As global warming raises concerns about potential spread of infectious diseases, a team of researchers has demonstrated a way to predict the expanding range of human disease vectors in a changing world.
Researchers from Australia and the University of Wisconsin-Madison have identified the key biological and environmental factors constraining a population of the dengue fever vector, the mosquito Aedes aegypti. In a study publishing online Jan. 28 in the British Ecological Society's journal Functional Ecology, they report that climate changes in Australia during the next 40 years and the insect's ability to adapt to new conditions may allow the mosquitoes to expand into several populated regions of the continent, increasing the risk of disease transmission.
While the current study focuses on the Australian population of the dengue mosquito, these mosquitoes live around the world and present a global threat similar in scope to malaria, according to the Centers for Disease Control and Prevention. Study author and UW-Madison zoologist Warren Porter says that the Australian findings are likely to apply to other worldwide mosquito populations as well.
Porter and his colleagues, led by Michael Kearney at the University of Melbourne, used software models to predict future mosquito habitat. Called Niche Mapper, the models use basic characteristics of an animal's body, metabolic needs and behaviors to determine where that animal can live and reproduce successfully.
"Where would a species with a particular set of properties best survive and function on our planet?" asks Porter, who developed the Niche Mapper software with Madison and Australian colleagues. "By answering this question, we are able not only to calculate what the current distributions are, but even identify places where they might flourish where they don't currently exist."
Currently, dengue mosquitoes in Australia are restricted to Queensland in the northeast. However, the new work shows that climate changes predicted by 2050 will increase suitable mosquito habitat across much of the continent.
Of even greater concern, they say, are changes in human water-storage practices that are being driven by reduced rainfall in some cities. Mosquitoes lay their eggs in water, and much of the dengue mosquito's favored breeding habitat is inadvertently provided by humans in the form of rainwater tanks and other open water containers. The study suggests that simple changes such as reducing or covering such tanks could counteract some of the climate change-driven habitat expansion.
However, the researchers also found a marked effect of something humans have less control over: the mosquito's potential for evolutionary change. In fact, the ability to account for such an effect sets this model apart from all others.
"All biological systems are adaptive," Porter says. "We have the capacity to not only look at climate change but at animal change as well."
Because of the importance of watery breeding sites, the scientists focused on how well the insect's eggs withstand desiccation during dry periods. By applying a model of rates of evolutionary change, they found that if the mosquitoes' eggs develop an increased resistance to drying out - a trait that has evolved in related insects - the species could spread into larger areas of the continent.