Sexual Dimorphism in Red-Eared Sliders (Trachemys scripta elegans) from the Wild Animal Triage Center of the Tiete Ecological Park, São Paulo, Brazil

Abstract

Background: Trachemys scripta elegans is an aquatic turtle native to North America and distributed geographically from the eastern United States to northeastern Mexico. In Brazil, it is an exotic and invasive species and the most illegally traded pet animal. When these turtles grow and they cease to be attractive as pets, they are released clandestinely in lakes, ponds, rivers, and other bodies of water, where they threaten biodiversity and native populations. The present study aimed to characterize specimens of T. s. elegans from the Centro de Triagem de Animais Silvestres do Parque Ecológico do Tiete by analyzing body biometrics, sexual dimorphism, and structure of specimens for sex ratio and size classes.Materials, Methods & Results: Trachemys scripta elegans turtles (39 females and 30 males) were anesthetized, euthanized and frozen. After being thawed, the turtles were sexed according to measurements on secondary sex characters such as claw length (CWL) of the third finger of the right forearm and length of the tail from the tip to the beginning of the cloacal opening (postcloacal tail length, PTL); subsequently, sex was confirmed through dissection. Subsequently, body mass (BM, g) and maximum carapace length (MCL, cm), maximum carapace width (MCW, cm), maximum plastron length (MPL, cm), maximum plastron width (MPW) and shell height (HGT, cm, measured laterally until obtaining the greatest value) were evaluated and the sexual dimorphism index (SDI) was also calculated. All analyses were performed using SAS v. 9.4 software. The results indicate a sex ratio of 1.3 females per male. The identification of males by secondary sex characteristics was performed using only claw length (CWL), which was related to sex and not to maximum carapace length (MCL). The most discriminatory variables were CWL in males and body mass (BM) in females. With the exception of CWL, the sexual dimorphism index (SDI) values all favored females and varied from 1.21 to 2.49, with the greatest value for BM and the lowest value for postcloacal tail length (PTL). Males exhibited a unimodal tendency at a classification interval of 15.0 cm MCL, and females exhibited a bimodal tendency at 21.0- and 22.0 cm MCL. Sexual maturity was identified at 12.0 cm MCL in males and at 12.5 cm MCL in females. The rate of CWL growth in males was higher at the beginning of sexual maturity and subsequently decreased, whereas in females, the rate of CWL escalated after 19.0 cm MCL. In both sexes, principal component 1 (PC1) was composed of the variables related to size and BM, and principal component 2 (PC2) and principal component 3 (PC3) were composed of variables related to secondary sex characteristics (CWL and PTL).Discussion: In members of the genus Trachemys, several secondary sex characteristics can be used to differentiate between the sexes, however, in the present study, recognition of males was performed only by claw length, as it was confirmed by the discriminate analysis and the principal components analysis (PCA) which showed that CWL was the variable that was most discriminatory in males (approximately 76.0%), followed by BM (approximately 50%) in females. The results reinforcing the claim that the degree of development of secondary sex characteristics varies between species as well as between distinct populations of the same species and establish that even under unnatural habitat, sexual dimorphism of size in favor of females is maintained for variables related to mass and size.

Morphology and biometry of the reproductive organs of adult males of Trachemys scripta elegans reared in São Paulo state, Brazil

“…Mean BM values of turtle sliders from the Wild Animal Triage Center (CETA) of the Tiete Ecological Park were similar to those of other specimens of the same origin described by Gradela et al (2017) and of Trachemys scripta elegans assessed in Brasília/DF (Vieira & Costa 2006), higher than those of Kinosternon scorpioides (Carvalho et al 2010), and lower than those of Trachemys dorbigni (Silveira et al 2012), whereas the minimum and maximum BM values were similar to the minimum and lower than the maximum values found for T. dorbigni (Bager 2003). Body development occurred in a harmonious and positive way between mass, carapace, plastron and height, differing from the findings reported in the study by Gradela et al (2017), in which uniformity in body development occurred positively only between carapace and plastron, and height was correlated only with MPL. In this study, the body biometry was slightly higher than that reported for the same species in the survey by Vieira & Costa (2006) except for MCW, lower than T. dorbignyi except for MPW and HGT (Silveira et al 2012), and T. dorbignyi for all measures (Bager et al 2010).…”

“…In this study, the body biometry was slightly higher than that reported for the same species in the survey by Vieira & Costa (2006) except for MCW, lower than T. dorbignyi except for MPW and HGT (Silveira et al 2012), and T. dorbignyi for all measures (Bager et al 2010). The frequency of distribution by size classes was unimodal, similarly to that of T. scripta (Gibbons Silveira et al 2012, Lovich et al 1990apud Silveira et al 2012, Gradela et al 2017 and T. dorbignyi (Bager et al 2010, Bujes et al 2011, Silveira et al 2012. Secondary sexual characters, represented by elongated claws and a greater tail-cloaca distance, assist with sex identification between male and female turtles (Readel et al 2008, Pérez et al 2010, because the development of these characters occurs rapidly during male maturation (Gibbons & Greene 1990apud Silveira et al 2012, Gibbons & Lovich 1990apud Vieira & Costa 2006, Dyce et al 1997, Duarte et al 2011.…”

Reproductive biology, morphology, and morphometry of ovaries and oviducts of Trachemys scripta elegans in Brazilian Cerrado

“…In all groups, there was a positive and harmonic development among mass, carapace, and plastron, which were positively correlated. These data corroborate with the results of Gradela et al (2017b) and diverge from Gradela et al (2017a) who observed development uniformity only between body mass and carapace length and width of the plastron, and between the carapace and plastron lengths.…”

“…The absence of significant difference in body biometry between groups (Table 1) suggested that all females were in the same stage of body development, with most females exhibiting from 17.00 to 21.00cm maximum carapace length (Fig.1). Average body mass values did not differ from Perez-Santigosa et al (2008) and Gradela et al (2017a), but were slightly higher than Vieira & Costa (2006); lower than those of Gradela et al (2017b) and well above those of Taniguchi et al (2017). The maximum carapace length did not differ from Perez-Santigosa et al (2008) and Gradela et al (2017aGradela et al ( , 2017b, but was slightly higher than described by Vieira & Costa (2006) and lower than Taniguchi et al (2017).…”

Genetic diversity, structure, and kinship analysis ofTrachemys venusta venustain Wildlife Management Units and wild populations in south Mexico. Implications for conservation and management

“…There are numerous studies on Trachemys spp, including topics such as general ecology [25, 55–56], biogeography [57], systematics [17, 58], and even as an invasive species [59–61]. This is probably because many species in this genus are included within the IUCN Red List and TFTSG list (Tortoise and Freshwater Turtle Specialist Group) or are not yet evaluated [62].…”