Male Fertility Rates Research Articles

Omega-3 Fatty Acids as Supplements and Cryoprotectants and Positive Outcomes for Human Seminal Cryopreservation: A Study in the Iraqi Context

Background: With the increasing deterioration in male fertility rates over the past few decades, assisted reproductive therapy via sperm banking has gained considerable attention from different health authorities worldwide. The process of sperm cryopreservation exerts certain harmful effects on sperm quality parameters. The aim of the current study was to examine the effect of omega-3 on human sperm cryopreservation as a dietary supplement and as a cryoprotectant stimulant.
 Methods: From healthy men, 120 seminal fluid samples were randomly collected for cryopreservation (for 30 days). All samples were divided into three groups (40 in each). The supplement group (SG) (first group) had been given dietary supplements of omega-3 (30% EPA: 20% DHA) for eight weeks before sample collection. The samples of the cryoprotectant group (CG) (second group) were treated with omega-3 additive in the diluent at the time of being collected and before we cryopreserved them. The samples from the control group (third group) were cryopreserved without any dietary or cryoprotectant supplementation. Initial seminal analysis was recorded and post-thawing assessment of sperm motility, vitality (using eosin test) and oxidative stress (using a nitro blue tetrazolium (NBT) test) were compared.
 Results and Conclusion: SG samples had greater initial seminal fluid volumes, as well as better sperm motility and vitality, but the oxidative stress assessment did not differ significantly pre-cryo. Post-thawing assessment revealed that the CG group had the best parameters of motility, vitality and oxidative stress. These results may be related to the positive effects of omega-3 fatty acids on reproductive glands, hormonal milieu, sperm function and structure, making it a suitable biostimulant for improving the outcome of human sperm banking. Results were comparable to multiple previous animal studies.

Infertility in Male Rats Induced by Diets Containing Whole Cottonseed Flour

It has recently been shown that gossypol, a component of the cottonseed, has clear antifertility properties. The present study was planned to determine whether diets containing cottonseed in different proportions and in nontoxic amounts, could produce infertility in male rats. Diets were formulated with different concentrations of whole cottonseed flour and stock diet (Purina Chow). After 4 weeks of feeding these diets, the male rats were mated with virgin female rats in order to test male fertility rate. Thereafter, the male rats went into a recovery period during which they were fed stock diet for 6 weeks and were again mated after 3 and 6 weeks on this diet. The results show that: 1) infertility was produced by cottonseed flour diets even with a low concentration of gossypol (defatted cottonseed flour); 2) this effect was reversible at least after 6 weeks off gossypol-containing diets, even in the groups fed diets with a high gossypol concentration. The gossypol present in the diets decreases the number and motility of spermatozoa, even when present in concentrations below its toxic level, which may have an important deleterious effect on animal reproduction, since cottonseed is frequently used in the preparation of balanced diets mainly for animal consumption.cottonseed male infertility gossypol

Aqueous extract of bay leaf (Laurus nobilis) ameliorates testicular toxicity induced by aluminum chloride in rats.

Human exposure to aluminum is inevitable, and one of the most adverse health effects of aluminum is a decrease in male fertility rates. Therefore, this study investigated the ameliorative effects of an aqueous extract from Laurus nobilis-bay leaf (BL) on aluminum chloride (AlCl3)-induced testicular toxicity in rats. Twenty-four Wistar rats were divided into four groups (n = 6, each group): The control (group 1) received normal saline; Group 2 animals were intraperitoneally administered with 30 mg/kg body weight (BW) AlCl3; and Groups 3 and 4 were co-administered AlCl3 with 125 or 250 mg/kg BW of BL extract, respectively, for 21 days. Testes, epididymis, and blood samples were collected. Testicular plasma enzyme activity was measured using a spectrophotometric assay, while concentrations of inflammatory biomarkers were determined using enzyme-linked immunosorbent assay kits. There was a significant increase (p < 0.05) in testicular enzyme activity in the group treated with AlCl3. However, there was no significant (p > 0.05) difference in testicular enzyme activity in groups co-administered AlCl3 and BL extract as compared with that in control. There was a significant (p < 0.05) increase in testicular nitrite concentration in the AlCl3-treated group, whereas the administration of BL extract significantly (p < 0.05) decreased nitrite concentration in Groups 3 and 4. Furthermore, the administration of BL extracts increased sperm count and improved the morphology of the testes in AlCl3-treated rats. Flavonoids, phenolic compounds, alkaloids, tannin, glycosides, saponin, anthraquinones, and steroids were identified in BL extract, with alkaloids and glycosides being the most abundant. Aqueous extract from BL ameliorated the toxic effect of AlCl3 and exhibited anti-inflammatory properties by inhibiting nitrite production while improving sperm count and morphology in AlCl3-treated rats. The bioactivity of the extract may be attributed to the presence of a wide range of phytochemicals. Therefore, BL aqueous extract could be a promising source of novel compounds with male fertility-promoting and anti-inflammatory properties.

Impacts of cadmium on male fertility: Lessons learnt so far.

Cadmium (Cd) is one of the most dangerous heavy metals in the world. Globally, toxicities associated with cadmium and its attendant negative impact on humans and animals cannot be under-estimated. Cd is a heavy metal, and people are exposed to it through contaminated foods and smoking. Cd exerts its deleterious impacts on the testes (male reproductive system) by inducing oxidative stress, spermatogenic cells apoptosis, testicular inflammation, decreasing androgenic and sperm cell functions, disrupting ionic homeostasis, pathways and epigenetic gene regulation, damaging vascular endothelium and blood testes barrier. In association with other industrial by-products, Cd has been incriminated for the recent decline of male fertility rate seen in both man and animals. Understanding the processes involved in Cd-induced testicular toxicity is vital for the innovation of techniques that will help ameliorate infertility in males. In this review, we summed up recent studies on the processes of testicular toxicity and male infertility due to Cd exposure. Also, the usage of different compounds including phytochemicals, and plant extracts to manage Cd reprotoxicity will be reviewed.

A 1-bp deletion in bovine QRICH2 causes low sperm count and immotile sperm with multiple morphological abnormalities

BackgroundSemen quality and insemination success are monitored in artificial insemination bulls to ensure high male fertility rates. Only ejaculates that fulfill minimum quality requirements are processed and eventually used for artificial inseminations. We examined 70,990 ejaculates from 1343 Brown Swiss bulls to identify bulls from which all ejaculates were rejected due to low semen quality. This procedure identified a bull that produced 12 ejaculates with an aberrantly small number of sperm (0.2 ± 0.2 × 109 sperm per mL) which were mostly immotile due to multiple morphological abnormalities.ResultsThe genome of this bull was sequenced at a 12× coverage to investigate a possible genetic cause. Comparing the sequence variant genotypes of this bull with those from 397 fertile bulls revealed a 1-bp deletion in the coding sequence of the QRICH2 gene which encodes the glutamine rich 2 protein, as a compelling candidate causal variant. This 1-bp deletion causes a frameshift in translation and a premature termination codon (ENSBTAP00000018337.1:p.Cys1644AlafsTer52). The analysis of testis transcriptomes from 76 bulls showed that the transcript with the premature termination codon is subject to nonsense-mediated mRNA decay. The 1-bp deletion resides in a 675-kb haplotype that includes 181 single nucleotide polymorphisms (SNPs) from the Illumina BovineHD Bead chip. This haplotype segregates at a frequency of 5% in the Brown Swiss cattle population. Our analysis also identified another bull that carried the 1-bp deletion in the homozygous state. Semen analyses from the second bull confirmed low sperm concentration and immotile sperm with multiple morphological abnormalities that primarily affect the sperm flagellum and, to a lesser extent, the sperm head.ConclusionsA recessive loss-of-function allele of the bovine QRICH2 gene likely causes low sperm concentration and immotile sperm with multiple morphological abnormalities. Routine sperm analyses unambiguously identify homozygous bulls for this allele. A direct gene test can be implemented to monitor the frequency of the undesired allele in cattle populations.

The protective effect of esculetin against aluminium chloride-induced reproductive toxicity in rats.

One of the prominent health problems caused by Aluminium was the decrease in male fertility rates. In the study, the protective effect of Esculetin (ESC) against the reproductive toxicity induced by Aluminium chloride (AlCl3 ) was investigated. For this purpose, AlCl3 was administrated to Wistar Albino rats at a dose of 34mg/kg and ESC was administrated at a dose of 50mg/kg for 70days. It was determined that AlCl3 treatment reduced sperm motility and concentration, increased dead/live rate and abnormal sperm rate. It decreased serum testosterone level, and co-treatment of ESC significantly regulated these values. In the AlCl3 -treated group, MDA level increased and GSH level, GPx and CAT activities decreased compared with those of the control group. However, co-treatment of ESC showed an amelioratory effect on the values except for CAT activity. It was observed that the expression level of NRF-2 increased in the ESC and AlCl3 +ESC groups, and NF-κB increased in the AlCl3 group with the control group. It was determined that Caspase-3 expression decreased, and Bcl-2 expression increased in AlCl3 +ESC group compared to AlCl3 group. It was also determined that AlCl3 -induced tissue injury was significantly prevented by ESC co-treatment.

Fertilization and male fertility in the rotifer Brachionus calyciflorus in the presence of three environmental endocrines

Many studies investigated the effects of environmental endocrine disruptors with the rotifer Brachionus calyciflorus. However, they focused on the reproductive behavior of rotifers, especially male–female fertilization, as a parameter in ecotoxicological and endocrine studies. In the present study, we used two environmental hormones (progesterone and testosterone) and one nonsteroidal antiandrogen (flutamide) at five different concentrations (0.5, 1, 2, 4, and 6 mg/L) to study the reproductive behavioral parameters of male rotifers. The average swimming speed of male rotifers in the blank group was 1.14 ± 0.43 mm/s. After exposure for 1 h, testosterone improved the swimming speed of males, with the greatest effect at a concentration of 2–4 mg/L, whereas flutamide and progesterone inhibited the swimming speed. Copulatory behavior experiments showed that, compared with the control group, the recognition ability of males was improved by testosterone at 1, 2, and 3 h (P < 0.05). After 4, 5, and 6 h, progesterone substantially suppressed the mating recognition ability of males, where the density of each group was extremely low at 6 h. Flutamide had a similar effect on the mating recognition ability of male rotifers as that of progesterone. The male fertilization rate in B. calyciflorus increased significantly under testosterone exposure at different concentrations (P < 0.05), with the highest level at 2 mg/L (male fertility rate = 48.61 ± 3.18%). The fertilization rate of male rotifers was suppressed by both progesterone and flutamide (P < 0.05), and higher drug concentrations had stronger suppressive effects.

Smoking-induced genetic and epigenetic alterations in infertile men.

Male fertility rates have shown a progressive decrease in both developing and industrialised countries in the past 50years. Clinical and epidemiological studies have demonstrated controversial results about the harmful effects of cigarette smoking on seminal parameters. Some studies could not establish a negative effect by tobacco smoking on sperm quality and function, whereas others have found a significant reduction in sperm quality and function. This study reviews the components in cigarette smoke and discusses the effects of smoking on male fertility by focusing extensively on smoking-induced genetic and epigenetic alterations in infertile men. Chromosomal aneuploidies, sperm DNA fragmentation and gene mutations are discussed in the first section, while changes in DNA methylation, chromatin remodelling and noncoding RNAs are discussed in the second section as part of epigenetic alterations.

Mater Certa Est, Pater Numquam: What Can Facebook Advertising Data Tell Us about Male Fertility Rates?

In many developing countries, timely and accurate information about birth rates and other demographic indicators is still lacking, especially for male fertility rates. Using anonymous and aggregate data from Facebook’s Advertising Platform, we produce global estimates of the Mean Age at Childbearing (MAC), a key indicator of fertility postponement. Our analysis indicates that fertility measures based on Facebook data are highly correlated with conventional indicators based on traditional data, for those countries for which we have statistics. For instance, the correlation of the MAC computed using Facebook and United Nations data is 0.47 (p = 4.02e -08) and 0.79 (p = 2.2e-15) for female and male respectively. Out of sample validation for a simple regression model indicates that the mean absolute percentage error is 2.3%.We use the linear model and Facebook data to produce estimates of the male MAC for countries for which we do not have data.

Comparison of serum oxidative stress markers among male partners of fertile and infertile couple at Nnamdi Azikiwe University Teaching Hospital, Nnewi, Anambra State, Nigeria

Infertility is a common cause of marital disharmony in Nigeria because of the high premium placed on child bearing. Male factor is a significant contributor and declining male fertility rate has been observed over the past decade. Oxidative stress has been implicated in the aetiology of male infertility. The objective of the study was to compare the serum levels of oxidative stress markers (TAC – Total Antioxidant Capacity, MDA - Malondialdehyde and SOD – Superoxide dismutase) in male partners of fertile and infertile couples. This was a case controlled study carried out over a period of 8 months on male partners of infertile couple. Thirty-six were male partners of fertile couple with normal semen parameters and no history of infertility while 73 were male partners of infertile couple which consists of 28 males with oligospermia, 28 with oligoasthenospermia and 17 with asthenospermia.. Serum markers of oxidative stress (TAC, MDA and SOD) were evaluated and compared among the group. The male partners of infertile couple showed significantly low levels of TAC (P = 0.000), SOD (P = 0.000) and significantly high levels of MDA (P = 0.000) when compared with male partners of fertile couple (750.93±146.37 versus 1269.20±330.79, 11.22±3.33 versus 13.96±1.38 and 2.48±1.20 versus 1.51±0.19). Oxidative stress may be a major contributor to male infertility. Its assay may be of importance in prevention and treatment of male infertility.

Measuring male fertility rates in developing countries with Demographic and Health Surveys: An assessment of three methods

Levels and patterns of male fertility are poorly documented in developing countries. Demographic accounts of male fertility focus primarily on developed countries, and where such accounts do exist for developing countries they are mainly available at the l

Immune mediators associated to male infertility in a mouse model of DNA immunization with the sperm protease proacrosin

The immune response has relevant physiological functions both in the male and female reproductive system, and must be tightly controlled to achieve a successful pregnancy. Several immune factors have been related to infertility, among them humoral and cellular immune responses triggered by sperm antigens. The present study was aimed at evaluating the immune profile induced by DNA immunization against the sperm protease proacrosin in CF1 male mice and its effect upon fertility.Immunized animals exhibited higher anti-proacrosin antibodies levels than controls (indirect ELISA), both in serum (p<0.01) and in seminal vesicle fluid (SVF; p<0.05). IgG2a levels were higher than IgG1 in serum (p<0.01) and similar in SVF. IL-10 and TGF-β1 mRNA levels were lower in testis (p<0.05), whereas TNF-α and IFN-γ transcript levels were increased in SV tissue (p<0.05). Immunized mice showed a trend toward higher IFN-γ concentration in serum and SVF than controls. Male fertility rate was diminished in immunized mice (p<0.01) and inversely correlated with serum and SVF anti-proacrosin IgG levels (p<0.001). Immunized animals also had fewer pups born than controls (p<0.01).To our knowledge, this is the first report on DNA immunization done in CF1 mice. Injection of proacrosin DNA induces an immune response in the male reproductive tract characterized by high levels of specific antibodies and cytokine changes. These factors may alter the crucial balance of the genital tract microenvironment required for adequate fertilization and pregnancy.

Morphological, cytological and fertility consequences of a spontaneous tetraploid of the diploid pear (Pyrus pyrifolia Nakai) cultivar ‘Cuiguan’

Chromosome multiplication, polyploidy, is usually correlated with improved agronomic performance. However, the lack of knowledge regarding variation in polyploids limits their efficient use in breeding. The main objective of this study was to demonstrate variations in morphology, cytology and fertility in the spontaneous ‘Cuiguan’ bud mutant (CBM). Using flow cytometry, we found that CBM was a new tetraploid pear with doubled 2C-DNA. Compared with its diploid donor, the ‘Cuiguan’ pear (control), CBM produced bigger flowers, anthers and leaves, longer guard cells, less and low-viability pollen grains, and faster growing fruits. In CBM fruits, the malic acid content was reduced more than 9%, but the glucose and sucrose contents were significantly increased by 38.6% and 72.9% respectively, which made the CBM fruits sweeter. Cross tests revealed that CBM, used as the male parent, showed a lower male fertility rate compared to the control and produced hybrid fruits with lower seed numbers and reduced seed germination rates. Additionally, the first filial generation (F1) plants were all diploids. However, CBM had the same female fertility as the control and mainly generated triploid or tetraploid F1 plants. Based on its quick fruit growth, fine fruit quality and potential for generating polyploids, CBM is a valuable germplasm for pear polyploid breeding.

Nuptial gift size, mating duration and remating success in a Neotropical spider

In many species the function and evolution of nuptial gifts have been explained by the male mating effort hypothesis; i.e., males increase their fertilization success by donating gifts to females. The gift size may determine copulation duration and consequently affects male fertilization rate. In the well-known spider Pisaura mirabilis, previous studies suggested that the brightness of the gift (a prey wrapped in silk) affects female acceptance and larger gifts promote longer matings, but little is known from other gift-giving spider species. In this paper we test if gift size affects mating and remating success in the Neotropical and semi-aquatic spider Paratrechalea ornata (Trechaleidae). We exposed virgin females to males offering one fly (OF group) or four flies (FF group) wrapped in silk, and afterwards mated females were exposed to remating. Males from FF showed both longer courtship and mating than males from OF. We found a positive linear relationship between insertion duration of male intromittent organs (during which sperm transfer occurs) and mating duration in both groups. Mated females were more reluctant to mate than virgin females, but contrary to our prediction, gift size and mating duration did not seem to influence remating success. Our findings show that large gifts prolong mating duration in P. ornata, supporting the mating effort hypothesis. Females would favour polyandry to gain direct benefits from the gifts, while males may improve success in sperm competition by inducing female reluctance for remating.

Counting your sperm before they fertilize: are sperm counts really declining?

A purported global decline in sperm counts has been a source of controversy since the early 1990s. Numerous studies performed since then, as well as re-analysis of the original data, show either no changes, or even increases, in sperm concentrations over time. In this review, we discuss the 1992 meta-analysis that initiated the continuing debate on whether sperm concentrations are declining, and the community discussion surrounding it over the past two decades. We also highlight studies evaluating sperm concentrations performed since the initial study that produced different results, and conclude that no definitive cause for a decrease in sperm counts has been established, and the effects of geography and environment on sperm counts are unclear. Approximately 15% of couples are considered infertile, with a male factor implicated in up to 50% of cases, underscoring the essential contribution of the male in conception.1 However, only over the past two decades have we begun to understand the degree to which men contribute to a couple's infertility, which historically was attributed to the female partner. One quarter or more of infertile men have an unknown cause for their infertility, and while recent work suggests that many of these etiologies are genetic, we cannot exclude the impact of environmental factors on the male reproductive system, which have been incompletely defined. Work over recent decades has identified a potential decline in sperm concentrations, with at least one explanation being an increase or change in environmental pollutant levels. In 1992, a meta-analysis of sperm concentrations derived from 61 papers dating between 1938 and 1990 involving semen quality from 14 476 men found that both sperm concentrations and seminal volumes had dropped significantly during that period.2 This was followed in 1993 by a manuscript suggesting that this decrease in sperm concentrations was partly due to environmental contamination with estrogenic compounds. However, there was little evidence identifying estrogens in the geographical areas where sperm concentrations appeared to be declining, or other evidence directly linking estrogenic pollution with declines in male fertility.3 These works triggered a continuing discourse and numerous investigations to evaluate the verity of these claims. However, current data have failed to demonstrate a decrease in either sperm concentrations or male fertility. Owing to the large amount of unclear and confounding data, it is difficult to determine whether male fertility rates are truly declining. Fertility assessment in both men and women is made more difficult by the wide range of sperm concentrations that can result in pregnancy. Indeed, sperm count alone cannot define the fertility potential of a couple. Nevertheless, from the authors' viewpoint, the available data do not support a global decline in sperm concentrations or male fertility. We highlight the limitations of the original work claiming this decline, and show that current data, including data by the authors of the original work, support the argument that sperm concentrations have overall remained stable or even increased. Furthermore, we find that there are few rigorously performed studies evaluating sperm concentrations, highlighting a need for such studies in determining the status of male reproductive function and the environmental factors that may affect it. Finally, we provide our views on the importance of peer review and the role of scientists as intermediaries with the press, and thereby the lay population, and how to maintain this relationship while providing accurate data without unnecessary sensationalism.

Using the product threshold model for estimating separately the effect of temperature on male and female fertility1

Animals under environmental thermal stress conditions have reduced fertility due to impairment of some mechanisms involved in their reproductive performance that are different in males and females. As a consequence, the most sensitive periods of time and the magnitude of effect of temperature on fertility can differ between sexes. The objective of this study was to estimate separately the effect of temperature in different periods around the insemination time on male and on female fertility by using the product threshold model. This model assumes that an observed reproduction outcome is the result of the product of 2 unobserved variables corresponding to the unobserved fertilities of the 2 individuals involved in the mating. A total of 7,625 AI records from rabbits belonging to a line selected for growth rate and indoor daily temperature records were used. The average maximum daily temperature and the proportion of days in which the maximum temperature was greater than 25°C were used as temperature descriptors. These descriptors were calculated for several periods around the day of AI. In the case of males, 4 periods of time covered different stages of the spermatogenesis, the transit through the epididymus of the sperm, and the day of AI. For females, 5 periods of time covered the phases of preovulatory follicular maturation including day of AI and ovulation, fertilization and peri-implantational stage of the embryos, embryonic and early fetal periods of gestation, and finally, late gestation until birth. The effect of the different temperature descriptors was estimated in the corresponding male and female liabilities in a set of threshold product models. The temperature of the day of AI seems to be the most relevant temperature descriptor affecting male fertility because greater temperature records on the day of AI caused a decrease in male fertility (-6% in male fertility rate with respect to thermoneutrality). Departures from the thermal zone in temperature descriptors covering several periods before AI until early gestation had a negative effect on female fertility, with the pre- and peri-implantational period of the embryos being especially sensitive (from -5 to -6% in female fertility rate with respect to thermoneutrality). The latest period of gestation was unaffected by the temperature. Overall, magnitude and persistency of the temperatures reached in the conditions of this study do not seem to be great enough to have a large effect on male and female rabbit fertility.

Sperm traits and male fertility in natural populations

Male fertility has seldom been studied in natural populations because it has been assumed that strong selection would result in uniformly high values among males, and therefore mating success has been equated with fertilisation success. In contrast, male fertility has received much attention in studies of domestic livestock, where economic benefits rely on improving productivity, and in human infertility studies, where the efficiency of treatments depends on understanding which ejaculate traits explain reproductive failures and predict success at assisted conception. Despite years of efforts, no conclusive results have been obtained, probably because such studies have focused on opposite extremes of the range with little variation: domestic livestock have often been subject to strong artificial selection for high fertility, and human patients requiring treatment have compromised fertility. Recent findings from natural populations of red deer have shown that males differ markedly in their fertility, and have revealed the degree of variation found in different semen traits, both between and within males. Fertility trials have shown that male fertility is determined mainly by sperm swimming speed and the proportion of normal sperm, when sperm numbers are kept constant. Sperm design exerts a strong influence on sperm swimming speed, with faster swimming sperm having elongated heads, shorter midpieces and a longer principal plus terminal pieces in relation to total flagellum length. Thus, the large inter-male variation in sperm design found among natural populations underlies differences in sperm swimming speed which, in turn, determine differences in male fertility rates. Secondary sexual characters are honest indicators of male fertility, so males with large and elaborated antlers have larger testes and faster swimming sperm. Testosterone does not seem to mediate the relationship between antler size and semen quality, since it is associated with sperm production, but not with sperm quality or antler size. Finally, more fertile males produce a greater proportion of sons, who will inherit the semen traits which will enhance their fertility.

La dystrophie myotonique: II nuptialité, fécondité et transmission du gène

A sociological study, using a representative sample (N = 218) of the myotonic dystrophy population, made possible an analysis of the relationship between certain demographic characteristics (marriage, fertility) and the mechanisms involved in the transmission of the deleterious gene. The results show a clear differentiation between the marriage rate of women and men affected by myotonic dystrophy. Whereas men show a considerable decline in marriage eligibility, women continue to marry at a young age and in a proportion almost equal to that of the unaffected population. The study also indicates that the average fertility rate among married patients in the Saguenay-Lac-Saint-Jean exceeds the fertility rate reported from affected populations found in other countries. Our study shows an above-normal male fertility rate. This demographic fact explains the overrepresentation of male transmitters noted in the affected population. However, if present trends remain unchanged, women will be more likely to transmit myotonic dystrophy to future generations. These conclusions illustrate how the transmission and spread of a dominant gene follow a pattern that cannot be dissociated from the socio-cultural characteristics taken as a whole, particularly demographic characteristics. They also provide us with useful avenues for setting up future prevention programmes.

Sperm Utilization Strategies in Nonsocial Insects

It is postulated that the sperm precedence characteristics of most insect populations have resulted primarily from selection on females (1) to optimize the genetic composition of their progeny; (2) to discourage or encourage multiple matings for reasons other than genetic considerations; (3) to optimize their sperm storage capacity and utilization. In addition, selection on males to maximize egg fertilization by reduced displacement of their sperm and increased displacement of other sperm to the extent that these can be achieved without sacrificing the optimal mating strategy (Parker 1970a) probably has been important in some species. Parker's (1970a) hypothesis that the amount of sperm displacement in a population should stabilize at the value which yields the optimal overall male fertilization rate is accepted as the optimal male strategy; however, it is suggested that females often largely determine, by their behavior and by the structure and functioning of their reproductive tract, the optimal male st...