Heritability of thermal tolerance
Higher heritability—the proportion of phenotypic variance in a population attributable to genetic effects—enables faster evolutionary rates because populations respond more efficiently to selection (Falconer and Mackay 1996). To our knowledge, there are no estimates of the heritability of trait thermal tolerance for mosquitoes. However, evolutionary theory and empirical work in other systems suggest that thermal tolerance heritability is generally low. In particular, highly polygenic, complex, or environmentally-dependent traits—as expected for thermal tolerances—typically have low heritability (Bay et al. 2017). Supporting this expectation, a meta-analysis of heritability data for upper thermal limits in Drosophila resulted in an overall estimate of 0.28 (i.e., 28% of the populations phenotypic variance is due to genetic variance; Diamond 2017), which is similar to heritability estimates for other Drosophila life history traits (average h2 = 0.26; Roff and Mousseau 1987, Mousseau and Roff 1987) and indicates moderately low heritability. However, more recent evidence suggests Drosophila can rapidly adapt to novel temperatures through multiple, alternative genetic pathways that lead to similar increases in thermal tolerance (i.e, ‘genetic redundancy’), challenging the notion that highly polygenic traits have low heritability (Barghi et al. 2019). In general, uncertainty surrounding the ecological relevance of laboratory measurements of insect thermal tolerance (Terblanche et al. 2007, Chown et al. 2009, Mitchell and Hoffmann 2010) and the divergent evolutionary histories of Drosopholids and mosquitoes limit our understanding of thermal tolerance trait heritability in mosquitoes.