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).