PhD week 5: Adaptive radiation

Hawaiian honeycreepers. Courtesy of the Smithsonian's National Zoo photostream. License: CC: BY-NC-ND

This week has been spent mainly reading about adaptive radiation. Adaptive radiation, according to the definition I find describes it the clearest is:

A proliferation of species within a single clade accompanied by significant interspecific divergence in the kinds of resources exploited and in the morphological and physiological traits used to exploit these resources (Schluter, 1996 in Givnish and Sytsma 2000)

One of the textbook examples of adaptive radiation are the Hawaiian honeycreepers (pictured above). These birds form a natural group, but their feeding habits differ between species, and are wildly different from the finches which are believed to be their nearest relatives. These differences are reflected in the variation which is most evident in the bill shapes of each of the species. A blog post discussing the evolution of the Hawaiian honeycreepers in greater detail has been written by GrrlScientist.

For me, the concept of adaptive radiations is important in providing a framework for my research. This allows questions to be asked, and predictions made, that will give my studies direction and purpose. The study of adaptive radiations also opens our eyes to our dynamic biological systems and organisms can be, and give us an appreciation of the richness of life on this planet.

Among the other things I did this week, was give a talk to some Year 9 students at Lincoln High School about my work as an entomologist, and what sort of things it involves. It was great to present to a class of interested kids, and it was followed by a question time with such queries as the most humane ways to kill insects, the taste of insects and whether they're suitable for vegetarians, and whether or not insects sleep.

References:
Schluter D. 1996. Ecological causes of adaptive radiation. American Naturalist 148:S40–S64.

Givnish TJ, Sytsma KJ (Eds). 2000. Molecular Evolution and Adaptive Radiation. Cambridge: Cambridge University Press

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Read:
Gillespie RG. 2008. Adaptive radiation. In: Gillespie RG, Clague DA (eds). Encyclopedia of islands Berkeley: University of California press, pp. 1–7

Grant PR, Grant BR. 2008. How and Why Species Multiply. The Radiation of Darwin's Finches. Princeton: Princeton University Press

McCulloch D. 2010. A History of Christianity: The First Three Thousand Years London: Penguin

Kirkpatrick R. 2009. Beyond the Wall of Time. Sydney: Voyager

Psalms 33–36; 104

Websites:
Evolving Thoughts—Bayes, evolutionary clocks, and biogeography

Listened:
Gotan Project—La Revancha del Tango

Radio NZ Classics podcast—Brahms Piano Quartet No 1 in G minor Op 25

Facedown Records–Facedown Festival 2011 Sampler

Watched:
The Hobbit: An Unexpected Journey movie trailer

Norma Jean—Absentimenal:Street Clam music video

Phylogeny of Pacific pigeons

Orange dove Ptilinopus victor. Picture courtesy of aviceda on Flickr

In the avifauna of the Pacific, pigeons rule. Considering the region as a whole, pigeons are one of the most widespread and speciose groups of birds in the area. In particular, the imperial pigeons (Genus Ducula) and the fruit doves (Genus Ptilinopus) are especially widespread, being found from South-east Asia to French Polynesia, and with most major islands having at least one endemic species. Despite this diversity however, South Pacific pigeons have tended to not be included in analyses of pigeon evolution as a whole.

To rectify this, Gillian Gibb and David Penny present a phylogeny estimated from a number of mitochondrial genes that includes 9 species of imperial pigeon, and 13 species of fruit dove (including the orange dove Ptilinopus victor shown above), along with representatives of a number of other pigeon genera. Australasia and Oceania have the bulk of the representation in this analysis—of the 25 genera represented, only 10 have no species in the region.

They found that the imperial pigeons are monophyletic (that is, they form a natural grouping) and are rather distinct from the remainder of the pigeons sampled. The fruit doves on the other hand are prevented from forming a natural clade by the presence of the cloven-feathered dove (Drepanoptila holosericea) of New Caledonia, and the blue dove (Alectroenas madagascariensis) of (you guessed it...) Madagascar. When you look at pictures of these two, it's not surprising that they might be fairly close to Ptilinopus. What is surprising though, is that these two species are resolved as being sister taxa, despite being so geographically distant from each other. This puzzle obviously requires rather more investigation.

References:
Gibb GC, Penny D. (2010). Two aspects along the continuum of pigeon evolution: A South-Pacific radiation and the relationships of pigeons within Neoaves. Molecular Phylogenetics and Evolution 56: 698–706

Vanuatu Birds Website

While reading the paper on white-eye blood parasites, I noticed a link to the VanBirds website. It is an incredible website, and an excellent resource for both casual bird watchers and serious ornithologists. It has photos of many of the bird species found in the archipelago. In addition, it has recordings of the calls of many of the species also. Most importantly though, the website collates records of birds throughout the archipelago and displays them on a map as shown by this map of the distribution of the Vanuatu endemic flycatcher, the buff-bellied monarch (Neolalage banksiana, pictured above). It appears to be well-maintained, being last updated on the 25th of May this year.

This website is very impressive and is a highly valuable resource for the ornithology of Vanuatu. It is all the more remarkable, as it appears to be very much a grass-roots type effort and claims to have had no external funding thus far. It would be awesome to see more sites like this spring up for the other Melanesian island groups.

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.

References:
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.

The bizarre family of the Silktail

The silktail (Lamprolia victoriae) is a small bush bird, restricted to the Fijian islands of Vanua Levu and Taveuni. From its first description in 1874 its systematic position has been debated with suggested closest relatives ranging from the australian robins (Petroicidae), and the monarch flycatchers (Monarchidae), to the birds of paradise (Paradisaeidae). The late, great Ernst Mayr famously called the silktail "One of the most puzzling birds of the world". Last year, a group of european, american and south african scientists headed up by Martin Irestedt brought DNA evidence to the party to shed further light on the subject. Their results were published here.

What they discovered was totally unexpected. Their data suggests that the closest living relative to the silktail is the Papuan mountain drongo (PMD, Chaetorhynchus papuensis), a little-known bird of the New Guinea highlands. The PMD has traditionally been grouped with the drongos (Dicruridae), but in the Irestedt study, both the silktail and PMD are sister to the fantail family (Rhipiduridae).

The authors discuss at length the biogeographic implications of their finding, suggesting either long distance dispersal or a vicariant metapopulation origin, but are unable to come to a conclusion either way. Unfortunately, they don't suggest ways of testing these hypotheses. I suggets it may be a little premature to speculate too seriously about this single result, interesting though it is. Future work on the geology of the region and further systematic research on the silktail and the remainder of the avifauna of Melanesia may reveal other potential explanations.

References:
Irestedt M., Ruchs J., Jonsson K., Ohlson J. I., Pasquet E., Ericson P. G. P. (2008) The systematic affinity of the enigmatic Lamprolia victoriae (Aves: Passeriformes) - An example of avian dispersal between New Guinea and Fiji over Miocene intermittent land bridges? Molecular Phylogenetics and Evolution 48: 1218-1222

Picture courtesy of Birdlife International