable indicator of male physical performance and gamete quality.

{And what does this mean, and why does it matter? Well, it means that mosquitofish may have higher reproductive outputs in warmer environments, and might do even better than they currently do when climates warm further. In Australia, mosquitofish are invasive and by out-competing and eating eggs and young of natives, they are aiding the decline of native fish populations.}

Not good. Who knew that global warming would increase phallus sizes ...

A Little Bit About Our Research on Performance

The basis of our lab's research is performance - performance of animals, including humans, in the context of their biotic or abiotic environments. We're interested in trade-offs between traits such as speed and endurance; the ways that changes in temperature or oxygen levels or life stages affect performance; and - in the case of sport - we're interested in optimising performance levels.

Currently, we're looking at projects such as:

1. Skill, balance, and athleticism in soccer performance (humans)

See the following posts for more detail:
Research and Innovation in Soccer (on our soccer website)
Measuring Individual Performance in a Team Context (on our soccer website)
The Importance of Effective Receiving and Passing (on our soccer website)
Assessment of Receiving and Passing Skills (on our soccer website)


 2. Weapon strength in signalling animals (crustaceans, lizards)

See the following publications for more details:
Wilson RS, James RS, Bywater C, Seebacher F. 2009. Costs and benefits of increased weapon size differ between sexes of the slender crayfish, Cherax dispar. Journal of Experimental Biology 212:853-858. View abstract here.

Seebacher F & Wilson RS. 2007. Individual recognition in crayfish (Cherax dispar): the roles of strength and experience in deciding aggressive encounters. Biology Letters 3:471-474. View abstract here. 

Seebacher F & Wilson RS. 2006. Fighting fit: Thermal plasticity of metabolic function and fighting success in the crayfish Cherax destructor. Functional Ecology 20: 1045-1053. View abstract here. 

crustaceans fighting to establish dominance

3. Tradeoffs in locomotor performance (fish, crustaceans, amphibians, insects, humans)

See the following publications for more details:
Angilletta MJ, Wilson RS, Niehaus AC & Ribiero P. 2008. The fast and the fractalous: tradeoffs between running speed and manoeuvrability in leaf-cutter ants. Functional Ecology 22:78-83. View abstract here.

James RS & Wilson RS. 2008. Explosive jumping: Morphological and physiological specialisations for extreme jumping in Australian rocket frogs. Physiological and Biochemical Zoology 81:176-185. View abstract here.

Wilson RS & James RS. 2004. Constraints on muscular performance: trade-offs between power output and fatigue-resistance in skeletal muscle. Proceedings of the Royal Society of London B 271: S222-S225.

Van Damme R, Wilson RS, Van Hooydonck B, & Aerts P. 2002. Performance constraints in decathletes. Nature 415:755-756. View abstract here.
do a male threadfin rainbowfish's streamers affect his swimming?

4. The myriad ways that the abiotic environment (i.e. temperature, pH, UV radiation, oxygen levels, etc) or the biotic environment (i.e. competitors, predators, etc) influences performance (frogs, fish, crustaceans, lizards)
See the following posts for more detail:
Run Gecko Run
Measuring Toad Jumps
Studying Mosquitofish in the South of France

And the following selected publications:
Wilson RS, Lefrancois C, Domenici P & Johnston IA. 2010. Environmental influences on unsteady swimming behaviour: consequences for predator-prey and mating encounters in teleosts In Fish Locomotion: An eco-ethological perspective (Eds Domenici, P & Kapoor, BG). Science Publishers, NH, USA. 

Barth B & Wilson RS. 2010. Life in Acid: interactive effects of pH and natural organic acids on growth, development and locomotor performance of larval striped marsh frogs (Limnodynastes peronii). Journal of Experimental Biology 213: 1293-1300. View full text here.

Condon CHL & Wilson RS. 2006. Effect of thermal acclimation on female resistance to forced matings in the eastern mosquito fish. Animal Behaviour 72: 585-593. View abstract here.

Wilson RS. 2005. Temperature influences swimming and sneaky-mating performance of male mosquitofish Gambusia holbrooki. Animal Behaviour 70:1387-1394. 

Billy measures jumping performance in a toad metamorph