Date of Award:

5-1-1996

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Committee Chair(s)

Diane G. Alston

Committee

Diane G. Alston

Committee

Vincent J. Tepedino

Committee

Paul G. Wolf

Abstract

Broad-spectrum insecticide spraying for the control of grasshoppers may have a detrimental effect of native pollinators of western rangelands. Many rangeland plants depend upon such pollinators for successful reproduction. Pollinators also transfer genes between plants via pollen, and pollinator movement between plants is related to pollinator density; thus insecticide application may alter gene movements in a plant population. This study uses a common forb, Echinacea angustifolia, to examine the potential negative effects of insecticide application on gene movements. I first determined the breeding system of E. angustifolia and specifically whether an insect vector is required for reproduction. Flowers set seed significantly more often when visited by insects, presumably the several bee and butterfly species found visiting the flowers. The breeding system is primarily xenogamous, but some self-fertilization does occur. Numbers of seed set between control and outcrossed flowers were statistically indistinguishable, indicating that plants were not pollinator limited. Secondly, I tested selfed against outcrossed achenes for a fitness decline by examining achene weight and germination rate (inbreeding depression). Selfed achenes had fewer fully developed endosperms and were less fit (e.g., had lower weight and germination) than outcrossed achenes. In the second portion of the study, I estimated genetic diversity and described genetic population structure of E. angustifolia populations in a large rangeland region in southwestern North Dakota. I found that genetic diversity was similar to estimates from other studies of E. angustifolia, and to other taxa with similar life history traits. I also found that populations across the study area were genetically homogenous, with little population subdivision. These findings were present in both the established population (P generation) and in the offspring produced during the study (F1 generation). Finally, I examined direct estimates of gene movements, outcrossing rates and mating distances, within populations subjected to different insecticide treatments. Neither outcrossing rates nor mating distances were significantly different between control and spray treatments in the same year insecticides were applied, nor among historical spray treatments (5, 2, or 1 year since spraying). There is thus no evidence that insecticide spraying on rangeland alters outcrossing rates or mating distances of this common prairie species. Implications for rare plant management are discussed.

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