Directionally biased habitat shifts and biogeographically informative cytonuclear discordance in the Hawaiian silversword alliance (Compositae)

PREMISE OF THE STUDY: Expanded phylogenetic analyses of the endemic Hawaiian silversword alliance (Argyroxiphium, Dubautia, Wilkesia; Compositae) were undertaken to obtain enhanced resolution of habitat shifts, interisland dispersal, evolutionarily relevant hybridization, and clade diversity in this prominent example of adaptive radiation.

METHODS: Samples spanning the geographic and ecological distributions of all recognized taxa were included in phylogenetic and biogeographic analyses of nuclear ribosomal DNA (nrDNA) and cpDNA sequences.  Bayesian model testing approaches were used to model habitat evolution and the evolution of nuclear chromosomal arrangements while accounting for phylogenetic uncertainty.

KEY RESULTS: Cytonuclear discordance detected previously appears to reflect chloroplast capture, at least in part, with nrDNA trees being largely congruent with nuclear chromosomal structural data and fine-scale taxonomy. Comparison of biogeographic histories estimated from t..., Population sampling—All 45 minimum-rank taxa (in 33 species) of Argyroxiphium, Dubautia, and Wilkesia recognized in the Flora of the Hawaiian Islands (Wagner et al., 2005) were sampled from all islands and most volcanoes of known occurrence for sequences of nrDNA (ITS and ETS) and cpDNA (3’-ndhF gene, 5’-trnK intron, rpl16 intron, and psbA-trnH intergenic spacer). The likely extinct A. virescens was represented by a putative natural hybrid (A. “Pu‘u ‘Alaea”) with A. sandwicense subsp. macrocephalum (Carr and Medeiros, 1998). Dubautia kenwoodii, also probably extinct, was sampled from the type specimen. Individuals representing extensive morphological diversity in Dubautia from the summit bog of Wai‘ale‘ale, Kaua‘i were sampled for ITS and ETS sequences to verify their identities, including parentage of putative hybrids (see “Assessment of natural hybridization” below). All DNAs examined earlier for cpDNA restriction sites and ITS sequences by Baldwin et al. (1990) and Baldwin and Robich...,