Population Genetics of the Invasive Grass Taeniatherum Caput-Medusae (L.) Nevski (Poaceae)

Publication Date


Type of Culminating Activity


Degree Title

Master of Science in Biology



Major Advisor

Stephen J. Novak


James F. Smith


Marcelo Serpe


The mating system of an introduced plant is critical to its establishment and proliferation. Taeniatherum caput-medusae (Poaceae) is a self-pollinating annual that has invaded large areas of the western United States. A preliminary investigation of allozyme variability detected several heterozygotes; therefore suggesting limited outcrossing occurs within introduced populations. Using progeny arrays, the mating system parameters were determined for a total of ten populations in California, Idaho, and Oregon. For each population, a total of ten individuals per family and ten families were analyzed (n = 1000). Seven of the populations contained no heterozygous individuals in any family, indicating complete selfing. In three populations, a total of 23 heterozygous progeny were detected. Two populations contained 21 heterozygous individuals across four families. Genotypes of the progeny in these four families conformed to Mendelian expectations, thus indicating that the maternal plants were likely heterozygous. In one population (Emigrant Hill, OR), two heterozygous individuals occurred in two separate families, and appear to be the result of outcrossing during the progeny generation. The single-locus outcrossing rate across all populations was very low (t = 0.002). Results suggest that low frequency genotypes present in several introduced populations may be the result of outcrossing, and probably do not represent separate introductions or spread into these populations. The creation of novel genotypes in introduced populations from outcrossing between genotypes originating from geographically disparate populations in the native range has consequences for the proliferation, success, and evolution of highly selfing invasive plants.

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