Bell, Hester L. , Harrington, Judy , Reid, Scott .
Patterns of speciation in Distichlis (Poaceae).
Hybridization is known to be a significant mechanism leading to speciation in plants and is often accompanied by karyotypic changes such as translocations and dysploidy. In grass subfamily Chloridoideae the most common base chromosome numbers are 9 and 10 and these are most frequently found as tetraploids. Recently an intensive study has found two cytoraces within Distichlis spicata sensu lato; one with 2n = 4x = 38 (38-chromosome cytorace) and the other 2n = 4x = 40 (40-chromosome cytorace). Do these cytoraces derive from independent hybridization events or from the same event via loss or gain of chromosomes? The 38-chromosome cytorace occurs in the western plains region and Great Basin desert of North America. In the ITS phylogeny, the 38-chromosome cytorace resolves as sister to a clade of D. spicata s.l. that includes specimens from New Mexico (known to be a 40-chromosome cytorace) and Virginia, USA, Mexico (Coahuila), Argentina (Chubut), Chile (Valpariso), and D. palmeri, Mexico (Sonora). The ITS phylogeny supports derivation of the 38-chromosome cytorace from the 40-chromosome cytorace. In another major clade within the genus, D. eludens (2n = 38) resolves in a derived position with respect to D. littoralis (2n = 40). However, the presence of 38 chromosomes in a named species and, distinctly, in multiple populations does not imply that the reduction in chromosome numbers represents the same evolutionary event. These taxa may or may not contain the same 38 chromosomes. And the complement of 38 chromosomes may have resulted from the same or different processes. Additional evidence for reticulation in Distichlis has been found in a hybrid population in Chile (D. humilis x D. spicata) and hard conflict between nuclear and chloroplast phylogenies in the placement of three South American endemics. Strategies to find explanations for these patterns of speciation in Distichlis will be discussed.
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1 - Rancho Santa Ana Botanic Garden, 1500 North College Avenue, Claremont, California, 91711, USA
2 - Colorado State University, Soil and Crop Sciences, 1170 Campus Delivery, Fort Collins, Colorado, 80523, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 553B/Convention Center
Date: Monday, August 2nd, 2010
Time: 5:00 PM