UBC Theses and Dissertations
Biosystematics of the annual species of the Mimulus guttatus species complex in British Columbia, Canada Benedict, Beverly G.
The M. guttatus species complex consists of several morphologically and ecologically distinct taxa, which, for the most part, are able to intercross; this makes it both an evolutionarily fascinating group to study and a taxonomic nightmare. In this study I found that on one ecologically diverse hillside on Vancouver Island, British Columbia (B. C.), Canada, three distinct species of the M. guttatus species complex grow sympatrically. These three species included: 1) M. guttatus, a large flowered, facultatively annual diploid 2) M. nasutus, a small flowered, annual diploid, and 3) a small flowered, annual tetraploid to which a previous name could not be applied. This taxon has been named M. queue. In addition to the B.C. populations, M. nasutus and M. guttatus populations from California and M. queue populations from Oregon were also studied. Pre-zygotic crossing barriers reduce gene exchange between M. nasutus and M. guttatus. Both pre- and post-zygotic crossing barriers have effectively isolated M. queue from M. guttatus and M. nasutus. Under most growing conditions, the three taxa can be distinguished morphologically. However, when collected from dry habitats the two small flowered species are difficult to separate. Nineteen different measurements of the flower and calyx were taken. The ranges of all 19 measurements were overlapping for M. nasutus and M. queue. Medians were significantly different for calyx measurements, the difference between calyx length and pistil length and the difference in length of the upper and lower corollalobes. Boxplot comparisons of the B.C. and California populations of M. nasutus revealed no significant differences in the medians of the floral measurements. Only one floral measurement was found to be significantly different when the Oregon populations of M. queue were compared to the B. C. populations of M. queue. Discriminant and principle component analysis grouped individuals moderately wellinto the proper species. Discrimination was poorest when very small flowers were used. Enzyme electrophoresis indicated distinct differences in genetic diversity and in the compartmentalization of the diversity between the primarily autogamous M. queue and M. nasutus, and M. guttatus with its mixed mating system. The southern populations of M. nasutus and M. queue exhibited somewhat greater gene diversity than the northern populations. The presence of fixed heterozygosity in all populations of M. queue indicated that it is likely an allopolyploid. Whether the B.C. and Oregon populations are directly related or independently derived could not be determined from the present data. More collecting is required to determine the geographic distribution of M. queue and to shed light on its evolutionary past.
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