Gas Absorption Detected from the Edge-on Debris Disk Surrounding HD32297

Near-infrared and optical imaging of HD32297 indicate that it has an edge-on debris disk, similar to beta Pic. I present high resolution optical spectra of the NaI doublet toward HD32297 and stars in close angular proximity. A circumstellar absorption component is clearly observed toward HD32297 at the stellar radial velocity, which is not observed toward any of its neighbors, including the nearest only 0.9 arcmin away. An interstellar component is detected in all stars >90 pc, including HD32297, likely due to the interstellar material at the boundary of the Local Bubble. Radial velocity measurements of the nearest neighbors, BD+07 777s and BD+07 778, indicate that they are unlikely to be physically associated with HD32297. The measured circumstellar column density around HD32997, log N(NaI) ~ 11.4, is the strongest NaI absorption measured toward any nearby main sequence debris disk, even the prototypical edge-on debris disk, beta Pic. Assuming that the morphology and abundances of the gas component around HD32297 are similar to beta Pic, I estimate an upper limit to the gas mass in the circumstellar disk surrounding HD32297 of ~0.3 M_Earth.Comment: 13 pages, 2 figures; Accepted for publication in ApJ Letter

Co-Infection by Chytrid Fungus and Ranaviruses in Wild and Harvested Frogs in the Tropical Andes.

While global amphibian declines are associated with the spread of Batrachochytrium dendrobatidis (Bd), undetected concurrent co-infection by other pathogens may be little recognized threats to amphibians. Emerging viruses in the genus Ranavirus (Rv) also cause die-offs of amphibians and other ectotherms, but the extent of their distribution globally, or how co-infections with Bd impact amphibians are poorly understood. We provide the first report of Bd and Rv co-infection in South America, and the first report of Rv infections in the amphibian biodiversity hotspot of the Peruvian Andes, where Bd is associated with extinctions. Using these data, we tested the hypothesis that Bd or Rv parasites facilitate co-infection, as assessed by parasite abundance or infection intensity within individual adult frogs. Co-infection occurred in 30% of stream-dwelling frogs; 65% were infected by Bd and 40% by Rv. Among terrestrial, direct-developing Pristimantis frogs 40% were infected by Bd, 35% by Rv, and 20% co-infected. In Telmatobius frogs harvested for the live-trade 49% were co-infected, 92% were infected by Bd, and 53% by Rv. Median Bd and Rv loads were similar in both wild (Bd = 101.2 Ze, Rv = 102.3 viral copies) and harvested frogs (Bd = 103.1 Ze, Rv = 102.7 viral copies). While neither parasite abundance nor infection intensity were associated with co-infection patterns in adults, these data did not include the most susceptible larval and metamorphic life stages. These findings suggest Rv distribution is global and that co-infection among these parasites may be common. These results raise conservation concerns, but greater testing is necessary to determine if parasite interactions increase amphibian vulnerability to secondary infections across differing life stages, and constitute a previously undetected threat to declining populations. Greater surveillance of parasite interactions may increase our capacity to contain and mitigate the impacts of these and other wildlife diseases

The Structure of the Local Interstellar Medium V: Electron Densities

We present a comprehensive survey of CII* absorption detections toward stars within 100 pc in order to measure the distribution of electron densities present in the local interstellar medium (LISM). Using high spectral resolution observations of nearby stars obtained by GHRS and STIS onboard the Hubble Space Telescope, we identify 13 sight lines with 23 individual CII* absorption components, which provide electron density measurements, the vast majority of which are new. We employ several strategies to determine more accurate CII column densities from the saturated CII resonance line, including, constraints of the line width from the optically thin CII* line, constraints from independent temperature measurements of the LISM gas based on line widths of other ions, and third, using measured SII column densities as a proxy for CII column densities. The sample of electron densities appears consistent with a log-normal distribution and an unweighted mean value of n_e(CII_SII) = 0.11^+0.10_-0.05 cm^-3. Seven individual sight lines probe the Local Interstellar Cloud (LIC), and all present a similar value for the electron density, with a weighted mean of n_e(LIC) = 0.12 +/- 0.04 cm^-3. The Hyades Cloud, a decelerated cloud at the leading edge of the platoon of LISM clouds, has a significantly higher electron density than the LIC. Observed toward G191-B2B, the high electron density may be caused by the lack of shielding from such a strong radiation source. Given some simple assumptions, the range of observed electron densities translates into a range of thermal pressures, P/k = 3300^+5500_-1900 K cm^-3. This work greatly expands the number of electron density measurements and provides important constraints on the ionization, abundance, and evolutionary models of the local interstellar medium. (abridged)Comment: 41 pages, 9 figures; Accepted for publication in Ap

Multiple stressor effects on ranavirus transmission and susceptibility

This thesis consists of three chapters that explore the effects of stressors on the amphibian disease, ranavirus, and the existence of ranavirus in southern Illinois. While these three chapters are distinct from one another, they are related in that they all seek to elucidate factors that allow the transmission and persistence of disease and how stressors may influence disease dynamics. Chapter one is a review of the effects of atrazine on amphibian physiology and behavior and seeks to summarize the existing literature on the subject into one succinct document. I reviewed all available literature and extracted the results while also reviewing the methods to ensure that the studies were reliable. I was mainly interested in direct effects of the pesticide atrazine on amphibians in order to elucidate how direct chemical contamination can influence disease susceptibility and spread. Atrazine is an herbicide used to control broadleaf weeds in agricultural fields. It is mainly used for weed reduction in cornfields with the heaviest use occurring in the Midwestern states. However, atrazine can be very persistent and highly mobile. Given the intensity and wide distribution of corn agriculture in the United States, atrazine is likely ubiquitous throughout North American waterways during the spring and summer. Amphibians are likely to come in to contact with atrazine during critical early life stages because atrazine is sprayed in the spring and summer when amphibian larvae are within eggs and developing as tadpoles. This is especially true in the Midwest where the heaviest atrazine use occurs. This suggests atrazine could impact larval development and immunity, thus worth considering as a possible factor in recent disease outbreaks. In my review, I discovered that the most devastating effect of atrazine on amphibians is endocrine disruption, specifically the feminization of male frogs. However, many other effects on physiology and behavior have been observed such as reduced immune function, developmental abnormalities, increased behavior, and decreased anti-predator behavior all of which could have profound effects on disease dynamics and survival. My second chapter sought to detect ranavirus in southern Illinois using Environmental DNA (eDNA) techniques. Environmental DNA is a fairly recent technology that allows researchers to nondestructively detect DNA within the environment using only water or soil samples. This is a great way to detect species that are rare or hard to find but also disease because you do not have to actually find a diseased animal to know if it is present. While there is evidence of ranavirus in southern Illinois, most of this is in box turtles with no positive identifications in amphibians. For this reason, using eDNA is beneficial because we can sample ponds where amphibians are known or expected to be present even if a diseased animal cannot be found and still be able to detect ranavirus. For this chapter, I collected water samples from southern Illinois water bodies were I knew or expected amphibians to be present. Water samples were filtered and analyzed using standard DNA extraction and qPCR protocols. I also validated the use of eDNA to detect ranavirus by making serial dilutions of the virus in water and analyzing them in the same manner as the samples. Ranavirus was detected in southern Illinois water bodies and I was able to validate the use of eDNA for ranavirus detection. My third chapter is the main portion of my thesis and explains an experiment that seeks to elucidate the role that multiple stressors such as thermal stress and chemical contamination play in disease dynamics. As climate change progresses, it is imperative that we understand how wildlife populations will respond and how their response will shape communities and ecosystems going forward. An increase in thermal stress coupled with the stressors that are already present, such as chemical pollution, could have unforeseen effects if scientists only look at one stressor at a time. That is why research exploring how stressors work in tandem is crucial if we are to understand what is actually happening in the environment as few wildlife populations are subjected to only one stressor at a time. This experiment used mesocosms to test the effects of atrazine and thermal stress on the transmission of ranavirus through alterations in behavior and physiology. I did this by setting up four treatments each with ten tubs and ten individuals per tub for a total of 400 animals. The treatments were Control-Ambient, Control-Heat, Atrazine-Ambient, and Atrazine-Heat. One focal animal from each tub was infected with ranavirus and placed in with its conspecifics to test differences in transmission. Animals were then placed into individual tubs and allowed to progress naturally. I found that atrazine and thermal stress increased survival of ranavirus infection and increased developmental rate. While this is the opposite of what might be expected it could be explained by critical windows of disease which in this case is metamorphosis. Animals that proceed through metamorphosis at a faster rate have a better chance of surviving ranavirus infection. We also found that animals in the atrazine treatments were much smaller at metamorphosis than animals from the control treatments so while atrazine may increase survival of ranavirus infection there is a substantial tradeoff. Animals in the Atrazine-Heat treatment also had much lower viral loads than the other treatments which likely also contributed to their increased survival. Viral loads may have been lower in this treatment because of the effect that multiple stressors would have on the secretion of glucocorticoids. Temporary elevation of glucocorticoids can induce a temporary boost to immune function and provide individuals in this treatment with the ability to fight off the virus

<i>Batrachochytrium dendrobatidis</i> and <i>Ranavirus</i> infection prevalence in ten species of frogs from Peru.

<p>Total sampled is the number of frogs examined, but does not always represent the number of samples for each assay (see text for details). 95% Bayesian credible intervals using Jeffrey’s priors.</p

Prevalence of infection by the emerging pathogens <i>Batrachochtrytium dendrobatidis</i> (Bd) and <i>Ranavirus</i> (Rv) in frogs sampled during 2012 (live trade only) and 2013 (wild and live trade frogs) in Peru.

<p>While <i>Telmatobius</i> were sampled from live trade sources, the other species were wild caught. Error bars are 95% Bayesian credible intervals using Jeffreys prior.</p

Infection loads in captive <i>Telmatobius</i> for both Bd and Rv (a); and in wild stream breeding <i>Hypsiboas gladiator</i> and in 7 species of terrestrial, direct-developing <i>Pristimantis</i> frogs (b).

<p>Infection loads in captive <i>Telmatobius</i> for both Bd and Rv (a); and in wild stream breeding <i>Hypsiboas gladiator</i> and in 7 species of terrestrial, direct-developing <i>Pristimantis</i> frogs (b).</p

The number of Bd and Rv infections in wild frogs in the genus <i>Pristimantis</i> (7 species) varied across an elevation range on the eastern slopes of the Andes (N = total sample size for each elevation range).

<p>The number of Bd and Rv infections in wild frogs in the genus <i>Pristimantis</i> (7 species) varied across an elevation range on the eastern slopes of the Andes (N = total sample size for each elevation range).</p