Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)



Committee Chair(s)

Ivan G. Palmblad


Ivan G. Palmblad


Frank B. Salisbury


Raymond Lynn


Martyn Caldwell


Keith L. Dixon


Mimulus guttatus populations in Yellowstone Park were studied in relation to their thermal habitat. Thermal areas have an extra-solar heat source, and are not snow covered in winter. Snow depth on adjacent non thermal soils may exceed 1 meter. The hypothesis that these populations have formed a distinct high temperature tolerant race was tested.

Thermal populations form two categories, based on habitat type: plants on sinter and plants in boggy areas. Plants growing on sinter are dwarfed, with an average height of 5.6 ±. 2.2 cm. They are facultative annuals which germinate in the fall, overwinter as rosettes, and flower the following spring. Plants in boggy areas average 27.7 ±. 4.3 cm in height, are perennials which colonize open areas by vegetative reproduction, and which also overwinter as rosettes. Plants removed from sinter and placed in conditions with ample water assume the morphological characteristics and perennial habit of plants from boggy sites. Summer leaf temperatures of healthy plants in thermal areas seldom exceed 36 C, but root temperatures may reach 40 - 45 C. The upper limit of root temperature in the field is about 45 C. Winter leaf temperatures ranged from 5 - 20 C and root temperatures from 10 - 29 C.

Seeds from thermal populations, germinated at four temperature combinations, show a negative correlation between germination success and increasing temperature of treatment. Germination was optimal at 10/5 C (day/night temperatures). In the laboratory, seed was obtained from artificial cross-pollination between Mimulus populations growing on sinter and in boggy areas. At 2 0/10 C germination success varied among populations from 62% to 81%. Seed from crosses between plants of thermal and nonthermal populations had germination success from 92% to 100% , varying with population.

Photosynthesis rates for nonthermal Mimulus at 8, 25, and 35 C showed a maximum at 25 C. Plants grown at low temperatures, but pretreated for 24 hours at 25 C had higher photosynthetic rates at 25 C and 35 C than plants pretreated at 10 C, indicating an ability to adapt quickly to temperature changes.

Plants from the thermal areas do not have high leaf temperatures, nor do they exhibit tolerance to high temperatures during germination or during photosynthesis. No significant reproductive barriers were found between thermal and nonthermal populations; the only criteria examined were seed set of cross-pollinated plants and germinability of the F1 seed. It is concluded that Mimulus guttatus in the Yellowstone thermal areas is probably not a high-temperature tolerant race. Its success in high temperature areas is derived from the ability to utilize more than one life cycle and growth form strategy in response to stress.



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