Sexual Ddimorphic Pattern that Characterize the External Genitalia in Juvenile Caiman latirostris is Modified in Sex Reversed Females

TRUTER, C.J.; LUQUE, E.H.; TAVALIERI, Y.E.; GALOPPO, G.H.; MUÑOZ DE TORO, M.M.; CANESINI, G.

Santa Fe

Congreso; 25th Working Meeting of the Crocodile Specialist Group (CSG/SSC/IUCN); 2018

Crocodile Specialists Group

Caiman latirostris (C. latirostris), the broad-snouted caiman, is a crocodilian species that inhabit South American wetlands. In C. latirostris, as in other reptiles, the incubation temperature of eggs during a critical thermo-sensitive window (TSW) of embryo development determines the hatchlings sex. This mechanism of sex determination is called temperature-dependent sex determination (TSD). In C. latirostris, as in many TSD species, the administration of 17-β-estradiol (E2) during the TSW overrides the effect of male-producing temperature, producing phenotypic females. This E2-mediated effect has been defined as hormone-induced sex determination (HSD). Previously, we have reported that endocrine-sensitive organs, such as ovaries, from females born to eggs incubated at male TºC and exposed either to E2 or to the xenoestrogen BPA during the TSW differ from the ovaries of TSD-females. Ovaries of neonatal to juvenile HSD-females show altered follicle dynamics and exhibit high incidence of polyovular follicles, changes preceded by abnormal expression patterns of molecules associated with ovarian development and function at embryonic stages. External genitalia, called phallus (or clitero-penis structure), is a sexual dimorphic hormone-sensitive organ. In male crocodiles, its principal function is intromission and fertilization during the copula. In females, aside from gross anatomy, neither data of phallus histoarchitecture nor data related to their functions are found in the literature. The aims of this study were to establish the temporal pattern of phallus growth, evaluate phallus histomorphological features and hormone dependence in male, TSD-females and HSD-females phalli and to establish differences and similarities among pre-pubertal juvenile males, TSD-females and HSD-females phalli. Archived paraffin embedded samples from juvenile caimans incubated at male or female producing temperatures prior to hatching were used. The groups were as follows: TSD-male, TSD-female and HSD-female (incubated at male producing TºC and exposed in ovo to 1.4 ppm of 17β-Estradiol). Our results show that the gross anatomy and the general histoarchitecture of the phallus of pre-pubertal juvenile male and female caimans are quite similar, whereas the phallus growth dynamics, many histomorphological features and hormodependence biomarkers are sexually dimorphic. In the phallus of HSD-females, many male characteristics remain, leading to a loss of sexual dimorphism. Loss of dimorphism in histofunctional parameters of the phallus could impair normal female phallus function and, subsequently, could affect C. latirostris population dynamics. Our results raise concern about xenoestrogen exposure during TSW and suggest that caution must be taken on using HSD as a tool to recover wild populations of reptiles.