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Population Genetics/Genomics

Harritt, Iris C. [1], Takebayashi, Naoki [2], Flint, Paul L. [3], Ruess, Roger W. [2], Wolf, Diana E. [2].

Carex subspathacea grazing lawns and their taxonomic affinity.

Sedges are notoriously difficult to identify, due to hybridization and a paucity of informative morphological characters, yet they are critically important to sub-arctic and arctic ecosystems. We studied the population genomic structure of sedges that serve as the main food source to Black Brant Geese (Branta bernicla nigricans) in their breeding grounds on the Yukon Kuskokwim Delta (YKD) on the western coast of Alaska, and the Arctic Coastal Plain (ACP). On the YKD, two sedge growth forms exist; a short (0.5-3cm) and a tall (>10cm) whereas only the short form exists on the ACP.   Previous researchers studying goose grazing systems considered the short lawns maintained by grazing to be C. subspathacea whereas the taller, ungrazed meadows were thought to be C. ramenskii.  This view was challenged by studies showing that the two growth forms could be switched by manipulation of grazing intensity.   Excluding the short lawns from grazing caused them to convert to a taller, less nutritious growth form. Likewise, tall meadows that were artificially grazed were subsequently adopted by geese and maintained as short lawns. However, this conversion required several years to occur, and it could have been caused by morphological changes in individual plants, or replacement of one species by the other.   To understand the functioning of these grazing systems and the taxonomic affinities of the short and tall grazing lawns, we conducted a population genomic study using sequence capture of 894 loci from 97 individual plants.   We sampled putative C. subspathacea, C. ramenski, and related taxa from the YKD and ACP, as well as from herbarium specimens throughout the species' ranges. PCA and STRUCTURE analysis showed that both the short and tall sedges on the YKD breeding grounds clustered with C. subspathacea, and were genetically indistinguishable from each other. Thus, C. subspathacea on the YKD is phenotypically plastic with two distinct growth forms - a tall form with low-nitrogen concentration, and a short form with high-nitrogen concentration that is maintained by grazing.   Lawns on the ACP, which only show the short morphology, also clustered entirely with C. subspathacea, although there was minor genetic differentiation between the YKD and ACP populations. This suggests that there is infraspecific geographic variation in terms of phenotypic plasticity in response to herbivory. Other herbarium specimens that had been identified as C. ramenskii were found to be hybrids between C. subspathacea and several other species.

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1 - University of Alaska Fairbanks, Department of Biology and Wildlife, 101 Murie Building, 2090 Koyukuk Drive, University of Alaska Fairbanks, Fairbanks, AK, 99775, USA
2 - University of Alaska Fairbanks, Institute of Arctic Biology, 2140 Koyukuk Drive, PO Box 757000, University of Alaska Fairbanks, Fairbanks, AK, 99775, USA
3 - US Geological Survey Alaska Science Center, 4210 University Drive, Anchorage, AK, 99508, USA

Targeted enrichment
population genetic structure
Population genomics.

Presentation Type: Oral Paper
Session: PGG2, Population Genetics and Genomics II
Location: /
Date: Wednesday, July 21st, 2021
Time: 11:45 AM(EDT)
Number: PGG2008
Abstract ID:684
Candidate for Awards:Margaret Menzel Award

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