Studies on sperm survival mechanisms in the female reproductive tract of hibernating bats. I. Cytology and ultra‐structure of intra‐uterine spermatozoa in Myotis lucifugus

Abstract

Among mammals prolonged survival of spermatozoa in the reproductive tract of the female (circa 7-t months) is known in only a few species of hibernating bats, but its physiological basis remains obscure. Presumably survival involves special physiological adaptations of the spermatozoa, the uterus, or both. We have initiated studies of sperm survival mechanisms in the hibernating bat Myotis lucifugus involving analysis of the cytology and fine structure of intra-uterine sperm, the morphology and histochemistry of sperm-uterus interactions, and selected biochemical parameters of the reproductive tract. This paper summarizes our findings concerning the morphology of epididymal and intra-uterine spermatozoa, and emphasizes those aspects not detailed by others. The microscopic organization of epididymal sperm is described in detail with particular attention to peculiarities of the head, middle piece and cytoplasmic droplet. The latter contains amylase-resistant PAS + granules and acid phosphatase, both possibly of lysosomal origin. Most ultrastructural features elucidated by Fawcett and collaborators are confirmed, but additional details concerning the head, post-nuclear sheath, origin of axial filament complex, and the outer coarse fibrils are provided. A functional interrelationship between coarse fibrils 3 and 8 and the longitudinal columns of the fibrous sheath is also postulated.Structural differences between epididymal and uterine sperm are minor, suggesting that uterine environmental factors are most important for sperm survival.

Relationship Between Stored Spermatozoa and the Uterine Epithelium in the Pipistrelle Bat (Pipistrellus Pipistrellus)

“…It seems unlikely, therefore, that the seminal plasma of the bat contains enough nutrient material for prolonged survival. In addition, Fawcett & Ito (1965) and Wimsatt et al ( 1966) found no evidence that bat spermatozoa contain a greater store of endo¬ genous substrates than the spermatozoa of other species. The endometrium must, therefore, supply the essential nutrients and the present work has shown it to be a highly active secretory gland.…”

“…Austin & Bishop (1959) examined P. pipistrellus and R. ferrum-equinum and confirmed Kohlbrugge's (1913) The fine structure of the epididymal spermatozoa of M. lucifugus and E. fuscus has been described by Fawcett & Ito (1965). Wimsatt et al (1966) subsequently found only minor differences between the fine structure of uterine and epididymal spermatozoa of M. lucifugus, and suggested that uterine environmental factors were most important for sperm survival.…”

Studies on prolonged spermatozoa survival in chiroptera: A morphological examination of storage and clearance of intrauterine and cauda epididymal spermatozoa in the bats Myotis lucifugus and M. velifer

“…Thus, increased phospholipid of mitochondria1 origin may be available for sperm metabolism and may contribute to their prolonged survival (Racey, 1979). Ejaculated (intrauterine) sperm differ only in the absence of the cytoplasmic droplet and neckpiece membranous scrolls (Wimsatt et al, 1966), characteristic of the epididymal sperm of Myotis lucifugus (Fawcett and Ito, 1965).…”

Male reproductive patterns in nonhibernating bats

“…It (Gopalakrishna & Madhavan, 1971;Racey, Suzuki & Medway, 1975;Myers, 1977) wherein spermatozoa are stored in the uteri of nonhibernating species much the same as in hibernating Myotis lucifugus (Wimsatt, Krutzsch & Napolitano, 1966 (Tamsitt & Mejia, 1962) and A. lituratus (Tamsitt & Valdivieso, 1965) (Richardson, 1977). It is possible that this delay in ejaculation permits the spermatozoa to undergo capacitation or some other physiological preparative process essential for successful fertilization.…”