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}.

image

{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 ...

Death After Sex in the Australian Bush

Charleston wasn't just about pizza and beer, though with any scientific conference that's always a part of it ...

First up, we'll hear about Jaime's poster. Jaime did a 1st class honours degree in the lab, studying the way Rhinella marinus (cane toad) tadpoles respond to the presence of predators in their environment. But that's not what she was presenting here ... Jaime also recently was accepted into the PhD program at UQ to study quolls on Groote Eylandt, and she was keen to get the word out there about her new study system.

Now.

More about quolls and sex and the bush, as conveyed by Jaime and her co-authors on the poster, Robbie and Billy {with clarifications from me along the way}

image by Candice Bywater

Death after Sex in the Australian Bush: determinants of survival and reproduction in males of the world’s largest semelparous* mammal {*meaning they die after breeding!}

The northern quoll (Dasyurus hallucatus) is a medium-sized (approx. 1 kg) predatory marsupial previously common across the entire top-end of Australia. This species is the largest known semelparous mammal in the world, which means mating is highly synchronous, males live for only one year, and males undergo total die-offs soon after the mating season.

Such population-wide male die-offs are presumably due to the physiological stress of procuring copulations and the intense fighting among males. A small proportion of females will survive to produce a second litter, but there are no documented cases of survival to a third breeding season. The young are born after a short gestation period and then carried in a rudimentary pouch for approximately 60-70 days.

Females will then leave young in dens while they forage, returning to suckle until young are independent at 4 – 5 months. Both sexes are solitary throughout the year with a home range averaging 35 ha for females and approximately 100 ha for males during the breeding season but varies greatly between individuals.

During {Jaime's} study, {she} will be investigating the morphological and performance determinants of both survival to reproductive-age and fecundity among males of this species on Groote Eylandt, an Indigenous-managed island off the coast of the Northern Territory. Northern quolls are still highly abundant on this island and this population offers a unique opportunity to understand the evolution of this extreme mating system and the role physical performance plays in the reproductive success of males.

We can't wait to hear more!

Our Collaborators

We've just added a new page that highlights some of our lab's key collaborators - with links to their webpages and information about what they do, this is a great resource for anyone interested in being part of our research group! Check it out here.

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