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Access Type

WSU Access

Date of Award

January 2017

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Physiology

First Advisor

Jeffrey L. Ram

Abstract

Water mites are a diverse group of arachnids that inhabit aquatic habitats and have been studied in the past for their biodiversity, unique lifecycle, bioindicator species use and for their impact as parasites on insects of human pathological significance such as the mosquito. Water mites are critical in their environment as possible apex predators however, their life cycle and morphological complexity has made taxonomy and description of water mites difficult. Although water mite species richness is estimated at over 6000 species described to date, descriptions of extant North American water mite species are estimated to be only 50% of the existing species. Water mite digestive physiology is also virtually unknown even though water mites are known to be efficient predators and parasites of dipteran pest such as chironomids. With the use of microscopic, biochemical and molecular genetic technologies this work aims to improve water mite knowledge in both digestive physiology and diversity of North American water mite populations.

Water mites from Blue Heron Lagoon at Belle Isle, Detroit were collected and processed for assessment of both species diversity and gut molecular contents. Using genetic and morphological methods, water mites and their prey were identified. Water mites in different genera are observed to be generalists as we did not see any water mite genera feeding exclusively on only one type of prey. Gut molecular contents were assessed using primers targeting the COI gene that has been used for molecular barcoding. Dipteran “specific” primers (mLep) were used to elucidate what prey were being consumed. These sequences were obtained by Sanger Sequencing and by Next Generation Sequencing. These sequences were compared to a large database of chironomid species that were generated from the same biogeographic region. The conclusion is that Lebertia water mites are generalist and opportunistic predators who consume a large diversity of chironomids, including various species of Cricotopus, Chironumus, and Paratanytarsus. A novel finding of this study is that for some mites the nearest matches to the DNA sequences of gut-associated DNA were sequences from oligochaetes, albeit in most cases the percentage identity to any GenBank sequence of oligochaetes was in the range of 80 – 90%.

Water mite diversity in the Blue Heron Lagoon is also reported here with a new record for Lebertia quinquemaculosa Marshall and the possibility of new Lebertia species descriptions from Blue Heron Lagoon. Scanning electron microscopy was used to verify morphological characters and to aid in describing the new Lebertia, which we are proposing to name L. davidcooki. L. quinquemaculosa and L. davidcooki were also studied to characterize the structures that facilitate digestive passage of ingested food. Fluorescein, a fluorescent metabolic product from fluorescein diacetate (FDA), was used to visualize the gut structures of the water mites by feeding them fluorescent chironomid larval prey that had been exposed to FDA. Water mites were also examined using confocal fluorescent microscopy to describe gut structures. Transmission electron (TE) microscopy was used to visualize the internal microstructures of L. quinquemaculosa and L. davidcooki for the first time. Digestive structures such as the excretory organ and mid-gut were observed from water mite dissections and further analyzed by toluidine blue staining of mite sagittal sections.

This work represents the first ever digestive physiology experiments on Lebertia. The results of this work have also contributed new North American DNA barcode genetic representation of water mites, chironomids, and a morphological and molecular description of a Great Lakes invasive copepod Eurytemora carolleae to the public databases. The importance and contribution of water mites to aquatic ecosystems validates this study which begins to fill in knowledge gaps on water mite physiology and biodiversity.

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