Browsing by Author "Raffel, Thomas"

Now showing 1 - 7 of 7
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    Effects of temperature acclimation and diet on energetics and behavior of the Mexican axolotl (Ambystoma mexicanum)
    McKeon, Amanda; Raffel, Thomas
    Many organisms exhibit physiological responses to monthly or seasonal temperature shifts, but mechanisms driving these “thermal acclimation” effects remain unclear. Prior work on Mexican axolotls (Ambystoma mexicanum) revealed that warm-temperature exposure led to reduced metabolic performance at a new test temperature. We postulated that this pattern was driven by a thermal mismatch between metabolic energy expenditures and energy assimilation (i.e., digestion), resulting in energetic stress at warm temperatures. The metabolic theory of ecology (MTE) predicts higher metabolic rates at warmer temperatures, whereas the dynamic energy budget (DEB) theory predicts that animals with a reduced energy reserve should have reduced metabolic performance. Linking these frameworks together might explain the observed thermal acclimation effects seen in axolotl metabolism. To test the proposed linkages between temperature, metabolism, energetics, and physiological stress, I exposed axolotls to two acclimation temperatures (7°C and 25°C) and three levels of food availability. I then measured their effects on metabolic rates, behavior, and blood lipids. I used linear regression models to test for main and interactive effects of acclimation temperature, performance temperature, and food availability on axolotl metabolic rate, activity levels, and blood lipids. Results generally showed support for the prediction of higher metabolic rates with warmer temperatures and higher levels of reserve energy, with the exception of warm-acclimated fasted animals that exhibited higher than expected metabolic rates at the cooler performance temperature. This result was driven by increased activity levels in this treatment combination, possibly due to increased foraging behavior in animals with the lowest levels of reserve energy. These results support the hypothesis that axolotl thermal responses are driven by thermal mismatches between energy assimilation and expenditure, as predicted by MTE and DEB.
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    Effects of temperature and thermal acclimation on frog metabolic performance
    Tituskin, Julia; Raffel, Thomas
    The threat of global climate change makes it critical to understand how changing patterns of temperature variability influence ecological processes such as population growth rates and predator-prey interactions. According to the metabolic theory of ecology (MTE), rates of ecological processes are fundamentally limited by organism metabolic rates. Metabolism has in turn been found to scale predictably with temperature according to the Boltzmann-Arrhenius (BA) equation for enzyme kinetics, which can be adapted to account for enzyme deactivation at high temperatures (e.g., Sharpe-Schoolfield model). An important outstanding question is how key metabolic parameters, such as the activation energy for metabolism, are influenced by organismal responses including thermal acclimation. In this study, I investigated how thermal acclimation influences key MTE model parameters for adult spring peeper frogs (Pseudacris crucifer), by using the rate of their observable respiratory movements as a proxy for metabolic rate. After holding frogs at one of three “acclimation temperatures” for two weeks, they were transferred to one of eight “performance temperatures.” I then recorded frog respiratory rates at several time points following the transfer. Statistical model fitting was used to estimate key MTE model parameters and to determine whether and how thermal acclimation influenced spring peeper thermal performance. I found that the Sharpe-Schoolfield model provided a better description of the thermal performance curve for spring peeper metabolism than the BA equation, and that thermal acclimation did not significantly alter metabolic responses to temperature so long as mass scaling effects were accounted for in the model.
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    Examining zebra mussel and crayfish effects on swimmer’s itch, a snail-borne parasitic disease
    Hajek, Aleena; Raffel, Thomas
    Abstract Swimmer’s itch is caused by avian schistosomes, snail-borne parasites that normally use birds as definitive hosts but sometimes try to infect humans. Although it is clear that higher densities of waterfowl and snail hosts lead to increased swimmer’s itch incidence, the effects of other ecological variables on these parasites are less well understood. Preliminary data collected by the Raffel lab in 2015 suggested links between urbanization and swimmer’s itch in northern MI lakes, apparently mediated by effects of increased water clarity and growth of attached algae (i.e., snail food) on snail populations. Urbanization might lead to (1) increased introductions of invasive species like zebra mussels, which increase water clarity, and (2) insecticide runoff leading to declines in crayfish, the most important invertebrate predators of snails and mussels. My project investigated relationships between abundances of zebra mussels, crayfish, snails, and avian schistosomes in MI lakes as well as environmental and habitat data, such as water temperature, algae, and substrate type, as part of a large-scale survey effort being conducted by the Raffel lab in 2016. Our findings will help to determine the causes of swimmer’s itch in northern MI lakes and inform future management efforts, so perhaps one day our kids will no longer have to worry about it.
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    GHPI Biodiversity Subcommittee Report, 2022
    (2022-05) Banes-Berceli, Amy; Berven, Keith; Carlson, Matthew; Diesing, Eric; Hartson, Mary; Jamieson, Mary; Jamison, Megan; LaLone, Douglas; Raffel, Thomas
    Assessment of biodiversity and wildlife habitats on campus; recommendations
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    Medically Relevant Genome Diversity in Ukraine
    (2023-01-01) Shchubelka, Khrystyna; Oleksyk, Taras K; Battistuzzi, Fabia; Raffel, Thomas
    Ukraine, the second-largest country in Europe, has a rich history characterized by migrations, epidemics, famines, wars, and occupations, all of which have contributed to the formation of the modern Ukrainian population. However, the genetic composition of Ukraine remains understudied. Previous population genetic studies have largely overlooked the unique genetic makeup of Ukraine due to lack of publicly available genomic data. Yet, recent global assessments of genome diversity have highlighted the presence of numerous endemic variants, underscoring the significance of investigating genetic variation in underrepresented regions like Eastern Europe and, specifically, Ukraine. Such research is vital in the context of worldwide clinical trials and the development of personalized medicine. Local populations, shaped by their distinct histories, harbor a wealth of unexplored genomic variation, which may impact drug response, influence the risk of common and rare diseases, and shape lifestyle adaptations.Comprehensively understanding the genetic makeup of specific populations facilitates more effective identification of genetic markers for disease gene mapping, including family linkage and genome-wide association studies. These investigations aim to uncover susceptibility genes or loci for both Mendelian and complex diseases. Therefore, in this discovery-based study, our objective is to characterize the extensive genetic variation of medically relevant alleles in contemporary Ukraine across various levels of population structure: within major regions of Ukraine, and among the multiethnic population of Transcarpathia. Additionally, we will explore the relationship between lactose persistence genotypes and phenotypes, as well as the genetic factors underlying global developmental delay and intellectual disability in Ukraine.
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    Temperature effects on production of infectious zoospores from chytrid-infected Xenopus laevis
    Spengler, Kyle; Raffel, Thomas
    A leading cause of global declines in amphibian populations is chytridiomycosis, the temperature-dependent pandemic disease, caused by the fungal pathogen Batrachochydrium dendrobadtidis (Bd). Temperature fluctuations caused by climate change could exacerbate this disease. Temperature-dependent models of Bd infections can provide important insights into Bd transmission dynamics in frog populations to help inform management actions. The Raffel lab has been working on a novel type of mechanistic model to predict Bd and host responses to fluctuating temperatures, based on a combination of metabolic theory and a type of dynamic model traditionally used to describe macroparasite dynamics. In this model shedding rate (i.e., the number of zoospore equivalents released per minute) of Bd zoospores from an infected host’s skin constitutes an important parameter which we were able to measure. We infected 124 juvenile Xenopus laevis and subjected them to acclimation temperatures of 10 °C, 15 °C, or 20 °C for 35 days. All frogs were inoculated the day of performance temperature switch which happened at the end of the acclimation period; however, 38 were also inoculated 35 days before the switch. During the performance period frogs were subjected to temperatures of 10 °C, 15 °C, 20 °C, or 25 °C for 35 days. Shed zoospores were collected 7 days and 35 days post performance temperature switch. On day 7 of the performance period, shedding rate differed between each performance temperature, but not with acclimation temperature (Table 3). A higher shedding rate was also observed with lower performance temperatures. Shedding rate on day 35 of the performance period did not differ between each performance temperature and acclimation temperature. Shedding rate was also significantly lower on day 35 (Table 3). Frogs inoculated 35 days before the performance temperature switch did not differ between frogs inoculated the day of the switch. We also found Infection intensity and levels of shed zoospores were correlated (Table 3), with filters having detected more zoospores day 7 of the performance period compared to swabs collected at the same time point. We conclude shedding rate from X. laevis is affected by temperature, and infection load. This research will help to inform the transmission parameter for the mathematical model our lab has been generating to untangle the complex temperature dependence of Bd disease dynamics in frog populations which will potentially help conservation programs.
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    Testing for effects of pollution on a snail-borne parasite in Michigan Lakes
    Bageris, Alexander; Raffel, Thomas
    My thesis project focused on testing for potential effects of herbicides, specifically 2,4-D and glyphosate, on avian schistosome parasites in Michigan lakes. Avian schistosomes are a diverse group of snail-borne flatworm parasites that cause a rash called “swimmer’s itch” in humans. My project was part of a larger effort by Dr. Raffel’s lab team to measure the abundance of these parasites at 38 inland lake shorelines across Michigan. My own project focused on how pollutants affect the parasite’s intermediate hosts, snails. Chemical pollutants might affect snail populations by killing the invertebrate predators of snails or by influencing the growth rates of the snail’s food source (algae). We collected water samples from each site at two time points during the summer and brought them back to the lab for chemical analysis. We also measured population densities of snails and potential invertebrate predators of snails (i.e., crayfish), and measure algal growth rates using standard periphyton samplers and a chlorophyll assay. Ultimately, I hope my work will help to inform management efforts by local lake associations by determining whether and how pollution influences these parasites and their snail hosts.