Distribution of free and glycosylated sterols within Cycas micronesica plants

Marler, Thomas E.; Shaw, Christopher A.

doi:10.1016/j.scienta.2009.11.009

Cited by 7 publications

(3 citation statements)

References 37 publications

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“…Sterols and derived glucosides vary among locations throughout Guam (Marler et al. 2005, 2007; Marler & Shaw 2010). In particular, cycads on sandy soils from the littoral habitat have higher seed concentrations of steryl glucosides than plants on upland regions of Guam (Marler 2002).…”

Section: Discussionmentioning

confidence: 99%

When North and South don’t mix: genetic connectivity of a recently endangered oceanic cycad, Cycas micronesica, in Guam using EST-microsatellites

et al. 2010

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Subject to environmental changes and recurrent isolation in the last ca. 250 Ma, cycads are often described as relicts of a previously common lineage, with populations characterized by low genetic variation and restricted gene flow. We found that on the island of Guam, the endemic Cycas micronesica has most of the genetic variation of 14 EST-microsatellites distributed within each of 18 genetic populations, from 24 original sampling sites. There were high levels of genetic variation in terms of total number of alleles and private alleles, and moderate levels of inbreeding. Restricted but ongoing gene flow among populations within Guam reveals a genetic mosaic, probably more typical of cycads than previously assumed. Contiguous cycad populations in the north of Guam had higher selfrecruitment rates compared to fragmented populations in the south, with no substantial connection between them except for one population. Guam's genetic mosaic may be explained by the influence of forest continuity, seed size, edaphic differences, and human transport of cycads. Also important are the extent of synchrony among flushes of reproductive female seed-bearing sporophylls and restricted pollen movement by an obligate mutualist and generalist insects. An NADH EST-locus under positive selection may reflect pressure from edaphic differences across Guam. This and three other loci are ideal candidates for ecological genomic studies. Given this species' vulnerability due to the recent introduction of the cycad aulacaspis scale, we also identify priority populations for ex situ conservation, and provide a genetic baseline for understanding the effects of invasive species on cycads in the Western Pacific, and islands in general.

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Section: Discussionmentioning

confidence: 99%

When North and South don’t mix: genetic connectivity of a recently endangered oceanic cycad, Cycas micronesica, in Guam using EST-microsatellites

et al. 2010

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“…Total stem height and stem diameter at the base were measured ( Table 1). Field methods for excision of stem tissue were patterned after Marler and Shaw [20]. A 2.54 cm hole saw was installed in a hand drill and a core was extracted at 30 cm below the oldest leaf petiole.…”

Section: Field Methodsmentioning

confidence: 99%

Cycas micronesica Stem Carbohydrates Decline Following Leaf and Male Cone Growth Events

Marler

Cruz

2020

Plants

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The growth of synchronized leaf flushes or male cones on Cycas trees is an ephemeral event, and non-structural carbohydrates (NSCs) are likely deployed from stem and root storage tissues to support their construction. The relationships among various stem NSCs and these rapid growth events have not been studied to date. Monosaccharides, disaccharides, and starch were quantified in Cycas micronesica stem tissue prior to and immediately after the growth of leaf flushes or male cones to determine the influences on the concentration of these carbohydrates. The pre-existing leaves were removed from half of the plants to determine if the elimination of this carbon source would influence the NSC behaviors. Starch and sucrose dominated the NSC profiles, and these two NSCs declined following cone or new leaf growth. Removal of pre-existing leaves generated a greater decline in starch and sucrose for cone growth, and a greater decline in sucrose, but not starch following new leaf growth than in control trees with no leaf removal. The initial differences in starch and sucrose among cortex, vascular, and pith tissues disappeared as the concentrations declined in all three tissue categories to reach similar post-growth concentrations among the stem tissue categories. The fructose, glucose, and maltose behaviors were not consistent, and their concentrations were low such that their influence on the total NSC behaviors was minimal. These results provided indirect evidence that stem NSCs were mobilized to support ephemeral male cone and new leaf growth for this arborescent cycad. Growth of female strobili is slow and lengthy, so we did not include female trees in this study. The contributions of stem NSCs to female strobili growth remain to be studied with alternative methods.

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“…Cycads produce several toxic compounds in their leaves and other tissues, including steryl glycosides, β‐Methylamino‐ l ‐alanine (BMAA) and methylazoxymethanol acetate (MAM) (Laquer and Spatz, 1968; Morgan and Hoffman, 1983; Spencer et al ., 1987; Marler and Shaw, 2010; Kisby et al ., 2013). These compounds are toxic to most animals (Whiting, 1963) and are therefore presumed to function as anti‐herbivore defences, though MAM is the only compound for which experimental evidence exists for insect deterrence (Bowers and Larin, 1989; Castillo‐Guevara and Rico‐Gray, 2003; Prado et al ., 2014).…”

Section: Defensive Ecologymentioning

confidence: 99%

Ecology and evolution of cycad‐feeding Lepidoptera

Whitaker

Salzman

2020

Ecology Letters

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Cycads are an ancient group of tropical gymnosperms that are toxic to most animals – including humans – though the larvae of many moths and butterflies (order: Lepidoptera) feed on cycads with apparent immunity. These insects belong to distinct lineages with varying degrees of specialisation and diverse feeding ecologies, presenting numerous opportunities for comparative studies of chemically mediated eco‐evolutionary dynamics. This review presents the first evolutionary evaluation of cycad‐feeding among Lepidoptera along with a comprehensive review of their ecology. Our analysis suggests that multiple lineages have independently colonised cycads from angiosperm hosts, yet only a few clades appear to have radiated following their transitions to cycads. Defensive traits are likely important for diversification, as many cycad specialists are warningly coloured and sequester cycad toxins. The butterfly family Lycaenidae appears to be particularly predisposed to cycad‐feeding and several cycadivorous lycaenids are warningly coloured and chemically defended. Cycad–herbivore interactions provide a promising but underutilised study system for investigating plant–insect coevolution, convergent and divergent adaptations, and the multi‐trophic significance of defensive traits; therefore the review ends by suggesting specific research gaps that would be fruitfully addressed in Lepidoptera and other cycad‐feeding insects.

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Distribution of free and glycosylated sterols within Cycas micronesica plants

Cited by 7 publications

References 37 publications

When North and South don’t mix: genetic connectivity of a recently endangered oceanic cycad, Cycas micronesica, in Guam using EST-microsatellites

When North and South don’t mix: genetic connectivity of a recently endangered oceanic cycad, Cycas micronesica, in Guam using EST-microsatellites

Cycas micronesica Stem Carbohydrates Decline Following Leaf and Male Cone Growth Events

Ecology and evolution of cycad‐feeding Lepidoptera

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