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Fishbein, Mark [1], Mandracchia, Therese [2], Bryan, Alessandra [3], Riser, James [4], Boutte, Julien [5], Straub, Shannon [6].

Big Data for Small Plants: Phylogenomics and Systematics of the Dwarf Milkweeds.

Complexes of cryptic species challenge systematists because blurred species boundaries may result from distinct evolutionary processes. For example, some patterns of phenotypic and genetic population structure are shared by both primary divergence of incipient or recent species and secondary contact involving hybridization of species that diverged some time in the past. However, extensive sampling of genetic variation across nuclear and cytoplasmic genomes obtained from a large number of individuals can provide a fine scale understanding of such histories, in which primary and secondary gene exchange are not mutually exclusive. The “dwarf milkweeds” (Apocynaceae, Asclepias) are a clade of four species inhabiting arid and semi-arid grasslands of the western United States and northwestern Mexico. They have been variously treated as comprising 1-4 species, with disagreements among taxonomists based largely on the significance and consistency of subtle variation in leaf shape and vestiture. Recent population genetic and climatic niche modeling analyses support the recognition of four species: A. eastwoodiana in south-central Nevada, A. ruthiae in east-central Utah, A. sanjuanensis in Four Corners region of the Colorado Plataeu, and A. uncialis across the High Plains from northern Colorado to northeastern Sonora. These species are now completely allopatric. We sampled 12-18 individuals (61 total) from across the ranges of all four species, for which we obtained sequences of plastomes and 3,301 nuclear loci targeting intronic regions. We confirmed the results of population genetic analysis of simple-sequence repeats (SSRs) that support the recognition of four species in this complex. The plastomes of each species were recovered as monophyletic lineages with no evidence for incomplete lineage sorting (ILS) or plastome capture. The phylogenetic history of the clade is inferred to have progressed by the initial divergence of A. eastwoodiana, the westernmost species, followed by A. uncialis, the easternmost species. The most recent species divergence is inferred between A. ruthiae and A. sanjuanensis. We also present previously unrecognized morphological distinctions between the four species that allow their identification without reference to geography.

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1 - Oklahoma State University, Dept Of Plant Biology, Ecology & Evolution, 301 Physical Science, Stillwater, OK, 74078, United States
2 - Penn State University, Biochemistry and Molecular Biology, State College, PA, 16801, USA
3 - Hobart & William Smith Colleges, Biology, Geneva, NY, 14456
4 - 701 S Midvale Blvd., Madison, WI, 53711, United States
5 - A2Bio2, Molleges, 13940, France
6 - Hobart And William Smith Colleges, Department Of Biology, 300 Pulteney St., Geneva, NY, 14456, United States

nuclear loci
incomplete lineage sorting
North America
species delimitation.

Presentation Type: Oral Paper
Session: SYSTII, Systematics II: Basal Asterids & Euasterids I
Location: Virtual/Virtual
Date: Tuesday, July 20th, 2021
Time: 12:45 PM(EDT)
Number: SYSTII002
Abstract ID:773
Candidate for Awards:None

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