The influence of herbivores other than P. brassicae for plant fitness could not be examined in the study population because of their low abundance. The hairy phenotype may be advantageous in populations which harbor different herbivore communities. If gene flow occurs between local populations, geographic variation in selection on trichome variation can affect the phenotypic frequency of single populations. Thus, it will be valuable to investigate relative effects of local selection, demography and gene flow on trichome variation in a metapopulation framework. It remains to be answered why hairy and glabrous plants exhibited equivalent fitness under intense herbivory despite the cost of trichome production. The lack of a fitness difference between the two trichome phenotypes may be due to highly intense herbivory. Nearly half of the naturally grown plants did not produce any fruit, and 70% of plants produced five or less fruits. Thus, in terms of fruit production, intense herbivory is likely to hinder the cost of trichome production becoming apparent. Alternatively, the cost of trichome production in hairy plants might be counterbalanced by a small advantage of defense under intense herbivory. This is less likely, however, because the abundance of beetles found on hairy and glabrous plants did not differ significantly. All of the glabrous plants we examined were homozygous for the large insertion that originated from a CACTA-family transposon, while the polymorphisms found in two putative adjacent genes were not associated with trichome phenotypes. Furthermore, these flanking genes are not known to be involved in trichome development in A. thaliana . It is less likely that a mutation that AB1010 disrupts the function of the regulatory region causes the loss of trichomes, because GL1 was transcribed in both trichome phenotypes . Dinaciclib CDK inhibitor Although we cannot rule out the possibility that mutation in other linked loci is responsible for the glabrous phenotype, our finding of 100% association of the homozygosity of the large insertion with the glabrous phenotype suggests that GL1 is involved in trichome variation.