UC Santa Cruz

Native biodiversity loss and the introduction of exotic species have caused substantial changes in community composition of local communities, with unknown effects on pathogen transmission. Avian malaria (Plasmodium relictum) has driven population declines in native Hawaiian birds, but the role of native and introduced bird species in transmission is poorly understood. Transmission may differ in communities composed primarily of introduced birds compared to communities with natives because natives mount high parasitemia and may have longer-lived infections relative to introduced birds. My dissertation applies fieldwork and molecular tools to investigate the effect of host community composition and land use on malaria transmission in lowland forests on Hawaii Island. In my first chapter, I explore the influence of host community composition on infection prevalence in Culex quinquefasciatus, the primary vector of avian malaria in Hawaii, and examine the reciprocal effect of transmission on the Hawaii amakihi, Chlorodrepanis virens. I found that prevalence in mosquitoes increased with native bird density. Transmission intensity depressed population growth rates of amakihi, but were projected to be above 1 even if incidence was 100%. These results suggest that native birds increase disease transmission, likely because of increased host competence in native compared to introduced birds. In my second chapter, I investigated feeding patterns of Cx. quinquefasciatus and avian malaria infection patterns. I found that Cx. quinquefasciatus fed almost exclusively on birds, with most blood meals coming from Japanese white-eye, Zosterops japonicus, suggesting that ornithophilic feeding by Cx. quinquefasciatus facilitates avian malaria transmission. In my third chapter, I examined land use, larval habitat, and climate drivers of Cx. quinquefasciatus, and another vector species, Aedes albopictus. I found that both species were positively correlated with the proportion of surrounding developed land and the availability of larval habitat, which were themselves positively correlated. These results suggest that conversion of natural habitats to residential and agricultural land may increase larval habitats, with implications for avian malaria transmission in developed areas. This work provides insight into native bird recovery in Hawaii, and underscores the importance of host community composition and land use on the transmission of multi-host vector-borne pathogens.