Size does matter!

The larger or bigger you are, the easier it is to drive away other suitors and win your mate, says new study.

Size does matter when it comes to choosing and inviting your mate as the larger or bigger you are, the easier it is to drive away other suitors and win your mate.

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A new study conducted by scientists at the Universities of Bath, Oxford and East Anglia, has explained the reason behind the rule,identified over forty years ago by German scientist Bernhard Rensch, for the first time.

Rensch's rule states that the ratio between the sizes of the sexes is related to body size with very few exceptions throughout the animal kingdom.

Sexual selection is the key factor that drives the Rencsh's rule and this research explains how exactly it works.

In this new research, the scientists carried out statistical analyses of the mating behaviour, body size and ecology of more than 100 different shorebird species from around the world.

The researchers found that where there was high competition between males, the difference in the ratio between the sizes of the sexes increases, explaining the changing ratios identified by Rensch. In contrast, in species with low intensity of competition amongst males, females tend to be the larger of the sexes.

For example, it was found that in the larger shorebirds the battle between males for a mate is highly competitive and larger size offers an advantage over other potential suitors as they battle aggressively on the ground. The evolutionary result is that male Ruffs, a large shorebird, are about twice the size of females.

"We have known about Rensch's rule for many years but didn't have a clue what drives it. Many biologists had considered sexual selection to be the most likely answer, but nobody really knew how," Dr Tamas Szekely from the University of Bath who led the project, said.

"Once we started analysing the data the story shaped up perfectly. I believe that sexual selection is the driver behind Rensch's rule throughout the animal kingdom and we are already finding this is the case in other bird species we are studying such as Bustards.There's no reason why it would not apply in many other animals from gorillas living on the rainforest floor to monkeys living high up in the canopy too," he added.