Surviving in Isolation: Are the Chilean Patagonia South American fur seals doomed to succumb to parasitic infections?

Kennesaw State University Biology Major Victoria Mendiola, worked in the lab of Dr. Nicole Gottdenker to study hookworm infectioun in South American fur seals.

Abstract: Hookworm infection is endemic in many otaiird species and can cause up to 70 % pup mortality in some populations (Lyons 2001, Seguel in press). South American fur seal (SAFS) neonates are able to clear hookworm infection in a matter of months, which is vital for pup survival (Seguel in press). Regardless of the significance of parasite clearance, little is known about the mechanisms involved in this process in wild populations. The aim of this research was to identify the mechanisms the fur seal pups use to expel the hookworms. In order to do so, the immune response was split into cell mediated and humoral responses.  Blood and hookworm samples were collected from Guafo Island, Chile during breeding seasons 2013 to 2015, with the inclusion of a control group (treatment of SAFS with Invermectin) starting in 2014. Blood smear slides were used for differential counting of leukocytes (cellular immune response), which was performed at the University of Georgia by standard methods. To detect antibodies in SAFS pup against hookworm parasites (humoral immune response), sections of Uncinaria sp. nematodes were incubated with sera from a pup that had successfully expelled the hookworms. The SAFS antibodies were labeled and visualized by standard immunohistochemistry techniques. Our examination of blood smears found there is a proportional increase in the number eosinophils with the severity of hookworm infection. The number of basophils and lymphocytes were highest in the group with mild hookworm infection, which suggests these leukocytes could play a role on regulating the severity of the hookworm infection. We also found evidence that the pups are able to produce an antibody that binds to in intestinal tract of the hookworm. The identification of fur seal antibodies reacting to the brush borders of the hookworm’s gastrointestinal tract suggests this is a necessary immune response for the fur seals to successfully expel the hookworms. In conclusion, we believe that a combination of these immune responses contribute to the successful expulsion of the parasite. The Chilean population of South American fur seals has declined more than 50% over the last 20 years. The most important breeding colony in Chile is located on Guafo Island, a remote island in the Northern Patagonia. Although this isolated population of fur seals lives in a very diverse and rich marine ecosystem, it has been in unrecoverable decline. The loss of genetic diversity is one of the consequences that face isolated mammal populations and low genetic variability has been associated with detrimental effects on marine mammals’ health (Acevedo et al. 2006). On Guafo Island, our prior research shows that hookworm infection is the major cause of pup mortality (Seguel et al. 2013) and that survival of hookworm infection is strongly mediated by the immune response to the parasite (Seguel et al. in preparation). Since the immune response is strongly linked to genetic variability, isolated populations are exposed to the expression of deleterious gene copies, which can limit the capacity to respond against parasites. Our hypothesis is that limited variability of the fur seal immune system genes is associated with susceptibility to hookworm disease. To test this we will extract DNA from fur seal skin samples and the genetic variability of each individual will be assessed by genotyping microsatellites loci cloned based on sequences published for other pinniped species and the MHC class II DQB locus. We expect to find lower genetic variability in animals with higher parasitic burden and clinical disease due to hookworms. Our student work will be centered on DNA extraction and PCR for the amplification of MHC II genes and later analyses of the sequence data.

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