Date of Award

2017-01-01

Degree Name

Master of Science

Department

Geological Sciences

Advisor(s)

Elizabeth J. Walsh

Abstract

Increases in UV radiation (UVR) reaching Earth's surface as a result of anthropogenic activities and changing climate patterns are having a variety of effects on ecosystems. Such effects have been observed in aquatic environments, although certain parameters such as dissolved organic carbon (DOC) concentrations can modulate the level of exposure. Bdelloid rotifers are aquatic micro-invertebrates that pose a remarkable variety of special abilities to survive adverse conditions, including a resistance to UVR. Previous studies have suggested this resistance may have evolved in response to episodes of desiccation that they experience in their natural habitats. This characteristic may be especially important for populations living in the dynamic, ephemeral waters of the North American desert southwest, where UV radiation is pronounced due to a lack of cloud cover for most of the year, and temporary aquatic habitats can undergo extensive periods of time without water. The objective of this study is to determine the impact of UV-B radiation on aquatic biota by investigating any differences in mortality post-exposure. Bdelloids from family Philodinidae were collected from four locations in two states: Texas (a man-made lake, a temporary rock-pool, and a dust sample with high UVR exposure potential) and Wisconsin (a permanent lake with low UVR exposure potential). Water samples from the lakes and the rock-pool were collected in a summer and a winter season for DOC measurements. Bdelloids were dehydrated under three desiccation regimens, after which they were exposed to UV-B radiation using four exposure levels in a laboratory setting. The rock-pool DOC concentrations were greater than the other two locations, although significant variation could not be determined due to a low sample size. There also appeared to be a seasonal variation between these locations, with winter DOC levels in the rock-pool being over twice the levels recorded at the man-made lake. These are the first measurements of their kind for these locations; however, since the number of samples were not sufficient to provide relevant differences, caution is advised when they are referenced. The probability of death was significantly heightened by the period of time for which the bdelloids were dried prior to exposure (X2 = 461.24, d.f. = 2, p<0.001), their population source (X2 = 1972.87, d.f. = 3, p<0.001), and the level of exposure UVR (X2 = 504.57, d.f. = 3, p<0.001). The 2-way interactions of these parameters also had a significant effect on bdelloid mortality (X2 = 34.73, d.f. = 9, p<0.001 for filter and population; X2 = 119.69, d.f. = 6, p<0.001 for desiccation time and population). Among the four populations, bdelloids from the Wisconsin lake had a significantly higher probability of mortality than the other three populations (GLM, p<0.05). The results of this study indicate that UVR tolerance among bdelloid rotifers likely varies according to their habitats. As changes in UVR exposures are predicted to occur in the future, these observed differences may be amplified, which may in turn lead to shifts in aquatic community structure.

Language

en

Provenance

Received from ProQuest

File Size

81 pages

File Format

application/pdf

Rights Holder

Maite Martin

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