A study on sexual dimorphism of body shape in Caucasian dwarf goby, Knipowitschia caucasica (Berg, 1916) using geometric morphometrics

Sexual dimorphism is a phenomenon in some fish species and its understanding is crucial for their taxonomic studies, biology and evolution. Regarding differences in body coloration patterns between male and female of Caucasian dwarf goby, Knipowitschia caucasica, the question arises whether they are different in their body shape or not? Hence, this investigation was conducted to study the sexual dimorphism in body shape of Caucasian dwarf goby from the Gorgan Bay using landmark-based geometrics technique. For this purpose, a total of 120 specimens were collected from two populations i.e. the Gorgan Bay and Gomishan Wetland. Then, their left side were photographed and 21 defined landmark-points were digitized on the obtained 2D images. After GPA analysis, the data of both populations were analyzed separately using multivariate discriminant analysis and Hotelling T-test. The results showed a significant difference between the body shape of male and female in both studied populations that the distinction rate in the population of the Gomishan Wetland was higher. Based on the observed differences, the male has a deeper head, lower body depth at the level of the dorsal fins and, longer and low depth of the caudal peduncle. According to the results, it can be stated that sexual dimorphism in this species has been probably evolved due to the mechanism of sexual selection, which can be consider as functional advantages in reproductive processes and swimming performance in males. Hence, due to the sexual dimorphism in this species, in further morphological studies, two sexes should be examined separately.