Thermal Constraints to the Sporogonic Development and Altitudinal Distribution of Avian Malaria Plasmodium relictum in Hawai'i

• Published in: The Journal of parasitology 2010-04, Vol.96 (2), p.318-324
• Main Authors: LaPointe, Dennis A, Goff, M. Lee, Atkinson, Carter T
• Format: Article
• Language: English
• Subjects: Altitude; Animal populations; Animals; Aves; Biological and medical sciences; Birds; Culex - parasitology; Culex quinquefasciatus; Ducks; Endangered & extinct species; Forests; Fundamental and applied biological sciences. Psychology; General aspects; General aspects and techniques. Study of several systematic groups. Models; Hawaii - epidemiology; Indigenous animals; Indigenous species; Insect Vectors - parasitology; INVERTEBRATE-PARASITE RELATIONSHIPS; Invertebrates; Islands; Linear Models; Malaria; Malaria, Avian - epidemiology; Malaria, Avian - parasitology; Marine; Memory interference; Mosquitoes; Mosquitos; Oocysts; Parasites; Passeriformes - parasitology; Passeriformes - physiology; Plasmodium - growth & development; Plasmodium - physiology; Plasmodium relictum; Salivary glands; Sea level; Species extinction; Sporogony; Sporozoites; Sucrose; Temperature; Topographical elevation; Vector-borne diseases; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution
• ISSN: 0022-3395; 1937-2345
• DOI: 10.1645/GE-2290.1

More than half of the Hawaiian honeycreepers (Drepanidinae) known from historical records are now extinct. Introduced mosquito-borne disease, in particular the avian malaria Plasmodium relictum, has been incriminated as a leading cause of extinction during the 20th century and a major limiting factor in the recovery of remaining species populations. Today, most native Hawaiian bird species reach their highest densities and diversity in high elevation (>1,800 m above sea level) forests. We determined the thermal requirements for sporogonic development of P. relictum in the natural vector, Culex quinquefasciatus, and assessed the current distribution of native bird species in light of this information. Sporogonic development was completed at constant laboratory and mean field temperatures between 30 and 17 C, but development, prevalence, and intensity decreased significantly below 21 C. Using a degree-day (DD) model, we estimated a minimum threshold temperature of 12.97 C and a thermal requirement of 86.2 DD as necessary to complete development. Predicted (adiabatic lapse-rate) and observed summer threshold isotherm (13 C) correspond to the elevation of high forest refuges on the islands of Maui and Hawai'i. Our data support the hypothesis that avian malaria currently restricts the altitudinal distribution of Hawaiian honeycreeper populations and provide an ecological explanation for the absence of disease at high elevation.