A male gambusia. Image: Bart Adriaenssens
A noxious fish species could benefit from increasing temperatures.
Gambusia are native to Southeastern US, but have been deliberately released in Australia and Europe in an attempt to control mosquito larvae. Like many other introduced pest-control species, they have become a notorious pest, preying on the eggs and larvae of other species and competing with them for resources.
“Gambusia are relatively small, but due to their high reproductive performance they quickly outcompete native species in numbers,” University of New South Wales scientist Dr Bart Adriaenssens says. “It is therefore not surprising that many countries at this moment rank them amongst the most noxious freshwater pests and several states in Australia put high fines on the release or import of gambusia.”
Adriaenssens and his colleagues are now warning that the environmental impacts from these fish may become worse if temperatures increase. In a new study published in Global Change Biology, they demonstrated that the male gambusia exposed to higher water temperatures have three times more sperm than those exposed to colder temperatures.
The scientists studied the sperm cells because there is very little known about how temperature affects sperm function within species that do not regulate their body temperatures. They anticipated that temperature would have an effect on gambusia sperm performance, as higher temperatures often cause damage to these cells.
When they analysed the sperm, however, they found that the warm-water sperm were not only more numerous, they also had faster swimming speeds. “In the population we studied it does not appear that water temperatures currently reach high enough to cause harm to the sperm,” Adriaenssens says. “Rather the opposite.”
He says that based on what scientists know about this species, it is very likely that that increasing temperatures will increase their reproductive capacity. “The exact future impact of this on native species is difficult to predict but judging from its previous impact on ecosystems this is no good news.”
Several studies have also suggested that the females reproduce more offspring and earlier when temperatures increase. They currently cease embryogenesis during winter, but warmer temperatures could result in continuous reproduction.
They can also store sperm from previous copulations for several months and use this if males become scarce. “This is a very dangerous trait for an invasive species because only one female can be enough to start a whole new population.”
An increase in the gambusia population could have serious implications for Australian frogs and fish.
