Hybrid Origin and Genomic Mosaicism of Dubautia scabra (Hawaiian Silversword Alliance; Asteraceae, Madiinae)

Abstract

Incongruence among different estimates of species relationships in plants, from different molecules, cytogenetic data, biogeographic data, morphological/anatomical data or other sources, has been used frequently as an indication of introgression, hybrid species origin, or chloroplast (cp) capture. In plants, these incongruences are most often seen between data derived from the nuclear vs. the cp genomes and the nuclear markers used for comparison usually have been from the nuclear ribosomal (nr) internal transcribed spacer region (ITS). The amount of genomic material shared between introgressing species can be highly variable. In some of these cases, other nuclear genomic regions have moved between species without leaving a signature on the nrITS. An example of well-supported phylogenetic incongruence is the placement of Dubautia scabra (DC.) D. D. Keck in the Hawaiian silversword alliance (HSA); evolutionary hypotheses for D. scabra based on molecular as opposed to cytogenetic data are strongly discordant. In this paper, we test these two conflicting phylogenetic hypotheses regarding the evolutionary relationships of Dubautia scabra using evidence from six low-copy nuclear genes, as well as multiple chloroplast noncoding regions and nrITS. The nrITS region is also examined for the presence of multiple copy types. Incongruence between inferred relationships based on nuclear chromosomal arrangements and molecular phylogenetic data from chloroplast DNA and nrITS is resolved in favor of a hypothesis of ancient hybridization rather than cytogenetic homoplasy involving dysploidy. Most single-copy nuclear genes track histories of D. scabra compatible with cytogenetic data whereas chloroplast and nrITS data track a common, different history that appears to reflect hybridization with a chromosomally distinct lineage that also occurs on Maui Nui and Hawai'i (the Big Island).

Diversification of HawaiianCyrtandra(Gesneriaceae) under the influence of incomplete lineage sorting and hybridization

“…These patterns are suggestive that either samples from the same species from different islands are in the process of diverging from each other, samples from the same species from different islands have introgressed with different species leading to different phylogenetic placements, or that samples from different islands were placed within the same taxonomic species in error and the entities on these islands are not closely related. Studies on the influence of hybridization on species boundaries in other Hawaiian plants have predominantly taken a population genetic/fragment analysis approach (Smith et al, ; Friar et al, ), or gene incongruence approach among a relatively limited number of sequenced loci (Friar et al, ; Willyard et al, ; Knope et al, ; Roy et al, ), and most evidence regarding Hawaiian plant hybridization is morphological (Wagner et al, , ). This study is the first for a Hawaiian plant lineage to explicitly test for the distinct influence of ILS and hybridization.…”

Phylogenetics of Puya (Bromeliaceae): Placement, major lineages, and evolution of Chilean species

“…7). Chloroplast capture and hybridization are well‐established explanations for points of conflict between cpDNA and nuclear DNA data, though assigning either as causation of the conflict should proceed with caution as other stochastic processes can create similar patterns (Smith and Sytsma, 1990; Baum et al, 1998; Wendel and Doyle, 1998; Linder and Rieseberg, 2004; Friar et al, 2008). Incomplete lineage sorting may be a pertinent explanation for such data set conflict, but generally it is invoked for groups that exhibit complex patterns of organellar DNA relationships within and among species generally not in sympatry (Wendel and Doyle, 1998; Comes and Abbott, 2001).…”

Reticulate evolution on a mosaic of soils: diversification of the New Caledonian endemic genus Codia (Cunoniaceae)

“…Despite this possibility, all species displaying alleles from two groups of GapC also showed alleles from two distinct groups in ncpGS , with the exception of Codia mackeeana . Furthermore, in homoploid hybrid species, one parental allele is commonly lost soon after formation (Howarth & Baum 2005; Friar et al . 2008).…”

“…Older homoploid hybrids would not be expected to exhibit both parental alleles, as demonstrated in Helianthus (Rieseberg et al . 2003), Scaevola (Howarth & Baum 2005) and Dubautia (Friar et al . 2008), and some of the ‘missing’ alleles in our study may no longer be present in the putative hybrid species.…”