CONICET | Buscador de Institutos y Recursos Humanos

The broad snouted caiman is a crocodylian native to South America that issubject to extensive conservation management in both wild and farming envi-ronments. Although reproductive behaviors like egg laying and clutch carehave been examined in this species, little else is known about their copulatorysystem. We examined the anatomy of male and female cloacal and genital tis-sues ex vivo to build hypotheses of their interactions during copulation andthe effects of that interaction on insemination. Male phallic glans tissues wereartificially inflated to expand into their copulatory state, allowing the examina-tion and quantification of structural changes at the gross and tissue levels. Dig-ital reconstruction of MRI stacks yielded three-dimensional tissuecompartment specific glans models of the inflated state. Silicone molds offemale cloacae and oviducts in conjunction with dissection and diceCT analy-sis allowed us to assess internal geometry and infer how male and female fea-tures interact in copulo. We observed glans expansion within the femaleproctodeum would result in a copulatory lock limiting deeper intromission orretraction. Intromission and subsequent creation of the copulatory lock pro-duces extensive clitoral compression, providing a possible mechanism forfemale assessment of male copulatory performance. Further, glans expansionforms a distal lumen that positions the glans tip in or near the vaginal open-ings. A coiled, muscular vagina provides a possible mechanism for post-copulatory sexual selection by excluding semen. Together, the complex male?female interaction supports evidence for cryptic selection by female choice,which can act as a driver of genital coevolution.

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