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

Abstract

Premise: Expanded phylogenetic analyses of the Hawaiian silversword alliance (Argyroxiphium, Dubautia, Wilkesia; Compositae) were undertaken to assess evolutionary and biogeographic informativeness of cytonuclear discordance and any biases in evolutionary directionality of ecological transitions within 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 ecological evolution and the evolution of nuclear chromosomal arrangements while accounting for phylogenetic uncertainty. 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 the posterior distributions of nrDNA and cpDNA trees, including inferred chloroplast-capture events, provides additional resolution of dispersal history, including a back-dispersal to Maui Nui from Hawai'i. A newly resolved major nrDNA clade of endemic Kaua'i taxa that mostly were described as new-toscience since the 1980s strengthens the earlier hypothesis that diversification on Kaua'i has not waned since the island began to decline in area through subsidence and erosion. Bias in habitat shifts was estimated, with transitions from dry-to-mesic or -wet and from wet-to-mesic or -bog habitats dominating diversification of the silversword alliance from a dry-adapted tarweed ancestor. Conclusions: The habitat-transition biases estimated here may indicate more limited pathways of ecological evolution than proposed previously for an adaptive radiation involving such major ecological shifts.

A simple conceptual framework and nomenclature for studying repeated, parallel and convergent evolution

“…Additionally, transitions between environments can be biased (Baldwin et al, 2021), and the biased and repeated occupation of habitats may lead to repeated phenotypic evolution. While we may intuitively think that repeated phenotypic evolution occurs only in the face of similar environmental conditions, this is not necessarily the case.…”

Genome Report: The reference genome of an endangered Asteraceae,Deinandra increscenssubsp.villosa, endemic to the Central Coast of California

“…Datasets using high-throughput sequencing are in development, however. Baldwin and colleagues report the development of a dataset of 100s of nuclear loci using a high-throughput, targeted sequencing approach to examine adaptive radiation of the tribe Madieae, inclusive of subtribe Madiinae (Baldwin et al 2021). A large population genomics project by a subgroup of the authors is underway, using a genome resequencing approach to assist in conserving D. increscens subsp.…”