Microclimate conditions alter Ixodes scapularis (Acari: Ixodidae) overwinter survival across climate gradients in Maine,United States |
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| Affiliation: | 1. School of Biology and Ecology, University of Maine, 5722 Deering Hall, Orono, ME 04469;2. Vector-Borne Disease Laboratory, Maine Medical Center Research Institute, 81 Research Drive, Scarborough, ME 04074;3. College of Arts and Sciences, University of Maine at Presque Isle, 181 Main Street, Presque Isle, ME 04769;1. Institute for Hygiene and Applied Immunology; Center for Pathophysiology, Infectiology and Immunology, Medical University of Vienna, Kinderspitalgasse 15, A-1090 Vienna, Austria;2. Department of Environmental Health, Center for Public Health, Medical University of Vienna, Kinderspitalgasse 15, A-1090 Vienna, Austria;1. Centre for Biosecurity and One Health, Harry Butler Institute, Murdoch University, Murdoch 6150, Western Australia, Australia;2. Behavioural Ecology Lab, School of Molecular and Life Sciences, Curtin University, Bentley 6102, Western Australia, Australia;1. Plataforma de Criação e Experimentação Animal, Fiocruz Rondônia, Fundação Oswaldo Cruz, Porto Velho, RO, Brazil;2. Laboratório de Entomologia, Fiocruz Rondônia, Fundação Oswaldo Cruz, Porto Velho, RO, Brazil;3. Programa de Pós-Graduação em Biologia Parasitária, turma especial de Doutorado em Ciências parceria IOC/Fiocruz Rondônia, Porto Velho, RO, Brazil;4. Bolsista Fundapam / Laboratório de Biologia do Carrapato, Embrapa Gado de Corte, Campo Grande, MS, Brazil;1. Division of infectious diseases, Inflammation Center, Helsinki University Hospital and University of Helsinki, Helsinki, Finland;2. Department of Clinical Medicine, University of Turku, Turku, Finland;3. Virology, University of Helsinki and Helsinki University Hospital, Helsinki, Finland;4. Department of Infectious Diseases, Turku University Hospital and University of Turku, Turku, Finland;5. Department of Biostatistics, University of Turku, Turku, Finland |
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| Abstract: | The incidence and geographic range of vector-borne diseases have been expanding in recent decades, attributed in part to global climate change. Blacklegged ticks (Ixodes scapularis), the primary vector for multiple tick-borne pathogens in North America, are spreading rapidly beyond their historic post-colonial range and are thought to be constrained mainly by winter temperature at northern latitudes. Our research explored whether winter climate currently limits the distribution of blacklegged ticks and the pathogens they transmit in Maine, U.S.A., by contributing to overwinter mortality of nymphs. We experimentally tested tick overwinter survival across large-scale temperature and snowfall gradients and assessed factors contributing to winter mortality in locations where blacklegged tick populations are currently established and locations where the blacklegged tick has not yet been detected. We also tested the hypothesis that insulation in the tick microhabitat (i.e., by leaf litter and snowpack) can facilitate winter survival of blacklegged tick nymphs despite inhospitable ambient conditions. Overwinter survival was not significantly different in coastal southern compared to coastal and inland northern Maine, most likely due to sufficient snowpack that protected against low ambient temperatures at high latitudes. Snow cover and leaf litter contributed significantly to overwinter survival at sites in both southern and northern Maine. To further assess whether the current distribution of blacklegged ticks in Maine aligns with patterns of overwinter survival, we systematically searched for and collected ticks at seven sites along latitudinal and coastal-inland climate gradients across the state. We found higher densities of blacklegged ticks in coastal southern Maine (90.2 ticks/1000 m2) than inland central Maine (17.8 ticks/1000 m2) and no blacklegged ticks in inland northern Maine. Our results suggest that overwinter survival is not the sole constraint on the blacklegged tick distribution even under extremely cold ambient conditions and additional mechanisms may limit the continued northward expansion of ticks. |
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