The function of the hygroscopic awn of<i>Themeda triandra</i><sup>1</sup>

Adams, Kathy; Tainton, N.M.

doi:10.1080/02566702.1990.9648248

Cited by 7 publications

(18 citation statements)

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“…Hygroscopic awns, with their complex cellular morphology (see Elbaum and Abraham 2014) are probably metabolically expensive to construct, especially at the end of winter when resources are scare (Adams and Tainton 1990). Therefore, as Charles Darwin and his son believed, they likely evolved to serve an ecological purpose (Darwin 1876).…”

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confidence: 99%

Is a long hygroscopic awn an advantage forThemeda triandrain drier areas?

Morris

2020

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Themeda triandra has bigeniculate hygroscopic lemma seed awns that twist when wet and drying, thereby transporting the caryopsis across the soil surface into suitable germination microsites. The prediction that awns would be longer in drier grassland and have greater motility to enable them to move quickly and further to find scarce germination sites was tested in KwaZulu-Natal. Awns (n = 100) were collected from 16 sites across a mean annual precipitation gradient (575-1223 mm), ranging from 271-2097 m a.s.l. The daily movement of hydrated long and short awns (n = 10) across blotting paper was tracked for five days, and the rotational speed of anchored awns was measured. Awn length varied considerably (mean: 41.4-63.2 mm; sd: 3.44-8.99) but tended to increase (r = 0.426, p = 0.099) not decline, with increasing MAP. Awn length was unrelated to elevation, temperature and aridity indices. Long awns rotated at the same rate (2 min 48 sec) but moved twice as fast (46.3 vs. 22.1 mm day -1 ) and much further (maximum: 82.1 vs. 38.6 mm day -1 ) than short awns. Whether moisture limits awn development, the benefit of longer awns to negotiate densely tufted mesic grassland, and the multifunctionality of awns require investigation.

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confidence: 99%

Is a long hygroscopic awn an advantage forThemeda triandrain drier areas?

Morris

2020

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“…While the influence of abiotic and biotic vectors on diaspore dispersal are well understood, the ability of diaspores to disperse autochorously (self-disperse) is less well studied. Central to this process are awns, a long and rigid bristle-like seed appendage (Murbach, 1900;Peart, 1979;Stamp, 1984;Peart and Clifford, 1987;Adams and Tainton, 1990;Sindel et al, 1993;Garnier and Dajoz, 2001;Elbaum et al, 2007;Johnson and Baruch, 2014).…”

Section: Introductionmentioning

confidence: 99%

“…This hygroscopic ability enables awns to mechanically move the attached seed across the soil surface and then bury it (Stamp, 1989;Garnier and Dajoz, 2001). Hygroscopic awns have been found to move diaspores across a soil surface up to 6 cm per day (Adams and Tainton, 1990) and have a competitive advantage over passively-awned diaspores in finding a safe-site (sensu Harper et al, 1965;Peart and Clifford, 1987). This dispersal capability is enhanced if the awn is geniculate, that is, it contains a sharp bend (Peart, 1979).…”

Section: Introductionmentioning

confidence: 99%

“…Longer-awned diaspores have also been found to bury deeper into soil than diaspores with shorter awns of the same species (Garnier and Dajoz, 2001). In some species, however, the presence of an awn may hinder burial (Adams and Tainton, 1990).…”

Section: Introductionmentioning

confidence: 99%

“…Given that awns are a large resource investment for many grass species and potentially convey important plant fitness benefits (Adams and Tainton, 1990), it is surprising that more consideration has not been given to this variation. While some previous studies have examined the effect of awn morphology on diaspore dispersal (e.g., Peart, 1979Peart, , 1981, microsite selectivity (e.g., Fowler, 1986) and diaspore burial (e.g., Tothill, 1969;Peart, 1979), most studies on awns have been on the mechanics of hygroscopic awn movement (e.g., Murbach, 1900;Abraham and Elbaum, 2013;Elbaum and Abraham, 2014;Jung et al, 2014;Masrahi and Shaye, 2017), and the comparison between these active awns and rigid, passive awns (e.g., Peart, 1984;Peart and Clifford, 1987).…”

Section: Introductionmentioning

confidence: 99%

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Awn Morphology Influences Dispersal, Microsite Selection and Burial of Australian Native Grass Diaspores

2020

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Diverse ecological functions and the convergent evolution of grass awns

Petersen

Kellogg

2022

American J of Botany

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The awn of grasses is a long, conspicuous outgrowth of the floral bracts in a grass spikelet. It is known to impact agricultural yield, but we know little about its broader ecological function, nor the selective forces that lead to its evolution. Grass awns are phenotypically diverse across the extant ~12,000 species of Poaceae. Awns have been lost and gained repeatedly over evolutionary time, between and within lineages, suggesting that they could be under selection and might provide adaptive benefit in some environments. Despite the phylogenetic context, we know of no studies that have tested whether the origin of awns correlates with putative selective forces on their form and function. Presence or absence of awns is not plastic; rather, heritability is high. The awns of grasses often are suggested as adaptations for dispersal, and most experimental work has been aimed at testing this hypothesis. Proposed dispersal functions include soil burial, epizoochory, and aerial orientation. Awns may also protect the seed from drought, herbivores, or fire by helping it become buried in soil. We do not fully understand the fitness or nutrient costs of awn production, but in some species awns function in photosynthesis, providing carbon to the seed. Here we show that awns likely provide an adaptive advantage, but argue that studies on awn function have lacked critical phylogenetic information to demonstrate adaptive convergent evolution, are taxonomically biased, and often lack clear alternative hypotheses.

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The function of the hygroscopic awn ofThemeda triandra¹

Cited by 7 publications

References 3 publications

Is a long hygroscopic awn an advantage forThemeda triandrain drier areas?

Is a long hygroscopic awn an advantage forThemeda triandrain drier areas?

Awn Morphology Influences Dispersal, Microsite Selection and Burial of Australian Native Grass Diaspores

Diverse ecological functions and the convergent evolution of grass awns

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The function of the hygroscopic awn ofThemeda triandra1

Cited by 7 publications

References 3 publications

Is a long hygroscopic awn an advantage forThemeda triandrain drier areas?

Is a long hygroscopic awn an advantage forThemeda triandrain drier areas?

Awn Morphology Influences Dispersal, Microsite Selection and Burial of Australian Native Grass Diaspores

Diverse ecological functions and the convergent evolution of grass awns

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The function of the hygroscopic awn ofThemeda triandra¹