FISH who have a number of partners during mating may still be able to colonise if they curtail their rampant sexual habits, a new study has found.

Researchers at St Andrews University have made the surprise discovery that restricting a normally multiply mating fish to monogamy does not impair their colonisation ability.

The findings show releasing just one or two fish into the wild may be enough to trigger an aquatic invasion.

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They tested whether forcing female guppies to be monogamous would impede their ability to establish viable populations.

The guppy (Poecilia reticulata) is a successful invasive species throughout the tropics. In the wild it employs a 'multiple mating' strategy, and resulting broods commonly contain offspring sired by up to five different fathers.

Previous studies have shown that mating with multiple partners carries a range of benefits, including increased genetic and phenotypic diversity of offspring, and inbreeding avoidance -which are potentially advantageous for a species attempting to colonise a new environment.

The latest paper found female guppies were either allowed to mate with four males, or were restricted to one partner. Pregnant females were then left to establish populations in large tanks in the laboratory. After one year, the two treatments were compared.

Dr Amy Deacon, one of the researchers, said: "One of our key findings was that mating history did not predict establishment success, which was 88 per cent in both treatments".

The researchers had expected that inbreeding depression might be evident in the behaviour of fish in the monogamous treatment, which would suggest that their ability to persist once established could be limited. However, newborn and adult male offspring of both treatments were equally good at avoiding predators and at courting females.

The research paper is published in the journal BMC Ecology.