Little Spiderhunter Arachnothera longirostra is species of sunbird Nectariniidae, widely distributed from India across southern China and South-East Asia through to the southern Philippines. Such a geographically fragmented distribution has resulted in 13 recognised subspecies, though most of the land in question was connected during the last glaciation.
A small Malaysian and American team analysed the mitchondrial DNA of five of these subspecies as well as the related Thick-billed Spiderhunter A crassirostris, to see what effects the comparatively recent isolation of populations may have had on variation in the species.
Not unexpectedly, the team found that the amount of divergence in each form correlated with the amount of hypothesised geographical isolation in recent history. The Malaysian and Bornean populations exhibited little divergence, and these land masses are known to have been connected several times during the glacial period, enabling the interbreeding of the populations.
However, the story was different on Mindanao, Philippines, home of the subspecies A l flammifera, which was found to have a divergence of at least 7.6 per cent from other subspecies, indicative of status as a good species. A l dilutior on Palawan also showed a divergence of 2.7 percent, which when combined with its drabber plumage and bright yellow eye-ring, also suggests that it should be split. Neither island has ever been connected to the Asian mainland.
The Bornean subspecies A l buettikoferi and that of the nearby Malaysian mainland A l cinereicollis may actually be too similar to even suit subspecific status, but an population from Thailand (either pallida or included in cinereicollis - the authors are unclear on this point) appears divergent enough to warrant promotion to a new subspecies. As ever, more comprehensive analyses will clarify these relationships further, particularly if they incorporate a wide sample of the mainland Asian populations.
Rahman, M A, Gawin, D F A and Moritz, C. 2010. Patterns of genetic variation in the Little Spiderhunter (Arachnothera longirostra) in Southeast Asia. The Raffles Bulletin of Zoology 58: 381-390.