Date of Award

Spring 2015

Document Type


Degree Name

Doctor of Philosophy (PhD)

Committee Director

Daniel E. Sonenshine

Committee Member

David T. Gauthier

Committee Member

Jing He

Committee Member

Christopher Osgood

Committee Member

R. Michael Roe


The neurobiology of the synganglion (central nervous system) of the Lyme disease tick, Ixodes scapularis and the soft tick Ornithodoros turicata was evaluated using Illumina GAII high throughput sequencing which generated high coverage cDNA libraries (transcriptomes). These ticks exhibit different biological patterns of feeding, blood meal water, and salt elimination, cuticle plasticity versus cuticle synthesis, development and reproduction. RNA sequencing of I. scapularis, and Ornithodoros turicata yielded a total of 117,900,476 raw reads which were assembled to 30,838 contigs and a total of 63,528,102 also assembled to 132,258 contigs, respectively. Comparison of Gene Ontology (GO) mapping success for genes in 32 important GO molecular categories showed little difference between the two species.

Functional assignments of transcripts predicting neuropeptides, neuropeptide receptors and neurotransmitter receptors was done, supported by strong e-values (< -6), and high consensus sequence alignments. For the synganglion of I. scapularis, transcripts predicting 23 neuropeptides and/or their receptors were identified. For the synganglion of O. turicata, 25 neuropeptides and/or their receptors were identified. Both species had transcripts predicting all of the same neuropeptides and/or their neuropeptide receptors in common except for allatotropin peptide, found only in I. scapularis, and allatostatin C, bursicon β, and glycoprotein B, which were found only in O. turicata.

If the repertoire of neuropeptide and neurotransmitter messages expressed in the synganglia of O. turicata and I scapularis is so similar, how can we explain the very different physiological processes that occur in these two very different tick species? Real time PCR assays were used to study the expression of candidate genes in response to blood feeding. My study shows a strong similarity in gene identity (annotation/alignments) of both species but marked differences in the gene expression, extent of up-regulation or down-regulation, and the timing of their expression in response to feeding. This may indeed help explain many of the differences in the biology of the two different species. The diversity of messages predicting important genes identified in this study and differences in their expression in response to feeding offers a valuable resource useful for understanding how the tick synganglion regulates important physiological functions in ticks.