Morphology of the copulatory organ in Ortalis canicollis (Aves: Cracidae) and early evolution of the phallus in birds

Abstract

We studied the morphology of the copulatory organ of Ortalis canicollis and its evolution in birds. The phallus of O. canicollis is intromittent, with a blind tubular cavity and two distinct regions when erect: the base of the phallus, which shows the mucosa smooth and lined by a pseudostratified columnar epithelium, and the tubular portion, which shows the mucosa lined by a keratinized stratified squamous epithelium with little knobs. The phallus includes two vascular bodies at the cranial portion in the urodeum. A fibrocartilaginous body anchors the tubular portion therefrom up to the eversible portion. A branched elastic ligament inserts on different regions of the tubular portion. The phallus is plesiomorphic in birds and it has disappeared in Megapodius, Leipoa and Neoaves. The asymmetric phallus evolved early and it was retained in the basal branches of birds. The intromittent phallus is plesiomorphic in birds (found in Archosauria's ancestor), but Crypturellus, Numididae, Odontophoridae and Phasianidae have developed a non‐intromittent phallus a posteriori. The blind tubular cavity and the fibrocartilaginous body evolved as an adaptive convergence many times in birds. Therefore, this study shed some light on morphological aspects of the phallus and contributed to understand its evolution in birds.

Physiological factors influencing female fertility in birds

“…In the majority of bird species (greater than 97%), sperm are obtained by the female through cloacal contact during copulation, although there are a few examples of extant bird species that copulate with the use of a true intromittent organ (e.g. in the ratites, many Tinamiformes, Anseriformes and Cracidae), or a pseudo-phallus (such as in some Galliformes) [125][126][127].…”