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Coexistence of trichome variation in a natural plant population: a combined study using ecological and candidate gene approaches.

Kawagoe T, Shimizu KK, Kakutani T, Kudoh H - PLoS ONE (2011)

Bottom Line: The fitness of hairy and glabrous plants showed no significant differences in the field during two years.A similar result was obtained when sibling hairy and glabrous plants were transplanted at the same field site, whereas a fitness cost of trichome production was detected under a weak herbivory condition.Although balancing selection under fluctuating biotic environments is often proposed to explain the maintenance of defense variation, the lack of clear evidence of balancing selection in the study population suggests that other factors such as gene flow and neutral process may have played relatively large roles in shaping trichome variation at least for the single population level.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Faculty of Science, Kobe University, Kobe, Japan. kawagoe.t@ecology.kyoto-u.ac.jp

ABSTRACT
The coexistence of distinct phenotypes within populations has long been investigated in evolutionary ecology. Recent studies have identified the genetic basis of distinct phenotypes, but it is poorly understood how the variation in candidate loci is maintained in natural environments. In this study, we examined fitness consequences and genetic basis of variation in trichome production in a natural population of Arabidopsis halleri subsp. gemmifera. Half of the individuals in the study population produced trichomes while the other half were glabrous, and the leaf beetle Phaedon brassicae imposed intensive damage to both phenotypes. The fitness of hairy and glabrous plants showed no significant differences in the field during two years. A similar result was obtained when sibling hairy and glabrous plants were transplanted at the same field site, whereas a fitness cost of trichome production was detected under a weak herbivory condition. Thus, equivalent fitness of hairy and glabrous plants under natural herbivory allows their coexistence in the contemporary population. The pattern of polymorphism of the candidate trichome gene GLABROUS1 (GL1) showed no evidence of long-term maintenance of trichome variation within the population. Although balancing selection under fluctuating biotic environments is often proposed to explain the maintenance of defense variation, the lack of clear evidence of balancing selection in the study population suggests that other factors such as gene flow and neutral process may have played relatively large roles in shaping trichome variation at least for the single population level.

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The intensity of herbivory and fruit production in census plots for two years.(A) Mean (+SD) number of P. brassicae larvae on hairy and glabrous plants (filled and open bars, respectively) during the flowering seasons of 2005 and 2006 (left and right graphs, respectively). (B) Number of fruits (mean+SD) produced by hairy and glabrous plants (filled and open bars, respectively) for two years. The numbers of hairy and glabrous plants examined were 202 and 262 in 2005 and 160 and 199 in 2006.
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pone-0022184-g003: The intensity of herbivory and fruit production in census plots for two years.(A) Mean (+SD) number of P. brassicae larvae on hairy and glabrous plants (filled and open bars, respectively) during the flowering seasons of 2005 and 2006 (left and right graphs, respectively). (B) Number of fruits (mean+SD) produced by hairy and glabrous plants (filled and open bars, respectively) for two years. The numbers of hairy and glabrous plants examined were 202 and 262 in 2005 and 160 and 199 in 2006.

Mentions: We then examined the effect of trichomes on the abundance of P. brassicae larvae. The number of P. brassicae larvae per plant did not differ between the hairy and glabrous phenotypes throughout the flowering seasons in 2005 and 2006 (Figure 3A). The trichome term in the statistical model did not improve the explanatory power for the number of beetles, as shown by the almost equivalent AICs of the models with and without the term for 2005 and 2006 (Table S1). The presence or absence of damage on apical meristems did not depend on trichome production (Fisher's exact test, P = 0.75 in 2005, and P = 0.43 in 2006). Furthermore, the level of damage to the leaves also did not differ between hairy and glabrous plants (Figure S1). As expected from the lack of obvious effects of trichomes on herbivory, no significant difference in fruit production was found between hairy and glabrous plants for both years (Figure 3B; Table 1). Plants with a larger rosette size produced more fruits (Table 1), but the rosette size did not differ between hairy and glabrous plants (ANOVA, P = 0.49).


Coexistence of trichome variation in a natural plant population: a combined study using ecological and candidate gene approaches.

Kawagoe T, Shimizu KK, Kakutani T, Kudoh H - PLoS ONE (2011)

The intensity of herbivory and fruit production in census plots for two years.(A) Mean (+SD) number of P. brassicae larvae on hairy and glabrous plants (filled and open bars, respectively) during the flowering seasons of 2005 and 2006 (left and right graphs, respectively). (B) Number of fruits (mean+SD) produced by hairy and glabrous plants (filled and open bars, respectively) for two years. The numbers of hairy and glabrous plants examined were 202 and 262 in 2005 and 160 and 199 in 2006.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3139618&req=5

pone-0022184-g003: The intensity of herbivory and fruit production in census plots for two years.(A) Mean (+SD) number of P. brassicae larvae on hairy and glabrous plants (filled and open bars, respectively) during the flowering seasons of 2005 and 2006 (left and right graphs, respectively). (B) Number of fruits (mean+SD) produced by hairy and glabrous plants (filled and open bars, respectively) for two years. The numbers of hairy and glabrous plants examined were 202 and 262 in 2005 and 160 and 199 in 2006.
Mentions: We then examined the effect of trichomes on the abundance of P. brassicae larvae. The number of P. brassicae larvae per plant did not differ between the hairy and glabrous phenotypes throughout the flowering seasons in 2005 and 2006 (Figure 3A). The trichome term in the statistical model did not improve the explanatory power for the number of beetles, as shown by the almost equivalent AICs of the models with and without the term for 2005 and 2006 (Table S1). The presence or absence of damage on apical meristems did not depend on trichome production (Fisher's exact test, P = 0.75 in 2005, and P = 0.43 in 2006). Furthermore, the level of damage to the leaves also did not differ between hairy and glabrous plants (Figure S1). As expected from the lack of obvious effects of trichomes on herbivory, no significant difference in fruit production was found between hairy and glabrous plants for both years (Figure 3B; Table 1). Plants with a larger rosette size produced more fruits (Table 1), but the rosette size did not differ between hairy and glabrous plants (ANOVA, P = 0.49).

Bottom Line: The fitness of hairy and glabrous plants showed no significant differences in the field during two years.A similar result was obtained when sibling hairy and glabrous plants were transplanted at the same field site, whereas a fitness cost of trichome production was detected under a weak herbivory condition.Although balancing selection under fluctuating biotic environments is often proposed to explain the maintenance of defense variation, the lack of clear evidence of balancing selection in the study population suggests that other factors such as gene flow and neutral process may have played relatively large roles in shaping trichome variation at least for the single population level.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Faculty of Science, Kobe University, Kobe, Japan. kawagoe.t@ecology.kyoto-u.ac.jp

ABSTRACT
The coexistence of distinct phenotypes within populations has long been investigated in evolutionary ecology. Recent studies have identified the genetic basis of distinct phenotypes, but it is poorly understood how the variation in candidate loci is maintained in natural environments. In this study, we examined fitness consequences and genetic basis of variation in trichome production in a natural population of Arabidopsis halleri subsp. gemmifera. Half of the individuals in the study population produced trichomes while the other half were glabrous, and the leaf beetle Phaedon brassicae imposed intensive damage to both phenotypes. The fitness of hairy and glabrous plants showed no significant differences in the field during two years. A similar result was obtained when sibling hairy and glabrous plants were transplanted at the same field site, whereas a fitness cost of trichome production was detected under a weak herbivory condition. Thus, equivalent fitness of hairy and glabrous plants under natural herbivory allows their coexistence in the contemporary population. The pattern of polymorphism of the candidate trichome gene GLABROUS1 (GL1) showed no evidence of long-term maintenance of trichome variation within the population. Although balancing selection under fluctuating biotic environments is often proposed to explain the maintenance of defense variation, the lack of clear evidence of balancing selection in the study population suggests that other factors such as gene flow and neutral process may have played relatively large roles in shaping trichome variation at least for the single population level.

Show MeSH
Related in: MedlinePlus