Costing reproduction

The placing of animal behaviour in an evolutionary context is one of the great achievements of biologists in the last century. Life history theory has been a powerful tool in explaining both adaptation and constraint in phenotypic evolution, but rarely addresses the mechanistic bases of the traits it discusses. Recent advances in molecular biology have begun to uncover these mechanisms, and provide a challenge to the traditional view that life history trade-offs are the result of the differential allocation of limiting resources. In particular, costs of reproduction in Caenorhabditis elegans appear to arise from molecular signals, which have been claimed to be arbitrary with respect to fitness. We review the evidence that costs of reproduction in C. elegans are not resource based, and find that this is not necessarily the case. However, we welcome the challenge to traditional thinking, and suggest that integrating an understanding of mechanisms into life history theory will be one of the most exciting tasks facing evolutionary biologists in the 21st century. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Sexuality and reproduction

The relationship between coital rates, a quantitative index of sexuality, and the quality and quantity of reproduction is discussed in terms of sex ratio, delayed fertilization, frequency of intercourse, intercourse distribution within the menstrual cycle, acceleration of ovulation, and the quality of intercourse. Frequency of intercourse affects chances of conception, but its effect on twinning and sex ratio are unclear. Current research on reproduction offers little evidence of the effect of intercourse quality on reproduction in fully fecund individuals; research into the possible effect on reduced fecundity would be desirable.     

Fibronectin in reproduction

The fibronectin (FN) levels in human follicular fluids have been shown to correlate well with follicular size and oocyte maturity, suggesting a role of FN in oocyte maturation. When added to the culture medium, the synthetic peptide Gly-Arg-Gly-Asp-Ser (GRGDS), which specifically inhibits the cell-binding of FN, has been shown to inhibit both spontaneous resumption of meiosis and gonadotropin-releasing hormone-induced meiosis of the oocytes. In another set of experiments, GRGDS has been found to inhibit the in vitro cleavage of mouse embryos by a still unknown mechanism.     

Mitochondria and reproduction

Mitochondria play a primary role in cellular energetic metabolism. They possess their own DNA, which is exclusively maternally transmitted. The relatively recent idea that mitochondria may be directly involved in human reproduction is arousing increasing interest in the scientific and medical community. It has been shown that the functional status of mitochondria contributes to the quality of oocytes and spermatozoa, and plays a part in the process of fertilisation and embryo development. Moreover, new techniques, such as ooplasm transfer, compromise the uniquely maternal inheritance of mitochondrial DNA, raising important ethical questions. This review discusses recent information about mitochondria in the field of human fertility and reproduction.     

Ghrelin与生殖

ghrelin是1999年发现的一个含有28个氨基酸残基的多肽,为生长激素促分泌素受体(GHS-R)的内源性配体。具有调节能量平衡等多种生物学功能。近年来许多研究表明ghrelin对生殖激素、性腺、胎儿的发育、妊娠和泌乳均有一定的影响,并且,ghrelin及其受体广泛存在于生殖轴中。提示ghrelin对生殖系统具有重要的调节作用。     

Estrogens and male reproduction

The role of estrogen on male reproductive function has become clearer in the last decade. During these years the study of the effect of testosterone, estrogen or an aromatase inhibitor in hypogonadal men provided a first evidence of the effects of estrogens in the regulation of gonadotropin secretion. At the same time, the development of a line of transgenic male mice lacking estrogen receptor α, estrogen receptor β or aromatase gene provided further evidence about the role of estrogens not only in the regulation of gonadotropin secretion, but also on the effects of estrogens on testicular function and development. A confirmation of these actions of estrogens came from the observation of naturally occurring mutations of the estrogen receptor and of the aromatase gene in human males. Based on these data it has been demonstrated that estrogens are major regulators of gonadotropin secretion acting both at pituitary and hypotalamic level. The presence in the human reproductive structures of estrogen receptor α, estrogen receptor β and the aromatase enzyme indicates the existence of receptor α, estrogen receptor β or aromatase estrogen actions at this level. Anyway, the precise role of estrogens in testicular development and function and on the regulation of human spermatogenesis has not yet been precisely clarified.     

Unisexual reproduction among vertebrates

The past decade has seen a remarkable revision of perspectives on unisexual reproduction in vertebrates. One can no longer view it as a rare curiosity far outside the mainstream of evolution. More than 80 taxa of fish, amphibians, and reptiles are now known to reproduce by parthenogenesis (Greek for 'virgin birth') or its variants, and they persist in nature as all-female lineages. Other lower vertebrates that ordinarily rely on sexual reproduction can resort to facultative parthenogenesis under extenuating circumstances that isolate females from males. Molecular tools have now been applied to the study of unisexual organisms, and fascinating insights have emerged regarding the molecular mechanisms that preserve heterozygosity and increase genetic diversity in all-female populations. A deeper understanding of the underlying genetics increasingly calls into question the assumption that unisexuality in vertebrates is an evolutionary dead-end.