Submitted to: Reproductive Biology
Publication Type: Book / Chapter
Publication Acceptance Date: 12/29/2005
Publication Date: 1/17/2007
Citation: Stepinska, U., Bakst, M.R. 2007. Fertilization. In:Jamieson, B.G.M.,editor. Reproductive Biology and Phylogeny of Aves (Birds). Volume A. Enfield, NH: Science Publishers. p. 149-179.
Interpretive Summary: This review addresses important aspects of the fertilization process in birds. We cover what is known about the fate of sperm in the oviduct, sperm:egg interaction, and the subsequent onset of development of the embryo and attempt to draw comparisons to similar processes in mammals. Citing the most recent articles, we approach these topics from both a cellular and molecular perspective. Where there are gaps in our knowledge we offer some speculation on what is transpiring in the oviduct or in the fertilized ovum. This work is aimed at reproductive physiologists, avian physiologists, developmental biologists and anyone else interested in a better understanding of the processes that lead to fertilization and activation of development in the bird.
Technical Abstract: Until recently, the cellular and molecular events comprising fertilization in birds were rather poorly understood. However, several recent studies in mammals as well as in birds have considerably contributed to our knowledge of the fertilization process. Mammals exhibit physiological monospermy, that is, only a single sperm enters the ovum. Monospermy is ensured by a variety of mechanisms, which is collectively known as the block to polyspermy. Unlike mammals, the principal feature of fertilization in birds, as well as in many fishes, amphibians and reptiles, is physiological polyspermy, that is, penetration of the ovum by many sperm. It has been suggested that polyspermy occurs in animals that produce large yolky (megalecithal) ova. This review is not a comprehensive account of all aspects of avian fertilization, but rather concentrates on the following: oviductal sperm selection, storage and transport; the interaction of gametes; the role of ovum’s envelope; and formation and further fate of pronuclei. The main focus is on the complexities of polyspermic fertilization and the mechanisms preventing excessive pathological polyspermy that ensure normal embryonic development. This chapter also includes some data on assisted reproductive technologies used in birds, such as artificial insemination (AI), in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). Although the latter two methods have yet to find practical application, they can shed some light on at least some mechanisms of avian fertilization in vivo. Most of the available information on avian fertilization relates to the chicken (Gallus gallus), since it is commonly used as an experimental bird. In this chapter, all observations will be derived from research with the chicken unless otherwise noted.