Females range in size more than males

By Aaron Hall, EEB

Why do closely related species vary so much in size? This is the question on the lips of evolutionary biologists Stephen De Lisle and Locke Rowe from University of Toronto.

The team compared the body size of  over a thousand species of amphibians, from the centimetre long Brazilian Flea Frog to the half meter long Cayenne Caecillian. Based on previous findings, they expected that males would show more variation in body size than females. Their work, published in The American Naturalist, instead shows that when looking at families of amphibians, females are more variable in body size than males.  This is particularly true when one sex is much larger than the other across the entire family.

Why females show more variation in size isn’t fully worked out.  But the researchers think that these findings could allow a species to occupy new habitats and eventually evolve into many new species.