Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Zoology and Genetics


Ecology and Evolutionary Biology

First Advisor

Brent J. Danielson

Second Advisor

Richard J. Hoffmann


The Iowa Pleistocene snail, Discus macclintocki, is a federally endangered land snail found only in northeast Iowa and northwestern Illinois. This species is believed to be a glacial relict with populations isolated for the last 16,000 years. In this study, I investigated the amount of genetic variation within, and the gene flow among, ten isolated populations of the Iowa Pleistocene snail, Discus macclintocki (Baker). I sequenced part of the 16s region of the mitochondrial DNA from 175 snails. Populations clustered clearly by watershed, suggesting that flooding events may have been the historical avenue of gene flow rather than overland dispersal. On a single small watershed, Buck Creek, individuals could not reliably be assigned to their population, suggesting that either gene flow is still occurring or the populations have not been separated as long as the others. Within populations, an extremely high amount of variation was observed. Polymorphism was very high, with up to seven haplotypes per population;The high level of genetic variation observed is not purely a population size effect, as polymorphism was not related to size estimates determined in a mark-recapture study I conducted. Population sizes were estimated at fourteen sites using standard mark-recapture analyses, as well as Bayesian estimates, which account for small sample sizes. Discus macclintocki has a very high mutation rate and seems to have a very healthy amount of genetic variation. When the number of variable sites in 16s rDNA was compared among species in a variety of taxonomic groups, snails showed an extremely high level of variability;Although I only investigated mitochondrial genetic variation in Discus macclintocki, many organisms have been examined for variation in the nuclear genome as well. These studies sometimes give conflicting results of how much variation is present within a population. One potential reason for differences in levels of nuclear variation and mitochondrial variation is due to differential dispersal rates and/or dispersal distances between the sexes. These ideas are explored through an analysis of data from the literature.



Digital Repository @ Iowa State University,

Copyright Owner

Tamara Kay Ross



Proquest ID


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File Size

180 pages