Term of Award

Fall 2015

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.


Department of Biology

Committee Chair

Lorenza Beati

Committee Member 1

Laura Regassa

Committee Member 2

Lance Durden


The blacklegged tick, Ixodes scapularis (Acari: Ixodidae) is the subject of intense research due to its economic importance from being a vector of several diseases. Previous studies have examined its taxonomic status and more recently, its genetic structure. This study embarked upon resolving the questions surrounding the genetic structuring of the tick, by using different molecular markers. Molecular data were first phylogenetically analyzed by using four different mitochondrial and nuclear markers (12SrDNA n=483, Dloop n=432, ITS2 n=156, Actin n=117). A Bayesian tree was inferred from the concatenated mitochondrial dataset, whereas nuclear gene markers were found to be uninformative. Nine microsatellites loci (n=462) were also genotyped and used to study the population structure of the same individual tick samples used for phylogenetic analysis. Information generated with the different markers was compared. As other studies have reported, the Bayesian analysis identified six clades, all with strong support. Microsatellite analysis showed that I. scapularis is genetically structured at the “state” level, and that genetic distance increases with geographic distance (r = 0.582, p = 0.001; r = 0.704 p = 0.005). However, it found no correlation between distances generated from microsatellites and mtDNA sequences (r =0.025 p = 0.0964), further supporting the opinion that mitochondrial gene sequences should be used cautiously when delimiting species as they can be mere witnesses of past vicariant events that did not result in speciation. Our work indicates that microsatellite markers, codominant bi-parentally inherited markers, can elucidate long-standing questions better than other markers.

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