When it comes to wooing the ladies in a crowded room evolutionary biologists at The University of Western Australia have found that tough guys trade their combat capability for speed.
The study lead by Dr Joseph Tomkins focussed on a mite Rhizoglyphus echinopus that has two different types of male - ‘fighters' which posses weapons that are used to kill their rivals and ‘scramblers' which are incapable of harming each other.
Over ten generations, some populations lived in empty Petri dishes representing a simple habitat while others lived in a dish forested with drinking straws. The team then looked at how the two alternative male types evolved over time.
When it comes to securing a mate, fighter males have the advantage of their thick spiked legs and can kill their rivals but they suffer in a complex environment because they are less mobile. Scrambler males are more nimble though, and put this to their advantage -outclassing their bulky rivals in the complex world.
Dr Tomkins and his team, including researchers from the United States and Poland, found that the generations produced in the crowded 3D habitats produced fewer fighters such that only the very largest mites became fighters.
"What's neat is that we were able to construct these different habitats and then let evolution take its course. With these mites, we can watch as evolution happens in real time," Dr Tomkins said.
"Evolutionary theory predicts that the decreased fitness of the fighters should lead to a decline in their frequency over evolutionary time; and this is what we saw.
"What happened in the 3D environment is that the mobility of fighter males decreased limiting their access to females and reducing the advantages of that body type.
"Our results show how important the three dimensional environment can be to evolutionary outcomes, few studies have been able to manipulate this as we have done," Dr Tomkins said.
The results of the report Habitat Complexity Drives Experimental Evolution of a Conditionally Expressed Secondary Sexual Trait have been published in Current Biology.