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

Authors

  • William A. Wimsatt,

    1. Division of Biological Sciences, Cornell University, Ithaca, New York and Department of Anatomy, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
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  • Philip H. Krutzsch,

    1. Division of Biological Sciences, Cornell University, Ithaca, New York and Department of Anatomy, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
    Current affiliation:
    1. Department of Anatomy, University of Arizona College of Medicine, Tucson, Arizona
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  • Leonard Napolitano

    1. Division of Biological Sciences, Cornell University, Ithaca, New York and Department of Anatomy, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
    Current affiliation:
    1. Department of Anatomy, University of New Mexico School of Medicine, Albuquerque, New Mexico
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  • Supported by research grants from the National Science Foundation and the National Institutes of Health as follows: NSF G-24043 (W.A.W.); NIH RG 6599 C-5 (P.H.K.); NIH AM 09432--01 (L.N.).

  • Shortly after an original draft of this article had been completed, the splendid study of Fawcett and Ito ('65) on the fine structure of bat sperm was published. The overlap between their observations and ours was substantial and we have felt obliged to revise our fine structure section to avoid publishing frankly repetitive material. The present section on ultrastructure is a substantially shortened version of the original. We obviously could not eliminate all redundant observations and still achieve a coherent account, but those retained for the most part complement, differ from, or confirm where this was deemed desirable the observations of Fawcett and Ito. Furthermore, our primary objective has been and is to determine the bases of sperm longevity in the uterus, and our observations of fine structure are focused mainly on intra-uterine sperm, whereas those of Fawcett and Ito dealt wholly with unejaculated sperm from the epididymis. Characterization of the fine structure of surviving sperm in utero as compared with those still within the epididymis is essential to the achievement of our main objective. The section summarizing our microscopic and histochemical observations has not been altered from the original since these observations are not duplicated in the study of Fawcett and Ito.

Abstract

Among mammals prolonged survival of spermatozoa in the reproductive tract of the female (circa 7 ± 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.

A new basis is suggested for the apparent helical arrangement of mitochondria in the middle piece; in Myotis sperm the configuration is illusory, being the result of an orderly alternation in the staining of the serially arranged mitochondrial pairs. We suggest that the “patterned” staining of mitochondria may reflect sequential, cyclic functional alterations of significance in the initiation and/or coordination of the geometrically oriented tail movements.

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