This book offers the reader an integrated point of view of fertilization in the animal kingdom. As the research at the molecular and cellular level is scarce compared to the huge diversity of animal species, for each phylum or class representative species have been chosen. Each phylum/class begins with a general description of the sexual and asexual reproduction strategies of the respective species, followed by a description of the reproductive cycle as well as of its reproductive system. The main focus is on the cellular and molecular aspects of fertilization of all the selected representative species, and the book is fully illustrated with photographs and drawings to facilitate understanding.

The increasing awareness on the varied consequences of hypogonadism in distinct organs and systems has supported the notion of estrogens as systemic agents. This observation is congruent with the variety of tissues affected by - trogens when used in hormone therapy formulations on hypogonadic women. Apart from the genital tract and the breast, recognized as traditional targets for estrogens, the skeleton, the vascular tree, or the central nervous system, are good examples of territories that have demonstrated sensitivity to estrogens. This evidence has created great interest, as shown by the great amount of lit- ature that has been produced on the bene?ts and risks associated with the use of estrogens. In parallel to the clinical interest, basic research has improved our kno- edge on the complexities involved in estrogen action at the molecular level. Together with effects mediated through speci?c receptors, a concept that has been the mainstay of the interpretation of estrogen action for years, there is enough evidence to hold the notion of receptor-independent effects. The substantial advances in modern technology applied to research have helped in enlightening the particulars of this versatile action of estrogens. This more detailed knowledge on the sophisticated mechanism of action of estrogens has nourished the emergence of multiple hypotheses speculating with the p- sibility of manipulating estrogen action. The notion that a widely extended regulatory system of cell function, as it is the estrogen receptor machinery, might be modulated at wish has arisen as an attractive, although still elusive postulate.

The increasing awareness on the varied consequences of hypogonadism in distinct organs and systems has supported the notion of estrogens as systemic agents. This observation is congruent with the variety of tissues affected by - trogens when used in hormone therapy formulations on hypogonadic women. Apart from the genital tract and the breast, recognized as traditional targets for estrogens, the skeleton, the vascular tree, or the central nervous system, are good examples of territories that have demonstrated sensitivity to estrogens. This evidence has created great interest, as shown by the great amount of lit- ature that has been produced on the bene?ts and risks associated with the use of estrogens. In parallel to the clinical interest, basic research has improved our kno- edge on the complexities involved in estrogen action at the molecular level. Together with effects mediated through speci?c receptors, a concept that has been the mainstay of the interpretation of estrogen action for years, there is enough evidence to hold the notion of receptor-independent effects. The substantial advances in modern technology applied to research have helped in enlightening the particulars of this versatile action of estrogens. This more detailed knowledge on the sophisticated mechanism of action of estrogens has nourished the emergence of multiple hypotheses speculating with the p- sibility of manipulating estrogen action. The notion that a widely extended regulatory system of cell function, as it is the estrogen receptor machinery, might be modulated at wish has arisen as an attractive, although still elusive postulate.

Reproduction is the origination of new organisms from pre-existing ones. Among more than 35 separated forms of reproduction including several types of gamogony, parthenogenesis, agamogenesis, fission and division, and plas motomy, the bisexual mode of reproduction via fertilization provides genetic variability that allows species to adapt quickly to competitive and constantly changing environments. Several excellent reviews and books have been written in the past to analyse the mechanisms of fertilization in different eukaryotic species. During the last few years, however, renewed attention has been paid to examining the process of oocyte fertilization at the cellular/molecular level not only within a single species/group but also through different phylogenetic lineages. As a result of this effort, knowledge of the molecular pathways used by oocytes and spermatozoa at fertilization has increased, but still many ques tions remain to be answered. Being aware of the necessity of providing an inte grated view of the process of fertilization, this book has been entirely devoted to reviewing the process of oocyte fertilization at the cellular/molecular level in two different and separated groups of eukaryotic organisms: protozoa and metazoan animals. The book is organized into six sections dealing with oocyte fertilization in protozoa, invertebrates, teleost fishes, amphibians, birds and mammals. These sections are followed by a summary/concluding chapter that provides a com parative overview of the process of fertilization in these groups of eukaryotes."