SSD in marine turtles
Availability of body sizes for both sexes within a single population varied widely among the seven species of marine turtles (Supplementary Table S2). By far the most data were available for the green turtle (Chelonia mydas ), which yielded credible estimates from 18 studies (Fig. 1A), with six populations for the loggerhead (Caretta caretta ), four populations for the olive ridley (Lepidochelys olivacea ), three populations for the hawksbill (Eretmochelys imbricata ), two populations for the leatherback (Dermochelys coriacea ), and two studies for the Kemp’s ridley (Lepidochelys kempii ), and a single population of the flatback (Natator depressus ). The sex-specific means and samples sizes are shown in Figure 1B and summarised in Supplementary Table S2. For the species for which we have estimates from five or more populations (C. mydas , C. caretta ), it is noteworthy that the degree and direction of SSD varies.
Figure 1A also illustrates the regression of sex-specific mean values (male vs female) for all populations. Neither the slope nor the intercept of this regression differed significantly from the null expectation (slope: t(33)=0.052, tcrit=2.034, p=1; intercept: t(33)=-0.514, tcrit=2.034, p=0.611). The upper 95% confidence interval of the regression is slightly below the 1:1 line, indicating a weak female-biased SSD. Examination of the scatter suggests that this overall pattern is driven largely by C. mydas .