PARENT SESSION
Poster Session #19: Invasive Species Ecology: Deserts and Rangelands.
Tuesday, August 6. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

A RAPD assessment of outcrossing and invasion in cheatgrass (Bromus tectorum).

Ashley, Michael^*,1, Longland, William^*,1,2, ¹ United States Department of Agriculture, Reno, NV² University of Nevada, Reno, Reno, NV

ABSTRACT- Cheatgrass (Bromus tectorum) is a self-pollinating exotic invasive weed that typically invades new habitats following disturbance whether natural or anthropogenic. Cheatgrass invasion of novel habitats in the absence of disturbance is rare. It has been hypothesized that obligate self-pollinators will outcross under ideal conditions, shuffling genotypes within a population and producing propagules that may be preadapted for novel environments. Once established, it is expected that self-pollination will resume, preserving successful genotypes. We documented a 1995 cheatgrass invasion of a sand dune system in W. Nevada, where cheatgrass was previously absent. We collected samples in 1995 and subsequent years. We used randomly amplified polymorphic DNA (RAPD), dominant markers, to evaluate 46 of the 1995 invaders for evidence of outcrossing (i.e.; genetic variation). Using Operon Technologies primer kit P (n = 20) we found 18 primers that produced a total of 98 repeatable bands, 21 polymorphic, yielding 21 phenotypes. Null allele frequency within individuals ranged from 1 to 10 (&xmacr;= 4.20, S.E. = 0.26) with average estimated heterozygosity of 0.31 (S.E. = 0.02). Seventeen individuals (37%) shared a single phenotype, the remaining phenotypes differing by up to six alleles (&xmacr; = 2.50, S.E. = 0.37). Relatedness ranged from 0.48 to 0.95 (&xmacr;= 0.86, S.E. = 0.09). We identified seven RAPD phenotypes that could have given rise through outcrossing to all the observed combinations. It is possible that as few as one or two source populations in more typical habitats nearby could have accumulated the critical phenotypes as inbred matrilines through normal dispersal. We expect that RAPD profiles of subsequent generations will show a decrease in polymorphism as a result of a return to selfing. These results support the hypothesis that facultative outcrossing by a self-pollinating species is a potential means of facilitationg invasion through production of novel gene combinations.

KEY WORDS: Invasiveness, Exotic Species, RAPD Markers, Bromus tectorum