As reported in the May 2004 issue of Birding World, a recent genetic study (Liebers, de Knijff, and Helbig 2004) has shed some fascinating light on the evolution of the Herring Gull complex, and incidentally therefore on the relationships of some of the larger larids of South Korea.
The authors studied the mitochondrial DNA variation of 21 large gull taxa in an attempt to reconstruct their evolutionary history. Contrary to the expected "ring species" model, members of this complex apparently differentiated largely in geographical separation, not through isolation-by-distance. The divergence started from two glacial refugia, one in the North Atlantic and one in the Aral-Caspian region. Great Black-backed Gull Larus marinus, Yellow-legged Gull L. michahellis, Armenian Gull L. armenicus, and Herring Gull L. argentatus all originated from the North Atlantic refugium. However, the Lesser Black-backed Gull group (including - according to the authors - heuglini and barabensis), Caspian Gull L. cachinanns and a Pacific-North American clade (consisting of vegae, mongolicus, schistisagus, glaucoides, thayeri, and smithsonianus) derive from the Aral-Caspian refugium: it has only been this latter group that has attained circumpolar distribution.
The study revealed some very interesting taxonomic relationships - many confirming views that WBKE has been proposing for some time and that run contrary to those put forward in eg "Gulls of Europe, Asia and North America".
For instance:
Mongolian Gull L. mongolicus is not closely related to L. cachinnans (as "Gulls..." suggests) but in fact shares most recent common ancestors with Slaty-backed Gull L. schistisagus, which colonised inner Asian wetlands from the Pacific. Whilst WBKE was aware that Mongolian Gull was genetically closer to the Pacific gulls than to west Asian taxa, its relationship to L. schistisagus is somewhat unexpected.
Of further note is the assertion that there is a clade that contains (amongst others) mongolicus and vegae: differences in various plumages and ecological preferences suggest to us a rather wide separation between Mongolian Gull and Vega Gull (rather contra Yesou's 2002 paper), and that identification of extralimital mongolicus and vegae will be easier once the criteria are fully known.
Confidence in criteria for the identification in north-east Asia of immature American Herring Gull L. smithsonianus is somewhat undermined by the discovery that it is close genetically to Vega Gull L. vegae, and that the two taxa are liable to appear closer to each other in the field than is often presently appreciated.
The most ecologically diverse/least specialised member of the complex, fieldwork in South Korea has consisitently shown that some vegae at least APPEAR to be the "middle-step" morphologically for the East Asian region's gulls, with some close in appearance to American Herring Gull, some close to Slaty-backed, some close to taimyrensis ( future studies are surely needed to reveal the validity or otherwise of taimyrensis as a discrete taxon), and some close to Mongolian in appearance. Further studies obviously need to be done.
A third discovery is that the taxon barabensis (usually designated as a subspecies of Caspian Gull L. cachinanns) is most closely related to (and genetically indistinguishable from) the taxon heuglini - as alluded to in our three-part paper on the Herring Gull complex in South Korea.
Without knowing full details of study and the depth of work done, WBKE would expect that future DNA studies of a wider number of geographically discrete populations will reveal even further insights into the relationships of the various taxa - particularly the possibility that various discrete populations of Mongolian Gull likely exist and are waiting proper description.
For more on Gulls in Korea on this website, go to:
References:
- Liebers, D., de Knijff, P. & Helbig, A. Ornithonews: Herring Gull is no longer "Lord of the Rings". Birding World 17 (4): 176.
- Olsen, K.M & H. Larsson (2003). Gulls of Europe, Asia and North America. Published by Helm.