Guppy love and the origin of species

Cute, wide-eyed and unobtrusive, the guppy is the nation's favourite pet fish - but behind this innocent exterior lies an animal with a torrid and tangled sex life, according to a team of researchers from University of St Andrews.

The researchers are studying Trinidadian guppies because they are in the process of splitting into two new species. The guppies have been divided into two groups that have been living in separate Trinidad river systems for about two million years – but the team have been introducing males and females from the different populations in the laboratory to gain an insight into how reproductive isolation develops.

And during their research the team, led by Professor Anne Magurran of the University's School of Biology, have discovered a web of sexual conflict, interbreeding, sneaky mating behaviour and sperm competition.

Using methods similar to those adopted in human DNA fingerprinting, the research team are hoping for insights into how the 'battle of the sexes' influences evolution. Although scientists have developed many theories about species formation, they have only recently had tools, such as DNA fingerprinting, to test them.

"It really goes back to Darwin and his ideas about how species arise," said Professor Anne Magurran, who leads the group.

"One possibility is that female guppies prefer to mate with native males. If animals always mate within their own group reproductive isolation is very quickly established. Male guppies charm females with a courtship dance, and a female will usually pick several of them to father her offspring. Her aim is to ensure that her babies have the best genes possible. But we found that females do not have it all their own way. Wily males often creep up behind unsuspecting females and quickly mate with them by surprise," said Professor Magurran.

"This sneaky mating tactic means that there are many matings between the two groups of guppies and probably counteracts the effect of female choice on reproductive isolation.

"Some experts estimate that as many as three species in the world become extinct every hour. The fact that the emergence of new species is a slow and complex process emphasises the importance of conserving those that already exist on Earth," Professor Magurran said.

The team's findings, 'Guppy love: sex and speciation', will be on show at the Royal Society's Summer Science Exhibition which begins next week (Tuesday 1st July - Thursday 3rd July, 2003).

(GMcG)