Sperm morphology, and macro and microscopic description of male and female reproductive tract in the North African houbara bustard (Chlamydotis undulata)

Abstract

Ex-situ conservation programs are useful tools for preserving endangered species, and knowledge of their reproductive physiology is essential for achieving conservation objectives in captive breeding programs. The North African houbara bustard (Chlamydotis undulata) is a vulnerable bird species bred in captivity to restore its natural populations. To better understand the reproductive biology of this species, we first described the anatomy and histology of the reproductive tracts of male and female North African houbara bustards. We described and classified the normal and abnormal sperm morphologies for the species. The reproductive tracts of males and females were collected during the breeding season (BS) (21 males and 14 females) and the non-breeding season (NBS) (four males and two females). Pictures and measurements of the testes and oviducts were taken, and testis colour was graded from 1 (black) to 6 (white). Organs were fixed and processed for histological analysis, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The testis, epididymis, oviduct size, testicular capsule thickness, seminiferous tubule (ST) diameter, and histological layers of the oviduct were compared between the BS and NBS groups. Sperm morphometry was evaluated using fixed ejaculates (n=22, from 22 males). Ejaculates (n=417, 166 males) were collected and fixed during the BS, and their morphology and morphometry were evaluated using phase-contrast microscopy. Ejaculate mixes (n=12) were fixed and analysed using SEM and TEM. Overall, the anatomical structure and histology of the male and female reproductive tracts were similar to those of other avian species. The testes were symmetric, and a regression of testis and oviduct size, the thickness of the mucosa and serosa of the oviduct, and ST diameter (p<0.001) were observed during NBS compared with those during BS. Sperm storage structures are located inside the oviduct at the uterovaginal junction and infundibulum. Melanin granules were observed in the interstitial space of the seminiferous epithelium, which explains the testis pigmentation. Melanin was also found in the ovaries and the uterus. Houbara sperm have an elongated nuclear form and a round-shaped acrosome lacking perforatorium and rostrum. Most analysed samples were limitrophe normospermic (normal= 68.5 ± 14.7%), houbara sperm morphology could be classified into eight categories: normal sperm, acrosome, head, midpiece, tail, and teratogenic defects, swollen head, and cytoplasmic droplet. This study provides the first anatomical and histological descriptions of the male and female reproductive tracts of the North African houbara bustard. Further investigation into the functional role of melanin in the testes is warranted.