Dr. Susan Jarvi, Research Geneticist, PIERC/PCSU at UH Manoa
Dr. Carter Atkinson, Microbiologist, PIERC
Project: SIS 5001768.
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Worldwide extinction rates are estimated to have increased five-fold and, nationwide, Hawaii ranks top in numbers of endangered forest birds. Although a number of factors have contributed to the decline and extinction of this unique biological resource, introduced avian malaria (Plasmodium relictum), is probably the single most important factor preventing recovery of these birds in low elevation habitats. Susceptibility to malaria differs among honeycreeper species and their current elevational distribution can be explained by relative susceptibility or resistance to this disease. Continued decline in numbers, fragmentation of populations, and extinction of species that are still relatively common will likely continue without new, aggressive approaches to managing avian disease. Methods of intervention in the disease cycle, such as vector control, chemotherapy or vaccine development, are not entirely feasible because of the efficient immune-evasion strategies evolved by the parasite, technical difficulties associated with treating wild avian populations and the increased risk of selection for more virulent strains of the parasite. Understanding the disease cycle involves evaluation of the complex interactions between malarial parasites and the avian immune system.
Toward a better understanding of the avian immune system, we are exploiting the natural evolution of disease resistance in some low elevation native bird populations, such as the Hawaii Amakihi (Hemignathus virens) and also in a highly susceptible species which currently exists primarily at higher (mosquito-free) elevations, the I'iwi (Vestiaria coccinea).
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Amakihi Hemignathus Virens
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I'iwi Vestiaria Coccinea
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We are attempting to perfect genetic methods for identifying individuals with a greater immunological capacity to survive malarial infection. In collaboration with the National Zoological Park, Smithsonian Institution, Washington DC (Dr. R.C. Fleischer), we are focusing on genetic analyses of the major histocompatibility complex, due to its critical role in both humoral and cell-mediated immune responses. In the process, we expect to provide population managers with new criteria for maintaining long-term population stability for threatened species through the development of methods for evaluating and maintaining genetic diversity in small populations at loci important in immunological responsiveness to pathogens.
Additional efforts to save remaining species are currently underway and, for some, involve the artificial manipulation of populations through captive breeding and geographic translocations. When birds are moved from one geographic area to another, the parasites they harbor move with them. Thus, studies of the diversity and virulence of the parasite have been initiated in hopes of reducing the risk of unintentional introduction of a new variant of the parasite. To gain a better understanding of parasite diversity, we are evaluating conserved ribosomal genes and genes encoding more variable cell-surface molecules as a first step in developing a better understanding of these complex host-parasite relationships.
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