Publications by authors named "Rebekah Mohn"

2 Publications

  • Page 1 of 1

The phylogeographic history of a range disjunction in eastern North America: the role of post-glacial expansion into newly suitable habitat.

Am J Bot 2021 06 22;108(6):1042-1057. Epub 2021 Jun 22.

Center for Conservation and Sustainable Development, Missouri Botanical Garden, 4344 Shaw Blvd., St. Louis, Missouri, 63110, USA.

Premise: A disjunct distribution, where a species' geographic range is discontinuous, can occur through vicariance or long-distance dispersal. Approximately 75 North American plant species exhibit a ~650 km disjunction between the Ozark and Appalachian regions. This disjunction is attributed to biogeographic forces including: (1) Eocene-Oligocene vicariance by the formation of the Mississippi embayment; (2) Pleistocene vicariance from interglacial flooding; (3) post-Pleistocene northward colonization from separate glacial refugia; (4) Hypsithermal vicariance due to climate fluctuations; and (5) recent long-distance dispersal. We investigated which of these pathways most likely gave rise to the Appalachian-Ozark disjunction in Delphinium exaltatum.

Methods: We genotyped populations of D. exaltatum from five Ozark and seven Appalachian localities, analyzed genetic structure, tested the order and timing of divergences using DIYABC, and conducted niche reconstructions up to 21,000 years before present (YBP).

Results: Populations fell into five main genetic clusters, i.e., a group in the central Appalachians, and four "lowland" groups. DIYABC analyses showed the central Appalachian and lowland lineages diverging 11,300 to17,000 YBP, and the lowland groups diverging 6800 to 10,900 YBP. Niche reconstructions showed that suitable climate for the central Appalachian lineage experienced large spatial discontinuity starting 14,000 YBP, such that divergence and persistence before this period is less plausible than divergence thereafter.

Conclusions: Our results did not fully support any of the original hypotheses. Rather, the oldest divergence likely occurred after 13,500 YBP through expansion into newly opened habitat in the Appalachians. The Appalachian-Ozark disjunction likely resulted from northward dispersal of the lowland lineage as climate warmed during the Holocene.
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http://dx.doi.org/10.1002/ajb2.1686DOI Listing
June 2021

Topological Data Analysis as a Morphometric Method: Using Persistent Homology to Demarcate a Leaf Morphospace.

Front Plant Sci 2018 25;9:553. Epub 2018 Apr 25.

Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT, United States.

Current morphometric methods that comprehensively measure shape cannot compare the disparate leaf shapes found in seed plants and are sensitive to processing artifacts. We explore the use of persistent homology, a topological method applied as a filtration across simplicial complexes (or more simply, a method to measure topological features of spaces across different spatial resolutions), to overcome these limitations. The described method isolates subsets of shape features and measures the spatial relationship of neighboring pixel densities in a shape. We apply the method to the analysis of 182,707 leaves, both published and unpublished, representing 141 plant families collected from 75 sites throughout the world. By measuring leaves from throughout the seed plants using persistent homology, a defined morphospace comparing all leaves is demarcated. Clear differences in shape between major phylogenetic groups are detected and estimates of leaf shape diversity within plant families are made. The approach predicts plant family above chance. The application of a persistent homology method, using topological features, to measure leaf shape allows for a unified morphometric framework to measure plant form, including shapes, textures, patterns, and branching architectures.
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http://dx.doi.org/10.3389/fpls.2018.00553DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5996898PMC
April 2018
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