Inheritance of mating-system modifier genes in Eichhornia paniculata (Pontederiaceae)

Abstract

The evolutionary breakdown of tristyly to predominant self-fertilization in Eichhornia paniculata (Pontederiaceae) is associated with the spread and fixation of floral variants of the mid-styled morph (M) with modified short-level stamens. Reduced stigma–anther separation in the variants results in a high degree of self-fertilization. To investigate if the genetic basis of mating-system modification differs among floral variants from different parts of the geographical range of the species we performed controlled crosses on genotypes from six populations from N.E. Brazil and Jamaica. Measurements of floral traits in self and F₁ crosses grown under uniform glasshouse conditions demonstrated that the gene(s) modifying stamen position in the M morph are largely recessive, have no apparent phenotypic effects on other floral characters and are only expressed in the M morph. Crosses between modified genotypes from northern and southern parts of N.E. Brazil resulted in F₁ progeny with unmodified flowers, indicating that different recessive genes are responsible for stamen modification in the two regions. Crosses between modified genotypes from Jamaica and the two regions of N.E. Brazil indicated a more complex basis for stamen modification in Jamaica, and confirmed that the genetic basis of selfing differed between the two regions of Brazil. Our results provide evidence that the evolution of self-fertilization in E. paniculata has occurred by different genetic pathways. In addition, the data suggest that the sequence of events commences with the fixation of recessive alleles affecting only filament length, followed by evolution at modifier loci responsible for larger phenotypic changes to floral architecture.