Publication Date


Type of Culminating Activity


Degree Title

Master of Science in Biology



Major Advisor

Stephen J. Novak


Invasive species are novel to a region, thus their timely and accurate identification is a critical first step in recognizing and managing the threats that they may present in their new habitats. Accurate identification of an introduced species in its new range can prove difficult however for a species that displays taxonomic complexity in its native range, i.e. consists of multiple, morphologically similar subspecies.

Across its native range, Taeniatherum caput-medusae (medusahead) exhibits taxonomic complexity. Three subspecies have been recognized: T. caput-medusae ssp. caput-medusae, T. caput-medusae ssp.asperum, and T. caput-medusae ssp. crinitum. While subspecies caput-medusae is found in the western Mediterranean and subspecies crinitum occurs from eastern Europe to Central Asia, subspecies asperum is distributed across the geographic distribution of the species. Only subspecies asperum is believe to occur in the United States, where it is now invasive in portions of California, Idaho, Nevada, Oregon, Utah, and Washington. As part of ongoing research to better understand and manage this invasion, genetic analyses of both native and invasive populations of medusahead were conducted. An important prerequisite to these analyses is the proper identification of the three subspecies. In the current study, plants from each native population were grown in a greenhouse common garden, harvested at maturity, and measured using previously described morphological characters. After Bonferroni correction, three characters, glume length, glume angle, and

palea length, were found to be statistically significant. Thus, these three characters were quite useful in assigning plants to each of the three subspecies. I found that two other characters, lemma hairs and conical cells, were less informative. Differentiation among native populations of medusahead was further assessed using a molecular genetic marker. The results of a UPGMA cluster diagram based on allozyme data indicates that subspecies crinitum is genetically differentiated from the other two, some populations of subspecies caput-medusae and asperum co-occur within different clusters, and subspecies asperum is the most variable. Results of the analysis of multilocus genotypes are generally consistent with the UPGMA diagram (e.g., subspecies caput-medusae and asperum share six multilocus genotypes). This research confirms the need of such studies to disentangle the taxonomic complexity that can be found in the native range of invasive species.

The results of an earlier allozyme analysis were consistent with the genetic signature associated with multiple introductions, although this finding can only be confirmed with the analysis of native populations. In the current study, I compared allozyme diversity in native and invasive populations of medusahead to: identify the geographic origin(s) for the U.S. invasion, test the multiple introduction hypothesis, and determine the genetic consequences of these events. Five of the seven homozygous multilocus genotypes previously observed in the western U.S. have been detected in native populations. The geographic origins for these introductions appear to have been drawn from France, Sardinia, Greece, and Turkey, although additional analyses are ongoing. These findings provide support for the multiple introduction hypothesis. Results of this study have implications for the biological control of medusahead: i) the search for effective and specific biological control agents will have to occur broadly across the species’ native range, ii) multiple agents may be required to control invasive populations that are admixtures, and iii) because invasive population are genetically depauperate, highly adapted biocontrol agents are likely to be quite effective.