Observations on genital morphology and anatomy of a hybrid male muriqui (Genus Brachyteles)

The reproductive anatomy of the muriqui (genus Brachyteles) is poorly known. This paper describes the anatomy of the testis, penis and striated penile muscles in a young adult (5.25-year-old) captive-born muriqui which died at the Rio Primate Center. Two forms of muriqui occur in the Atlantic coastal forests of Brazil, and both are endangered. The form which is found north of 21degrees00' S latitude is classified as B. hypoxanthus by some authorities and is considered to be a species separate from B. arachnoides. The male specimen described here was a hybrid (the sire was B. arachnoides and the mother B. hypoxanthus). Hybridization was associated with absence of spermatozoa in the testis and with degeneration of the seminiferous epithelium. The structure of the prominent penis and striated penile muscles is discussed in relation to patterns of copulatory behavior and the likely occurrence of sperm competition in the muriqui. In addition, the occurrence of a baculum (os penis) is confirmed for this genus, and the first description of its morphology is provided.