Heritability of thermal tolerance traits.

Thermal tolerance traits in the Magnetic Island (MI), and the Orpheus Island (OI) population of Acropora millepora and their respective symbiont populations (Symbiodinium clade D and type C2) under bleaching conditions (32°C). Broad-sense heritabilities and their standard errors (SE) are shown. Significant heritabilities are indicated bold with asterisks (*), and values usually vary between zero and one (0 = all variation due to environmental variation; 1 = all variation due to genetic factors). Phenotypic variation in natural populations is typically caused by both genetic and environmental factors. Genetic variation is the working-substrate for natural selection that facilitates adaptation.