http://hdl.handle.net/10177/1070 http://libmedia.willamette.edu:8080/xmlui/retrieve/4398 http://hdl.handle.net/10177/1070 http://hdl.handle.net/10177/2113 Comparing Insect Pollinator Community Associations Between Sympatric Species of Camassia (Agavaceae) and the Potential for Pollinator-Mediated Reproductive Isolation Kotaich, Adam In this study we examined the composition of a generalist insect pollinator community associated with populations of Camassia (Agavaceae) in the Willamette Valley, Oregon. Two species, C. quamash and C. leichtlinii, occur in sympatry at Kingston Prairie. We investigated whether visitation from the shared pollinator community differed between these Camassia species, which are morphologically similar and able to hybridize, yet remain genetically distinct throughout their range. Surveys conducted over a 3-week period confirmed that both Camassia species are visited by a diverse array of generalist pollinators and further indicate that overall insect pollinator visitation is 1.5 times greater to C. leichtlinii than to C. quamash along unispecific transects. Moreover, surveys along mixed transects (with both co-flowering species) revealed overall pollinator visitation was 2.9 times greater to C. leichtlinii than to C. quamash. These results suggest a preference for C. leichtlinii by insect pollinators, which is made more apparent when the two species flower concurrently. The overall preference for C. leichtlinii is greatly influenced by solitary bees, the most abundant group of insect pollinators. Social bees were less abundant, yet also showed a similar visitation preference toward C. leichtlinii. This preference, which preliminary data suggest is influenced by a greater nectar reward produced by C. leichtlinii, may contribute to pollinator-mediated reproductive isolation, thus limiting interspecific pollen movement and maintaining species distinctions. http://hdl.handle.net/10177/2103 The Effects of the Hormonal Herbicide, 2,4-Dichlorophenoxyacetic Acid, on Xenopus laevis Sperm Viability and Motility Lane, Alicia The troubling decline of amphibian populations worldwide may be tied an overall decline in fertility caused by prolonged environmental exposure to endocrine disruptors. The effects of concentration- and time- dependent exposure to 2,4-dichlorophenoxyacetic acid (2,4-D), a synthetic auxin hormonal herbicide, on Xenopus laevis sperm viability and motility were tested in vitro using microscopy with trypan blue staining. Exposure to environmentally relevant concentrations of 2,4-D caused a significant concentration-dependent and time-independent decline in sperm viability. 2,4-D exposure also resulted in decline in sperm motility that appeared to be both concentration- and time-dependent. The observed negative effects of 2,4-D exposure on sperm viability and motility could inhibit the ability of the sperm to successfully fertilize eggs, which would in turn alter reproductive success. http://hdl.handle.net/10177/2101 Xenopus laevis Oocyte Maturation Following Maternal Exposure to Environmentally-Relevant Doses of the Hormonal Herbicide, 2,4-D Aney, Jordan Hormones regulate many sensitive life processes and play key roles in animal reproduction, growth and development. Endocrine disrupting chemicals (EDCs) are factors in the environment which can derail these processes by mimicking, promoting or interfering with natural hormones. Thus, EDCs create serious concerns for sensitive species. The early aquatic life stage, permeable skin and biphasic life cycle of amphibians make them highly susceptibility to exogenous chemicals, making them convenient models for reproductive toxicology studies. Oocyte maturation is an excellent system for testing developmental influences of EDCs, and its biochemical pathway has been elucidated. Endocrine-disruption studies in amphibians are timely, as the current dramatic declines in global amphibian populations may have basis in environmental accumulation of EDCs. 2,4-Dichlorophenoxyacetic acid (2,4-D) is the most widely used broadleaf herbicide on the planet. The synthetic auxin acts by a hormonal mechanism and is suspected to be an endocrine disruptor in animals as well. Oocytes of the South African Clawed Frog (Xenopus laevis) exposed to high doses of the herbicide in vitro fail to mature, drawing into question its effects on reproduction. Nevertheless, maternal exposure to environmentally-relevant doses of 2,4-D has yet to be explored. In this experiment, we use progesterone-induced oocyte maturation and western blot analysis to test the effects of in vivo exposure to low doses of 2,4-D. Our results suggest that 2,4-D does not significantly impact the ability of oocytes to mature after 30 days of environmentally-relevant maternal exposure. http://hdl.handle.net/10177/2094 Heat Suppresses Rac GTPase-Mediated Auxin-Induced Gene Expression in Cultured Guard Cell Protoplasts of Tree Tobacco (Nicotiana glauca) Anderson, David The plant hormone auxin regulates cell wall formation, cell growth, cell division and differentiation processes in plants. At 38°C, cultured guard cell protoplasts (GCP) of tree tobacco (Nicotiana glauca) acquire thermotolerance within 24 h but develop insensitivity to an exogenously supplied auxin (1-napthaleneacetic acid; NAA). Specifically, heat suppresses activation of the auxin-responsive BA promoter in GCP. Rac GTPases, a subset of small, monomeric G-proteins, have been shown to mediate auxin signaling in cells of other plant species and are likely candidates in the auxin-signaling pathway of GCP. We hypothesized 1) that GCP contain a native Rac GTPase similar to NtRac1 of Nicotiana tabacum that functions in auxin-induced gene expression; and 2) that heat would not be able to suppress activation of the auxin-responsive BA promoter by the constitutively active Rac GTPase, NtRac1-CA. At 32°C in media containing NAA, ca. 50% of GCP expressed GFP when they were transformed with BA-mgfp5-ER, a plasmid in which the BA promoter regulates transcription of the thermostable green fluorescent protein (GFP) gene, mgfp5-ER. Under the same conditions, only ca. 23% of cells expressed GFP when they were cotransformed with the BA reporter and 35S-NtRac1-DN, in which the 35S CaMV promoter activates transcription of a dominant negative (DN) mutant NtRac1. At 32°C in media lacking NAA, ca. 19% of GCP expressed GFP when there were cotransformed with BA-mgfp5-ER and 35S-NtRac1-CA containing a constitutively active (CA) NtRac1. At 38°C, regardless of whether media contained NAA, cells transformed with wild-type NtRac1 or with NtRac1-CA were unable to activate the BA promoter. These data suggest that cultured GCP of N. glauca contain at least one native Rac GTPase ortholog similar to NtRac1 that mediates auxin signaling at lower temperatures, and that heat suppresses auxin-induced gene expression at, or downstream of, this Rac GTPase.