'Plenty of fish' effect down to single wild females, say scientists
A joint study involving the University of St Andrews discovers the secret behind guppy fish's reproductive success.
Scientists have discovered that an invasive species of tropical fish can colonise whole stretches of water with just one female specimen.
The guppy's prodigious ability to reproduce has led to a dramatic increase in its numbers over the last century, and it is now found in every continent except Antarctica.
Biologists at the University of St Andrews and the University of the West Indies believe the secret lies in the females' ability to store sperm for months.
They conducted an experiment in which single wild female guppies were placed in outdoor tanks. After two years, almost all the tanks contained guppy populations.
The researchers said tropical fish owners should be aware of the findings, as releasing the fish into waters where there is no guppy population could upset the ecosystem.
The popular ornamental fish, whose native home is Trinidad and the north-eastern fringe of South America, can now be found in more than 70 countries.
In places such as southern India, guppies are routinely released into water troughs, wells and small ponds for mosquito control. Heavy rains and flooding mean that the fish can find their way to streams and rivers, where they come into contact with native fish.
The lead researcher at St Andrews, Dr Amy Deacon, said: "Our findings show that the guppy's range has expanded dramatically since the early 1900s.
"Usually only one or a few fish are released. We know that the vast majority of species introduced to a new habitat in this way are unable to survive, let alone establish a population, which left us with a huge question mark.
"Sperm storage is an excellent adaptation for living in constantly changing habitats, and it might also explain the guppies' global success. Female guppies can store sperm in their reproductive tracts for many months after mating, and this enables single fish to establish populations even when no males are present.
"We also found that these populations kept all of the important behaviours that wild guppies have, so they would be well-equipped for surviving in a new environment."
The research, funded by the Natural Environment Research Council and the European Research Council, is published in the journal PLoS ONE.