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Fine ‐ scale frequency differentiation along a herbivory gradient in the trichome dimorphism of a wild Arabidopsis

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ABSTRACT

Geographic variation is commonly observed in plant resistance traits, where plant species might experience different selection pressure across a heterogeneous landscape. Arabidopsis halleri subsp. gemmifera is dimorphic for trichome production, generating two morphs, trichome‐producing (hairy) and trichomeless (glabrous) plants. Trichomes of A. halleri are known to confer resistance against the white butterfly, cabbage sawfly, and brassica leaf beetle, but not against flea beetles. We combined leaf damage, microclimate, and microsatellite loci data of 26 A. halleri populations in central Japan, to explore factors responsible for fine‐scale geographic variation in the morph frequency. We found that hairy plants were less damaged than glabrous plants within populations, but the among‐site variation was the most significant source of variation in the individual‐level damage. Fixation index (Gst″) of a putative trichome locus exhibited a significant divergence along population‐level damage with an exception of an outlier population, inferring the local adaptation to herbivory. Notably, this outlier was a population wherein our previous study reported a balancing role of the brassica leaf beetle Phaedon brassicae on the morph frequency. This differentiation of the trichome locus was unrelated to neutral genetic differentiation (evaluated by Gst″ of microsatellite loci) and meteorological factors (including temperature and solar radiation). The present findings, combined with those of our previous work, provide suggestive evidence that herbivore‐driven divergence and occasional outbreak of a specific herbivore have jointly contributed to the ecogeographic pattern in the frequency of two morphs.

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Population differentiation (Gst″) of a putative trichome locus along the gradient of the population‐level damage (a), neutral genetic differentiation (b), or meteorological components (c, d). The leaf damage and meteorological PCs are shown as differences of a focal variable between sites. Gray closed circles represent a site pair. Red open circles highlight site pairs including the outlier polymorphic population (site 25; Figure 2). Trend lines are added to the entire dataset (dashed line) or to the dataset excluding the outliers (solid line) in panel (a)
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ece32830-fig-0004: Population differentiation (Gst″) of a putative trichome locus along the gradient of the population‐level damage (a), neutral genetic differentiation (b), or meteorological components (c, d). The leaf damage and meteorological PCs are shown as differences of a focal variable between sites. Gray closed circles represent a site pair. Red open circles highlight site pairs including the outlier polymorphic population (site 25; Figure 2). Trend lines are added to the entire dataset (dashed line) or to the dataset excluding the outliers (solid line) in panel (a)

Mentions: Next, we examined ecological and genetic factors responsible for population differentiation in the frequency of hairy and glabrous plants (Table 2). Based on the largest amount of the among‐site variation in the individual‐level damage (Table 1), the population‐level damage was represented as an average leaf damage pooled among the trichome phenotypes and study years. We found a marginally significant tendency in trichome Gst″ increase along with the increased difference in the population‐level damage (Table 2a, Figure 4a); however, this increase in trichome Gst″ became significant when site 25 (the site where the brassica leaf beetle P. brassicae was especially prevalent) was excluded as an outlier (Table 2b, Figure 4a). These correlations were detected even when the population‐level damage was evaluated using the dataset of glabrous plants only (partial Mantel test with 9,999 permutations, trichome Gst″ versus damage, r = .06, p = .57 for all dataset; r = .27, p = .001 for data excluding site 25). The trichome Gst″ was not significantly correlated with either the microsatellite Gst″ (Figure 4b) or the meteorological components (Table 2, Figure 4c,d).


Fine ‐ scale frequency differentiation along a herbivory gradient in the trichome dimorphism of a wild Arabidopsis
Population differentiation (Gst″) of a putative trichome locus along the gradient of the population‐level damage (a), neutral genetic differentiation (b), or meteorological components (c, d). The leaf damage and meteorological PCs are shown as differences of a focal variable between sites. Gray closed circles represent a site pair. Red open circles highlight site pairs including the outlier polymorphic population (site 25; Figure 2). Trend lines are added to the entire dataset (dashed line) or to the dataset excluding the outliers (solid line) in panel (a)
© Copyright Policy - creativeCommonsBy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5383478&req=5

ece32830-fig-0004: Population differentiation (Gst″) of a putative trichome locus along the gradient of the population‐level damage (a), neutral genetic differentiation (b), or meteorological components (c, d). The leaf damage and meteorological PCs are shown as differences of a focal variable between sites. Gray closed circles represent a site pair. Red open circles highlight site pairs including the outlier polymorphic population (site 25; Figure 2). Trend lines are added to the entire dataset (dashed line) or to the dataset excluding the outliers (solid line) in panel (a)
Mentions: Next, we examined ecological and genetic factors responsible for population differentiation in the frequency of hairy and glabrous plants (Table 2). Based on the largest amount of the among‐site variation in the individual‐level damage (Table 1), the population‐level damage was represented as an average leaf damage pooled among the trichome phenotypes and study years. We found a marginally significant tendency in trichome Gst″ increase along with the increased difference in the population‐level damage (Table 2a, Figure 4a); however, this increase in trichome Gst″ became significant when site 25 (the site where the brassica leaf beetle P. brassicae was especially prevalent) was excluded as an outlier (Table 2b, Figure 4a). These correlations were detected even when the population‐level damage was evaluated using the dataset of glabrous plants only (partial Mantel test with 9,999 permutations, trichome Gst″ versus damage, r = .06, p = .57 for all dataset; r = .27, p = .001 for data excluding site 25). The trichome Gst″ was not significantly correlated with either the microsatellite Gst″ (Figure 4b) or the meteorological components (Table 2, Figure 4c,d).

View Article: PubMed Central - PubMed

ABSTRACT

Geographic variation is commonly observed in plant resistance traits, where plant species might experience different selection pressure across a heterogeneous landscape. Arabidopsis halleri subsp. gemmifera is dimorphic for trichome production, generating two morphs, trichome‐producing (hairy) and trichomeless (glabrous) plants. Trichomes of A. halleri are known to confer resistance against the white butterfly, cabbage sawfly, and brassica leaf beetle, but not against flea beetles. We combined leaf damage, microclimate, and microsatellite loci data of 26 A. halleri populations in central Japan, to explore factors responsible for fine‐scale geographic variation in the morph frequency. We found that hairy plants were less damaged than glabrous plants within populations, but the among‐site variation was the most significant source of variation in the individual‐level damage. Fixation index (Gst″) of a putative trichome locus exhibited a significant divergence along population‐level damage with an exception of an outlier population, inferring the local adaptation to herbivory. Notably, this outlier was a population wherein our previous study reported a balancing role of the brassica leaf beetle Phaedon brassicae on the morph frequency. This differentiation of the trichome locus was unrelated to neutral genetic differentiation (evaluated by Gst″ of microsatellite loci) and meteorological factors (including temperature and solar radiation). The present findings, combined with those of our previous work, provide suggestive evidence that herbivore‐driven divergence and occasional outbreak of a specific herbivore have jointly contributed to the ecogeographic pattern in the frequency of two morphs.

No MeSH data available.


Related in: MedlinePlus