Sexual selection and the maintenance of sexual reproduction

The maintenance of sexual reproduction is a problem in evolutionary theory because, all else being equal, asexual populations have a twofold fitness advantage over their sexual counterparts and should rapidly outnumber a sexual population because every individual has the potential to reproduce. The twofold cost of sex exists because of anisogamy or gamete dimorphism-egg-producing females make a larger contribution to the zygote compared with the small contribution made by the sperm of males, but both males and females contribute 50% of the genes. Anisogamy also generates the conditions for sexual selection, a powerful evolutionary force that does not exist in asexual populations. The continued prevalence of sexual reproduction indicates that the 'all else being equal' assumption is incorrect. Here I show that sexual selection can mitigate or even eliminate the cost of sex. If sexual selection causes deleterious mutations to be more deleterious in males than females, then deleterious mutations are maintained at lower equilibrium frequency in sexual populations relative to asexual populations. The fitness of sexual females is higher than asexuals because there is no difference in the fecundity of sexual females and asexuals of the same genotype, but the equilibrium frequency of deleterious mutations is lower in sexual populations. The results are not altered by synergistic epistasis in males.     

A protein kinase encoded by the t complex responder gene causes non-mendelian inheritance

Males heterozygous for the t-haplotype form of mouse chromosome 17 preferentially transmit the t-chromosome to their progeny. Several distorter/sterility loci carried on the t-haplotype together impair flagellar function in all spermatozoa whereas the responder, Tcr, rescues t-sperm but not wild-type sperm. Thus, t-sperm have an advantage over wild-type sperm in fertilizing egg cells. We have isolated Tcr by positional cloning and show that it is a member of a novel protein kinase gene family, designated Smok, which is expressed late during spermiogenesis. Smok kinases are components of a signal cascade which may control sperm motility. Tcr has a reduced kinase activity, which may allow it to counterbalance a signalling impairment caused by the distorter/sterility loci. Tcr transgene constructs cause non-mendelian transmission of chromosomes on which they are carried, which leads to sex-ratio distortion when Tcr cosegregates with the Y chromosome.     

Directional postcopulatory sexual selection revealed by artificial insemination

Postcopulatory sexual selection comprises both sperm competition, where the sperm from different males compete for fertilization, and cryptic female choice, where females bias sperm use in favour of particular males. Despite intense current interest in both processes as potential agents of directional sexual selection, few studies have attributed the success of attractive males to events that occur exclusively after insemination. This is because the interactions between pre- and post-insemination episodes of sexual selection can be important sources of variation in paternity. The use of artificial insemination overcomes this difficulty because it controls for variation in male fertilization success attributable to the female's perception of male quality, as well as effects due to mating order and the relative contribution of sperm from competing males. Here, we adopt this technique and show that in guppies, when equal numbers of sperm from two males compete for fertilization, relatively colourful individuals achieve greater parentage than their less ornamented counterparts. This finding indicates that precopulatory female mating preferences can be reinforced exclusively through postcopulatory processes occurring at a physiological level. Our analysis also revealed that relatively small individuals were advantaged in sperm competition, suggesting a possible trade-off between sperm competitive ability and body growth.     

V-J joining of immunoglobulin kappa genes only occurs on one homologous chromosome

In general, heterozygous animal cells express both alleles at a particular locus. The only exceptions are cells of XX genotype after inactivation of one X chromosome, and immunoglobulin-producing cells; in each case only one of the two alleles is expressed in differentiated cells and their progeny. This phenomenon, termed allelic exclusion, has been described for several mammalian species including man and mouse. It has been shown that the variable (V) and constant (C) region genes of immunoglobulins undergo a rearrangement during ontogeny. We wished to test whether allelic exclusion in B cells could be the consequence of V- and C-region rearrangement on one of the two homologous chromosomes only. For that reason we chose to analyse the rearrangement of immunoglobulin light chain genes in normal B lymphocytes isolated on the fluorescence-activated cell sorter. We now present evidence that during normal B-lymphocyte differentiation V-C rearrangement occurs only on one chromosome.     

Sperm competition between Drosophila males involves both displacement and incapacitation.

Females in almost all animal groups copulate with multiple males. This behaviour allows different males to compete for fertilization and gives females the opportunity to mediate this competition. In many animals and most insects, the second male to copulate with a female typically sires most of her offspring. In Drosophila melanogaster, this second-male sperm precedence has long been studied but, as in most species, its mechanism has remained unknown. Here we show, using labelled sperm in doubly mated females, that males can both physically displace and incapacitate stored sperm from earlier-mating males. Displacement occurs only if the second male transfers sperm to the female, and in only one of her three sperm-storage organs. Incapacitation can be caused by either fertile or spermless second males, but requires extended intervals between matings. Sperm from different males are not 'stratified' in the storage organs but mix freely. Many animal species may have multiple mechanisms of sperm competition like those observed here, and revealing these mechanisms is necessary to understand the genetic and evolutionary basis of second-male sperm precedence in animals.     

Genetic effects on sperm design in the zebra finch

Sperm design and function are important determinants of male reproductive success and are expected to be under strong selection. The way that spermatozoa phenotypes evolve is poorly understood, because there have been few studies of the quantitative genetics of sperm. Here we show, in the zebra finch Taeniopygia guttata, an extraordinary degree of inter-male variation in sperm design that is independent of sperm swimming velocity. A quantitative genetics study using data from over 900 zebra finches in a complex breeding experiment showed that sperm head, mid-piece and flagellum length are heritable, that negative genetic correlations exist between sperm traits, and that significant indirect (maternal) genetic effects exist. Selection on the zebra finch sperm phenotype may be low because sperm competition is infrequent in this species, and this, in combination with negative genetic correlations and maternal genetic effects, may account for the variation in sperm phenotype between males. These results have important implications for the evolution of sperm in other taxa.     

6个小鼠ES细胞系的建立和鉴定

报道从小鼠129/ter品系中建成6个胚胎干细胞系,经过核型检查,体内、体外分化等鉴定后发现,6个细胞系中有2个细胞系是正常二倍体,其中ES细胞系MESPU 13为XY型,其核骨架蛋白质成分相当于3～4d(天)的鼠胚细胞的核骨架成分,可长期维持二倍体未分化状态,并具有高效的嵌合能力。核型不正常的细胞系所形成的畸胎瘤生长较快,但细胞的分化程度与核型正常的ES细胞有所不同。对影响建系结果的各种因素进行了讨论。     

A common sequence of calcium and pH signals in the mitogenic stimulation of eukaryotic cells

When normal quiescent (G0) cells are stimulated by mitogens to enter the cell cycle, the metabolic derepression which occurs is similar in a variety of cells. The mechanisms initiating these responses and their relationship to subsequent progression through G1 to DNA synthesis in S phase, however, are generally undefined. The clearest evidence has been obtained in sea urchin eggs, where fertilization by sperm causes a rapid, transient increase in the concentration of free cytoplasmic Ca2+ [(Ca]i), followed by a sustained increase in cytoplasmic pH (pHi). It has been demonstrated clearly that these ionic responses are obligatory for progression to DNA synthesis by the normal pathway after fertilization, although the Ca2+ signal can be bypassed by parthenogenetic agents which elevate directly pHi (for example, NH+4 ions). These observations raise the questions of whether other eukaryotic cells show the same sequence of ionic responses when stimulated by mitogens and whether such signals are an obligatory component of their mitogenic pathways. We show here that a common sequence of [Ca]i and pHi responses occurs in both quiescent mouse thymocytes and Swiss 3T3 fibroblasts stimulated by appropriate mitogens. Furthermore, 'opportunistic' mitogens (those that do not act on the cells in vivo, such as concanavalin A (Con A), the Ca2+ ionophore A23187 and 12-o-tetradecanoyl phorbol 13-acetate CTPA] that are mitogenic for both mouse thymocytes and 3T3 fibroblast, each produce characteristic ionic responses that are the same in both types of cell.     

标记减数分裂遗传重组的免疫荧光染色方法

通过免疫荧光染色方法制备小鼠精母细胞联会复合体, 研究其形态组成与遗传重组特征,展示雄性小鼠遗传重组图谱并分析其重组位点(MLH1位点)的分布特征.4只小鼠共145个精母细胞在平均每个细胞的MLH1位点数为23.3±2.4; 在19个常染色体联会复合体中, 未发现有3个MLH1位点的, 具有1个MLH1位点数的较多, 平均为14.2; 无XY联会复合体的细胞占所有细胞的4.1%, XY联会复合体上有MLH1位点的细胞占30.2%; 联会复合体上有裂缝的细胞占0.7%.通过联会复合体免疫荧光染色可以清晰地分辨出联会复合体(红色)、着丝粒(蓝色)和MLH1位点(绿色), 是遗传重组分析的是一种强有力工具.     

Sperm death and dumping in Drosophila

Mating with more than one male is the norm for females of many species. In addition to generating competition between the ejaculates of different males, multiple mating may allow females to bias sperm use. In Drosophila melanogaster, the last male to inseminate a female sires approximately 80% of subsequent progeny. Both sperm displacement, where resident sperm are removed from storage by the incoming ejaculate of the copulating male, and sperm incapacitation, where incoming seminal fluids supposedly interfere with resident sperm, have been implicated in this pattern of sperm use. But the idea of incapacitation is problematic because there are no known mechanisms by which an individual could damage rival sperm and not their own. Females also influence the process of sperm use, but exactly how is unclear. Here we show that seminal fluids do not kill rival sperm and that any 'incapacitation' is probably due to sperm ageing during sperm storage. We also show that females release stored sperm from the reproductive tract (sperm dumping) after copulation with a second male and that this requires neither incoming sperm nor seminal fluids. Instead, males may cause stored sperm to be dumped or females may differentially eject sperm from the previous mating.     

Ex vivo expansions and transplantations of mouse bone marrow－derived hematopoietic stem／progenitor cells

To examine the effects of co-culture with bone marrow mesenchymal stem cells on expansion of hematopoietic tem/progenitor cells and the capacities of rapid neutrophil engraftment and hematopoietic reconstitution of the expanded ells, we expanded mononuclear cells (MNCs) and CD34^ /c-kit^ cells from mouse bone marrow and transplanted the expanded cells into the irradiated mice. MNCs were isolated from mouse bone marrow and CD34^ /c-kit^ cells were selected from MNCs by using MoFlo Cell Sorter. MNCs and CD34^ /c-kit^ cells were co-cultured with mouse bone marrow-derived mesenchymal stem cells (MSCs) under a two-step expansion. The expanded cells were then transplanted into sublethally irradiated BDF 1 mice. Results showed that the co-culture with MSCs resulted in expansions of median total nucleated cells, CD34^ cells, GM-CFC and HPP-CFC respectively by 10.8-, 4.8-, 65.9- and 38.8-fold for the mononuclear cell culture, and respectively by 76.1-, 2.9-, 71.7- and 51.8-fold for the CD34^ /c-kit^ cell culture. The expanded cells could rapidly engraft in the sublethally irradiated mice and reconstitute their hematopoiesis. Co-cultures with MSCs in conjunction with two-step expansion increased expansions of total nucleated cells, GM-CFC and HPP-CFC, which led us to conclude MSCs may create favorable environment for expansions of hematopoietic stem/progenitor cells. The availability of increased numbers of expanded ceils by the co-culture with MSCs may result in more rapid engraftment ofneutrophils following infusion to transplant recipients.     

Genetic evidence equating SRY and the testis-determining factor

The testis-determining factor gene (TDF) lies on the Y chromosome and is responsible for initiating male sex determination. SRY is a gene located in the sex-determining region of the human and mouse Y chromosomes and has many of the properties expected for TDF. Sex reversal in XY females results from the failure of the testis determination or differentiation pathways. Some XY females, with gonadal dysgenesis, have lost the sex-determining region from the Y chromosome by terminal exchange between the sex chromosomes or by other deletions. If SRY is TDF, it would be predicted that some sex-reversed XY females, without Y chromosome deletions, will have suffered mutations in SRY. We have tested human XY females and normal XY males for alterations in SRY using the single-strand conformation polymorphism assay and subsequent DNA sequencing. A de novo mutation was found in the SRY gene of one XY female: this mutation was not present in the patient's normal father and brother. A second variant was found in the SRY gene of another XY female, but in this case the normal father shared the same alteration. The variant in the second case may be fortuitously associated with, or predisposing towards sex reversal; the de novo mutation associated with sex reversal provides compelling evidence that SRY is required for male sex determination.     

Exceptional sperm cooperation in the wood mouse

Spermatozoa from a single male will compete for fertilization of ova with spermatozoa from another male when present in the female reproductive tract at the same time. Close genetic relatedness predisposes individuals towards altruism, and as haploid germ cells of an ejaculate will have genotypic similarity of 50%, it is predicted that spermatozoa may display cooperation and altruism to gain an advantage when inter-male sperm competition is intense. We report here the probable altruistic behaviour of spermatozoa in an eutherian mammal. Spermatozoa of the common wood mouse, Apodemus sylvaticus, displayed a unique morphological transformation resulting in cooperation in distinctive aggregations or 'trains' of hundreds or thousands of cells, which significantly increased sperm progressive motility. Eventual dispersal of sperm trains was associated with most of the spermatozoa undergoing a premature acrosome reaction. Cells undergoing an acrosome reaction in aggregations remote from the egg are altruistic in that they help sperm transport to the egg but compromise their own fertilizing ability.     

Behavioural ecology: transient sexual mimicry leads to fertilization

Sexual mimicry among animals is widespread, but does it impart a fertilization advantage in the widely accepted 'sneak-guard' model of sperm competition? Here we describe field results in which a dramatic facultative switch in sexual phenotype by sneaker-male cuttlefish leads to immediate fertilization success, even in the presence of the consort male. These results are surprising, given the high rate at which females reject copulation attempts by males, the strong mate-guarding behaviour of consort males, and the high level of sperm competition in this complex mating system.     

Male mammals respond to a risk of sperm competition conveyed by odours of conspecific males

Sperm competition occurs when a female copulates with two or more males and the sperm of those males compete within the female's reproductive tract to fertilize her eggs. The frequent occurrence of sperm competition has forced males of many species to develop different strategies to overcome the sperm of competing males. A prevalent strategy is for males to increase their sperm investment (total number of sperm allocated by a male to a particular female) after detecting a risk of sperm competition. It has been shown that the proportion of sperm that one male contributes to the sperm pool of a female is correlated with the proportion of offspring sired by that male. Therefore, by increasing his sperm investment a male may bias a potential sperm competition in his favour. Here we show that male meadow voles, Microtus pennsylvanicus, increase their sperm investment when they mate in the presence of another male's odours. Such an increase in sperm investment does not occur by augmenting the frequency of ejaculations, but by increasing the amount of sperm in a similar number of ejaculations.     

Outbred embryos rescue inbred half-siblings in mixed-paternity broods of live-bearing females

Females commonly mate with more than one male, and polyandry has been shown to increase reproductive success in many species. Insemination by multiple males shifts the arena for sexual selection from the external environment to the female reproductive tract, where sperm competition or female choice of sperm could bias fertilization against sperm from genetically inferior or genetically incompatible males. Evidence that polyandry can be a strategy for avoiding incompatibility comes from studies showing that inbreeding cost is reduced in some egg-laying species by postcopulatory mechanisms that favour fertilization by sperm from unrelated males. In viviparous (live-bearing) species, inbreeding not only reduces offspring genetic quality but might also disrupt feto-maternal interactions that are crucial for normal embryonic development. Here we show that polyandry in viviparous pseudoscorpions reduces inbreeding cost not through paternity-biasing mechanisms favouring outbred offspring, but rather because outbred embryos exert a rescuing effect on inbred half-siblings in mixed-paternity broods. The benefits of polyandry may thus be more complex for live-bearing females than for females that lay eggs.     

The genetic basis of Haldane's rule

'Haldane's rule', formulated by J. B. S. Haldane in 1922, states that: "When in the F1 offspring of two different animal races one sex is absent, rare, or sterile, that sex is the heterozygous [heterogametic] sex". His rule is now known to apply in mammals, lepidopterans, birds, orthopterans and dipterans. In Drosophila, for example, Bock cites 142 cases of interspecific hybridizations that produce one sterile and one fertile sex in the offspring, all but one of these crosses yielding sterile XY males and fertile XX females. Despite much speculation, however, the genetic basis of Haldane's rule remains unknown. Haldane himself rejected the simple explanation that males are innately more sensitive than females to the effects of hybridization because groups with heterogametic females (such as birds and butterflies) usually show female sterility in hybrids, so that heterogamety itself is the critical feature. He and others suggested that heterogametic infertility or inviability in hybrids arises by a genetic imbalance between X chromosomes and autosomes. An alternative explanation is that this syndrome is caused by a mismatch of X and Y chromosomes. Here I show that in the Drosophila melanogaster subgroup, Haldane's rule for fertility apparently arises from a genetic interaction between X and Y chromosomes and not from an imbalance between sex chromosomes and autosomes. This finding has important implications for understanding the evolution of interspecific reproductive isolation.     

饲养条件下太行山猕猴幼仔某些生长指标的研究

本文报导了太行山猕猴幼仔某些生长指标的变化规律.从初生到18月龄,太行山猕猴幼仔体重绝对增长率呈逐渐上升趋势,而相对增长率则呈逐渐下降趋势,3月龄以前为体重快速增长期.体重增长的回归方程:()W=689.67+130.58t;(♀)W=587.19+116.82t.体尺变化表明:除胸围外,其它各项指标表现了雌雄同步增长的趋势.     

Effects of ubiquitin-protea-some pathway on mouse sperm capacitation, acrosome reaction and in vitro fertilization

Chlortetracycline (CTC) fluorescence patterns were used to study changes in the patterns B and AR of mouse sperm after incubation with reagents that would block the UPP. They were the monoclonal antibody against ubiquitinated proteins-UCP1; the polyclonal antibody against ubiquitin anti-Ub, and a special inhibitor against proteasome ALLN. Furthermore, we treated the capacitated sperm or the eggs with these reagents separately and tested whether the normal in vitro fertilization was blocked or not. Results illustrate that UCP1, anti-Ub, and ALLN have little effects on sperm capacitation and acrosome reaction,but they do inhibit fusion of mouse sperm with eggs, which suggests that UPP play an important role in mouse in vitro fertilization.``