A century old mystery as to why, for some animals, it's the father rather than the mother that takes care of their young has been cracked by researchers at the University of Sheffield.
A study carried out by a Marie Curie fellow, Andras Liker, has helped shed light on why shorebirds reverse the roles of the sexes, with males carrying out the parental duties.
The study, made by the University of Sheffield in collaboration with the University of Bath (both in the UK) and the University of Veszprém (in Hungary), reports that an imbalance between the number of males and females triggers the change - the switch occurs when there is a higher ratio of males to females.
"Sex role reversal has been a formidable puzzle for evolutionary biologists ever since Darwin. Our study is the first supporting the idea that sex ratio plays an important part in the evolution of role reversal," says Andras Liker.
Females in the sex role reversed species also take on the traditional male role of being bigger and compete with each other for males.
The story has been featured in Nature Communications and the BBC.