title: Effects of apomixis and polyploidy on diversification and geographic distribution in Amelanchier (Rosaceae).
abstract: •
  
  
  OBJECTIVE
  Amelanchier polyploid apomicts differ from sexual diploids in their more complex diversification, 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 flow cytometry to estimate genome size of 1355 plants. We estimated the frequency of apomixis from flow-cytometrically 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.•
  
  
  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 first 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 find 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 diversification, 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.
authors.affiliation: Department of Biological Sciences, State University of New York, Plattsburgh, Plattsburgh, New York 12901 USA.
authors.forename: Michael B
authors.initials: MB
authors.lastname: Burgess
authors.affiliation: School of Biology and Ecology, University of Maine, Orono, Maine 04469 USA.
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Cushman
authors.affiliation: School of Biology and Ecology, University of Maine, Orono, Maine 04469 USA.
authors.forename: Eric T
authors.initials: ET
authors.lastname: Doucette
authors.affiliation: Royal Ontario Museum, Department of Natural History, 100 Queen's Park, Toronto, M5S 2C6, Canada.
authors.forename: Nadia
authors.initials: N
authors.lastname: Talent
authors.affiliation: Maryland Department of Natural Resources, Natural Heritage Program, 909 Wye Mills Road, Wye Mills, Maryland 21679 USA.
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Frye
authors.affiliation: School of Biology and Ecology, University of Maine, Orono, Maine 04469 USA.
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Campbell
mesh_terms: D060832:Apomixis; D044822:Biodiversity; D032461:Chromosomes, Plant; D017753:Ecosystem; D056625:Endosperm; D049810:Genetic Speciation; D018745:Genome, Plant; D009656:North America; D063148:Plant Dispersal; D011003:Ploidies; D011058:Pollen; D011123:Polyploidy; D012098:Reproduction / Q000235:genetics; D027824:Rosaceae / Q000235:genetics / Q000502:physiology*; D012639:Seeds; D013045:Species Specificity
keywords: apomixis; endosperm balance; flow cytometry; geographic parthenogenesis; microspecies; polyploidy; semi-cryptic ploidy variation; triploid block; triploid bridge