The evolutionary pathway from outcrossing to high levels of self-fertilization has been followed in numerous taxa of herbaceous flowering plants.  

Because of the profound influence of this change in mating system on the biology of populations, there has been sustained interest in the determination of the selective mechanisms and evolutionary consequences of the transition. The breakdown of heterostyly to homostyly is a classic system for the investigation of evolutionary transitions from outcrossing to selfing. 

Recently, the research group led by Prof. LI Dezhu and Prof. WANG Hong from Kunming Institute of Botany, Chinese Academy of Sciences, cooperating with Prof. Spencer Barrett from University of Toronto and Dr. WU Zhikun form Lijiang Forest Ecosystem Research Station, performed a molecular phylogeographic study to investigate the geographical context for the breakdown process in Primula chungensis, a species with distylous and homostylous populations.  

The marker data identified two multi-population lineages (Tibet and Sichuan) and one single-population lineage (Yunnan), a pattern consistent with at least two independent origins of homostyly.  

Evidence from flower and pollen size variation is consistent with the hypothesis that transitions to selfing have arisen by the same genetic mechanism involving recombination and/or mutation at the distyly linkage group.  

Nevertheless, flowers of homostylous lineages have followed divergent evolutionary trajectories following their origin, resulting in populations with both approach and reverse herkogamy.  

The study illustrates a rare example of the near-complete replacement of sexual polymorphism by floral monomorphism in a heterostylous species. 

This study entitled “Phylogeographic insights on the evolutionary breakdown of heterostyly” was published on New phytologist.  

This work was financially supported by the National Key Basic Research Program of China, the Joint Fund of the National Natural Science Foundation of China-Yunnan Province, the Major International Joint Research Project of the National Natural Science Foundation of China, Light of West China Program of the Chinese Academic of Sciences, the National Natural Science Foundation of China.  

 Fig. Floral morph, morphology, and population genetic differenciation in Primula chungensis (Primulaceae). (Image by KIB)