Chemical and thermal effects on the viability and motility of spermatozoa from the turtle epididymis.

Turtles are among the most primitive of reptiles, divergingfrom other reptilian stock in the Paleozoic era. As such,turtles are the first extant group to show characteristics ofamniote vertebrates. One of these characters is internalfertilization. Although external fertilization occurs in mostfish and amphibians, all but a few amniote vertebratesdeposit spermatozoa directly into the female reproductivetract in a copulatory act. Thus, a change from external tointernal fertilization might be accompanied by changes inthe structure or behaviour of the male gamete, but this issuehas received little attention from gamete biologists. Spermatozoa are among the most fragile of cells and donot survive for long outside the male reproductive tract(Restall, 1967). Fish spermatozoa live only minutes afterspawning or artificial stripping (Billard and Cosson, 1992).The motility of spermatozoa within the ductus deferens ofthe quail declines markedly after 72 h (Clulow and Jones,1982) and diluted rooster spermatozoa are viable for only12–24 h after collection (Bakst, 1988). Despite the fragility ofspermatozoa, fertility is preserved in those species in whichspermatozoa are stored within the female tract. For example,bat spermatozoa are fertile after overwinter storage in thefemale uterus (Wimsatt, 1942, 1944). The life of spermatozoastored within the sperm storage tubules of birds (SST) isprolonged and the storage time is correlated with theinterval between egg clutches (Birkhead and Moller, 1992).Salamander spermatozoa stored within the spermathecae offemales remain morphologically intact up to 60 days aftercessation of sexual activity (Zalisko and Larsen, 1989).Spermatozoa are stored within the oviducts of many reptilesand fertile eggs may be oviposited up to several years afterisolation from males (Gist and Jones, 1987). Freshwater turtles are excellent models to test whether theextended fertility of spermatozoa is a property of the malegamete or of the storage structures in the female oviduct.These turtles possess an unusual reproductive cycle in whichthe production and maturation of male and female gametesis not synchronized (Licht, 1984). In males, spermatogenesiscommences in spring and is completed by autumn, whereasin females vitellogenesis begins after oviposition in early