MORPHOLOGY AND EVOLUTIONARY IMPLICATIONS OF THE ANNUAL CYCLE OF SECRETION AND SPERM STORAGE IN SPERMATHECAE OF THE SALAMANDER AMBYSTOMA-OPACUM (AMPHIBIA, AMBYSTOMATIDAE)

Females of the marbled salamander, Ambystoma opacum, store sperm in ex ocrine glands called spermathecae in the roof of the cloaca. Eggs are fertilized by sperm released from the spermathecae during oviposition. Some sperm remain in the spermathecae following oviposition, but thes e sperm degenerate within a month and none persists more than 6 mo aft er oviposition. Thus, sperm storage between successive breeding season s does not occur. Apical secretory vacuoles are abundant during the fa ll mating season and contain a substance that is alcian blue+ at pH 2. 5. Production of secretory vacuoles decreases markedly after ovipositi on, and the glands are inactive by the summer months. Ambystoma opacum is a terrestrial breeder, and some mating occurs prior to arrival at pond basins where oviposition occurs. Mating prior to arrival at the o vipository site may prolong the breeding season, leading to fitness im plications for both males and females. Females have opportunities for more matings, and the possibilities for sperm competition in the sperm athecae are enhanced. (C) 1995 Wiley-Liss, Inc.