Intra-horn Penile Intromission in the Alpaca <i>Vicugna pacos</i> and Consequences to Genital Morphology

Synopsis Copulatory behavior and genital morphology interact to deliver sperm more effectively during mating, but the nature of this interaction has not been explored in depth most vertebrates. Alpacas have unusually long copulations lasting 15–20 min, a unique copulatory behavior, where penis intromits all way past cervix, into uterine horns. Here we describe male female genitalia report morphological characteristics that may be associated with unusual insemination mode. Vaginal shape is highly variable, seemingly age or parity. The cranial vagina varies between bulbous cylindrical, while caudal typically narrower always cylindrical. cervix consists series two three spirals rings, it often found relaxed state prevent damage caused by cartilaginous tip as pushes through reach uterus horns complex multiple constrictions. sharp urethral process help push against these diameter vaginal lumen much greater than suggesting there little direct them, under strong selection. In effect, entire reproductive tract interacting copulation.