Friday, 19 October 2007

Homona mermerodes eats a lot.

With the advent of cheap and effective DNA amplification and sequencing methods, there has been an increased appreciation of biological diversity. In particular, a field that has particularly benefited from the techniques has been the detection of cryptic species. These are groups of organisms that appear the same, but a look into the DNA of the creatures reveal that they are complexes of genetically different populations. Frequently, these cryptic species are found to be host specific to certain food types, while the former "superspecies" was thought to have a range of hosts.

There has been a lot of work done recently on the northern coast of Papua New Guinea by the Binatang Research Centre. Their research has a focus on rainforest invertebrate dynamics and ecology, and they have done a sterling job in encouraging science in the country. They've trained several PNG citizens as parataxonomists, and a look at their publication list is rather impressive. As part of this research, they have investigated the population structure of the leafroller moth Homona mermerodes (Lepidoptera: Tortricidae). They used the fabled cytochrome oxidase gene (commonly abbreviated to cox1 or COI) to investigate whether the species is a widespread polyphagous species, or whether it is made up of a lot of cryptic species that are specific to certain plants. The COI gene is found in the mitochondrial DNA, and is famous as the gene of choice for what has become known as barcoding. This is an ambitious scheme to sequence the COI gene region for every organism on the planet to allow it to be quickly and easily identified.

Hulcr et al published the results of the work on Homona in Molecular Ecology Notes in July this year. Their analysis shows that the use of COI made some very nice distinct groups (clades), with big differences between the different clades. The interspecific genetic distances are larger than the intraspecific distances, forming a bimodal (twin-peaked) distribution with very marginal overlap. There were certainly no genetic differences between H. mermerodes reared on different plants, nor were there major differences between PNG and Australian (Queensland) populations.

One of the things that impressed me by this paper was the incorporation of pictures of the moth including both adult, larvae, and genitalia. It has been a concern of mine that much of the rhetoric surrounding barcoding seems to neglect other taxonomic evidence, whether it's morphological or other genes. I believe this is from the enthusiasm surrounding the power of the techniques as opposed to deliberately believing that barcoding is the ONLY way. Single-character taxonomy will always provide misleading results, whether it's in a morphological sense, or if it's only single gene region being looked at. I have experienced this myself when trying to identify things and getting involved with single things rather than looking at the organism as a whole. Good taxonomy takes a lot of information into account in order to try and infer species limits.

It is also good to have an example where a wide ranging, generalist and morphologically variable species has a well-defined genetic structure. Frequently it seems that the genetics of creatures that display these traits suggests that there are a number of cryptic species. It is gratifying (to me at least) to know that these cryptic species groups aren't a given. Further research that attempts to deduce the factors that influence the formation of cryptic species groups will be highly interesting.

Hulcr J, Miller SE, Setliff GP, Darrow KA, Mueller ND, Hebert PDN, Weiblen GD. 2007
DNA Barcoding confirms polyphagy in a generalist moth, Homona mermerodes (Lepidoptera: Tortricidae).
Molecular Ecology Notes 7: 549-557

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