Abstract

Understanding the role of the environment on an organisms’ life history is a fundamental goal of evolutionary ecology because environmental variation may select for certain life histories over others. Crucially, sex differences may be exacerbated or diminished in response to environmental change. Urbanization presents an opportunity for rapid change in aquatic environments, especially with the introduction of road salts. Salinization disturbs freshwater communities and increases salt-tolerant taxa populations, like mosquitoes. Still, little is known about sex-specific salt tolerance within this salt-tolerant species, which is important for disease transmission because only adult females consume bloodmeals for egg production. The objective of my PhD thesis is to investigate how the environment influences mosquito sexual dimorphism. In Chapter 1, I conducted a field experiment to examine the difference in emergence sex ratios of mosquitoes in salt and no-salt mesocosms. I found that road salt shifts sex ratios from female-bias towards parity (1:1), suggesting that salinity can limit juvenile female survival to emergence. In Chapter 2, I examined how different geographic mosquito populations responded to salt at multiple life stages (i.e., oviposition, larvae, etc) through a combined field-laboratory approach. While urban populations typically laid more egg rafts than rural populations, I found that all populations: 1. prefer ovipositing in salt, and 2. survive equally well in salt. Consistent with the literature, I also found that female mosquitoes take longer to pupate and emerge as adults than males. In Chapter 3, I will perform a meta-analysis to determine regional and taxonomic patterns of mosquito sexual dimorphism. Finally, in Chapter 4, I will explore the synergistic effects of two common urban stressors, road salt pollution and urban heat islands, on mosquito oviposition in a manipulative field experiment. Ultimately, my thesis will help urban ecologists and evolutionary ecologists learn more about how certain species and/or sexes persist in new hostile environments.