Effects of Apomixis and Polyploidy on Diversification and Geographic Distribution in Amelanchier (Rosaceae)
Burgess MB, Cushman KR, Doucette ET, Talent N, Frye CT, Campbell CS. 2014. Effects of Apomixis and Polyploidy on Diversification and Geographic Distribution in Amelanchier (Rosaceae). American Journal of Botany. 101(8):1375 – 1387
• Premise of the study: Amelanchier polyploid apomicts differ from sexual diploids in their more complex diversifi cation, greater species problems, and geographic distribution. To understand these differences, we investigated the occurrence of polyploidy and frequency of apomixis. This research helps clarify species delimitation in an evolutionarily complex genus. • Methods: We used fl ow cytometry to estimate genome size of 1355 plants. We estimated the frequency of apomixis from fl owcytometrically determined ploidy levels of embryo and endosperm and from a progeny study using RAPD markers. We explored relationships of triploids to other ploidy levels and of ploidy levels to latitude plus elevation. • Key results: Diploids (32% of sample) and tetraploids (62%) were widespread. Triploids (6%) mostly occurred in small numbers with diploids from two or more species or with diploids and tetraploids. Seeds from diploids were 2% apomictic, the fi rst report of apomixis in Amelanchier diploids. Seeds from triploids were 75% apomictic. We documented potential triploid bridge and triploid block from unbalanced endosperm and low pollen viability. Seeds from tetraploids were 97% apomictic, and tetraploids often formed microspecies. We did not fi nd strong evidence for geographical parthenogenesis in North American Amelanchier . Most currently recognized species contained multiple ploidy levels that were morphologically semicryptic. • Conclusions: Documentation of numerous transitions from diploidy to polyploidy helps clarify diversifi cation, geographic distribution, and the species problem in Amelanchier . Despite the infrequent occurrence of triploids, their retention of 25% sexuality and capacity for triploid bridge may be important steps between sexual diploids and predominantly apomictic tetraploids.
- Type
- Journal Article
- Authors
- Burgess, Michael; Cushman, Kevin; Doucette, Eric; Talent, Nadia; Frye, Christopher; Campbell, Christopher
- Units
- GRSM
- Keywords
- Amelanchier, apomixis, endosperm balance, flow cytometry, geographic parthenogenesis, microspecies, polyploidy, Rosaceae, semicryptic ploidy variation, shadbush, triploid block, triploid bridgem GRSM-01003