Fig. 2
Sex as a threshold trait and manifestation of female choosiness. Sex chromosomes A and a produce different amounts of the ‘male signal’ factor. An individual becomes male if its male signal level exceeds its individual threshold defined by the individual’s thr genotype (according to one of the three vertical lines). Production of male signal is increased by environmental temperature experienced during a sensitive period of early individual development; the Gaussian curves represent the distribution of individual signal levels due to variation in environmental temperatures. Before climate warming, most individuals develop sexual phenotype corresponding to their sex-chromosome genotype (bottom curves in each panel), and only occasional events of masculinization occur in some thrlowthrlow individuals (yellow area). Climate warming (illustrated by grey-orange arrows) increases the production of male signal by both sex chromosomes, resulting in more frequent masculinization (top curves in each panel). When both normal and sex-reversed males are present, females can choose based on their preference-allele expression (CR or CN)