Mosquito evolution spells trouble for Galapagos wildlife

02/06/2009 09:14:55 Darwin style evolution threatening Galapagos wildlife

June 2009. The Galapagos giant tortoise and other iconic wildlife species are facing a new threat from disease, as some of the islands' mosquitoes develop a taste for reptile blood.

Scientists from the University of Leeds, the Zoological Society of London (ZSL) and the Galapagos National Park have discovered that while its mainland ancestors prefer the blood of mammals and the occasional bird, the Galapagos form of the black salt marsh mosquito (Aedes taeniorhynchus) has shifted its behaviour to feed mainly on reptiles - primarily Galapagos giant tortoises and marine iguanas.

The findings raise fears that these changes could devastate the islands' unique native wildlife if a new mosquito-borne disease is introduced - a scenario which is increasingly likely with the continuing rise in tourism.

Mosquitoes colonised Galapagos Islands 200,000 years ago
Using genetic techniques, the researchers showed that the mosquito colonised the Galapagos around 200,000 years ago and was not introduced by humans as previously thought, giving them time to adapt to conditions in Galapagos. They have also found that unlike the mainland populations that normally live in mangroves and salt marshes along the coast, the Galapagos form of the mosquito can also breed up to 20 km inland and at altitudes of up to 700 metres. The research team believe the shift in feeding behaviour is an adaptation to life in Galapagos, since the islands had few mammal species prior to the arrival of Man some 500 years ago.

Evolving into a new species
"When we started the work we thought that this species was also introduced by humans, so it was a surprise that it turned out to be so ancient," says Arnaud Bataille, the University of Leeds and ZSL PhD student who carried out the work. "The genetic differences of the Galapagos mosquitoes from their mainland relatives are as large as those between different species, suggesting that the mosquito in Galapagos may be in the process of evolving into a new species."

No disease at present - But would be devastating
Mosquitoes are known to transmit important wildlife diseases, such as avian malaria and West Nile fever. While there is no evidence that such diseases are currently present on Galapagos, the widespread presence of the mosquito, and the fact that it feeds on a broad range of the native species, means that any new disease that arrives from the continent could spread rapidly to a wide variety to wildlife throughout the islands. Due to its long isolation, Galapagos wildlife is not likely to have much immunity to new diseases, so the effects could be devastating.

Tourism danger
"With tourism growing so rapidly the chance of a disease-carrying mosquito hitching a ride from the mainland on a plane is also increasing, since the number of flights grows in line with visitor numbers" says Dr Andrew Cunningham, from the Zoological Society of London, one of the authors of the study. "If a new disease arrives via this route, the fear is that Galapagos' own mosquitoes would pick it up and spread it throughout the archipelago."

Rather than implementing control measures against Galapagos' own unique mosquito, the research team argues that it is imperative that measures are taken to avoid introducing new diseases to the islands.

The Ecuadorian government recently introduced a requirement for planes flying to Galapagos to have a residual insecticide treatment on the interior surfaces, and spraying in the hold and cabin on each flight. However, similar controls are yet to be implemented for ships.

Co-author Dr Simon Goodman, of Leeds' Faculty of Biological Sciences says: "It is absolutely vital that these control measures are maintained and carried out rigorously, otherwise the consequences could be very serious indeed."

The research is published online this week in the US journal Proceedings of the National Academy of Sciences (PNAS).

Galapagos mosquitos The two other mosquito species in Galapagos are Culex quinquefasciatus (the southern house mosquito) and Aedes aegypti. Culex quinquefasciatus, which is also an important carrier of wildlife diseases, was introduced around 1985, but so far it is largely restricted to areas of human habitation because of its dependency on fresh water for breeding. Aedes aegypti arrived in the mid-1990s but this species is not such a great concern for wildlife because it specialises in feeding on humans. However, it is a concern for human health, particularly because it transmits Dengue fever, a debilitating viral illness.

galapagos wildlife Compared to other isolated archipelagos, the Galapagos Islands are still relatively pristine with 95% of its original biodiversity intact. Although 4 sub-species of Galapagos tortoise, and 3 endemic rodent species have been lost since the arrival of humans, the number of vertebrate extinctions to date are still small. However, a large proportion of the remaining species of all kinds are threatened due to habitat loss, invasive species or over-exploitation. Galapagos is most famous for its endemic reptiles (11 sub-species of giant tortoise; 3 species of land iguana and the world's only species of sea going lizard, the marine iguana; 7 species of lava lizard; 5 endemic and 1 native species of gecko), terrestrial birds (22 endemic species), and large sea bird colonies (including the only penguins and albatrosses found on the equator, and the worlds only flightless cormorant species). However, it also has many lesser known species including 3 species of endemic rice rat, 57 endemic species of land snail, and a very large number of insect species, which grows each year as more are discovered. In addition there are 560 native plant species (180 endemic), but this is now exceeded by the number of introduced plant species which stands at more than 700.