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.