Big, strong males have the best chances of mating and reproducing – or do they? Puny male fish called desert gobies, which, despite their small size, are always ready to pick a fight, are helping to refine the Darwinian thinking that shaped the scientific principles of sexual selection in evolution.
“The small goby might have a chance of getting the girl after all,” says biologist Dr Bob Wong from Monash University, an expert in behavioural and evolutionary ecology.
The tiny Australian desert goby, Chlamydogobius eremius, uses bluff – a high-aggression strategy – to dispatch larger rivals that might otherwise take over its territory.
Dr Wong says this high-aggression strategy may cause would-be challengers to retreat before they can properly size up their opponent or evaluate the territory at stake. This hinders their ability to calculate the probability of defeat (and thus survival) before fighting.
Working with researchers in Sweden and Finland, Dr Wong found that small males attack intruders sooner and with greater intensity than larger ones, regardless of the other male’s size.
Charles Darwin thought the two main processes of sexual selection – male competition and female mate choice – worked in unison. For example, the horns of mountain sheep are used to seduce females as well as to fight rivals.
Dr Wong says the common assumption has been that females should prefer, as Darwin stated, “the most vigorous and well-armed” males. In other words, females want large, dominant males that are better at beating up rivals.
But the goby research is showing that intimidation can enhance a smaller male’s reproductive opportunities by allowing him to avoid fights he is likely to lose. This opens up the intriguing prospect that this may also be the case for other animal species. Already, scientists have found a jumping spider and a freshwater swordtail fish that use goby-like bluffing to hold their ground against larger males.
Dr Wong says this shows that females do not necessarily prefer males that are dominant because they are big. In fact, large males could prevent females from gaining access to a preferred partner – perhaps one of the smaller male gobies that other studies indicate also make better dads.
