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Mosquito evolution spells trouble for Galapagos wildlife

The Galapagos giant tortoise and other iconic wildlife 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), the University of Guayaquil 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.

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.

"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."

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.

"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).

Press contacts:
University of Leeds: Jo Kelly,
tel: 0113 258 9880,
mobile 07980 267756
email: jokelly@campuspr.co.uk

ZSL: Victoria Picknell,
tel: 02074496361
email: victoria.picknell@zsl.org

A range of high resolution images are available on request

Notes for editors
1. The research paper, Natural colonization and adaptation of a mosquito species in Galapagos and its implications for disease threats to endemic wildlife (DOI:
10.1073/PNAS.0901308106), is available on EurekAlert.org at www.eurekalert.org/jrnls/pnas/subject.htm. Only EurekAlert users registered to have access to PNAS material will be able to view this
link.

Alternatively the paper is available on request from the PNAS news office Tel: +1-202-334-1310, email: PNASNews@nas.edu

2. The research was carried out in the Genetics, Epidemiology and Pathology Laboratory of the Galapagos National Park, Ecuador; the University of Leeds, UK; and the Natural Environment Research Council's Molecular Genetics Facility at the University of Sheffield, UK.

3. The work was funded by the UK government's Darwin Initiative scheme, grants 162-12-17 and EIDPO15, by the 'AGAPE' Marie Curie Training Centre grant awarded to the University of Leeds Faculty of Biological Sciences, and the Natural Environment Research Council. The research forms part of Arnaud Bataille's PhD thesis to determine the impact of mosquitoes and their role in the emergence of diseases that could threaten Galapagos biodiversity.

4. The Genetics, Epidemiology and Pathology Laboratory of the Galapagos National Park was established in 2004 with funding from the UK government's Darwin Initiative to the Galapagos National Park, the University of Guayaquil (Ecuador), the Zoological Society of London and the University of Leeds.  The laboratory was set up to identify and control disease threats to Galapagos wildlife.

5. The Faculty of Biological Sciences at the University of Leeds is one of the largest in the UK, with over 150 academic staff and over 400 postdoctoral fellows and postgraduate students.  The Faculty is ranked 4th in the UK (Nature Journal, 457 (2009) doi:10.1038/457013a) based on results of the 2008 Research Assessment Exercise (RAE).  The RAE feedback noted that "virtually all outputs were assessed as being recognized internationally, with many (60%) being internationally excellent or world-leading" in quality.    The Faculty's research grant portfolio totals some £60M and funders include charities, research councils, the European Union and industry.  www.fbs.leeds.ac.uk

6. Founded in 1826, the Zoological Society of London (ZSL) is an international scientific, conservation and educational charity: our key role is the conservation of animals and their habitats.  The Society runs ZSL London Zoo and ZSL Whipsnade Zoo, carries out scientific research in the Institute of Zoology and is actively involved in field conservation in other countries worldwide. For further information please visit www.zsl.org

7. 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.

8. The Galapagos Islands and their flora and fauna are famous for the role they played in inspiring Charles Darwin's thinking on the theory of evolution by natural selection. Discovered in 1535 by the 4th Bishop of Panama after his ship drifted off course, the archipelago consists of 13 main islands, 6 smaller islands, and 107 islets.  Administered by Ecuador, the islands straddle the equator in the Pacific, 1000km from the continent. Around 90% of the land area of the archipelago is national park, and a zone extending 40km offshore from the islands is a marine reserve, forming one of the largest marine protected areas in the world.

The islands are a UNESCO World Heritage site, but were placed on the 'Sites in Danger' list in 2007, due to threats from introduced species and other factors driven by rapidly growing immigration and tourism. Since 1991 visitor numbers have increased from 41,000 to greater than 160,000 annually, while the local population exceeds 40,000, with a growth rate of around 4% per year. Growth in the tourist economy has averaged 14% per year since 1992, which means that if Galapagos were a country, it would have one of the fast growing gross domestic products in the world. In 2007 the Galapagos tourist economy generated more than US$418 million.

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.