Theses (Biology)
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Theses from the Dept. of Biology.
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Item Proanthocyanidins in poplar roots - effects on mycorrhizal colonization and nitrogen uptake(2024) Yamakawa, Daisuke; Hawkins, Barbara J.; Constabel, Carsten PeterProanthocyanidins (PAs), also known as condensed tannins, are widespread plant secondary metabolites, especially common in trees. PAs are known for their roles in plant defense and soil nutrient cycling, and their many applications in human medicine and diet. Although substantial research has focused on PA function in plant shoots, few studies have investigated their roles in roots. Some research indicates that PAs act as anti-fungal compounds, suggesting PAs in roots could negatively affect beneficial fungi in soils such as mycorrhizal fungi, which provide nutrients, including nitrogen (N), to host plants. Notably, the growth of the ectomycorrhizal (EcM) fungus Laccaria bicolor was inhibited in vitro by a purified extract of poplar PAs. Therefore, I aimed to evaluate the effects of PAs in roots on mycorrhizal colonization as well as on N uptake by colonized roots. Poplar (Populus. tremula x P. tremuloides) was chosen as the study species because poplars produce a wide range of phenolic compounds, including PAs. I utilized transgenic lines developed previously that have high and low PA concentrations in plant tissues, including roots. Plants from each line were equally divided into two treatment groups inoculated with either the EcM fungus L. bicolor or the arbuscular mycorrhizal (AM) fungus Rhizophagus irregularis, and one non-inoculated control group. Plants were grown in a sandwich culture system that allows co-culture of the mycorrhizal fungi and roots, or inoculated with the fungi in soil in a greenhouse experiment. Uptake of ammonium (NH4+) and nitrate (NO3−) by plant roots was measured using a microelectrode ion flux measurement system (MIFETM), and by 15N-labelling. Successful EcM colonization on poplar roots was confirmed in all the plant lines, while no AM structures were observed in the roots. Contrary to my prediction, the poplar line with low-PAs/phenolics in roots was less colonized by EcM fungi in both sandwich and soil culture. Additionally, plants from all lines inoculated with EcM fungi in sandwich culture system tended to have lower root PA concentrations. Although no significant difference in N uptake among plant lines or mycorrhizal treatments was observed, NH4+ uptake was greater than NO3− uptake. Understanding the effects of the interaction of root PAs and mycorrhizal fungi on mycorrhizal colonization and N uptake will contribute to our knowledge of the ecological and physiological impacts of PAs in the rhizosphere.Item Oceanic atoll provides refuge for elasmobranchs amidst global declines and promotes opportunities to finance conservation(2024) Zerr, Kaitlyn; Baum, Julia KathleenSharks and rays (elasmobranchs) are charismatic megafauna that support healthy ecosystems and can serve as flagship species for marine conservation. Elasmobranchs tend to be highly mobile, mid- to high trophic level predators, with slow population growth rates that render them vulnerable to overexploitation. While many species have experienced widespread and ongoing population declines, some nations have recognized the value of elasmobranchs to the tourism industry. The Republic of Maldives has protected sharks and rays from exploitation within their national waters since 2014 because of the significant amount of revenue lost from the tourism industry when populations there began to show signs of overexploitation. However, local threats such as bycatch, entanglement in fishing gear, and unregulated tourism may continue to negatively impact populations, highlighting the need for additional conservation measures. Known as ‘Shark Island’, Fuvahmulah Atoll, a recently designated UNESCO Biosphere Reserve, has recently experienced a steep rise in dive tourism due to improved accessibility to, and awareness of, its abundant and diverse shark and ray megafauna. Although a marine protected area (MPA) has been designated at the southern end of the atoll, a management plan has not yet been developed and species-specific information is lacking. Furthermore, it is unclear if dive tourists are willing to contribute financially to help conserve the biodiversity upon which their tourism depends. Here, we sought to inform management plans and policy design by 1) quantifying elasmobranch assemblages on Fuvahmulah Atoll’s reefs and 2) examining tourists’ willingness to pay for increased conservation action on the atoll. In Chapter 2, we deployed remote timelapse cameras at three shallow fore reef sites and collected images on 63 days over a 6-month period. From a total of 1,629,756 images, we calculated the occurrence and relative abundance within days and hours to assess spatial and temporal variations in elasmobranch visitation to the sites. Sharks and rays were captured on 72% of hours and 95% of days, with the highest number of occurrences recorded at the site within an MPA, Farikede, followed by Kedevari and Hudhekede. Both reef sharks and apex sharks were represented, with whitetip reef sharks, pelagic threshers, grey reef sharks, tiger sharks, and silvertip sharks, representing the most frequently observed species. We show that Farikede MPA is a hotspot for reef sharks and tiger sharks. However, Kedevari appears to be an ecologically significant site for pelagic threshers. In Chapter 3, we conducted stated preference surveys with tourists visiting Fuvahmulah to assess tourists’ willingness to pay a one-time “Reserve” entrance fee, the factors that influence the value of the fee, and their preferences for conservation measures proposed by the community. Virtually all (97%) tourists were supportive of paying a one-time reserve entrance fee, with an average fee of US$58 per person. Tourists with more positive environmental attitudes, those more committed to dive tourism (higher skill levels and more frequent trips), and those who encountered specific shark species (tiger sharks or pelagic threshers) in Fuvahmulah were willing to pay higher entrance fees. Visitors to Fuvahmulah Atoll highly value marine conservation, and their financial support creates unique opportunities to safeguard biodiversity and ensure the sustainability of the tourism industry. Increasing our understanding of the biological community while exploring avenues to finance conservation can provide opportunities to create informed and comprehensive management plans. While many elasmobranch populations continue to experience global declines, protected and well-managed sites may increase resilience on a global scale.Item Improving our understanding of vertebrates in nutrient recycling and ecological stoichiometry(2024) May, Emily M.; El-Sabaawi, RanaNutrient-rich, large, long-lived, and mobile, vertebrates may uniquely impact nutrient recycling and thus ecosystem function by storing copious nutrients within their bodies, by producing large quantities of waste, and by transporting nutrients long distances within and across ecosystems. Currently, vertebrates face myriad threats, leaving many ecosystems to face a future with reduced vertebrate biomass and diversity; understanding how vertebrates affect nutrient cycles thus provides valuable insight into how vertebrate extinctions will impact ecosystems. Broadly, I characterize variation in how vertebrates store phosphorus (P) within their bodies and recycle P from their diets in their excreted and egested wastes. To accomplish this, I link bone investment, bodily elemental content, and waste production. Bone, a P-rich tissue (mean of ~12%) unique to vertebrates, can alter vertebrate-driven nutrient recycling both by increasing P storage within vertebrate bodies and by changing P demand and thus P release in waste. Given this, my dissertation has three goals: (1) quantify how vertebrates vary in bone content and whole-body %P, (2) determine how this variation affects dietary intake and waste production, and (3) evaluate how bone may affect P demand differently from other P-rich bodily components. To fully characterize this, I used ecological stoichiometry (ES), a framework that uses mass-balance to conceptualize organismal and ecological processes, including nutrient uptake and processing by animals. I therefore begin my dissertation by developing methods to measure all factors effectively and simultaneously, which is rarely achieved in current literature. Using these methods, I then performed a field study to examine how intraspecific bone variation in the threespine stickleback (an evolutionary model fish species with well-characterized bone variation) affected whole-body %P, dietary %P, and P release in excreta and egesta. ES predicts that bone increases whole-body %P and should therefore increase P demand and decrease P release. Counter to these predictions, I found that although stickleback with more bone indeed had higher whole-body %P, bone did not clearly impact P demand. Stickleback with more bone showed similar diets, nutrient absorption, and egestion to those with less bone. Additionally, stickleback with more bone excreted more P, perhaps implying that bone mitigates P demand rather than causing it. More broadly, I found considerable variation in bone, whole-body %P, and waste production within and across sites, most of which was unexplained by size, sex, or environmental characteristics. Bone also causes interspecific and ontogenetic differences. In a systematic review of vertebrate elemental content, I found whole-body %P ranging from 0.39 – 6.91% P, suggesting strong bone variation across taxa (interspecific) and life stages (intraspecific). Given my previous findings, this variation may impact P demand and release in unexpected ways. Thus, I finish by integrating osteological and stoichiometric literature to examine how bone’s unique physiology affects its relationship with P demand and release. While ES implicitly assumes all tissues impact demand equally, bone’s unique characteristics change how it affects elemental demand. Primarily, bone’s ability to self-destroy and provide mineral nutrients to the rest of the body allows bone to directly mitigate a vertebrate’s increased P or calcium demands. This may make vertebrates with more bone more resilient to dietary P limitation, rather than the opposite. Ideally, future research will build on these findings to improve our overall understanding of vertebrate-driven nutrient recycling.Item Molecular characterization of the Neodiprion abietis nucleopolyhedrovirus(2002) Young, Aaron MichaelItem Infectivity of Agrobacterium tumefaciens and proteins of crown gall tumors in Helianthus annuus(1985) Wu, Hsiao-ChiangItem Furocoumarin production by pastinaca sativa and apium graveolens(1988) Woodcock, Paul VincentItem Characterization of the multigene family encoding endopolygalacturonase in the basidiomycete Chondrostereum purpureum(2001) Williams, Holly LouiseItem Some aspects of the reproductive biology of Fusitriton oregonensis (Redfield) (Gastropoda, Prosobranchia)(1976) Williams, Daphne EiriItem Life histories and post-glacial origins of tundra caddisflies (Trichoptera) from the Tuktoyaktuk Peninsula, Northwest Territories(1984) Winchester, Neville NormanItem Age determination of individual garter snakes (Thamnophis spp.) using skeletochronology(1995) Waye, Heather LouiseItem Production of antiserum to a goldfish visual pigment opsin(1996) Veldhoen, Kathleen MariaItem Diurnal and annual fluctuations of gibberlins in the leaves of Coffea arabica L.(1972) Trythall, Dianne Marguerite