Sexual shape dimorphism in the monomorphic fish Decapterus macrosoma (Teleostei: Carangidae)

Abstract

Monomorphism is prevalent among fishes consequently sexually dimorphic traits are unknown. Discrimination between sexes is often achieved through direct examination of the gonads. However, at present, patterns of sexual dimorphism are known through the analysis of body shapes. Thus, this study used landmark based geometric morphometrics to investigate and describe sexual dimorphism in the body shape of Decapterus macrosoma. Fourteen landmarks from images of 60 individuals (25 males and 35 females) were subjected to geometric morphometric analysis. Variability in body shapes between sexes was visualized by generating thine-plate spline expansion plots. Results showed that females exhibited a deeper body depth, broader belly region, bigger head, and wider caudal fin while males exhibited a narrow body depth, smaller head, and wider dorsal and caudal fins. Multivariate analysis of variance and discriminant function analysis showed significant difference in the body shapes between sexes of this fish species (p<0.05). The results were discussed as results of sexual and natural selection in fishes.

Keywords

• morphology
• relative warps
• landmark-based morphometrics
• sexual selection