Seasonal effects and fine-scale population dynamics of Aedes taeniorhynchus, a major disease vector in the Galapagos Islands ARNAUD BATAILLE,*†‡§ 1 ANDREW A. CUNNINGHAM,†§ MARILYN CRUZ,§ VIRNA CEDENO§ – ** and SIMON J. GOODMAN*§ 2 *Institute of Integrative and Comparative Biology, University of Leeds, Leeds LS2 9JT, UK, †Institute of Zoology, Zoological Society of London, Regent’s Park, London NW1 4RY, UK, ‡NERC Biomolecular Analysis Facility (Sheffield), Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK, §Gala ´pagos Genetics, Epidemiology and Pathology Laboratory, Gala ´pagos National Park, Puerto Ayora, Gala ´pagos Islands, Ecuador, –Concepto Azul, Cdla. Vernaza Norte Mz 10 Villa 34, PO Box 09-02-142A, Guayaquil, Ecuador, **Biotechnology Program, Universidad de Guayaquil, Guayaquil, Ecuador Abstract Characterization of the fine-scale population dynamics of the mosquito Aedes tae- niorhynchus is needed to improve our understanding of its role as a disease vector in the Galapagos Islands. We used microsatellite data to assess the genetic structure of coastal and highland mosquito populations and patterns of gene flow between the two habitats through time on Santa Cruz Island. In addition, we assessed possible associations of mosquito abundance and genetic diversity with environmental variables. The coastal and highland mosquito populations were highly differentiated from each other all year round, with some gene flow detected only during periods of increased precipitation. The results support the hypothesis that selection arising from ecological differences between habitats is driving adaptation and divergence in A. taeniorhynchus, and maintaining long-term genetic differentiation of the populations against gene flow. The highland and lowland populations may constitute an example of incipient speciation in progress. Highland populations were characterized by lower observed heterozygosity and allelic richness, suggesting a founder effect and ⁄ or lower breeding site availability in the highlands. A lack of reduction in genetic diversity over time in highland populations suggests that they survive dry periods as dormant eggs. Association between mosquito abundance and precipitation was strong in the highlands, whereas tide height was the main factor affecting mosquito abundance on the coast. Our findings suggests differences in the infection dynamics of mosquito-borne parasites in the highlands compared to the coast, and a higher risk of mosquito-driven disease spread across these habitats during periods of increased precipitation. Keywords: adaptation, microsatellite, mosquito, population dynamics, selection, speciation Received 30 May 2010; revision received 9 August 2010; accepted 21 August 2010 Introduction The black salt-marsh mosquito (Aedes taeniorhynchus Wiedemann) is the only native mosquito in the Galapa- gos Islands, where it is distributed widely. It feeds on a wide range of endemic taxa and is likely to play Correspondence: Arnaud Bataille, Fax: +31 30 2521887; E-mail: a.m.a.bataille@uu.nl 1 Present address: Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 7, 3584 CL Utrecht, The Netherlands. 2 E-mail: s.j.goodman@leeds.ac.uk Ó 2010 Blackwell Publishing Ltd Molecular Ecology (2010) 19, 4491–4504 doi: 10.1111/j.1365-294X.2010.04843.x