By Matt McGrath
Science reporter, BBC News
The giant tortoise of the Galapagos islands is an icon of evolution
The famous Galapagos giant tortoises could be at serious risk from mosquitoes that have developed a taste for reptile blood, experts have warned.
Scientists say increased tourism means there is now a greater risk of a disease-carrying insect being transported to the islands.
Local mosquitoes that have evolved to feed on reptiles could then pick up the diseases and pass them on.
Galapagos wildlife has little immunity to mosquitoes due to their isolation.
The study was published in the US journal Proceedings of the National Academy of Sciences.
The world's largest living tortoises are an icon of evolution, growing so large on the isolated islands because of the absence of natural predators.
But recent observations by scientists suggest that it is the evolution of mosquitoes that could now pose a very real threat to island wildlife.
On the mainland of South America, the insects prefer to bite mammals but they have adapted their behaviour to favour reptile blood on the Galapagos.
Increasing tourism means there is now a concern about the arrival of infected mosquitoes carrying diseases like avian malaria and West Nile fever, against which giant tortoises and marine iguanas have no immunity.
Mosquitoes arrived 200,000 years ago and evolved to feed on reptiles
Arnaud Bataille from the University of Leeds in the UK carried out the research.
He said that mosquitoes arrived on the Galapagos 200,000 years ago and were not introduced by humans as previously thought.
But he said when the mosquitoes first arrived on the islands, the only mammals were sea lions.
"It [the mosquito] was looking for some blood. What it was going to find is these huge reptiles and marine iguanas, so I think it gave it a go and liked it a lot," he said.
In an effort to cut the risk of mosquitoes and other insects being transported to the islands, the Ecuadorian government now require planes flying to the Galapagos to be sprayed with insecticide.
Similar measures have yet to be introduced on ships.