Functional long-term storage of spermatozoa in oviducts of the common house gecko, Hemidactylus frenatus

Murphy-Walker, Susan Gene
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The functional life span of mature gametes is generally quite short and, as a result, mating occurs at or near the time of ovulation in order to maximize fertilization potential. Prolonged sperm survival (and delayed fertilization) within the oviduct has been reported for almost every vertebrate class, being particularly common among reptiles. Most reports involve temperate species. Fall matings are followed by an overwintering period during which females do not ovulate. Oviductal sperm storage, therefore, promotes reproductive success by allowing fertilization to occur in the spring when females resume ovulation. Oviductal sperm storage in tropical reptiles is less commonly reported, perhaps because year-round reproduction is generally observed. This dissertation verifies oviductal sperm storage in the tropical gekkonid lizard, Hemidactylus frenatus, and proposes several advantages associated with this capacity. Hemidactylus frenatus produces clutches consisting of a maximum of two calcareous-shelled eggs at variable intervals throughout the year. Histology revealed the presence of sperm sequestered within crypts located in a particular region of the oviduct. This was observed in virtually every adult female examined, regardless of her ovarian condition. Isolated from males, captive females each produced several viable clutches for up to nine months, demonstrating that sequestered sperm remained viable over several ovarian cycles. Scanning elecron microscopy revealed that distension of the oviduct released sperm from storage crypts as a result of egg passage through the oviduct following ovulation. Transmission electron microscopy revealed cyclical secretory activity within the oviduct which correlated with ovulation, and may prove to be beneficial to sperm, either while in storage or after release. That oviductal sperm storage exists in Hemidactylus frenatus is certain. Although the mechanism is yet unclear, there appear to be both mechanical and physiological contributing factors. The advantages of oviductal sperm storage to this tropical reptile may derive from reproductive (small, irregularly produced clutches), behavioral (temporal separation of males and females), and distributional characteristics (dispersal events) of the species; advantages which provide almost guaranteed reproductive success.
Thesis (Ph. D.)--University of Hawaii at Manoa, 1994.
Includes bibliographical references (leaves 90-99).
x, 99 leaves, bound ill. 29 cm
Geckos -- Reproduction
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