Tag Archives: Fieldwork

Sensing Your Friends Getting Eaten is Stressful, Having a Parasite Makes it Worse

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Helen Gloege, a student in Mount Holyoke College, worked in the lab of Dr. Andy Davis

Abstract Daphnia and other animals face a multitude of different stressors in their daily lives. Parasites can cause various physiological changes in animals, yet few prior studies have looked at the combination of parasitism and stress in animal models. This study used Daphnia which are microscopic plankton that may have ectoparasite-like organisms attached to their surface. Vorticella, a single-celled ectoparasite, is one of these organisms that can be found attached to Daphnia. During this experiment, when Daphnia ambigua were exposed to a “stressor” the vorticella parasite led to an increased heart rate in the Daphnia. The “stressor” was made of macerated Daphnia and aimed to simulate a predation event. Daphnia without vorticella present appeared to have no discernable reaction to the stressor. While Daphnia with vorticella increase the heart rate and physiological stress reaction in Daphnia. When over twenty vorticella were present on the daphnia the heart rate continued to increase during the study period.

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Temperature fluctuation on disease transmission in multi-host communities

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Jenavier Tejada, a student at Denison University, worked in the lab of Dr. Alex Strauss

Abstract The dilution effect seeks to explain disease transmission in environments with multiple species. Essentially, the dilution effect predicts an increase in diversity will lead to a decrease in disease transmission. In zooplankton communities, the resistant diluter, Ceriodaphnia dubia can lessen disease in the host Daphnia dentifera caused by the parasite Metschnikowia bicuspidata. However, dilution is only effective when diluters and hosts co-exist; because when they compete, competitive exclusion can occur. Fitness of both D. dentifera, and C. dubia depend on temperature. Specifically, C.dubia benefits in warmer temperatures and D. denifera in cooler temperatures. Therefore, in environments where temperatures fluctuate,  this may lead to co-existence, greater abundances of the diluter, and less disease transmission. We are testing whether the dilution effect reduces infection prevalence when a diluter is present, and how dilution effects differ at a constant 20˚C versus a fluctuating temperature around the same mean. We designed a multi-generational mesocosm experiment with communities that contained the host and parasite, and communities that contained the hosts, parasites, and diluters at both constant and fluctuating temperatures. We hypothesize that the changing environmental conditions caused by fluctuating temperature will lead to more diluters, causing a greater dilution effect via co-existence of the host and diluter. This project will help us learn more about the possible effects of climate change – especially variable temperature – on disease dynamics in communities with multiple species.

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Approximating abundance of Daphnia dentifera using environmental DNA (eDNA) samples

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Emily Landolt, a student in St. Norbert College, worked in the lab of Dr. Alex Strauss

Abstract Freshwater zooplankton, such as Daphnia dentifera, are helpful model organisms for studying infectious disease dynamics and are ecologically important because of their role in food webs. They are consumers of primary producers like algae and are prey for other organisms such as fish. However, field sampling of freshwater zooplankton can be costly in terms of time and effort. The use of eDNA to estimate species abundances rather than an assessment of presence/absence in aquatic ecosystems is an exciting concept because it allows for more efficient and potentially more accurate field sampling. eDNA sampling methods for this study system can also be important for monitoring populations and epidemics in the field to ensure ecosystem health. This methodology has been studied in fish but is not yet well understood for invertebrates. We explored this idea by generating artificial mesocosm populations of Daphnia. Sampling for species abundance was done in two ways: using a traditional observational method of taking a subsample and counting the number of Daphnia, and a novel molecular method to quantify the amount of eDNA using a qPCR assay. Our results are a correlation between the observed species abundance and the molecular quantification of eDNA. Preliminary results show insignificant relationships indicating complexity that needs to be explored. Possible factors that affected the amount of eDNA in the water include water chemistry (i.e. pH), age structure, time since introduction, and water replenishment from evaporation/sampling. In the future, more research will be needed to explore the factors of eDNA persistence and how it can be used to better approximate species abundances of aquatic invertebrates like Daphnia.

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Spatial Variation in Oyster Macroparasites Across the Georgia Coast

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Sofia Markiewicz, a student at Scripps College, worked in the lab of Dr. Jeb Byers

Abstract Oysters are a key coastal foundation species that have declined drastically across the US coasts due to the combined effects of overharvesting, pollution, and disease. With climate change, there The eastern oyster (Crassostrea virginica) is a keystone species and ecosystem engineer that stabilizes sediments, cycles nutrients, improves water quality, and provides habitat for fish and crustaceans. Oysters are prone to several macroparasites, including pea crabs (Zaops ostreum), mud blister worms (Polydora websteri), and boring sponge (Cliona spp.), all of which can damage their gill tissue and shells. Although oyster populations have been widely studied in other areas of the eastern United States, the geographic and environmental factors that influence macroparasite infection in Georgia’s oyster population are still largely unknown. In this study, we sampled oysters from 24 reefs across eight distinct sites along the Georgia coastline and examined them for macroparasite infection. The relationships between macroparasite prevalence and geographic location and environmental conditions (specifically reef complexity, reef shell density, dissolved oxygen, water temperature, and salinity) were examined. We found no correlation between location and macroparasite prevalence for any of the macroparasites examined. However, increased prevalence of blister worms was correlated with low salinity and low reef complexity. Prior research has also shown that shellfish infected with blister worms exhibit decreased shell strength, and are therefore more vulnerable to damage and predation. Understanding what conditions affect blister worm prevalence and how they may be altered by by climate change (e.g. changing salinity) is important for evaluating locations where oyster reefs are likely to have low macroparasite infection and be less prone to damage, in order to better maintain high-quality reef habitat. This is especially crucial in a relatively understudied environment such as Georgia, where the effects of these conditions are less well known. 

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Infection and Spore Yield of Daphnia Microsporidian

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Hannah O’Grady, a student at Mount Holyoke College, worked in the lab of Dr. Alex Strauss.

Abstract An important part of understanding how diseases spread and impact a community is understanding the tradeoffs that occur when a parasite generalizes. While sampling ponds in Whitehall Forest we discovered a potentially novel microsporidian that was able to infect at least five zooplankton in the Cladocera superorder at relatively high infection prevalence. We designed an experiment to investigate the potential costs of its generalism. We exposed isoclonal lines of two different species of Daphnia, each from two different lakes, to spores gathered from the dominant host in each lake to test whether the microsporidian was 1) more successful at infecting Daphnia of one species over the other or 2) whether it was more successful at infecting Daphnia from the same lake or 3) the same species from which the parasite spores were gathered. We also counted spore yield (a metric of parasite fitness) from the six infected species gathered from the field to test for differences across species, lakes or time. None of the Daphnia exposed to the spores in the lab became infected, leading us to hypothesize that there is an intermediate host for this parasite. Spore yields from field-collected hosts did differ significantly among host species, with higher spore yields in D. laevis (mean=446,415.55±412,977.53) and Diaphanosoma (mean=253,888.83±78,085.34) than in D. ambigua (mean=40729.12±41,396.68), D. parvula(mean=46250.06±49,432.78), and Simocephalus (mean=17083.17±13,025.14). There were no significant differences in spore yield across lakes or days. More research will be needed to find the intermediate host for the microsporidian as well as to determine its exact genus and species.

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