Research Note: Muscle hypertrophy is associated with reversed sexual dimorphism in body size of quail

Sexual dimorphism is phenotypic differences between males and females in the same species. In general, males in most animals are larger than females at the same age, however, in quail, females have a larger body size with greater muscle mass than males. To understand what characteristics in muscle growth play roles in reversed sexual dimorphism in quail, the weights and the characteristics of the pectoralis major and gastrocnemius muscles (PM and GM, respectively) of male and female quail were compared in the current study. The data showed that 15-wk old female quail have significantly heavier bodies, and PM and GM weights compared to male quail (1.27-folds, 1.29 folds, and 1.16-folds, respectively). To compare muscle characteristics such as hypertrophy (increased size) and hyperplasia (increased cell number), the PM and GM were stained using hematoxylin and eosin, and then histological characteristics such as total cross-sectional area (CSA), number and size of myofibers, and muscle bundle of the muscles were measured and analyzed. In both PM and GM, there were no differences in total numbers of myofibers and muscle bundles as well as the average numbers of myofibers per bundle between sexes. However, the sizes of myofiber and the bundle were significantly increased in female compared to male (1.33-folds and 1.28-folds in PM, and both 1.23-folds in GM, respectively). The findings of the current study suggest that muscle hypertrophy in female quail, not hyperplasia, can be attributed to the sexual dimorphism in quail size.

Automated summary

Sexual dimorphism refers to the phenotypic differences between males and females in the same species. This study focused on the reversed sexual dimorphism observed in quail, where females have larger body size and greater muscle mass than males. The researchers compared the weights and characteristics of different muscles between male and female quail and found that female quail had significantly heavier bodies and larger muscles. Further analysis revealed that the increased muscle size in female quail can be attributed to muscle hypertrophy rather than increased cell number. These findings provide insights into the understanding of sexual dimorphism in quail.