Populations Of Primula Vulgaris Research Articles

Genomic analyses elucidate S-locus evolution in response to intra-specific losses of distyly in Primula vulgaris.

Distyly, a floral dimorphism that promotes outcrossing, is controlled by a hemizygous genomic region known as the S-locus. Disruptions of genes within the S-locus are responsible for the loss of distyly and the emergence of homostyly, a floral monomorphism that favors selfing. Using whole-genome resequencing data of distylous and homostylous individuals from populations of Primula vulgaris and leveraging high-quality reference genomes of Primula we tested, for the first time, predictions about the evolutionary consequences of transitions to selfing on S-genes. Our results reveal a previously undetected structural rearrangement in CYPᵀ associated with the shift to homostyly and confirm previously reported, homostyle-specific, loss-of-function mutations in the exons of the S-gene CYPᵀ. We also discovered that the promoter and intronic regions of CYPᵀ in distylous and homostylous individuals are conserved, suggesting that down-regulation of CYPᵀ via mutations in its promoter and intronic regions is not a cause of the shift to homostyly. Furthermore, we found that hemizygosity is associated with reduced genetic diversity in S-genes compared with their paralogs outside the S-locus. Additionally, the shift to homostyly lowers genetic diversity in both the S-genes and their paralogs, as expected in primarily selfing plants. Finally, we tested, for the first time, long-standing theoretical models of changes in S-locus genotypes during early stages of the transition to homostyly, supporting the assumption that two copies of the S-locus might reduce homostyle fitness.

Spatial genetic structure and reproductive success in fragmented and continuous populations ofPrimula vulgaris

In Flanders (northern Belgium),Primula vulgaris, a self-incompatible long-lived perennial herb, is rare and consists of a network of fragmented populations in the intensively used agricultural landscape. We investigated genetic variation and structure using 27 allozyme loci in 41 populations, and reproductive success to assess the effect of fragmentation on gene flow and the influence of the nearest neighbouring (large and/or highly genetically diverse) population on within-population genetic variation and reproductive success. Isolation by distance was found among and within populations. Smaller and more isolated populations showed a slight loss of allelic variation, but maintained high levels of observed heterozygosity. They were not more differentiated from each other than large populations. No significant difference in the regression slopes of the spatial autocorrelation analysis was found between two continuous populations and two groups of fragmented populations with similar distance classes. Multiple regression showed that population allelic richness and reproductive success were higher when the nearest neighbouring population was genetically more diverse. These results suggest moderate current gene flow within and among populations rather than historical gene flow. We conclude that small and isolated populations ofP. vulgaris should be considered not only as remnants of previously larger populations, but also as potential stepping stones insuring gene flow processes. For conservation, all highly variable and flowering populations should be considered, irrespective of their size or their isolation from large and continuous populations.

Homostyle primroses re-visited. I. Variation in time and space

Populations of Primula vulgaris L. generally consist of two self incompatible heterostyle morphs, but in Somerset, S.W. England, a third type, homostyle, also occurs and was studied in the 1940s and 1950s by J. Crosby and others. A more extensive mapping of the distribution and frequencies of the three morphs has now been carried out and 30 well defined local populations have been re-scored after 25–40 years have elapsed. The observed changes in morph frequency were only slight but showed a frequency dependent pattern. This is contrary to the prediction of Crosby who expected the homostyles would increase in all cases because they self fertilise and can pollinate one of the heterostyle morphs. Computer simulations of this breeding system combined with other fitness variables showed that a restricted range of values for inbreeding depression, inviability of the homozygous homostyle and gene flow between populations would give frequency dependent change of the kind which was observed.

High Proportions of Homostyle Plants in Populations of Primula vulgaris

As part of a study of heterostyly in Primula, with particular reference to the fertility relations existing between the two normally occurring types, pin and thrum, counts of their proportions in natural populations have been made. My own data have been supplemented by some counts made by friends and colleagues in various parts of Britain.