title: Inferring species networks from gene trees in high-polyploid North American and Hawaiian violets (Viola, Violaceae).
abstract: The phylogenies of allopolyploids take the shape of networks and cannot be adequately represented as bifurcating trees. Especially for high polyploids (i.e., organisms with more than six sets of nuclear chromosomes), the signatures of gene homoeolog loss, deep coalescence, and polyploidy may become confounded, with the result that gene trees may be congruent with more than one species network. Herein, we obtained the most parsimonious species network by objective comparison of competing scenarios involving polyploidization and homoeolog loss in a high-polyploid lineage of violets (Viola, Violaceae) mostly or entirely restricted to North America, Central America, or Hawaii. We amplified homoeologs of the low-copy nuclear gene, glucose-6-phosphate isomerase (GPI), by single-molecule polymerase chain reaction (PCR) and the chloroplast trnL-F region by conventional PCR for 51 species and subspecies. Topological incongruence among GPI homoeolog subclades, owing to deep coalescence and two instances of putative loss (or lack of detection) of homoeologs, were reconciled by applying the maximum tree topology for each subclade. The most parsimonious species network and the fossil-based calibration of the homoeolog tree favored monophyly of the high polyploids, which has resulted from allodecaploidization 9-14 Ma, involving sympatric ancestors from the extant Viola sections Chamaemelanium (diploid), Plagiostigma (paleotetraploid), and Viola (paleotetraploid). Although two of the high-polyploid lineages (Boreali-Americanae, Pedatae) remained decaploid, recurrent polyploidization with tetraploids of section Plagiostigma within the last 5 Ma has resulted in two 14-ploid lineages (Mexicanae, Nosphinium) and one 18-ploid lineage (Langsdorffianae). This implies a more complex phylogenetic and biogeographic origin of the Hawaiian violets (Nosphinium) than that previously inferred from rDNA data and illustrates the necessity of considering polyploidy in phylogenetic and biogeographic reconstruction.
authors.affiliation: 1Department of Biology, Centre for Ecological and Evolutionary Synthesis (CEES), University of Oslo, PO Box 1066 Blindern, NO-0316 Oslo, Norway.
authors.forename: Thomas
authors.initials: T
authors.lastname: Marcussen
authors.forename: Kjetill S
authors.initials: KS
authors.lastname: Jakobsen
authors.forename: Jirí
authors.initials: J
authors.lastname: Danihelka
authors.forename: Harvey E
authors.initials: HE
authors.lastname: Ballard
authors.forename: Kim
authors.initials: K
authors.lastname: Blaxland
authors.forename: Anne K
authors.initials: AK
authors.lastname: Brysting
authors.forename: Bengt
authors.initials: B
authors.lastname: Oxelman
mesh_terms: D002467:Cell Nucleus / Q000235:genetics; D018742:DNA, Chloroplast / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D019143:Evolution, Molecular; D005956:Glucose-6-Phosphate Isomerase / Q000235:genetics; D006254:Hawaii; D009656:North America; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D011123:Polyploidy; D018749:RNA, Plant / Q000235:genetics; D017422:Sequence Analysis, DNA; D032413:Viola / Q000737:chemistry / Q000145:classification* / Q000235:genetics*
chemical_list: D018742:DNA, Chloroplast; D018744:DNA, Plant; D018749:RNA, Plant; D005956:Glucose-6-Phosphate Isomerase