Coexistence of Trichome Variation in a Natural Plant Population: A Combined Study Using Ecological and Candidate Gene Approaches

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

Inheritance of glabrous plants in Helianthemum oelandicum var. oelandicum and spatial patterns of allele frequencies in local populations

Helianthemum oelandicum var. oelandicum is an endemic taxon on the Baltic island of Öland, SE Sweden. Plants can be classified into two morphs: the bristled morph (with bristles and with or without scattered stellate hairs) and the glabrous morph (without bristles and stellate hairs). In crosses between plants assumed to be homozygous for the trait that characterises the phenotypes of the two morphs, offspring in F1 could not be distinguished from the bristled morph. Segregation in F2 did not deviate from the expected 3:1 ratio (bristled morphs/glabrous morphs), indicating one major gene with a dominant allele for the phenotype of the bristled morph and a recessive allele for the phenotype of the glabrous morph. Besides the Mendelian inheritance of presence/absence of hairs, the density of hairs appeared to be further modified by quantitative genes. The frequency of the recessive allele for the phenotype of the glabrous morph varied among local populations and showed a geographical structure, both on local and regional scales. Possible mechanisms behind the spatial variation in indumentum are discussed