Phenotypic variation in populations of the mosquito vector, <em>Aedes aegypti</em>, and implications for predicting the effects of temperature and climate change on dengue transmission

There is concern that increases in temperature due to climate change could lead to shifts in the dynamics and distribution of mosquito vectors. Many current models assume there are 'average' thermal performance curves for a given vector species transmission. However, this ‘one-size-fits-all’ assumption ignores the potential for local adaptation to create population-specific differences in thermal performance. In this study, we explored thermal performance of five independent field populations of Ae. aegypti from Mexico, together with a standard laboratory strain. We reared these six populations at temperatures between 13°C and 37°C to generate thermal performance curves for a suite of life-history traits. Composite models integrating these traits revealed the effects of temperature on population growth rates and dengue virus transmission potential. The results provide strong evidence for the potential for local adaptation in Ae. aegypti populations, challenging applicability of ‘one-size-fits-all’ thermal performance models to assess climate impact on mosquito-borne diseases. Methods Methods used in the current study closely follow those outlined in Dennington et al. 2024. Mosquito Collection Aedes aegypti mosquitoes were collected from the field in five different locations in Mexico (Cabo San Lucas, Acapulco, Monterrey, Ciudad Juárez, and Jojutla) using ovitraps. Populations from Mexico were founded with at least 100 females and to remove the influence of maternal effects, mosquitoes were reared in the lab for at least one generation in standard laboratory conditions (27°C, 80% humidity, 12:12hr photoperiod) prior to experimentation. Two populations, Jojutla and Ciudad Juárez, were reared for an additional generation to ensure a large enough population for subsequent experiments. The field locations were chosen to capture a gradient of the climate and landscape. The field populations were compared to a standard laboratory population (Rockefeller strain) that were maintained at Penn State University under standard insectary conditions over many years. Experiments to Generate Temperature-Dependent Data Mosquito life-history traits including egg-to-adult survival, mosquito development rate, mean adult survival, fecundity, and biting rate were measured in mosquitoes reared at 13°C, 15°C, 19°C, 23°C, 25°C, 27°C, 29°C, 31°C, 33°C, 35°C, 37°C, each ± 0.2°C and 80 ± 10% relative humidity in environmentally controlled incubators. These life-history measurements were replicated three times at each temperature for each population. We began with eggs from the five field populations and one laboratory line were hatched at 27°C for 24 hours. Then, 200 first instar larvae were put into 1.89 L containers with 1 L of deionized water and 0.20 mg of larvae bovine liver powder (MP Biomedicals) and each of the three replicates were placed in the incubator at their respective temperatures. We fed larvae 0.20 mg of liver powder per larvae every other day until pupation, but once pupation began we scaled their food to the remaining number of larvae. Pupae, both living and dead, were removed and counted on the day of pupation and placed in a small cup (30 mL) with water from their original environment to allow for eclosion. Pupae were then added to a small cage (17.5 cm3) with continuous** access to 10% sugar solution (dextrose anhydrous and deionized water). We counted the number of adults that eclosed every day. After 95% of surviving females emerged, we blood-fed females after 3-5 days. We used blood from de-identified human donors (BioIVT, Corp.) and so IRB approval and human subjects’ approval was not needed. We immediately counted the total number of blood-fed females and placed up to 10 individual females into separate containers (50 mL polypropylene centrifuge tubes) that were lined with filter paper and 7 mL deionized water to measure individual fecundity. We also placed up to 20 females into two small cages (10 in each) with a small filter paper for egg laying to monitor adult survival. We recorded the day that females in individual containers first laid eggs, which we used for fecundity measures and to approximate the biting rate (1/gonotrophic cycle length), after which we removed them from their containers and placed them into the group cages. We extracted the water from the containers to let the filter paper dry in their respective incubators and then we counted the number of eggs from individual mosquitoes. For the course of the experiment, we offered each cage of females a blood meal every 4 days, and counted the number of adults that died every day. We censored this experiment 4 weeks after the first egg lay at each temperature.