Fig. 4

Association between inter-birth interval (next offspring) and estimated between-individual variance in creatinine levels in males (squares, n = 31) and females (crosses, n = 23). Points indicate variance of the random effect of subject as obtained from the ‘effects of maternal presence’ model (taking into account subjects’ age and sex, the urine sample’s specific gravity, maternal loss, group identity, and seasonal variation). The solid or dashed lines represent the regression of relative muscle mass on inter-birth interval in females and males, respectively