Reproductive phenotype predicts adult bite-force performance in sex-reversed dragons (Pogona vitticeps)

Abstract

Sex-related differences in morphology and behavior are well documented, but the relative contributions of genes and environment to these trait s are less well understood. Species that undergo sex reversal, such as the central bearded dragon(Pogona vitticeps), offer an opportunity to better understand sexually dimorphic traits because sexual phenotypes can exist on different chromosomal backgrounds.Reproductively female dragons with a discordant sex chromosome complement(sex reversed), at least as juveniles, exhibittraitsincommonwithmales (e.g., longer tails and greater boldness). However, the impact of sex reversal onsexually dimorphic traits in adult dragons is unknown. Here, we investigate the effect of sex reversal on bite-force performance, which may be important in resource acquisition (e.g., mates and/or food). We measured body size, head size,and bite force of the three sexual phenotypes in a colony of captive animals.Among adults, we found that males (ZZm) bite more forcefully than either chromosomally concordant females (ZWf) or sex-reversed females (ZZf), and this difference is associated with having relatively larger head dimensions. Therefore,adult sex-reversed females, despite apparently exhibiting male traits as juveniles,do not develop the larger head and enhanced bite force of adult male bearded dragons. This pattern is further illustrated in the full sample by a lack of positive allometry of bite force in sex-reversed females that is observed in males.The results reveal a close association between reproductive phenotype and bite force performance, regardless of sex chromosome complement