Term of Award

Spring 2012

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

Lance A. Durden

Committee Member 2

William Irby


Ixodes scapularis, the black legged tick, is a species endemic to North America with a range including most of the eastern-half of the United States and portions of Canada and Mexico. The tick is an important vector of diseases transmitted to humans and animals. Since its first description in 1821, the taxonomy of the species has been controversial. Biological differences have been identified in the northern and southern populations, yet no consensus exists on population structure and the causes of this disparity. Earlier molecular studies utilizing nuclear and mitochondrial genetic markers have revealed the occurrence of two distinct lineages: a genetically diverse southern clade found in the southern-half of the distribution area of I. scapularis, and a more genetically homogeneous American clade found throughout the I. scapularis range. Although mitochondrial markers have assisted in clarifying the population history of the tick, nuclear, bi-parentally inherited markers such as microsatellite loci can provide additional information at a finer scale. Furthermore, previous studies were based on either limited sampling, which did not represent the whole geographic range of the tick, or were based on single molecular markers. In this study, we (a) generated a new dataset by collecting samples throughout the distribution range of I. scapularis; (b) developed microsatellite markers for the study of the genetic structure of I. scapularis; (c) amplified and sequenced two different mitochondrial datasets and analyzed them phylogenetically in order to compare our data with previously published reconstructions; and (d) analyzed population genetics parameters and compared results obtained by analyzing mitochondrial vs. microsatellite markers. Our data confirm some of the earlier findings, but provide additional information on the geographically distinct genetic diversity of the species, and the evolutionary mechanisms that shaped its present structure. These data may further help our understanding of how pathogens circulate within I. scapularis populations.

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