Systematic and evolutionary inferences from isozyme studies in the genus Eremaea (Myrtaceae)

Abstract

Eremaea is a genus of woody shrubs endemic to the south-west of Australia. With the exception of E. pauciflora all species are restricted to the kwongan or sandplain regions of the coastal plain northwards from Perth. Forty four populations covering the seven recognised species and a further 12 putative taxa were examined for allozyme variation at 15 polymorphic loci. Gene diversity statistics indicated that a greater proportion of genetic variability in Eremaea species was due to within- rather than among-population differences. The allozyme data supported morphological studies which indicated five species groups or complexes. Differentiation among and within species complexes was examined using gene frequency and genetic distance data. The average genetic distance (Nei's D) among populations within species ranged from 0.011 (E. acutifolia) to 0.051 (E. aff. brevifolia 3). Within species complexes the average genetic distance between taxa ranged from 0.050 to 0.157 while between complexes it ranged from 0.164 to 0.558.

Of the 159 possible pairwise combinations between the 19 morphologically distinct taxa, 15 showed little allozyme divergence. Lack of allozyme divergence was attributed to either rapid and recent speciation or to introgressive hybridisation. Based on allozyme data E. aff. brevifolia x violacea is either of hybrid origin or is a recently derived hybrid, and field observations indicated that interspecific hybridisation occurs within Eremaea. Rapid and recent speciation, combined with hybridisation have resulted in a reticulate pattern of evolution in sections of this genus.

Phylogenetic analyses based on these allozyme data were generally consistent with those based on morphological data except for the placement of E. purpurea and E. aff. pauciflora 4.