Evolutionary and ecological relationships between Quail-thrushes

Abstract

Cladistic and phenetic clustering methods indicate two main groups of species in the quail-thrush genus Cinclosoma: a closely linked group composed of cinnamomeurn, alisteri, castaneothorax and marginatum, and a looser group containing punctatum, ajax and castanotum. The first cluster is an example of allopatric speciation and subspeciation within the deserts of Australia; the second provides an example of the derivation of a semi-arid form from a wet-country one. Members of the cinnamomeum group are allopatric except for parapatry between cinnamomeum and castaneothorax, these two forms hybridizing in some areas but not in others. No more than two taxa occur in the same geographical area and wherever there is overlap, one taxon is always castanotum which is partly sympatric with marginatum and cinnamomeum, marginally sympatric with punctatum and parapatric with alisteri. All quail-thrush taxa breed in the winter semester and dry-country populations also breed in the summer semester. Overlap in food between quail-thrushes is considerable but potential competitors generally segregate by habitat or substrate. Members of the cinnamomeum complex prefer stony substrates and where they overlap geographically with castanotum, the latter inhabits sandy substrates though elsewhere it may also frequent stony ground. The parapatric boundaries between cinnamomeum and castaneothorax and between castanotum and alisteri coincide with sharp changes in habitat. It is concluded that allopatry and parapatry in Cinclosoma is caused not only by competitive interactions but also by recency of speciation and subspeciation and by adaptation to different habitats, climates and substrates.