Abstract Detail

Systematics

Hayes, Drew [1], Smith, Tyler [1], Whittemore, Alan [2].

Genetic diversity of Celtis pumila, an apomictic triploid, and its diploid relatives in eastern North America.

The taxonomic diversity of North American Celtis L. (Hackberries) remains uncertain. This is due in large part to variable and over-lapping morphology among putative species, often interpreted as evidence of widespread hybridization. As C. pumila Pursh (Dwarf Hackberry) is a Threatened species in Canada, this has important conservation implications. Unfortunately, agency biologists cannot reliably distinguish it from the widespread C. occidentalis L. (Common Hackberry), and are uncertain how best to manage populations of suspected hybrids. We addressed these issues by assessing the genetic diversity of Celtis populations across eastern North America, using microsatellite markers, flow cytometry and morphology. We found two genetically discrete diploid groups corresponding to C. occidentalis and C. laevigata Willd., with a small number of hybrids where their ranges overlap in southern Missouri and Illinois. We could not identify a diploid group corresponding to Celtis pumila; this species appears to be predominantly or completely triploid. Genetically, C. pumila is intermediate to the diploids, consistent with expectations for an allopolyploid. Its distribution is broader than either of the diploids, extending further north than C. laevigata, and further south than C. occidentalis. Celtis pumila had limited intra-population genetic diversity, consistent with apomictic reproduction. A single genotype was shared by 72 individuals sampled from 6 populations up to 700 km apart in Michigan, Ohio, and Pennsylvania, and also accounted for more than 95% of the plants sampled in Ontario. Individuals with this genotype exhibited remarkable morphological and ecological diversity, including stunted dwarf forms less than 1.5 m tall, growing in open alvars; and understory trees 5 m tall, growing in mesic forests. While C. pumila has apparently formed multiple times, we found no evidence for contemporary hybridization with C. occidentalis. Lacking any fixed differences in SSR loci, assessing ploidy with flow cytometry provides a reliable method for distinguishing C. pumila from its diploid relatives. We are currently developing ddRAD markers to further resolve the genetic relationships among these species.

1 - Agriculture And Agri-Food Canada, 960 Carling Avenue, Ottawa, ON, K1A 0C6, Canada
2 - UNITED STATES NATIONAL ARBORETUM, 3501 New York Ave NE, Washington, DC, 20002, USA

Keywords:
taxonomy
polyploidy
Microsatellites
flow cytometry
population genetics.

Presentation Type: Oral Paper
Session: SYS2, Systematics II: Rosids part 1 to Asterids part 1
Location: Tucson G/Starr Pass
Date: Wednesday, July 31st, 2019
Time: 9:00 AM
Number: SYS2005
Abstract ID:822
Candidate for Awards:None