09/05/2011
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Little Shrike-thrush reveals its hidden diversity

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The Little Shrike-thrush of the subspecies group rufogaster could find itself with more relatives soon. Glen Fergus (common.wikimedia.org)
The Little Shrike-thrush of the subspecies group rufogaster could find itself with more relatives soon. Glen Fergus (common.wikimedia.org)

Shrike-thrushes (Colluricinclidae)are a near-endemic Australo-Papuan family (they just encroach into Indonesia), generally viewed to consist of six or seven species in one genus Colluricincla. They are closely allied to the more diverse Whistlers Pachycephalidae, and were considered to be part of the same family. One of the most widespread species is Little or Rufous Shrike-thrush, a species which, like the two more well-known pitohui species, contains traces of the batrachotoxin found in the lethal poison dart frogs, making it the third known poisonous bird species.

Rufous Shrike-thrush has 30 described subspecies, and due to this extensive variation is ripe for a phylogeographic study - that is, tracing the species distribution and dispersal through its evolution and genetic divergence. One such study has now been performed by an American team working on 174 specimens collected from 45 Papua New Guinean (PNG) localities, a protocol that incorporated 23 subspecies in total.

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Perhaps, unsurprisingly, a high level of genetic divergence was found, as the lowland species has a patchwork range divided up by mountains and rivers (as well as sea) both currently and historically. Averaging the different genetic sequences used, a divergence of 5 to 11 per cent was found within the species as it is currently understood, in some cases between subspecies that exist directly adjacent to one another without gene flow occurring. Eight clear lineages were found, all with genetic distances greater than many closely-related species, although the authors stopped short of declaring any new species and warn that more studies will be needed to confirm the cryptic forms.

Even so, it appears to be likely to be split in due course, particularly as divergences are so wide and are old enough to have coincided with mountain-building events in the islands when calibrated to a standard 'molecular clock' - a method that ties molecular changes to geological time. No work was done on the species' Australian forms, where there are seven subspecies found, currently believed to fall into two separate groups. Existing subspecies names have not yet been allied to any of the team's new groupings, and birders who have visited PNG are advised to keep their eyes on this space.

Aside from the interesting taxonomic results, there is a question of morality involved in the field protocols used in this study. In a time when DNA analysis can be performed on a clearly-labelled blood or tissue sample, should biologists still kill - sorry, euthanise - wild and possible declining animal species to provide museum specimens?

Reference
Deiner, K, Lemmon, A R, Mack, A L, Fleischer, R C and Dumbacher, J P. 2011. A passerine brd's evolution corroborates the geologic history of the island of New Guinea. PLoS ONE 6: e19479.