Chloroplast DNA polymorphism signals complex interspecific interactions in Eucalyptus (Myrtaceae)

Abstract

Variation in the chloroplast genome of 44 accessions representing 14 Eucalyptus L'Hér. species from the series Viminales (sensu Pryor and Johnson 1971) was investigated. Southern analysis of the chloroplast genomes restricted with 12 enzymes revealed 20 restriction-site polymorphisms of which 7 were autapomorphic to individual trees. The 13 informative restriction-site polymorphisms were distributed between individuals of different species, but none was species-specific. Fourteen chloroplast haplotypes were identified for south-eastern Australian individuals. In endemic Tasmanian species, five haplotypes were identified. Chloroplast haplotypes appear to have a mosaic distribution in south-eastern Australia, more closely associated with geographical regions than with morphological species boundaries. The biogeographic distribution of chloroplast haplotypes may be explained by a combination of interspecific hybridisation and introgression, and convergent evolution. The lack of species-specificity of cpDNA variation indicates that, although cpDNA is not appropriate for species-level phylogeny analysis in the series Viminales, it may provide useful information in studies of biogeography and gene flow in Eucalyptus.

Chloroplast DNA phylogeography reveals the island colonisation route of Eucalyptus urophylla (Myrtaceae)

“…Chloroplast DNA variation in Eucalyptus generally appears to be geographically structured, but does not always conform to species boundaries as a result of hybridisation (Steane et al 1998;Jackson et al 1999;McKinnon et al 1999McKinnon et al , 2001b. For example, intraspecific cpDNA polymorphism in 14 of 17 species sampled in Tasmania was coupled with extensive sharing of identical haplotypes across populations of different species in the same geographic area (McKinnon et al 2001b).…”

“…Chloroplast DNA variation has also been extensively examined in Eucalyptus (Byrne and Moran 1994;Steane et al 1998;Jackson et al 1999;McKinnon et al 1999). These studies were based on restriction fragment length polymorphism (RFLP) variation in cpDNA.…”

Using matK sequence data to unravel the phylogeny of Casuarinaceae

“…It is possible that within Allocasuarina, reproductive isolation between some species is incomplete, and interspecific hybridisation may occur among some sympatric species from different sections (e.g., the Western Australian species in clade A3), a phenomenon that could result in the sharing of chloroplast genomes among morphologically distinct taxa. Extensive sharing of chloroplast haplotypes-attributed to some form of horizontal transfer, such as hybridisation-between species has been observed among Tasmanian species of Eucalyptus (Steane et al, 1998;McKinnon et al, 2001), as well as northern hemisphere Armeria (Guti e errez Larena et al, 2002), Quercus (Belahbib et al, 2001) and Pinus (Matos and Schaal, 2000). Some Western Australian eucalypts also demonstrate extensive sharing of chloroplast haplotypes, but in this case lineage sorting, rather than hybridisation, has been proposed as the most likely mechanism [Dean Nicolle, (Flinders University, South Australia), pers.…”

A plastid tree can bring order to the chaotic generic taxonomy of Rytidosperma Steud. s.l. (Poaceae)

“…Geographical patterning in cpDNA markers has been reported for the Tasmanian eucalypts (McKinnon et al, 2001(McKinnon et al, , 2004, for Iberian species of Phlomis (Albaladejo et al, 2005) and for white oaks in Europe (Dumolin-Lapé-gue et al, 1997;Petit et al, 2002). In these plant groups there is mounting evidence for the presence of several haplotypes within a single species, shared among species within geographical regions, with introgression and hybridisation being invoked as the most likely cause (Dumolin-Lapégue et al, 1997;Steane et al, 1998;Fuertes Aguilar et al, 1999a;Jackson et al, 1999;McKinnon et al, 2001;Petit et al, 2002). Given that the species in the present analysis hybridise in nature (Brock and Brown, 1961;Spies et al, 1992;Visser and Spies, 1994a, b, c, d;Waters, 2007), the occurrence of several ploidy forms within a single species, haplotype sharing among species from the same area (Waters, 2007;Waters et al, 2008) and continuous variation in morphological characters among several species, geographical patterning could offer an explanation to some of the patterns evident in the plastid tree presented here (Fig.…”