Hybrid Zones in Australian Birds

Abstract

Summary Ford, J. (1987). Hybrid zones in Australian birds. Emu 87, 158-178.Geographic patterns in positions of 79-87 avian hybrid zones and 12 parapatric contacts in Australia are analysed in the context of past climates, palaeo-refugia, mechanisms of origin, and temporal stability. No hybrid zone occurs in rain-forest species and differentiated vicariant forms of these are generally separated by unsuitable tracts of sclerophyll forest or savanna woodland. Most hybrid zones occur in semi-arid and sub-humid species. The zones appear to have originated by secondary contact of differentiated vicars rather than by parapatric divergence, because most lie between refugia postulated on the basis of late Pleistocene climates; their widths are generally in accord with those predicted from dispersion rates. The evidence suggests that most, if not all, hybrid zones were formed when expansion of isolates from refugia became possible following the marked improvement in climate at the close of the severe arid phase of about 17 000 y before present. The persistence of hybnd zones since then and their widths offer no support for the concept of reinforcement of previously acquired differences in recognition (signalling) systems. Where a hybrid zone coincides closely with the boundary of a presumed refuge, a semiarid form has differentially expanded towards its subhumid counterpart.

Phylogeography: its development and impact in Australo-Papuan ornithology with special reference to paraphyly in Australian birds

“…5) has been recognised as an agent of vicariance giving rise to eastern and western differentiates in the Australian Ringneck and the Splendid Fairy-wren (Ford 1987). Phylogeographic studies of these two species Kearns et al 2008) each detected major phylogeographic breaks into two clades that are essentially concordant with the position of the Eyrean Barrier.…”

“…Geographical variation in plumage and morphology within Australian bird species has overwhelmingly been attributed to vicariant origins in historical allopatry followed by population expansion leading to secondary contact and hybrid zones (Keast 1961;Ford 1987;Schodde and Mason 1999). The alternative of geographically structured variation being in response to selection along environmental gradients has certainly been championed (Ford 1981) and occasionally argued (Wooller et al 1985;Schodde and Mason 1999) but has rarely been rigorously tested.…”

“…5 shows hybrid zones and putative historical biogeographical barriers recognised for Australian birds (see Keast 1961;Ford 1974aFord , 1987Schodde and Mason 1999). Only a few phylogeographic studies have tested this rich literature, however.…”

“…We hope to clarify relevant issues, especially in an AustraloPapuan context. Also, ornithologists and Australo-Papuan ornithology have tackled questions on the spectrum from historical biogeography, taxonomy and hybrid zones through phylogeography to landscape genetics (Keast 1961;Ford 1987;Schodde and Mason 1999;Schodde 2006;Christidis and Boles 2008;review in Joseph 2008a). That literature is now a wealth of questions and hypotheses for the resources and tools of phylogeography to address.…”

Population structure and host-plant specialization in two Scaptodrosophila flower-breeding species

“…Hibiscus meraukensis is known (records of the Queensland Herbarium) from a number of localities in northwest Queensland -the region between the known distributions of S. hibisci and S. aclinata. This region (the Carpentaria gap), recognized as a phylogeographic break for many species (primarily birds), was fairly arid at the glacial maximum of 20 000-15 000 years BP (Ford, 1987). It is not known if either S. hibisci or S. aclinata are now present and breeding on H. meraukensis in this region, but it is hoped that this will be investigated.…”