Buzz-pollinated Dodecatheon originated from within the heterostylous Primula subgenus Auriculastrum (Primulaceae): A seven-region cpDNA phylogeny and its implications for floral evolution

Abstract

We sequenced seven cpDNA regions from 70 spp. in Dodecatheon, Primula subgenus Auriculastrum, and outgroups, reconstructed their cpDNA phylogeny with maximum parsimony, and determined branch support with bootstrap frequencies and Bayesian posterior probabilities. Strongly supported conclusions include the (1) paraphyly of Primula subgenus Auriculastrum with respect to a monophyletic Dodecatheon, (2) sister relationship between the North American Dodecatheon and the Californian P. suffrutescens, (3) novel basal split in Dodecatheon to produce one clade with rugose and one clade with smooth anther connectives, (4) monophyly of all sections of Primula subgenus Auriculastrum, and (5) exclusion of the enigmatic Primula section Amethystina from the similar Primula subgenus Auriculastrum. These results support the origin of the monomorphic, buzz-pollinated flower of Dodecatheon from the heterostylous flower of Primula. We marshal evidence to support the novel hypothesis that the solanoid flower of Dodecatheon represents the fixation of recessive alleles at the heterostyly linkage group (pin phenotype). Of the remaining traits associated with their solanoid flowers, we recognize at least six likely to have arisen with the origin of Dodecatheon, one that preceded it (flower coloration, a transfer exaptation in Dodecatheon), and one that followed it (rugose anther connectives, an adaptation to buzz pollination).