what can rodent midden fossils tell us about polyploid evolution?

The Bouteloua curtipendula (Poaceae) complex (BCC) is presently identified as 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 aneuploid 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 are examining 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.