Environmental sensitivity of selection
Environmental sensitivity of selection refers to how the optimum phenotype shifts with changes in the environment and is typically measured as the slope of the relationship between the optimal trait value and the environmental variable (e.g., the rate of change in the optimal upper thermal limit of adult life span against maximum summer temperature; Chevin et al. 2010, 2015). A larger difference between the environmental sensitivity of selection and phenotypic plasticity (i.e., a greater deviation in the phenotype from the optimal value) necessitates faster adaptation (Chevin et al. 2010). For mosquitoes, as for nearly all other organisms, the environmental sensitivity of trait thermal tolerance has not been empirically measured (Chevin et al. 2010). However, across mosquito populations (Lyons et al. 2012, Vorhees et al. 2013) and species (Mordecai et al. 2019), upper thermal limits for most mosquito life history traits were less variable than lower thermal limits and optima. These patterns could reflect strong environmental sensitivity on lower thermal tolerance, intermediate sensitivity for the optimum, and weak sensitivity on upper thermal tolerance. However, it may more likely reflect evolutionary constraints on upper thermal tolerance (Kellermann et al. 2012, Hoffmann et al. 2013), or result from competing selection pressures, genetic constraints, or gene flow hindering thermal adaptation (Angilletta 2009).