Figure 1.

Illustrating the continuum of genetic and environmental sex determination. Examples of possible effects of environmental factors (e.g. temperature or concentration of endocrine-disrupting micropollutants) on sex determination in (a) a hypothetical population with genetic sex determination and the female genotype being susceptible to environmental factors that masculinize (i.e. turning some XX or ZW individuals into males) and (b) a population with genetic sex-determining factors and the male genotype being susceptible to environmental factors that feminize (i.e. turning some XY or ZZ individuals into females). The shaded area indicates the within-population variance that could be due to additive genetic variance in the reaction norms or due to random effects at the start of the sex determination cascade. The hatched line gives the population sex ratio (proportion of males) if all clutches experience the same environmental conditions. This population sex ratio will equal adult sex ratio (ASR) if there is no sex-specific mortality.