Doctor of Philosophy (Ph.D.)
Virginia Institute of Marine Science
Jeffrey D. Shields
Hamish J. Small
Ryan B. Carnegie
Spencer J. Greenwood
Herein, I have completed several experiments which encompass developing fiddler crabs as a model system, as well as sentinel and temperature studies to investigate biotic and abiotic factors in parasite transmission. My studies show which factors prevent, delay, or accelerate transmission and progression of H. perezi. The fiddler crab experiments by chapter are as follows: Chapter 1. I screened adult and juvenile fiddler crab populations for naturally occurring H. perezi infections at endemic and non-endemic sites. No natural infections were found in the adult or juvenile populations (Chapter 1 and 3). I completed inoculation trials with U. minax, U. pugnax, and U. pugilator, demonstrating that the parasite can survive and replicate in these species. Fiddler crabs can live for several months with patent infections. For example, I successfully transferred H. perezi from blue crab to fiddler crab and back to blue crab. Through serial inoculations I was able to serially maintain the parasite in the lab year-round. Building on the above experiments, I completed minimum dose studies which showed that a minimum inoculum of 1,000 parasite cells was required for patent infections. Additionally, I evaluated parasite progression through studies using Uca minax. These studies which used an inoculum in the ameboid trophont and clump colony stages showed that H. perezi progresses through its life-history stages in fiddler crabs as it would in blue crabs, with the filamentous trophont stage first observed in the hemolymphs smears followed by the ameboid trophont stage. Chapter 2. Intertidal environments are well known as areas of environmental extremes, and accordingly the animals that reside there have adapted to those conditions out of necessity. One abiotic factor that can have large diel variation is temperature. to address the impact of temperature variation of the marsh and subtidal habitat on H. perezi, I developed laboratory temperature experiments with nascent infections (7 °C, 15°C, 20°C, 25°C, 30°C), with patent infections (10°C, 15°C, 20°C, 30°C), and a progression series over fine scale (15°C, 17°C, 19°C, 20°C) temperature increments. These studies demonstrated that growth of the parasite is limited at the higher and lower temperatures, and that H. perezi is eliminated from the host at 30°C. This was confirmed by hemolymph smears, histology, and PCR. Chapter 3. The successful laboratory inoculations and lack of infections in fiddler crabs from endemic areas led to additional field deployments. These experiments aimed to address the dissonance of the initial results. My sentinel studies included fiddler crabs deployed in a crab pot from a pier touching bottom, deployed from the pier approximately mid-tidal height, deployed mid-marsh in mesh cages without access to bury, and deployed mid-marsh with access to bury. Fiddler crabs can obtain H. perezi infections in the marsh when caged without access to bury or when fully or partially submerged from a pier. However, they do not obtain H. perezi infections when given access to bury. Natural behaviors, such as burying along with elevated marsh temperatures likely prevent the establishment of H. perezi in the natural fiddler crab population.
© The Author
O'Leary, Patricia Anne, "The Development of Fiddler Crabs (Uca Spp.) as a Comparative Model System for the Parasitic Dinoflagellate, Hematodinium Perezi and its Natural Host the Blue Crab, Callinectes Sapidus" (2018). Dissertations, Theses, and Masters Projects. Paper 1550153657.