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Abstract Phylogenomic data from a rapidly increasing number of studies provide new evidence for resolving relationships in recently radiated clades, but they also pose new challenges for inferring evolutionary histories. Most existing methods for reconstructing phylogenetic hypotheses rely solely on algorithms that only consider incomplete lineage sorting (ILS) as a cause of intra- or intergenomic discordance. Here, we utilize a variety of methods, including those to infer phylogenetic networks, to account for both ILS and introgression as a cause for nuclear and cytoplasmic-nuclear discordance using phylogenomic data from the recently radiated flowering plant genus Polemonium (Polemoniaceae), an ecologically diverse genus in Western North America with known and suspected gene flow between species. We find evidence for widespread discordance among nuclear loci that can be explained by both ILS and reticulate evolution in the evolutionary history of Polemonium. Furthermore, the histories of organellar genomes show strong discordance with the inferred species tree from the nuclear genome. Discordance between the nuclear and plastid genome is not completely explained by ILS, and only one case of discordance is explained by detected introgression events. Our results suggest that multiple processes have been involved in the evolutionary history of Polemonium and that the plastid genome does not accurately reflect species relationships. We discuss several potential causes for this cytoplasmic-nuclear discordance, which emerging evidence suggests is more widespread across the Tree of Life than previously thought. [Cyto-nuclear discordance, genomic discordance, phylogenetic networks, plastid capture, Polemoniaceae, Polemonium, reticulations.]
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Sage Insights Into the Phylogeny of Salvia: Dealing With Sources of Discordance Within and Across Genomes
Next-generation sequencing technologies have facilitated new phylogenomic approaches to help clarify previously intractable relationships while simultaneously highlighting the pervasive nature of incongruence within and among genomes that can complicate definitive taxonomic conclusions. Salvia L., with ∼1,000 species, makes up nearly 15% of the species diversity in the mint family and has attracted great interest from biologists across subdisciplines. Despite the great progress that has been achieved in discerning the placement of Salvia within Lamiaceae and in clarifying its infrageneric relationships through plastid, nuclear ribosomal, and nuclear single-copy genes, the incomplete resolution has left open major questions regarding the phylogenetic relationships among and within the subgenera, as well as to what extent the infrageneric relationships differ across genomes. We expanded a previously published anchored hybrid enrichment dataset of 35 exemplars of Salvia to 179 terminals. We also reconstructed nearly complete plastomes for these samples from off-target reads. We used these data to examine the concordance and discordance among the nuclear loci and between the nuclear and plastid genomes in detail, elucidating both broad-scale and species-level relationships within Salvia . We found that despite the widespread gene tree discordance, nuclear phylogenies reconstructed using concatenated, coalescent, and network-based approaches recover a common backbone topology. Moreover, all subgenera, except for Audibertia , are strongly supported as monophyletic in all analyses. The plastome genealogy is largely resolved and is congruent with the nuclear backbone. However, multiple analyses suggest that incomplete lineage sorting does not fully explain the gene tree discordance. Instead, horizontal gene flow has been important in both the deep and more recent history of Salvia . Our results provide a robust species tree of Salvia across phylogenetic scales and genomes. Future comparative analyses in the genus will need to account for the impacts of hybridization/introgression and incomplete lineage sorting in topology and divergence time estimation.
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- Award ID(s):
- 1655606
- PAR ID:
- 10378946
- Date Published:
- Journal Name:
- Frontiers in Plant Science
- Volume:
- 12
- ISSN:
- 1664-462X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3389/fpls.2021.767478
