Friday, 16 July 2010

Blood parasites in Melanesian White-eyes

The white-eyes are a group of small birds in the genus Zosterops with an interest out of all proportion to their size. As a genus, they range from Africa, through Asia and Australia to many islands in the Pacific where they are fairly common. In the islands they have diversified to the extent that most archipelagos have at least one endemic species present. This is most impressive in the New Georgia group of the Solomon Islands, where six species are present over six different islands---many of which are separated only by a few kilometres of ocean. Additionally, one particular species, the silver-eye (Zosterops lateralis) has a wide range across Australia and into the central Pacific As such, there are many different questions regarding their dispersal, rate of speciation and the relationships between the different species.

In a paper by Farah Ishtiaq and coauthors, the birds themselves are not so much of interest. Rather, it's the prevalence of parasites in the blood of the birds found in Vanuatu and New Caledonia. More specifically, they look at the protozoans Plasmodium (more commonly known as avian malaria) and Haemoproteus that are spread from bird to bird by blood-sucking flies and mosquitoes. They took blood samples from a number of specimens, comprehensively sampling five different species of white-eye from Vanuatu (13 islands represented), mainland New Caledonia and the Loyalty Islands. Within these, they found seven different lineages of Haemoproteus and 14 lineages of Plasmodium. Most lineages were fairly scarce, with one lineage of each parasite genus being the most common and widespread.

When they looked at the number of parasite lineages on each island, they found that the larger islands had more lineages of Plasmodium than smaller islands. This trend was much less evident in Haemoproteus, being not statistically significant. The pattern of increasing numbers of lineages or species with increasing island area is a very well-known relationship that forms the basis of the Theory of Island Biogeography, first postulated by Robert MacArthur and EO Wilson in the 1960s. It is interesting that these parasites show the pattern also, despite the additional variables of requiring a host and a vector insect to be present.

Why is this of interest? Parasites have a huge effect on their hosts which is often invisible. They are also a part of the natural heritage of this world and so are worthy of study in their own right. These findings share a small glimpse into a world that is usually hidden, and increases our awareness of the biota of the Melanesian region. As with a lot of scientific research, progress is incremental with many small, initially insignificant findings building into a body of knowledge that can be extremely important for health, conservation, or technological impact.

Ishtiaq F, Clegg SM, Phillimore AB, Black RA, Owens PF, Sheldon BC. 2010. Biogeographical patterns of blood parasite lineage diversity in avian hosts from southern Melanesian islands. Journal of Biogeography 37: 120-132.

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