Single Wild Female
The release of a single female guppy into the wild can generate entire new populations, even with no males present, according to research by Dr Amy Deacon and Professor Anne Magurran of the Biodiversity and Behaviour Research group, in collaboration with Professor Indar Ramnarine of The University of the West Indies, Trinidad.
The study, which is published in PLoS ONE and funded by the Natural Environment Research Council and the European Research Council, reveals how the apparently harmless release of guppies into the wild has led to the fish being found in every continent with the exception of Antarctica. The guppy, whose native home is Trinidad and the north-eastern fringe of South America, is now present in over 70 countries worldwide. Since a single female guppy can establish a viable new population, this demonstrates that even well-intentioned releases of discarded pets can contribute to the loss of biological diversity.
We began by surveying hundreds of fish biologists around the world. Responses confirmed that the two most important routes of guppies finding their way into the wild are the escapes of ornamental fish, and deliberate introductions designed to control the larvae of mosquitoes that spread malaria.
In places such as Southern India, guppies are routinely released into water troughs, wells and small ponds for mosquito control. Although self-contained at first, heavy rains and flooding mean that the fish eventually find their way to streams and rivers where they come into contact with native fish.
Often only one or a few fish are released in these situations, and 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.
To try to solve this mystery, we conducted a simple experiment, in which single wild female guppies were placed into outdoor tanks. After two years, we discovered that almost all of the tanks contained populations of guppies, each founded by just one female.
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. Sperm storage is an excellent adaptation for living in constantly changing habitats, and it might also explain the guppies’ global success.
The study also found the tank populations kept all of the important behaviours that wild guppies have, so they would be well-equipped for surviving in a new environment.
Our study emphasises why we should always be cautious when releasing exotic species – and especially live-bearing fish. Seemingly harmless activities such as a child freeing a few pet fish or a concerned householder using guppies to control mosquitoes, can ultimately contribute to the reduction of biodiversity in freshwater habitats across the world.
Citation: Deacon AE, Ramnarine IW, Magurran AE (2011)How Reproductive Ecology Contributes to the Spread of a Globally Invasive Fish.PLoS ONE6(9):e24416.doi:10.1371/journal.pone.0024416