Long-Term Sperm Storage in the Desert Tortoise (Gopherus agassizii)

Many reptilian species exhibit the ability to store sperm in the female reproductive tract for extended periods of time (Gist and Jones, 1987; Birkhead and Moller, 1993). Sperm storage may be used to separate reproductive events such as copulation, fertilization, and hatching to optimize timing of these events (Birkhead and Moller, 1993). The redsided garter snake (Thamnophis sirtalis) ovulates and produces offspring in the spring but mate in the fall (Whittier and Crews, 1986). In this species, sperm from fall matings are thought to overwinter in the oviduct and fertilize ovum the following spring (Crews, 1984; Whittier and Crews, 1986). Reports of delayed egg laying in other species support the hypothesis that stored sperm are viable and used to fertilize subsequent clutches. Sperm storage has been inferred from oviductal flushings and/or observations of sperm in histological preparations of the oviduct (Gist and Jones, 1989; Gist et al., 1990). However, only controlled-mating experiments can demonstrate whether stored sperm are viable. Sperm storage and multiple insemination may play a significant role in turtle reproduction (Gist and Jones, 1989). The ability to store sperm from previous matings and produce viable offspring using these sperm would be necessary for species whose male and female reproductive cycles do not coincide. Discordant cycles have been observed in temperate-zone turtles where time of mating and gamete maturation do not always occur simultaneously (Moll, 1979; Licht et al., 1985). In males of Gopherus agassizii, spermatogenesis begins in early summer and terminates with the onset of fall