Fertilization in Amphibians: The Ancestry of the Block to Polyspermy

Abstract

Publisher Summary Amphibians exhibit both styles of fertilization: monospermy and polyspermy. Monospermy is confined to tailless frogs and toads that comprise the order Anura, while physiological polyspermy is found in the tailed newts and salamanders of the order Urodela. This chapter reviews the process of fertilization in amphibians, particularly as it relates to polyspermy. The chapter discusses ways to explore the nature of the cytological ancestry. Amphibians exhibit a great diversity of reproductive patterns. This diversity makes the amphibians ideal animals for examining the cellular evolution of developmental processes. Fertilization in anurans and urodeles is so different that it represents an important character distinguishing the orders. Comparison between fertilization in anurans and urodeles shows a mirror image dichotomy with respect to polyspermy. The anuran egg has a fast and slow block to polyspermy, and it has no protection when more than one sperm enters. On the other hand, the urodele egg lacks both external blocks to polyspermy but can deal with accessory nuclei within the egg. The arrangement of components in the membranes and in the cortical granules is considered important for the polyspermy-blocking reactions.