Date of Award
9-11-2024
Document Type
Thesis
Degree Name
Biology, MS
First Advisor
Kyle Gustafson
Committee Members
Andrew Sweet, Scott Mangan
Call Number
ISBN 9798384077206
Abstract
Spatial processes across both broad and fine scales are important for understanding ecosystem function. Broad-scale spatial processes can be defined as elevational, latitudinal, or longitudinal processes whereas fine-scale spatial processes represent movement and dispersal among habitat patches. Historically, studies on freshwater snail distributions have focused on fine-scale processes with secondary consideration given to spatial sampling. Species inventories for freshwater snails are outdated because historically snail species descriptions were based on shell morphology, which is highly plastic. In Arkansas, it is estimated that there are 36 freshwater snail species, but this estimate does not account for shell plasticity and does not provide information on snail species distributions within the state. My study aims to (1) quantify the number of snail species in the Ozark Highlands and Ouachita Mountains, (2) determine which abiotic factors correlate to patterns of snail occupancy, and (3) describe the mechanisms that drive snail species richness among two ecoregions. During the summer of 2022, I visited 44 sites (20 lentic, 24 lotic) in the Ozark Highlands and Boston Mountains ecoregions and collected 6,934 snails and identified 11 snail taxa. During the summer of 2023, we visited 65 sites (30 lentic, 35 lotic) in the Ouachita Mountains and collected 4,149 snails and identified 9 snail taxa. At each site we recorded elevation, GPS coordinates, and water chemistry metrics (e.g., water temperature, dissolved oxygen, conductivity, and pH). To detect spatial processes and to account for spatial autocorrelation, we used Moran’s Eigenvector Mapping (MEM). Using landscape layers, we analyzed each site in a 500m radius buffer to calculate landcover classes across sites. We sequenced representative snails using the mitochondrial gene 16S and the nuclear gene 28S. My multivariate analysis consistently returned MEMs as the most important predictor variables of snail occupancy, indicating that dispersal limitation was the most important process determining snail occupancy. This broad-scale effect being of primary importance deviates from classical literature suggesting that snail occupancy is driven primarily by local water chemistry. Species richness was higher in the 2022 Ozark sites compared to the 2023 Ouachita sites, but we did not find any significant difference in species richness when we visited a subset of Ozark and Ouachita sites in 2023. The top variables in our model for species richness include MEM2 and open water. The variable MEM2 represents an almost latitudinal process whereas open water represents the proportion of open wetland area at each site. Given my results, I suggest that the importance of local wetland characteristics in determining snail communities has been overstated and that dispersal limitation is the primary factor determining snail community structure. Further research on snail communities should account for spatial processes and dispersal limitation to understand the dynamics of snail occupancy. Parasites are one of the most biodiverse group of organisms on Earth, with every species being infected with at least one parasite and some estimates stating that 40% of described species are parasitic to some degree. One class of parasites that are of both medical and veterinary importance is Trematoda. Trematodes in the subclass Digenea are visceral molluscan parasites that require an obligate molluscan first-intermediate host to complete their life cycles. Although trematodes are important for human and wildlife health, few studies in Arkansas have described the native trematode species found. Furthermore, almost every study on trematodes in Arkansas comes from a few necropsies of vertebrate hosts and does not reveal the true diversity of trematodes in nature. My study aims to (1) quantify trematode-cercaria morphospecies prevalence among several snail taxa, (2) describe patterns of trematode prevalence and species richness among two ecoregions, and (3) investigate patterns of trematode prevalence and species richness across lotic and lentic communities. During the summer of 2022, we visited 44 sites (20 lentic, 24 lotic) in the Ozark Highlands and Boston Mountains ecoregions and assessed 6,934 individual snails for trematode infection. During the summer of 2023, we visited 65 sites (30 lentic, 35 lotic) in the Ouachita Mountains and assessed 4,149 individual snails for trematode infection. We identified 13 trematode morphotypes, with 3 unique to the Ozarks (furcocystocercous, Ha. occidualis, Ha. eccentricus) and 2 unique to the Ouachitas (clinostomoid, spiny-mutabile). We found no overall differences in trematode infection prevalence among the two ecoregions. Trematode infection prevalence in the caenogastropod Pleurocera potosiensis was significantly higher in the Ozarks compared to the Ouachitas. Notably, Helisoma anceps and Menetus dilatatus were only infected in the Ouachitas whereas Gyraulus parvus was only infected in the Ozarks. Trematode morphotype richness in Planorbella trivolvis was significantly higher in the Ouachitas compared to the Ozarks. The cercaria morphotype armatae was the most prevalent across host taxa and had a 3.4% prevalence in the Ozarks and a 2.1% prevalence in the Ouachitas. We did not observe any differences in trematode cercariae morphotype prevalence between lotic or lentic habitat types among both ecoregions. Similar patterns among ecoregions could mean that trematodes are using the same vertebrate definitive host species. Similar patterns of infection prevalence could also result from the similar snail communities among both ecoregions. Our findings represent one of the largest efforts to date in the literature and the first study in Arkansas to sample snails and their trematode parasites.
Rights Management
This work is licensed under a Creative Commons Attribution 4.0 International License.
Recommended Citation
Fiedor, Taylor Michelle, "Montane Molluscs: Factors Affecting Snails and Their Trematodes Throughout the Mountain Regions of Arkansas" (2024). Student Theses and Dissertations. 44.
https://arch.astate.edu/all-etd/44
