Guppy love

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 team led by Professor Anne Magurran of the University’s School of Biology, are investigating the sexual behaviour of the Trinidadian guppy and have discovered a web of sexual conflict, interbreeding, sneaky mating behaviour and sperm competition. Using methods similar to those adopted in human DNA fingerprinting, they are gaining insights into how the ‘battle of the sexes’ influences evolution.

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). They are studying the guppy’s fascinating mating behaviour because it can help answer one of the biggest mysteries in biology: how do new species form?

‘It really goes back to Darwin and his ideas about how species arise,’ says Professor Anne Magurran, who leads the group. Although scientists have developed many theories about species formation, they have only recently had tools, such as DNA fingerprinting, to test them.

The definition of a species is a group of creatures that can breed with each other, but not with others, even if they look similar. This inability to mix, called ‘reproductive isolation’ is the key to understanding how life evolved to give us the vast diversity of creatures we see today.

Professor Magurran and her colleagues (Dr Anna Ludlow, Dr Alfredo Ojanguren and Mr Stephen Russell), are studying Trinidadian guppies because they are in the process of splitting into two new species. The guppies are divided into two groups that have been living in separate river systems for about 2 million years. A fish native to one river drainage never normally meets a foreign fish from the other drainage, but Professor Magurran and her team have been introducing males and females from the different populations in the laboratory to gain an insight into how reproductive isolation develops.

“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.

“Studies on fruit flies show that sperm from the females’ own species outcompete sperm from other species at fertilisation. This is one of the ways in which species can become reproductively isolated,” she continued.

“We are asking if the same form of sperm competition occurs in guppies”.

To test this idea, the team impregnated females with equal numbers of sperm taken from a native and a foreign male. They are now performing DNA fingerprint tests – similar to those used in paternity tests in people – on the baby fish to find out who the father is; the first results indicate that native males do sire more of a female’s offspring.

The final test conducted by the St Andrews team examines the reproductive success of the offspring produced when foreign males and native females mate. They are finding that hybrid offspring are worse at reproducing than offspring produced by parents from the same group of guppies.

“These unfit offspring are another bar to interbreeding, and it seems that this mechanism is evolving simultaneously with sperm selection to cause reproductive isolation. The slow rate at which new species, such as these guppies, are formed contrasts with the rapid rate at which species are being lost as a result of human impacts on the environment.

“Some experts estimate that as many as 3 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,” said Professor Magurran.

Information on the exhibit ‘Guppy love: sex and speciation’ is available online at: www.sc1.ac.uk/discover/2003ex18.cfm

For more information about the Royal Society’s Summer Science Exhibition, call 020 7451 2574 or visit their website at www.royalsoc.ac.uk or www.sc1.ac.uk

ENDS

NOTES TO EDITORS:

PROFESSOR MAGURRAN IS AVAILABLE FOR INTERVIEW TODAY – TELEPHONE 01334 463506 / 463441 OR EMAIL [email protected]

For further information on the Summer Science Exhibition, contact: The Royal Society’s Press and Public Relations Officer, Tim Watson, on Tel: 020 7451 2508 or email [email protected]

NOTE TO PICTURE EDITORS:

CLOSE-UP IMAGES OF GUPPIES, IMAGES OF THE TRINIDADIAN SITE AND THE RESEARCH TEAM ARE AVAILABLE UPON REQUEST BY EMAIL – PLEASE CONTACT GAYLE COOK (CONTACT DETAILS BELOW)

Issued by Beattie Media On behalf of the University of St Andrews Contact Gayle Cook on 01334 467227, mobile 07900 050103, or email [email protected] Ref: guppy love pr 200603 View the latest University news at http://www.st-andrews.ac.uk