Figure 5.

Three-dimensional reaction norm describing the relationship between egg incubation thermal regimes and offspring sex ratios of jacky dragons (Amphibolurus muricatus). Data points represent single nests in the field and thermal parameters were calculated only from temperature data during the first 60% of incubation (i.e. during the thermo-sensitive period for sex determination; [18]). The plane (i.e. reaction norm) represents a parabaloid equation. The fluctuating thermal treatments from the laboratory experiment are represented by the diamond symbols (with drop lines). Note that the sex ratio produced under the 25 ± 8°C fluctuating treatment was substantially less female-biased than that predicted from the field data. This inconsistency may be explained by the relatively high egg mortality in nests with relatively high levels of thermal fluctuation [16]. Because of egg mortality in natural nests, field-based data are based on secondary sex ratios and laboratory data are based on primary sex ratios.