Resistance to avian malaria may lurk in endangered birds? genomes.
A native Hawaiian bird has surprised researchers with its ability to survive malaria, apparently thanks to a number of resistant populations that have spread throughout the Hawaiian forest. The discovery hints that genes for natural resistance to the avian disease may lurk inside the genomes of many of Hawaii?s endangered birds.
It has long been thought that avian malaria would spell the end for the remaining native birds on Hawaii, which have faced multiple onslaughts.
First there were the Hawaiians themselves, who arrived more than 1,000 years ago and, through hunting, sent most of the ground-dwelling species the way of the dodo. Then there were the rats, cats and mongooses, brought by Europeans, that ate birds and their eggs. Diseases such as avian pox followed. Avian malaria, which arrived some 60 years ago, is one in a long line of plagues. ?We really thought that malaria would be the final nail in the coffin,? says Jeffrey Foster of Northern Arizona University in Flagstaff, an author on the new study.
Two years ago, researchers reported that one species, the amakihi (Hemignathus virens), was making a miraculous recovery in the most heavily malaria-infested forests. Now a genetic study showing how these common songbirds have managed this gives some hope for other birds.
High and dry
More than 20 Hawaiian bird species are shielded from the disease because they live at high elevation near the tops of volcanoes, where it is too cold for the malaria parasite and the mosquitoes that carry it to survive.
The amakihi is one of only a few species that has populations at both high elevation and in lowland forests. When researchers discovered that the amakihi were recovering, they thought that, after being wiped out in the forests, amakihi from the higher elevations on the volcanoes were dispersing downslope into the forests to take advantage of the empty space.
A team led by Robert Fleischer of the Smithsonian Institution in Washington DC has shown that this is not the case.
The researchers analysed the genetics of 283 amakihi individuals found in the forests between 2001 and 2003, and report in Molecular Ecology1 that these lowland birds are genetically very different from the volcano dwellers. ?This important study clearly shows that source populations at high altitude were not involved in the recovery, but rather that the new lowland amakihi represent the remnants of the old population that was almost wiped out,? says ecologist Eric VanderWerf of Pacific Rim Conservation, an environmental consultancy based in Honolulu.
The research also shows that the forest amakihi are sufficiently different from one another to suggest that the resistance is not due to just one resistant individual that spread its genes, but rather that there were several isolated amakihi populations with resistant individuals that have thrived and spread. This, says Fleischer, suggests that the needed gene or genes were already present, if at low frequency, in the amakihi genome, rather than being the result of a new mutation.
That's good news. All of the native Hawaiian birds share a common ancestor of a finch that landed on the Hawaiian isles some five million years ago. So if the amakihi genome contains genes for malaria resistance, other modern species should, too.
?We really hope that we can find the gene or genes responsible for the resistance in the amakihi and then track down these genes in other species,? says Fleischer. As a last-ditch resort in saving the birds, selective breeding could be used to boost the frequency of these genes in other populations.
But the birds must still face other challenges. As global temperatures rise, malaria-bearing mosquitoes are climbing up the volcanoes. And feral cats and rats, as well as habitat destruction, are still rife. Getting those under control, says Foster, is the first and most important step to conservation.
Foster J., et al. Molecular Ecology (2007) doi: 10.1111/j.1365-294X.2007.03550.x
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Kaplan, M. Native genes may save Hawaiian birds. Nature (2007). https://doi.org/10.1038/news.2007.254