Morphogenesis of the External Genitalia in Broad-Snouted Caiman

MARIA LAURA BERÓN ; MARIA VIRGINIA PARACHÚ MARCÓ; NOELIA VILLAFAÑE; CARLOS IGNACIO PIÑA; JOSEFINA LUCIANA IUNGMAN

Santa Fe

Congreso; 25th Working Meeting of the IUCN-SSC Crocodile Specialist Group; 2018

Universidad Nacional del Litoral

In the most animals, an intromittent organ denominated phallus facilitated reproduction by internal fertilization. Considerable variation in phallus morphology among different amniote lineages has contributed to the debate about their structural homology. However, comparatively little is known about the development of reptilian external genital and how evolved in males and females. Here we described morphology development of the penis and clitoris in the Broad-snouted Caiman, Caiman latirostris. Consequently, we set embryos incubated at specific sex-determine temperatures: at 31°C (100% female) and 33°C (100% males), and hatchlings coming from these temperatures. The embryonic precursor of the penis and clitoris is the genital tubercle, which appear -at stages 4- as paired swellings of mesenchyme. By stage 8, a single cylindrical genital tubercle is forms. Outgrowth of the tubercle continues, and by stage18, it has an oval appearance and the indentation of the phallic sulcus running along its dorsal surface. At stage 20 (onset of the sexual differentiation), the tubercle is regionalized into the shaft, phallic ridge and glans. We used histology to examine the internal differentiation during the thermosensitive period. Up to 24 stage of development the genital tubercle at both temperatures comprise a sulcus lined with a bilaminar epithelium and bordered by the dense mesenchyme. Signs of corpora differentiation are first detected at stage 26 under male-producing temperatures, when a ring of vascular elements outlined the anlage of the corpora cavernosa from the corpus spongiosum. At feminizing temperatures such structures appeared later. At hatching, males and females exhibit corpora of the network of collagen fibers loosely organized. Our analysis suggests that initial external genital outgrowth occurs prior to temperature sex determination, and penis and clitoris development have similar trajectories.