PARENT SESSION
Contributed Oral Session 11: Invasive Species: Arid Lands
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 520 A, Level 5, Palais des congrès de Montréal
Genetic variation in Bromus tectorum: differentiation among populations in the mid-continent United States.
Schachner, Lauren *,1, Novak, Stephen2, Mack, Richard1, 1 Washington State University, Pullman, WA2 Boise State University, Boise, ID
ABSTRACT- The invasion of Bromus tectorum (cheatgrass) has accelerated throughout the mid-continent of the United States during the last century. We analyzed 54 populations of this grass with enzyme electrophoresis to determine its regional genetic variation and population structure in comparison to populations in the native Eurasian range and elsewhere in North America. The percentage of polymorphic populations rises from east to west across the U.S., caused by the co-occurrence of the descendants of multiple introductions. On average, populations in the mid-continent U.S. contain more alleles and polymorphic loci than populations in the eastern U.S. but less than the variation among western U.S. populations. Heterozygotes, which had not previously been detected in B. tectorum in North America, occur in at least three populations in the mid-continent. These out-crossing events have likely created novel multi-locus genotypes. Mid-continent U.S. populations of B. tectorum collectively display a much lower percentage of among-population variation (Gst = 0.290) than the among-population variation in Eurasian populations (Gst = 0.754). The regional restriction of specific allelic variants of B. tectorum across much of the U.S. is striking. Variants Pgm-1a and Pgm-2a occur widely among populations in the mid-continent, whereas the previously reported Got-4c is widespread throughout western U.S. populations. The continued spread of pre-adapted genotypes and the mixing of populations descended from once isolated multiple introductions in the mid-continent U.S. may be enhancing the cheatgrass invasion by increasing both the genetic variation within populations and the potential for the selection of novel genotypes arising from occasional out-crossing.
Key words: Bromus tectorum, biotic invasion, multiple introductions, allozyme variation