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Abstract Detail

Paleobotanical Section

Halbrook, Kandres [1], Smith, Steven [1], Columbus, J. Travis [2], Siqueiros-Delgado, Maria Elena [3].

What can rodent midden macrofossils tell us about polyploid evolution in Bouteloua curtipendula (Poaceae)?

THE Bouteloua curtipendula (Poaceae) complex (BCC) is a group of 11 species and five varieties widely distributed in North and South America. Bouteloua curtipendula var. caespitosa is the only apomictic and commonly polyploid taxon in the complex. It possesses chromosome numbers ranging from diploid (2n = 2x = 20) to high polyploid (2n = 41 to > 100). It is also the only widely distributed BCC taxon common within the most arid portions of the complex’s range. Given the close association between this taxon and contemporary aridity, we hypothesize that there is a positive relationship between the appearance and widespread persistence of high polyploidy in B. curtipendula and the increase in post-Pleistocene aridity in what is now the southwestern United States and extreme northern Mexico. To test this hypothesis we will examine BCC macrofossils preserved in rodent middens spanning the past 44,000 years. Our goals are to determine 1) when high polyploid BCC taxa enter the midden record and 2) whether this is related to the onset of environmental drying at that locale. Middens were located in the southeastern margin of the current range of var. caespitosa where putative diploid progenitors of this taxon are also found. Critical to our approach is the ability to differentiate spikelet structures derived from plants of different ploidy based on morphometric analysis of cellular characteristics. We report results of these analyses using contemporary BCC taxa of known ploidy.

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1 - University of Arizona, School of Natural Resources, 325 Biological Sciences East, Tucson, Arizona, 85721, USA
2 - Rancho Santa Ana Botanic Garden, 1500 North College Avenue, Claremont, California, 91711, USA
3 - Universidad Autónoma De Aguascalientes, Herbario, Centro Basico, Ave. Universidad # 940, Aguascalientes, Aguascalientes, 20100, Mexico


Presentation Type: Poster:Posters for Sections
Session: 48-102
Location: Auditorium/Bell Memorial Union
Date: Tuesday, August 1st, 2006
Time: 12:30 PM
Abstract ID:389

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