Analysis of variation within the E. saligna-E. botryoides complex indicates a continuum of morphological variation, particularly in bud, fruit and bark characters, between the taxa. The continuum occurs between populations north of Sydney (which had always been recognised as E. saligna), and populations restricted to the coastal fringe (which had always been recognised as E. botryoides). There is a suggestion of a latitudinal cline in morphology of the intermediate populations, although it is complex, and shows significant local variation. Analysis of allozyme data indicates that most of the genetic variation within the complex is contained within rather than between populations, and that genetic distances between populations are more typical of within-species rather than between-species differences. The lack of allozyme divergence is attributed to either relatively rapid and recent differentiation or to extensive introgression following secondary contact of the taxa. Analysis of environmental variables reveals two discriminating factors in relation to the current distributions of populations within the complex. Firstly, the morphological gradient appears to follow an underlying temperature gradient, and secondly, E. botryoides occupies a separate niche associated with the distinct coastal environment on which it occurs. These key environmental parameters may have been important in the evolution of the complex along axes of latitude or temperature, and coastal versus inland habitat. Additionally, changes in distribution of the taxa as a result of climatic changes associated with glacial-interglacial cycles may also have played an important role in the formation of the complex.
Phylogeny and biogeography of midwife toads (Alytes, Discoglossidae): a reappraisal