Matching Items (6)

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Occurrence of a Pathogenic Fungus in Captive Arizona Amphibians

Description

Amphibians have been experiencing a worldwide decline that is in part caused by an infectious disease, chytridiomycosis, specific to frogs and salamanders. Globally many species have declined or gone extinct

Amphibians have been experiencing a worldwide decline that is in part caused by an infectious disease, chytridiomycosis, specific to frogs and salamanders. Globally many species have declined or gone extinct because of the pathogenic fungus Batrachochytrium dendrobatidis, also known as the amphibian chytrid or Bd. By the time Bd was discovered it was too late to stop the spread and it has now been found on almost every continent. The trade of captive amphibians, used as pets, bait, and educational animals provides an opportunity to spread Bd. Because some amphibians can carry Bd without experiencing symptoms, it is possible for even healthy looking amphibians to spread the amphibian chytrid if they are moved from one location to another. Recently, a new species Batrachochytrium salamandrivorans (Bsal) was found on salamanders. Bsal was identified before it reached the United States, prompting concern regarding its spread and a call for regulation regarding the trade of captive amphibians. There are some regulations in place controlling the trade of amphibians, but they are insufficient to stop the spread of amphibian chytrid in captive populations. A 2016 law prohibits the importation of 201 salamander species. However, there is no central organization to sample or certify if amphibians are free from Bd or Bsal. Although some stores say they test for these pathogens the tests are unregulated and not reported to any central body. If the captive amphibian trade is to go disease free, there would need to be a significant push to coordinate testing efforts. To estimate Bd's prevalence in Arizona captive amphibian populations, I contacted pet stores, bait stores, and sanctuary or educational organizations to ask if I could sample their amphibian collections. My research built on the 2008 work of Angela Picco, who sampled for the amphibian chytrid in Arizona bait shops. I found that amphibian owners were often hesitant and unwilling to participate in this research opportunity. There are multiple reasons for this hesitancy including a fear of increased regulation, the potential for reporting to a government agency (USDA), or the eventual cessation of amphibian trade. The lack of willing participants suggests there may be difficulties in coordinating future sampling efforts for Bd and Bsal.

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Created

Date Created
  • 2018-05

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Analysis of Global Variance of the Thermal Maxima of an Amphibian Pathogen

Description

Batrachochytrium dendrobatidis (Bd), the amphibian chytrid fungus causing chytridiomycosis, is the cause of massive amphibian die-offs. As with any host-pathogen relationship, it is paramount to understand the growth and reproduction

Batrachochytrium dendrobatidis (Bd), the amphibian chytrid fungus causing chytridiomycosis, is the cause of massive amphibian die-offs. As with any host-pathogen relationship, it is paramount to understand the growth and reproduction of the pathogen that causes an infectious disease outbreak. The life-cycle of the pathogen, Bd, is strongly influenced by temperature; however, previous research has focused on Bd isolated from limited geographic ranges, and may not be representative of Bd on a global scale. My research examines the relationship between Bd and temperature on the global level to determine the actual thermal maximum of Bd. Six isolates of Bd, from three continents, were incubated at a temperature within the thermal range (21°C) and a temperature higher than the optimal thermal range (27°C). Temperature affected the growth and zoosporangium size of all six isolates of Bd. All six isolates had proliferative growth at 21°C, but at 27°C the amount and quality of growth varied per isolate. My results demonstrate that each Bd isolate has a different response to temperature, and the thermal maximum for growth varies with each isolate. Further understanding of the difference in isolate response to temperature can lead to a better understanding of Bd pathogen dynamics, as well as allow us the ability to identify susceptible hosts and environments before an outbreak.

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Created

Date Created
  • 2016-12

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Ecology of chytridiomycosis in boreal chorus frogs (Pseudacris maculata)

Description

Infectious diseases have emerged as a significant threat to wildlife. Environmental change is often implicated as an underlying factor driving this emergence. With this recent rise in disease emergence and

Infectious diseases have emerged as a significant threat to wildlife. Environmental change is often implicated as an underlying factor driving this emergence. With this recent rise in disease emergence and the acceleration of environmental change, it is important to identify the environmental factors that alter host-pathogen dynamics and their underlying mechanisms. The emerging pathogen Batrachochytrium dendrobatidis (Bd) is a clear example of the negative effects infectious diseases can have on wildlife. Bd is linked to global declines in amphibian diversity and abundance. However, there is considerable variation in population-level responses to Bd, with some hosts experiencing marked declines while others persist. Environmental factors may play a role in this variation. This research used populations of pond-breeding chorus frogs (Pseudacris maculata) in Arizona to test if three rapidly changing environmental factors nitrogen (N), phosphorus (P), and temperature influence the presence, prevalence, and severity of Bd infections. I evaluated the reliability of a new technique for detecting Bd in water samples and combined this technique with animal sampling to monitor Bd in wild chorus frogs. Monitoring from 20 frog populations found high Bd presence and prevalence during breeding. A laboratory experiment found 85% adult mortality as a result of Bd infection; however, estimated chorus frog densities in wild populations increased significantly over two years of sampling despite high Bd prevalence. Presence, prevalence, and severity of Bd infections were not correlated with aqueous concentrations of N or P. There was, however, support for an annual temperature-induced reduction in Bd prevalence in newly metamorphosed larvae. A simple mathematical model suggests that this annual temperature-induced reduction of Bd infections in larvae in combination with rapid host maturation may help chorus frog populations persist despite high adult mortality. These results demonstrate that Bd can persist across a wide range of environmental conditions, providing little support for the influence of N and P on Bd dynamics, and show that water temperature may play an important role in altering Bd dynamics, enabling chorus frogs to persist with this pathogen. These findings demonstrate the importance of environmental context and host life history for the outcome of host-pathogen interactions.

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Created

Date Created
  • 2012

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Herpetofauna community responses to saltcedar (Tamarix spp.) biological control and riparian restoration along a Mojave Desert stream, U.S.A

Description

In riparian ecosystems, reptiles and amphibians are good indicators of environmental conditions. Herpetofauna have been linked to specific microhabitat characteristics, microclimates, and water resources in riparian forests. My objective was

In riparian ecosystems, reptiles and amphibians are good indicators of environmental conditions. Herpetofauna have been linked to specific microhabitat characteristics, microclimates, and water resources in riparian forests. My objective was to relate herpetofauna abundance to changes in riparian habitat along the Virgin River caused by the Tamarix biological control agent, Diorhabda carinulata, and riparian restoration.

During 2013 and 2014, vegetation and herpetofauna were monitored at 21 riparian locations along the Virgin River via trapping and visual encounter surveys. Study sites were divided into four stand types based on density and percent cover of dominant trees (Tamarix, Prosopis, Populus, and Salix) and presence of restoration activities: Tam, Tam-Pros, Tam-Pop/Sal, and Restored Tam-Pop/Sal. Restoration activities consisted of mechanical removal of non-native trees, transplanting native trees, and introduction of water flow. All sites were affected by biological control. I predicted that herpetofauna abundance would vary between stand types and that herpetofauna abundance would be greatest in Restored Tam-Pop/Sal sites due to increased habitat openness and variation following restoration efforts.

Results from trapping indicated that Restored Tam-Pop/Sal sites had three times more total lizard and eight times more Sceloporus uniformis captures than other stand types. Anaxyrus woodhousii abundance was greatest in Tam-Pop/Sal and Restored Tam-Pop/Sal sites. Visual encounter surveys indicated that herpetofauna abundance was greatest in the Restored Tam-Pop/Sal site compared to the adjacent Unrestored Tam-Pop/Sal site. Habitat variables were reduced to six components using a principle component analysis and significant differences were detected among stand types. Restored Tam-Pop/Sal sites were most similar to Tam-Pop/Sal sites. S. uniformis were positively associated with large woody debris and high densities of Populus, Salix, and large diameter Prosopis.

Restored Tam-Pop/Sal sites likely supported higher abundances of herpetofauna, as these areas exhibited greater habitat heterogeneity. Restoration activities created a mosaic habitat by reducing canopy cover and increasing native tree density and surface water. Natural resource managers should consider implementing additional restoration efforts following biological control when attempting to restore riparian areas dominated by Tamarix and other non-native trees.

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Date Created
  • 2014

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Forecasting the Winners and Losers of a Riparian Herpetofauna in Response to Habitat Invasion and Xerification

Description

Riparian systems in the arid southwest are heavily altered and, based on relative land-area, provision a disproportionately high number of native wildlife. Amphibians and reptiles are collectively the most threatened

Riparian systems in the arid southwest are heavily altered and, based on relative land-area, provision a disproportionately high number of native wildlife. Amphibians and reptiles are collectively the most threatened vertebrate taxa and, in the Sonoran Desert, are often reliant on riparian habitat. The link between amphibians and environmental water characteristics, as well as the association between lizards and habitat structure, make herpetofauna good organisms for which to examine the effects of environmental change.

My objective was to relate capture rates of a fossorial anuran and lizard abundance to aspects of native, invaded, and shrub-encroached riparian habitats in order to forecast the potential winners and losers of riparian habitat xerification and invasion.

I measured habitat and monitored herpetofauna at 18 sites near the confluence of the San Pedro River and Gila River in Pinal County, Arizona in 2016 and 2017. Sites were divided into three categories based on dominant tree genus; Populus-Salix, Prosopis, and Tamarix, which represented native riparia, xeric riparia, and invaded riparia, respectively.

Habitat measurements indicated that sites varied significantly in structure, and that dominant tree species was a useful descriptor of habitat physiognomy. Results from herpetofauna trapping demonstrated that Scaphiopus couchii, a fossorial anuran, occupy Prosopis sites at a much higher rate than at Tamarix sites, which were almost completely avoided. S. couchii was also found to be closely tied to xero-riparian habitat components present at Prosopis sites and soil analyses indicate that aspects of soil moisture and texture play an important role in the partitioning of this species across altered riparian habitats. Lizard abundance was found to be significantly lower in Tamarix habitat, with the majority of captures attributed to the generalist whiptail Aspidoscelis tigris. Additionally, more than half of lizard species that were analyzed displayed a negative association to Tamarix habitat. Of the three habitat types considered, Populus-Salix supported the greatest abundance of lizards.

Based on this study, the deleterious effects of xerfication on a riparian herpetofauna community may be lesser than those of Tamarix invasion. These two forms of riparian habitat shift often co-occur, with the ultimate cause being changes in hydrologic regime. This may imply that a bottom-up approach, wherein historic hydrology is restored to restore or maintain native habitats, to riverine management is appropriate for riparian herpetofauna conservation.

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Date Created
  • 2018

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Seasonal changes in cell neogenesis in the brain and pituitary gland: a study in the adult male frog, Rana catesbeiana

Description

Though for most of the twentieth century, dogma held that the adult brain was post-mitotic, it is now known that adult neurogenesis is widespread among vertebrates, from fish, amphibians, reptiles

Though for most of the twentieth century, dogma held that the adult brain was post-mitotic, it is now known that adult neurogenesis is widespread among vertebrates, from fish, amphibians, reptiles and birds to mammals including humans. Seasonal changes in adult neurogenesis are well characterized in the song control system of song birds, and have been found in seasonally breeding mammals as well. In contrast to more derived vertebrates, such as mammals, where adult neurogenesis is restricted primarily to the olfactory bulb and the dentate gyrus of the hippocampus, neurogenesis is widespread along the ventricles of adult amphibians. I hypothesized that seasonal changes in adult amphibian brain cell proliferation and survival are a potential regulator of reproductive neuroendocrine function. Adult, male American bullfrogs (Rana catesbeiana; aka Lithobates catesbeianus), were maintained in captivity for up to a year under season-appropriate photoperiod. Analysis of hormone levels indicated seasonal changes in plasma testosterone concentration consistent with field studies. Using the thymidine analogue 5-bromo-2-deoxyuridine (BrdU) as a marker for newly generated cells, two differentially regulated aspects of brain cell neogenesis were tracked; that is, proliferation and survival. Seasonal differences were found in BrdU labeling in several brain areas, including the olfactory bulb, medial pallium, nucleus accumbens and the infundibular hypothalamus. Clear seasonal differences were also found in the pars distalis region of the pituitary gland, an important component of neuroendocrine pathways. BrdU labeling was also examined in relation to two neuropeptides important for amphibian reproduction: arginine vasotocin and gonadotropin releasing hormone. No cells co-localized with BrdU and either neuropeptide, but new born cells were found in close proximity to neuropeptide-containing neurons. These data suggest that seasonal differences in brain and pituitary gland cell neogenesis are a potential neuroendocrine regulatory mechanism.

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Agent

Created

Date Created
  • 2012