Phylogeographic insights on the evolutionary breakdown of heterostyly.
The breakdown of heterostyly to homostyly is a classic system for the investigation of evolutionary transitions from outcrossing to selfing. Loss of sexual polymorphism is characterized by changes to population morph structure and floral morphology. Here, we used molecular phylogeography to investigate the geographical context for the breakdown process in Primula chungensis, a species with distylous and homostylous populations. We genotyped plants from 20 populations throughout the entire range in south-west China using the chloroplast intergenic spacer (trnL-trnF), nuclear internal transcribed spacer (ITS) and 10 nuclear microsatellite loci, and determined the genetic relationships among populations and the variation in floral traits associated with homostyle evolution. 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. Our study illustrates a rare example of the near-complete replacement of sexual polymorphism by floral monomorphism in a heterostylous species.
Plant Germplasm and Genomics Center, Germplasm Bank of Wild Species, Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming, Yunnan, 650201, China.
Wei
W
Zhou
Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, M5S 3B2, Canada.
Spencer C H
SC
Barrett
Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming, Yunnan, 650201, China.
Hai-Dong
HD
Li
Lijiang Forest Ecosystem Research Station, Kunming Institute of Botany, Chinese Academy of Sciences, Lijiang, Yunnan, 674100, China.
Zhi-Kun
ZK
Wu
Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming, Yunnan, 650201, China.|University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing, 100049, China.
Xin-Jia
XJ
Wang
Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming, Yunnan, 650201, China.
Hong
H
Wang
Plant Germplasm and Genomics Center, Germplasm Bank of Wild Species, Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming, Yunnan, 650201, China.
De-Zhu
DZ
Li
D018742:DNA, Chloroplast / Q000235:genetics; D035264:Flowers / Q000235:genetics / Q000502:physiology*; D017343:Genes, Plant; D018895:Microsatellite Repeats / Q000235:genetics; D058974:Phylogeography; D031825:Primula; D019655:Quantitative Trait, Heritable
D018742:DNA, Chloroplast

Primula chungensis
; floral evolution; heterostyly; homostyly; mating systems; phylogeography; selfing