Abstract Detail


Dahal, Sushil [1], Siniscalchi, Carolina [2], Folk, Ryan [3].

Population genomics and biogeography of Symphyotrichum in Mexico and the eastern U.S.

Biotic disjunctions, the occurrences of related organisms in disconnected areas of the Earth, have attracted scientific attention for the past 200 years. The eastern North American (ENA) – eastern Asian (EA) disjunction is the classic and best studied pattern of disjunct distribution in plants. Large numbers of species and genera also show a secondary eastern North American (ENA) - Mexican (M) disjunction, but despite being represented in many familiar plants (bald cypress, flowering dogwood, sweetgum, partridgeberry, etc.) this remains poorly understood. In this project, we use Symphyotrichum subgenus Virgulus to investigate the origin and timing of biogeographic connections across Mexico and the eastern US. Symphyotrichum, comprising most species traditionally treated as asters in the New World, is one of the most diverse genera in the eastern US but also extends across North America, Mexico, South America, the Caribbean, and Eurasia. Its broad presence across major biomes makes it an excellent system for investigating phylogeographic breaks across eastern North America and Mexico. Our hypotheses are: (i) the earliest radiation of Symphyotrichum occurred across Mexico and eastern North America (as well as western North America), with biogeographic movements between these regions ending by the late Miocene (~5-10 mya), and (ii) the ENA – M floristic disjunction in Symphyotrichum and reduction of dispersal between these regions was primarily caused by aridification of the interior of North America beginning ~5 mya.We performed molecular work using herbarium specimens to sequence accessions representing most of the species diversity of broader Symphyotrichum and representative sampling of the North American clade of Astereae for outgroups; our sampling of section Virgulus was at the population level with an average of 14 accessions per species for 25 species. We performed a sequence capture approach on DNA libraries using the Angiosperms353 baitset. We then used HybPiper to assemble the sequence data and used concatenation in RAxML-NG and coalescence in ASTRAL-III to perform phylogenetic analysis and treePL to perform divergence time estimation. We then used the R package BioGeoBEARS to infer ancestral regions and biogeographic transitions between North America and Mexico. Finally, we used an ancestral niche reconstruction approach to test for a role of historical aridification in generating the disjunction.Our molecular data suggest a recent radiation of Symphyotrichum of about 5 million years ago (latest Miocene to Pliocene), with early connections to Mexico in ancestral lineages that closed off shortly after, contrary to the Quaternary date of disjunction traditionally favored. Overall, vicariance was recovered as the primary mechanism connecting these regions. With the exception of some present-day broadly distributed species, there is a complete lack of movement between eastern North America and Mexico after 3.5 mya suggesting that the aridification of the interior of North America was directly implicated in causing today’s disjunctions between these regions. A reconstructed disjunct distribution of suitable habitat using late Pliocene climatic models of precipitation corroborate results from biogeographic modeling and confirm a role for aridification.

1 - 202 Milford Street, Apt 167, Tupelo, MS, 38801, United States
2 - P.O. Box 2896, Apt 2, Mississippi State, MS, 39762, United States
3 - Mississippi State University, Biological Sciences, 295 E. Lee Blvd., P.O. Box GY, Mississippi State, MS, 39762, United States

Plant Biogeography

Presentation Type: Oral Paper
Number: BIOG II003
Abstract ID:561
Candidate for Awards:None

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