ID-1-P-3452 Correlative 3D imaging of bat penis micromorphology - validating quantitative microCT images with undecalcified serial ground section histomorphology

Shape and dimensions of the bat baculum (os penis) are established taxonomic characters. Detailed micromorphology of penis and baculum, however, have seldom been studied in bats [1]. The present preliminary study provides new insights into the 2D and 3D micromorphology of the Pipistrellus pipistrellus penis as a foundation for further functional research. Light microscopy of serial, surface-stained, undecalcified ground sections [1] of the penes of 3 P. pipistrellus specimens (1 of them sub-adult) was compared with microCT images (some penes iodine-stained [2]) of the bacula of P. pipistrellus (n=42, three of them sub-adult), P. pygmaeus (n=24), P. hanaki (n=9), and P. nathusii (n=11). The baculum in the studied species consists of a proximal base with two club-shaped branches, a long, slender shaft, and a small, forked distal tip. Proximally, entheses connect the corpora cavernosa to the branches, which consist of woven bone and contain a medullary cavity of variable size with fatty marrow. The shaft of the baculum consists of lamellar bone around a central vascular canal of variable length, surrounded by woven bone in the proximal part of the shaft. The distal end of the shaft consists of woven bone. The urethra, surrounded by the corpus spongiosum, lies ventral of the corpora cavernosa and the baculum. The dorsal half of the urethral meatus is encased by the forked distal tip of the baculum. The glans penis is made up mostly of an enlarged part of the corpus spongiosum, surrounding the baculum and urethra. In the sub-adult bats, the baculum appeared not to be fully developed. The proximal branches of the baculum where shorter and did not contain a marrow cavity, while distal tip seemed to be fully developed. The combination with histomorphological techniques enabled a more precise interpretation of the histological structures shown in microCT images from all four Pipistrellus species. The woven bone predominance in the baculum points to a tight functional connection with the surrounding erectile tissues.

References

[1] Herdina AN, Herzig-Straschil B, Hilgers H, Metscher BD, Plenk Jr. H. 2010. Histomorphology of the penis bone (baculum) in the gray long-eared bat Plecotus austriacus (Chiroptera, Vespertilionidae). The Anatomical Record 293: 1248–1258.

[2] Metscher BD. 2013.Biological applications of X-ray microtomography: imaging microanatomy, molecular expression and organismal diversity. Microscopy and Analysis, 27, 13–16.