Research

Exploring induced variation of Δ17O in deer mice (Peromyscus maniculatus) 

Δ17O is a parameter that combines measurements of all three stable oxygen isotopes (16O, 17O, and 18O) as a natural tracer of water sources. The amount of the heavier oxygen isotopes (17O and 18O) are measured relative to the common 16O, with the values recorded as δ‘17O and δ‘18O; when plotted against each other, they exhibit a near-constant relationship. Positive and negative deviations from this expected relationship represent Δ17O. The potential of Δ17O as a physiological metric is based on a) that the oxygen utilized in the formation of metabolic water by the mitochondria is inhaled atmospheric oxygen, which has a fixed Δ17O value of approximately - 0.441‰; and b) that the other major water source in an animal, meteoric water, has a fixed Δ17O value of approximately 0.041‰. Metabolic water and meteoric water together account for 80-99% of body water. Thus, measuring Δ17O in a body water sample from an animal provides insight about the contribution of metabolic water and therefore insight into their metabolic rate as well. For example, a body water Δ17O value of -0.321‰ would indicate that metabolic water was contributing roughly 75% of that animal’s body water. To further validate the potential of this metric, I will be conducting laboratory experiments with deer mice by manipulating housing temperatures and water intake, which should resulted in predictable shifts in the Δ17O of their body water.

Assessing seasonal variation in Δ17O of Merriam’s kangaroo rat (Dipodomys merriami) 

To compare the novel Δ17O method with other methods for assessing water intake and metabolism (e.g., the doubly labeled water technique), I will examine the Δ17O body water of Merriam’s kangaroo rat in May, June, and December in New Mexico. Sampling of kangaroo rats in May will generate the baseline (since water availability and temperature are stable). Since June is the rainy period in New Mexico, water availability should increase resulting in an increase in water intake and therefore an increased Δ17O of body water. However, in December when water availability and temperature are both low, metabolic rate should increase resulting in a decrease in the Δ17O of body water. 

Examining the impact of nursing on water intake and metabolism in female northern elephant seals (Mirounga angustirostris)

During nursing, northern elephant seal mothers are fasting from both food and water because they are restricted to the beach during this time. This presents a unique situation in which these adult seals are providing ample nourishment to their young with no nutritional or water intake themselves. Many of these seals lose roughly 40% of their body mass during nursing, with their pups assimilating about 55% of this lost mass into their own tissue as they grow. This provides a unique opportunity to better understand this phenomenon using Δ17O. I will be assessing how Δ17O varies during periods of lactation (February) and non-lactating periods during post-breeding migration (April-June) using historical samples provided by an ongoing study at University of California – Santa Cruz.

Assessing Seasonal, Environmental, and Artificial Water Influence on Water Intake and Metabolism of Rocky Mountain Mule Deer (Odocoileus hemionus hemionus)

Rocky Mountain mule deer from the Cache and Pine Valley regions of Utah are exposed to dramatically different winter and spring conditions. The two regions, which are <500 miles apart, provide an excellent opportunity to assess how differences in access to free-standing water and vegetation may impact an animal's metabolic rate and water intake. The Cache region, which is near Logan, has a much higher human population density, more access to free-standing water, and greener vegetation in comparison to the Pine Valley region outside Zion National Park. Both regions have high elevations and harsh winters as well. In collaboration with United States Forest Service's Rocky Mountain Research Station, female mule deer were sampled from both regions in Novemeber/December 2021, and then the same individuals were resampled again in March 2022 and December 2022. Samples are currently being processed and analyzed to determine their δ17O, δ18O, δ2H, deuterium-excess, and Δ17O values with a prediction that the mule deer in the Cache region will have a higher Δ17O value and a lower δ18O value (due to more water availability).

Exploring how Water Intake and Metabolism Influences Invasion Success in a Non-Native Population of Gemsbok (Oryx gazella) in New Mexico

Non-native gemsbok were introduced to New Mexico in the late 1960s to stimulate hunting opportunities. The population was introduced to the White Sands Missile Range region in a limited capacity but soon the population rapidly expanded and within 30 years there were over 2,000 gemsbok in the region, although the region the population inhabits remains relatively small. The factors leading to this population expansion are the lack of predators, the environmental similarities between their native range and their introduced range, and their ability to outcompete native ungulate species. Part of what may allow these gemsbok to outcompete native species is their ability to maximize resources during the rainy season and to endure during droughts. To explore this dynamic, my lab at ODU is collaborating with New Mexico Department of Game and Fish and White Sands Missile Range to explore how gemsbok water intake and metabolism fluctuates seasonally. We are currently gathering samples from public gemsbok hunters to assess how these metrics shift from September (at the tail end of the rainy season) to March (at the end of the harsh, dry winter).

Assessing Public Hunting Motivations, Perceptions, and Management Preferences of Non-Native Gemsbok (Oryx gazella) at White Sands Missile Range (New Mexico, US)

To supplement the project described above, I have also collaborated with New Mexico Department of Game and Fish and White Sands Missile Range to build two questionnaires to assess public hunting motivations, perceptions, and management preferences of these same gemsbok. These questionnaires are being distributed to both hunters who recently culled a gemsbok and hunters who have recently applied or are interested in applying for a gemsbok hunting tag. We predict that hunters who have recently completed a gemsbok hunt will have higher knowledge of gemsbok and be more supportive of management actions than those who have yet to complete a hunt.

Exploring Animal Body Water Pool Sources in Non-Native Brown Tree Snakes (Boiga irregularis) and Burmese Python (Python bivittatus)

The ability of various reptile species to generate meaningful amounts of metabolic water has been debated. Although the contribution of metabolic water to the body water pool is likely minimal, slight differences between species could be significant. In addition, reptiles that are able to comfortably maintain their water balance through their diet likely also have a competitive advantage, which is particularly important to introduced species such as the brown tree snake in Guam, and the Burmese python in Florida. Archived samples from both species obtained via collaborators at the University of Florida are currently being analyzed to assess the contribution of metabolic water and performed water (food and drinking water) to the body water pool.