Anatomical and histophysiological characterization of the male cloacal protuberance of the polygynandrous Alpine Accentor Prunella collaris

Abstract

This paper describes the morphology of the male cloacal protuberance (CP) of the polygynandrous Alpine Accentor Prunella collaris, with special reference to intense sperm competition in the mating system. The fully developed CP consisted of dorsal (DL) and ventral (VL) lobes. The DL was found to be a massive part formed by a highly convoluted extension of the distal vas deferens with a fibro‐muscular sheath. Here, the vas deferens contained abundant spermatozoa, round cells of unknown origin, and secretory droplets in the tubular lumen. The epithelium of the vas deferens was lined with columnar cells that showed numerous microvilli and apocrine processes in their periluminal portion, frequent engulfing of spermatozoa, and many mitochondria and vesicular endoplasmic reticula in their cytoplasm. The VL was a smaller subdivision distal to the DL and further connected to a terminal papilla. The VL was organized similarly to the DL, but showed different features: it lay beneath the thick skin; the fibro‐muscular sheath was more muscular; the epithelial cells were cuboid and showed poorly developed microvilli; and the figures of secretion and engulfed spermatozoa were infrequent. Thus, the CP of the male Alpine Accentor showed a clear regional differentiation, i.e. the DL for storing/maintaining spermatozoa and the VL for storing/ejaculating spermatozoa.