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Petersen, Kurt B. [1], Minx, Patrick [1], Biang, Kathrines [2], Clewell, Sarah [2], Bookout, Bess [3], McAllister, Chrissy [4], McKain, Michael [5], Kellogg, Elizabeth [6].

Insights into the evolutionary ecology of grass awns and spikelets within the Andropogoneae.

Flower-bearing structures (spikelets) of grasses are highly diverse in form. A particularly striking feature of the spikelets and grasses overall is the awn, which is a long extension generally originating from the lemma, but sometimes also from other structures such as the glume. Awns are usually hypothesized to be involved in dispersal, and with proposed functions in diaspore burial, wind dispersal, or animal dispersal attributed to them. However, the function of grass awns has been assessed in only a few species, leaving most of grass diversity unsampled. Grass awns can be broadly classified as hygroscopically active (twisting in response to moisture), passive and inactive, or completely missing. In this study we focused on awn morphology in a major clade of the grass tribe Andropogoneae (Andropogon, Schizachyrium, Diheteropogon, and Hyparrhenia). This study used whole plastome sequences to estimate phylogenetic relationships among 162 total plastomes representing 132 species. The phylogeny included 5 outgroup specimens and 157 in-clade specimens. Measurements of awn and spikelet morphology were correlated with environmental variables using data extracted from large scale public environmental databases. Environmental variables included aspects of fire ecology (burned area), plant cover, soil types, and environmental moisture. Phylogenetically adjusted generalised least squares analyses suggest that environments with larger areas burned on average per fire event have a positive relationship with awn length. In contrast, leaf area index, interpreted as denser foliage in the surrounding habitat has a negative relationship with awn lengths. Curiously, net primary productivity of the surrounding environment had no relationship to awn length. The results support previous limited experimental evidence that large awns bury seeds deeper to protect from fire, and may also indicate that large awns are selected against in more competitive foliage dense environments. This study suggests that awn morphology is likely multifunctional and selection may not always be acting on one single establishment or dispersal function.

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1 - Donald Danforth Plant Science Center, 975 N Warson Rd, Saint Louis, MO, 63132, USA
2 - Principia College, Biology and Natural Resources, Elsah, IL, USA
3 - Kansas State University, Manhattan, KS, 66506, USA
4 - Principia College, 1 Maybeck Place, Principia College, 1 Maybeck Place, Principia College, Elsah, IL, 62028, United States
5 - The University of Alabama, Biological Sciences, Tuscaloosa, AL, USA
6 - Donald Danforth Plant Science Center, 975 North Warson Road, St. Louis, MO, 63132, United States

floral evolution
C4  grasses
evolutionary ecology

Presentation Type: Oral Paper
Session: MACROIII, Macroevolution III
Location: Virtual/Virtual
Date: Friday, July 23rd, 2021
Time: 10:30 AM(EDT)
Number: MACROIII003
Abstract ID:787
Candidate for Awards:None

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