been disputed. Acanthiza pusilla and A. ewingii Acacia karroo Alauda skylarks (Alauda arvensis, A. japonica and A. gulgula) Alophoixus Aulostomus (Trumpetfish) Camarhynchus psittacula and C. pauper Chaerephon pumilus species complex Ensatina salamanders Euphorbia tithymaloides is a group within the spurge family that has reproduced and evolved in a ring through Central America and the Caribbean, meeting in the Virgin Islands where they appear to be morphologically and ecologically distinct. Great tit (however, some studies dispute this example) The greenish warbler (Phylloscopus trochiloides) forms a species ring, around the Himalayas. It is thought to have spread from Nepal around the inhospitable Tibetan Plateau, to rejoin in Siberia, where the plumbeitarsus and the viridanus appeared to no longer mutually reproduce. Hoplitis producta House mouse Junonia coenia and J. genoveva/J. evarete Lalage leucopygialis, L. nigra, and L. sueurii Larus gulls form a circumpolar "ring" around the North Pole. The European herring gull (L. argentatus argenteus), which lives primarily in Great Britain and Ireland, can hybridize with the American herring gull (L. smithsonianus), (living in North America), which can also hybridize with the Vega or East Siberian herring gull (L. vegae), the western subspecies of which, Birula's gull (L. vegae birulai), can hybridize with Heuglin's gull (L. heuglini), which in turn can hybridize with the Siberian lesser black-backed gull (L. fuscus). All four of these live across the north of Siberia. The last is the eastern representative of the lesser black-backed gulls back in north-western Europe, including Great Britain. The lesser black-backed gulls and herring gulls are sufficiently different that they do not normally hybridize; thus the group of gulls forms a continuum except where the two lineages meet in Europe. However, a 2004 genetic study entitled "The herring gull complex is not a ring species" has shown that this example is far more complex than presented here (Liebers et al., 2004): this example only speaks to the complex of species from the classical herring gull through lesser black-backed gull. There are several other taxonomically unclear examples that belong in the same species complex, such as yellow-legged gull (L. michahellis), glaucous gull (L. hyperboreus), and Caspian gull (L. cachinnans). Pelophylax nigromaculatus and P. porosus/P. porosus brevipodus (the names and classification of these species have changed since the publication suggesting a ring species) Pernis ptilorhynchus and P. celebensis Perognathus amplus and P. longimembris Peromyscus maniculatus Phellinus Platycercus elegans (Crimson rosella) complex Drosophila paulistorum Phylloscopus collybita