The principles of classification and a classification of mammals. Bulletin of the AMNH ; v. 85

It has long been known that primate species differ greatly in the weight of their testes relative to body weight1. Recently it has been suggested that among the three species of Pongidae (the great apes), the disparity in testes weights is associated with their different breeding systems2–4. Male gorillas and orangutans copulate infrequently, and when a female comes into oestrus she normally mates with only one male. However, in the chimpanzee, several males mate frequently with the oestrous females, so that each male has to deposit enough sperm to compete with the presence of sperm from other males. For the chimpanzee, therefore, we hypothesize that selection will favour the male that can deposit the largest number of sperm; thus the volume of spermatogenic tissue and hence testis size is far greater in the chimpanzee than in the gorilla or orangutan. If this is correct, it implies that primates in which more than one male mates with each oestrous female should have larger testes relative to their body weight than those with single-male breeding systems. We have tested this prediction across a wide range of primates, and the results support the hypothesis. The relative size of testes may, therefore, provide a valuable clue to the breeding system of a primate species.

Testis weight, body weight and breeding system in primates

The spermatozoa of most invertebrates (e.g., sea urchins) and nonmammalian vertebrates (e.g., fishes and amphibians) have full capacity to fertilize eggs upon leaving the testis. Testicular spermatozoa of mammals, on the other hand, do not possess the ability to do so. Their fertilizing capacity develops as they pass through the epididymis (Young, 1931; Nishikawa and Waide, 1952; Blandau and Rumery, 1964; Bedford, 1966; Orgebin-Crist, 1967). This process, apparently “unique” to mammals, is referred to as the epididymal maturation of spermatozoa. Even after their maturation, however, spermatozoa require an additional phase of maturation or capacitation within the female genital tract before they are able to fertilize eggs (Austin, 1951, 1952; Chang, 1951a). Thus, epididymal maturation and capacitation are two extra steps that mammaliam spermatozoa must take before they can effect fertilization. In this chapter, I will discuss how mammalian spermatozoa prepare themselves for fertilization and how the spermatozoa and eggs interact during fertilization. The process and mechanisms of sperm transport in the female genital tract will not be dealt with extensively here. Readers are referred to Bishop (1961, 1969), Blandau (1969), Bedford (1970b, 1972b), Thibault (1972, 1973a), Zamboni (1972), Blandau and Gaddum-Rosse (1974), Hafez and Thibault (1975), Overstreet and Katz (1977), Overstreet and Cooper (1978, 1979b), Overstreet et al. (1978), Shalgi and Kraicer(1978), Cooper et al. (1979) and Hunter (1975, 1980). The rejection or elimination of extra spermatozoa by the fertilized egg, one of the most fascinating events in fertilization, will not be discussed here. Instead, readers are referred to the chapter by Dr. Wolf in this volume. The physiology of egg activation has been described and discussed to some extent by Gwatkin (1977) and Yanagimachi (1978a). There are numerous reviews dealing with general aspects of mammalian fertilization. The following are recommended to aid in grasping the outline of mammalian fertilization: Austin and Bishop (1957), Austin and Walton (1960), Austin (1961, 1968), Blandau (1961), Piko (1969), Thibault (1969), Bedford (1970a,b, 1972b), Gwatkin (1976, 1977), Yanagimachi (1977, 1978a), Bedford and Cooper (1978) and Hunter (1980).

Mechanisms of Fertilization in Mammals

Publisher Summary This chapter discusses the hormonal control of ovoimplantation. The mammalian ovum undergoes several “trials” after its release from the ovarian follicule. The ovum must be fertilized as soon as possible after release otherwise it will degenerate within a few hours. It must then migrate or be transported through the oviduct within a definite interval, for if it arrives either too early or too late into the uterus it will encounter a hostile (toxic) environment. During the period of oviduct transit, the ovum must cleave and reach the morula stage of differentiation before it can coparticipate with the uterus in the initiation of implantation. Tubal or oviduct transit in most mammalian species occupies the first three–four days postfertilization. The interval between the arrival of the fertilized ovum into the uterus and the moment of its implantation is quite variable and depends on the species and on the physiological state of the female. The models of phases and states of uterine receptivity are also described in the chapter.

Hormonal control of ovoimplantation.

The aim of this review is to provide an integrative analysis of the role of FSH in the control of testicular function in higher primates, including man. Attention is focused on the action of FSH during neonatal development, puberty, and adulthood. Whether FSH is the major determinant of the adult complement of Sertoli cells and whether FSH is obligatory for the initiation, maintenance, and restoration of spermatogenesis is evaluated. The mechanism whereby the circulating concentration of FSH regulates spermatogonial proliferation to dictate the sperm production rate under physiological conditions in the adult is discussed in detail. Inhibin B is the major component of the testicular negative feedback signal governing FSH beta gene expression and FSH secretion, and the evidence for this view is presented. The review concludes with the presentation of a model for the operation of the FSH-inhibin B feedback control system regulating sperm production postpubertally in monkey and man, and with speculation on issues of clinical interest.

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The Functional Significance of FSH in Spermatogenesis and the Control of Its Secretion in Male Primates

Changes in Succinic Dehydrogenase Levels in the Rat Epididymis Under Normal and Altered Physiologic Conditions

Fertility control in male rats by continuous release of microquantities of cyproterone acetate from subcutaneous silastic capsules

Physiology of the sexual segment of the kidney in reptiles

Sialic acid is secreted by the testis, epididymis, ductus deferens and Cowper's gland of the male albino rat. Castration results in a considerable reduction in the sialic acid content of these organs. Androgen administration to castrated rats elevates the sialic acid levels in Cowper's gland to control values, while that of the other organs is only partially restored. This is probably due to the presence of spermatozoa in the epididymis in the control animals and is supported by the decreased values of sialic acid in animals with ligatures. The physiological integrity of the epididymal canal and Cowper's gland is thus dependent on the circulating levels of androgen.

Changes in the sialic acid content of the accessory glands of the male rat

Effect of sex hormones on the sexual segment of kidney and other accessory reproductive organs of the Indian house lizard Hemidactylus flaviviridis Ruppell

M. R. N. Prasad

Papers

Changes in Succinic Dehydrogenase Levels in the Rat Epididymis Under Normal and Altered Physiologic Conditions

Fertility control in male rats by continuous release of microquantities of cyproterone acetate from subcutaneous silastic capsules

Physiology of the sexual segment of the kidney in reptiles

Changes in the sialic acid content of the accessory glands of the male rat

Effect of sex hormones on the sexual segment of kidney and other accessory reproductive organs of the Indian house lizard Hemidactylus flaviviridis Ruppell