Date of Award:

5-2010

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Advisor/Chair:

James H. Cane

Abstract

Astragalus filipes Torrey ex. A. Gray (Fabaceae) is being studied and propagated for use in rangeland restoration projects throughout the Great Basin. Restoration forbs often require sufficient pollination services for seed production and persistence in restoration sites. Knowledge of a plant's breeding biology is important in providing pollination for maximal seed set. Reproductive output from four manual pollination treatments (autogamy, geitonogamy, xenogamy, and distant xenogamy) was examined in a common garden. Pod set, seed set, and seed germination were quantified for each of the treatments. Seed set from four wild populations was compared to that of an openly visited common garden array. A. filipes was found to be self-compatible, but to benefit greatly from outcrossing. Less seed germinated from distantly outcrossed treatments than for any other treatment, indicating possible outbreeding depression. Common garden plants set less seed per pod than any wild population, possibly due to a depauperate pollinator guild in the common garden. Bees were surveyed at wild A. filipes populations to identify common pollinators. Solitary and social bee species were observed visiting A. filipes to estimate aspects of their pollination efficacies, particularly foraging tempo and frequency of stigmatic contact. The nesting biologies of bees that visit A. filipes were considered as a component of bee manageability. Bees in the genus Osmia (Megachilidae) dominated this pollinator guild. Bombus nevadensis queens were the fastest foragers; honey bees and native solitary bees did not differ in foraging tempo. Megachilid bees consistently contacted the stigma during foraging, but honey bees exhibited sideworking behavior, contacting stigmas far less frequently than any other bee species observed. Two solitary bee species (Osmia bruneri and Hoplitis hypocrita) are recommended as prospective pollinators for management in association with Great Basin rehabilitation efforts.

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