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Alternative Title

Investigating speciation in the seal lungworm Otostrongylus circumlitus

Publication Date


First Advisor

Laura A. Katz

Document Type

Honors Project

Degree Name

Bachelor of Arts


Biological Sciences


Speciation, Nematodes, Pinnipeds, Phocid, Otostrongylus circumlitus, Seals, Parasites, Lungworm, Repeatexplorer, Next-generation sequencing, Assay, Phylogenetics, Species, Lungworms-Variation, Harbor seal-Parasites, Northern elephant seal-Parasites, Pinnipedia, Phylogeny


While many marine mammals are already struggling to thrive amidst climate change, global warming is predicted to increase the range, prevalence, and virulence of aquatic parasites (Harvell et al., 2002). Accurate identification of these parasites will help us better assess the threats to wild marine mammals and treat infections of those in rehabilitation facilities. The overarching goal of this project is to create sensitive, species-specific assays for post-mortem identification as well as diagnostic use in rehabilitating wild animals. To diagnose a live animal, regular PCR is often not sufficiently sensitive to pick up trace amounts of DNA from parasite eggs or larvae in the feces or blood. By using a repeat-based quantitative PCR assay, we gain sensitivity. In nematodes these repeats evolve quickly enough that they are also species-specific (Pilotte et al., 2016). Otostrongylus circumlitus (harbor seal lungworm), the focus of this thesis, is a metastrongyloid nematode that causes mild symptoms in its intended harbor seal host, Phoca vitulina, such as bronchitis. However, the parasite has also been found in the northern elephant seal, Mirounga angustirostris, where it migrates to the heart, causing a fatal heart condition, disseminated intravascular coagulation (Elson-Riggins et al., 2001). Nematodes morphologically identified as O. circumlitus from the Pacific appear negative on our qPCR test, which we developed to identify O. circumlitus infections based on a repetitive genomic region. While it is possible that the repeat is too specific, it is also possible that the Atlantic and Pacific parasite populations are speciating, much like their harbor seal hosts that became two different subspecies after isolation ~2.5 million years ago (Stanley et al., 1996). Preliminary barcoding data suggests the Pacific O. circumlitus population is distinct, though clearly derived from the Atlantic population. Analysis of genomic repeats from O. circumlitus samples from both the Atlantic and Pacific, will allow us to explore further the divergence of these populations, as well as to develop an assay that can identify Pacific Otostrongylus infections from fecal or sputum samples. However, the methodologies for use of genomic repeat families for phylogenetics is still in a prototype stage. While these methods show promise for resolving closely related groups, the pipeline for use of genomic repeat families for phylogenetics is still in optimization. Bearing in mind the developmental stage of the methods and the limited available samples, the data reveal a distinction between the Atlantic and Pacific O. circumlitus populations and homogeneity within the Pacific O. circumlitus population across harbor seal and northern elephant seal hosts.


2018 Kalani Marie Williams. Access limited to the Smith College community and other researchers while on campus. Smith College community members also may access from off-campus using a Smith College log-in. Other off-campus researchers may request a copy through Interlibrary Loan for personal use.




110 pages : color illustrations. Includes bibliographical references (pages 70-74)