Chances Of Fertilization Research Articles

Oncofertility: combination of ovarian stimulation with subsequent ovarian tissue extraction on the day of oocyte retrieval

BackgroundNew anticancer treatments have increased survival rates for cancer patients, but often at the cost of sterility. Several strategies are currently available for preserving fertility. However, the chances of achieving a pregnancy with one technique are still limited. A combination of methods is therefore recommended in order to maximize women’s chances of future fertility. In this retrospective study, ovarian stimulation with subsequent ovarian tissue extraction on the day of oocyte retrieval were combined and the quality of the ovarian tissue, the numbers and quality of oocytes, time requirements, and the safety of the strategy were examined.MethodsFourteen female patients suffering from malignant diseases underwent one in vitro fertilization cycle. Different stimulation protocols were used, depending on the menstrual cycle. Transvaginal oocyte retrieval was scheduled 34–36 h after human chorionic gonadotropin administration. Immediately afterwards, ovarian tissue was extracted laparoscopically.ResultsA mean of 10 oocytes were retrieved per patient, and 67% of the oocytes were successfully fertilized using intracytoplasmic sperm injection. No periprocedural complications and no complications leading to postponement of the start of chemotherapy occurred. The ovarian tissues were of good quality, with a normal age-related follicular distribution and without carcinoma cell invasion.ConclusionsAn approach using ovarian stimulation first, followed by laparoscopic collection of ovarian tissue, is a useful strategy for increasing the efficacy of fertility preservation techniques. The ovarian tissue is not affected by prior ovarian stimulation.

Electrophoretic profile of bull sperm membrane proteins as a tool for selection of breeding bull

Proteins present in the seminal plasma and sperm influence sperm function and fertilization. The present study was carried out to characterize the electrophoretic profile of bull sperm membrane proteins and to correlate with bull fertility. Semen samples were collected from 20 breeding bulls (10 Jersey and 10 Jersey crossbred) and the sperm membrane proteins were extracted by Triton X. Heparin binding proteins were eluted with heparin column, and the molecular weight of the proteins was assessed by discontinuous sodium dodecyl sulphate polyacrylamide gel elecrophoresis (SDS- PAGE). To assess the field fertility of the bulls, 50 frozen semen straws/bull were used for insemination. Results indicated that only 50 % of the bulls screened had 28– 30 kDa heparin binding proteins in their sperm and these bulls had 12 % higher conception than the bulls lack the protein. So, it can be concluded that the bulls positive for of 28– 30 kDa heparin binding proteins in sperm membrane protein had higher chance of fertility and screening for its presence can be used as a tool in addition to routine criteria for selecting bulls.

Chemotherapy and fertility

The overall increase in cancer prevalence and the significant increase in long-term survival have generated worldwide interest in preserving fertility in young women exposed to gonadotoxic chemo- and radiotherapy. Infertility represents one of the main long-term consequences of combination chemotherapy given for lymphoma, leukaemia and other malignancies in young women. The gonadotoxic effect of various chemotherapeutic agents is diverse, may involve a variety of pathophysiologic mechanisms, and is not unequivocally understood. Proliferating cells, such as in tissues with high turnover (i.e. bone marrow, gastrointestinal tract and growing ovarian follicles) are more vulnerable to the toxic effect of alkylating agents. These agents may also be cytotoxic to cells at rest, as they are not cell-cycle specific. Alkylating agents, the most gonadotoxic chemotherapeutic medications, cause dose-dependent, direct destruction of oocytes and follicular depletion, and may bring about cortical fibrosis and ovarian blood-vessel damage. The reported rate of premature ovarian failure after various diseases and chemotherapeutic protocols differ enormously, and depend mainly on the chemotherapeutic protocol used and age range of the woman. Several options have been proposed for preserving female fertility, despite gonadotoxic chemotherapy: ovarian transposition, cryopreservation of embryos, unfertilised metaphase-II oocytes and ovarian tissue, and administration of gonadotropin-releasing hormone agonistic analogs in an attempt to decrease the gonadotoxic effects of chemotherapy by simulating a prepubertal hormonal milieu. None of these methods is ideal and none guarantees future fertility in all survivors; therefore, a combination of methods is recommended for maximising women's chances of future fertility.

Klinefelter syndrome: the forgotten syndrome

Klinefelter syndrome: the forgotten syndrome

Senescence and sexual selection in a pelagic copepod.

The ecology of senescence in marine zooplankton is not well known. Here we demonstrate senescence effects in the marine copepod Oithona davisae and show how sex and sexual selection accelerate the rate of ageing in the males. We show that adult mortality increases and male mating capacity and female fertility decrease with age and that the deterioration in reproductive performance is faster for males. Males have a limited mating capacity because they can fertilize < 2 females day−1 and their reproductive life span is 10 days on average. High female encounter rates in nature (>10 day−1), a rapid age-dependent decline in female fertility, and a high mortality cost of mating in males are conducive to the development of male choosiness. In our experiments males in fact show a preference for mating with young females that are 3 times more fertile than 30-day old females. We argue that this may lead to severe male-male competition for young virgin females and a trade-off that favours investment in mate finding over maintenance. In nature, mate finding leads to a further elevated mortality of males, because these swim rapidly in their search for attractive partners, further relaxing fitness benefits of maintenance investments. We show that females have a short reproductive period compared to their average longevity but virgin females stay fertile for most of their life. We interpret this as an adaptation to a shortage of males, because a long life increases the chance of fertilization and/or of finding a high quality partner. The very long post reproductive life that many females experience is thus a secondary effect of such an adaptation.

Fertilität bei Patienten mit einem Klinefelter-Syndrom (47,XXY)

In the past 10 years, our knowledge about fertility chances of patients with Klinefelter syndrome (KS, 47,XXY) has changed considerably, especially when regarding the possibility of IVF ICSI treatment (in vitro fertilisation, intracytoplasmic sperm injection) with single testicular spermatozoa. Thus, it is important to take this knowledge into consideration when counselling Klinefelter patients.Germ cell degeneration in the testicles of Klinefelter patients due to their additional X chromosome is an important phenomenon in this disease which is not yet fully understood. When entering puberty, the testicular volume of KS patients increases for a short time with rising testosterone and inhibin B levels at the same time. These decrease, however, and FSH increases during puberty. This seems to indicate a critical point in time when spermatogenetic function of the testicles could still be existent. Thus, in early puberty there could possibly be a time slot when spermatozoa could be detected in the ejaculate or-if not-at least in the testicular tissue. These could be extracted by testicular sperm extraction, cryopreserved and used for intracytoplasmic sperm injection therapy later on. In the literature, a total of 133 births of children from Klinefelter fathers have been reported. This early specific procedure could lead to a better acceptance of their diagnosis and also offer the option of not being incurably infertile.

Reproductive biology of the deep-sea pennatulacean Anthoptilum murrayi (Cnidaria, Octocorallia)

Anthoptilum murrayi has been reported from the North Atlantic, northern Mid-Atlantic Ridge, Indian Ocean and in waters around New Zealand and Australia. Recently, this species was also recorded in deep waters off Brazil, southwestern Atlantic. It was from this region (13° to 22° S) that specimens were collected, in 1300 to 1799 m, to determine the reproductive biology of A. murrayi using histological methods. The colony polyparium was divided into 3 zones (distal, medial and basal) to evaluate differences in gamete development between zones; dissected polyps were examined from the 3 zones to estimate fecundity. The species appears to display a continuous and long breeding activity rather than any seasonal reproductive pattern. Most oocytes were in the earliest stages of development and basal polyps presented the highest frequency of small eggs. The large mature oocytes (up to 1200 μm) indicate that A. murrayi produces lecithotrophic larvae. Females had 0 to 90 oocytes per polyp and 25 713 to 35 918 oocytes per colony. Male colonies of similar size to the female samples were shown to have 6 to 76 cysts per polyp and 14 014 to 27 019 cysts per colony. A. murrayi is a sessile gonochoric species with a 1:1 sex ratio and is most likely a broadcast spawner. The species has high fecundity, large eggs that could represent larger targets for sperm, primitive spermatophores, as well as a large number of polyps per colony. These factors, along with a patchy distribution, would enhance the chance of fertilization for A. murrayi and may guarantee a successful reproductive strategy for this species.

High contraceptive failure rate of rhythm method: Possible involvement of pheromones

The rhythm method of birth control is a type of natural family planning and one of the practiced methods of contraception used by many couples through out the world. Couples who opt for contraception abstain from sex during the fertile period of women. The principle of this method is based on the knowledge of the life span of sperm ovum and the time of ovulation. Though the approximate time of ovulation can be calculated based on the duration of womens last menstrual cycle it is still subjected to individual variations. Hence the failure rates reported on this contraceptive method is comparatively higher than other methods available. Pheromones are airborne chemical signals released by an organism into the environment which can affect the physiological and behavioral responses of other organisms of the same species. Researchers have identified the presence of pheromones in human sweat urine and mucous secretions from the genitals. McClintock effect is a classical example which once again proves the presence of human pheromones and its influence. Olfactory mucosa is considered to be the major receptive area through which pheromones mediates their actions in humans. Altered behavioral responses were studied in women who are exposed to male pheromones. Pheromones also have strong influence in the modulation of ovulation in women. Considering the above findings we hypothesize that the presence of male pheromones which will be released from the bodily secretions of male partner at the time of sexual intercourse might be a cause for reducing the ovulation time in the female partner their by causing an early ovulation in her. This might result in high chances of fertilization. This pheromone interplay which alters the ovulation time in females could be one of the possible reasons of high failure rate observed in rhythm method of contraception. Just by knowing the time of ovulation it may not be sufficient enough to prevent pregnancy. It must be always coupled with other tests for the detection of ovulation. How much or to what extend pheromones influence the human nervous system functioning is of considerable interest. (full-text)

In the absence of a severe male factor ICSI is not justified for poor responders

OBJECTIVE: There is a growing body of evidence that ICSI should be used only in specific cases of male factor infertility. Yet it is still common belief that ICSI could give a better chance of fertilization, cleavage and general development to an embryo when compared with IVF. We set out to establish if ICSI is better than IVF in cases of poor ovarian responders (where three or less oocytes are collected) and absence of a severe male factor.DESIGN: This is an eight-year retrospective, electronic database and single chart review of all ART cycles undertaken in a tertiary referral/academic unit in Ireland.MATERIALS AND METHODS: All cycles with three or less oocytes retrieved were included in the study. This population (n=419) was divided according to the laboratory procedure performed (IVF: Group 1 or ICSI: Group 2). In the ICSI group we identified a sub-group of patients who had ICSI as per consent but based on their semen analysis on the day of oocyte collection would have fulfilled our criteria for IVF (Group 3). We compared Group 1 and Group 3 according to the following parameters: transfer, fertilization and cleavage rates; positive pregnancy test, number of pregnancy sacs and fetal hearts per cycle started.RESULTS: In the study groups (n=337), fertilization (65.8% vs. 67.5%) and cleavage rates (89.4% vs. 85.1%) were comparable. The transfer rate and mean number of embryos transferred were also similar, (70.2% vs. 71.0%) and (1.55 vs. 1.6) respectively. No significant differences were present in both implantation rates (p=0.18) and clinical pregnancy rates per cycle started (p=0.26), when comparing Group 1 with Group 3 (12.8% vs. 7.2% and 11.3% vs. 6.5%, respectively).CONCLUSIONS: This study shows that in the absence of a severe male factor and in the context of poor ovarian response (3 or less oocytes collected), ICSI does not offer a better chance of pregnancy. While not statistically significant, clinical pregnancy rates per transfer were nearly double in Group 1 when compared with Group 3 (16.1% vs. 9.1%). This demonstrates that IVF should be the procedure of choice rather than ICSI in this highly selected group of patients. Our findings suggest that a prospective randomized trail should be performed to further assess these results. OBJECTIVE: There is a growing body of evidence that ICSI should be used only in specific cases of male factor infertility. Yet it is still common belief that ICSI could give a better chance of fertilization, cleavage and general development to an embryo when compared with IVF. We set out to establish if ICSI is better than IVF in cases of poor ovarian responders (where three or less oocytes are collected) and absence of a severe male factor. DESIGN: This is an eight-year retrospective, electronic database and single chart review of all ART cycles undertaken in a tertiary referral/academic unit in Ireland. MATERIALS AND METHODS: All cycles with three or less oocytes retrieved were included in the study. This population (n=419) was divided according to the laboratory procedure performed (IVF: Group 1 or ICSI: Group 2). In the ICSI group we identified a sub-group of patients who had ICSI as per consent but based on their semen analysis on the day of oocyte collection would have fulfilled our criteria for IVF (Group 3). We compared Group 1 and Group 3 according to the following parameters: transfer, fertilization and cleavage rates; positive pregnancy test, number of pregnancy sacs and fetal hearts per cycle started. RESULTS: In the study groups (n=337), fertilization (65.8% vs. 67.5%) and cleavage rates (89.4% vs. 85.1%) were comparable. The transfer rate and mean number of embryos transferred were also similar, (70.2% vs. 71.0%) and (1.55 vs. 1.6) respectively. No significant differences were present in both implantation rates (p=0.18) and clinical pregnancy rates per cycle started (p=0.26), when comparing Group 1 with Group 3 (12.8% vs. 7.2% and 11.3% vs. 6.5%, respectively). CONCLUSIONS: This study shows that in the absence of a severe male factor and in the context of poor ovarian response (3 or less oocytes collected), ICSI does not offer a better chance of pregnancy. While not statistically significant, clinical pregnancy rates per transfer were nearly double in Group 1 when compared with Group 3 (16.1% vs. 9.1%). This demonstrates that IVF should be the procedure of choice rather than ICSI in this highly selected group of patients. Our findings suggest that a prospective randomized trail should be performed to further assess these results.

Exposure to endotoxin during estrus alters the timing of ovulation and hormonal concentrations in cows

The effect of intramammary (IMM) or intravenous (IV) administration of E. coli endotoxin (LPS), at the onset of estrus, at the time of ovulation was examined. Steroid and gonadotropin concentrations around ovulation were also determined. Lactating Holstein cows ( n = 33) were assigned to saline-controls ( n = 12) and treated with LPS-IV (0.5 μg/kg; n = 13) or LPS-IMM (10 μg; n = 8). Synchronized cows were observed continuously for estrus. LPS (or saline) was injected within 30 min from the onset of standing estrus, at peak estradiol concentrations. The typical rise of body temperature, somatic cell count, cortisol, and NAGase activity was noted. One-third of both LPS-IV- and LPS-IMM-treated cows were manifested by an extended estrus to ovulation (E–O) interval of around 75 h or did not ovulate, compared with about 30 h in the other 2/3 of LPS cows and all controls. Estradiol concentrations 24 h before and after LPS did not differ between groups. However, LPS-IV cows with extended intervals exhibited another estrus and an additional rise of estradiol followed by delayed ovulation. LPS-treated cows with a delayed E–O interval had low or delayed LH surge; two LPS-treated cows did not exhibit LH surge and did not ovulate. All control cows exhibited normal hormone levels. Delayed ovulation was associated with a delayed rise of luteal progesterone. The results indicated that exposing cows to endotoxin during estrus induced a decreased and delayed LH surge in one-third of the cows. This was associated with delayed ovulation, which reduces the chances of successful fertilization.

Syndrome de Prune Belly : aspects épidémiologiques, cliniques et thérapeutiques

Prune Belly syndrome (PBS) is a rare complex malformation with male predominance. His pathogeny is not yet completely elucidated. The goal of this work is to analyze the epidemiological, anatomoclinical and treatment aspects of a retrospective trial in Aristide-Le-Dantec Hospital. We carried out a retrospective study about 22 cases collected in the departments of urology-andrology and pediatric surgery in Aristide-Le-Dantec Hospital between April 1995 and November 2004. The mean age of the patients was 15 months with extremes of one day and 10 years. The somatic examination revealed 20 cases of complete abdominal muscle aplasia, one right partial form and the last case had a left partial form. Nineteen patients were managed with conservative treatment and three patients benefited a surgical act for urinary abnormalities. The Montfort intervention was performed in two patients respectively aged eight and 10 years. The orchidopexy, stage 1, by Fowler-Stephens technique was performed in 13 cases. Five cases of death and nine cases of testicular atrophy after orchidopexy occurred. The followings were satisfactory in the three operated patients for urinary abnormalities. The renal failure is the main cause of death. The management of the urinary tract abnormalities must be performed individually. The testis descending should be performed in newborn period to enhance the fertility chances. The abdominoplasty also should be done early for aesthetic reason and to improve pulmonary, defecation, and voiding functions.

Successful treatment of unilateral cryptorchid boys risking infertility with LH-RH analogue

Infertility is the primary concern for boys with uni- or bilateral undescended testes. An early and seemingly successful orchiopexy does not improve fertility in a substantial number of cryptorchid males. We confirmed that LH-RH analogue (LH-RHa) treatment induces an increase in and maturation of the germ cells; however, it was uncertain if treatment would improve the chance of fertility later in life. Thirty unilateral cryptorchid boys, with an average age of 3 years at the time of surgery, were included in the study. Testicular biopsy showed that they had impaired testicular maturation and were therefore at high risk for infertility. Fifteen of the 30 unilateral cryptorchid boys were treated with 10 microg LH-RHa (Buserelin) nasal spray, administered on alternate days for a period of 6 months, following orchiopexy. The control group consisted of 15 cryptorchid boys who had been treated by Schoemakers type of orchiopexy, alone. After puberty, the ejaculates of both groups were analyzed. All males in the untreated group were severely oligospermic, with 20% being azoospermic. In contrast, 86% of the treated ex-cryptorchid males had a sperm concentration within the normal range; this was significantly different from the sperm concentration found in the untreated group (p=0.000008). For the first time, we demonstrate that infertility in cryptorchidism can be successfully corrected when suitably treated with a LH-RHa. Sperm parameters normalized following therapy in the majority of cryptorchid males who, untreated, would have remained infertile. This innovative hormonal treatment will have a profound effect on the current recommended surgical treatment of boys with undescended testes.

Novel Adaptation of the Long Suppression Protocol for Fertility Preservation in a Woman With Stage I Receptor-Positive Breast Cancer (BrCa) and Age Factor

Background: Advances in diagnosis and therapy allow women with early BrCa to pursue fertility preservation. Most treatment options involve a modified short stimulation protocol with cryopreservation and offer them just a variable chance of future fertility. Only IVF with a gestational surrogate (IVF-GS) can result in an immediate pregnancy, although it requires more time for preparation and follow-up. Delay in treatment may increase BrCa recurrence risk through at least two mechanisms: 1) supraphysiologic estradiol (E2) levels during IVF; 2) prolonged exposure to physiologic E2 levels.

Semen Parameters in Infertile Nigerian Males: A critical Study

Introduction: Approximately one couple in ten are infertile during their reproductive lives. Male factors alone are responsible for infertility in 24% of couples and contributed to the cause in another 24%. The most important male factor is the semen parameter. Seminal fluid analysis is therefore the cornerstone of male infertility investigations. All the indicators suggest that a man had a reasonable chance of fertility with a sperm density exceeding 20x105/ml with more than 50% motility and a seminal volume of at least 1.5ml. Objective: To study the seminal parameters in infertile Nigerian male with a view to determining the distribution or pattern of semen abnormalities in them. Materials and Methods: Semen from 1129 infertile males were analyzed using conventional methods. The motility and the sperm density were estimated. The volume transparency, viscosity, the percentage of abnormal forms and abnormal cellular components were noted. The data were analyzed and displayed in tabular and graphical forms. Results: Two hundred and eighteen (218) (19.3%) were found to be azoospermic, 608 (53.85%) were oligospermic and 303 (26.83%) had normal sperm density. The motility at 2 hours was less than 50% in 66% of the specimen studied. The seminal volume was less than 1.5ml in 30.63% of the specimens. 36.7% had more than 50% abnormal forms. 23.7% and 12.8% of the specimens had significant white blood cells and immature/premature spermatogenic cells respectively. Conclusion: The most common abnormalities in the semen parameters of infertile Nigerian males are asthenozoopermia and oligoszospermia. Conventional technique of semen analysis gives reliable results on sperm characteristics. However, in some situations other tests may be necessary for complete evaluation. Keywords: Semen parameters Male infertility NigerianNQJHM Vol. 15 (2) 2005: pp. 87-91

Adaptation of Adults to Uncorrected Hypospadias

Surgery has been advocated for children with hypospadias to improve the appearance of the penis, allow voiding in the standing position, and improve the chance of fertility. We undertook a survey of adults with hypospadias to determine their adaptation to this congenital anomaly without surgical correction. In a 2-year prospective study, six urologists in the general practice of urology identified 56 adult patients from their practices with hypospadias. The urethral meatus was glanular in 21 patients, subcoronal in 23, distal penile in 7, mid-penile in 4, and proximal penile in 1. Nine patients had undergone failed or incomplete hypospadias repairs as children. Seven patients had mild to moderate chordee. Only 1 patient presented with a complaint referable to the hypospadias, and only 3 (5%) of the 56 patients expressed dissatisfaction with the appearance of their penis. Of the 56 patients, 18 (32%) stated that they were unaware that they had a congenital anomaly. The 2 patients who were known to be infertile were believed to be infertile on the basis of oligospermia. Although 20 (36%) of the 56 patients described angulation or spraying of the urinary stream, only 3 (5%) stated that they preferentially sat to void. No patient pursued an interest in corrective surgery. Of the adults we surveyed with hypospadias, most stated that they were satisfied with the appearance of the penis, voided in the standing position, and did not have infertility associated with the abnormal position of the urethral meatus.

Sex versus parasitism versus density

The Red Queen hypothesis predicts that sexual reproduction should be favoured when the risk of infection by parasites is high. However, this prediction may also be achieved independently by means of the reproductive assurance and the density-dependent transmission hypotheses because higher densities increase the chances of fertilization (i.e. mates are easier to find) and increase the risk of infection. Additionally, the Red Queen hypothesis makes a long-term prediction that infection should be genotype-specific, with time-lagged dynamics. In the present study, we attempt to consolidate these two predictions by investigating whether sexuality and parasitism alternate in a time-lagged fashion on an ecological time-scale. In a 3-year study, we examined the time-lagged dynamics between male frequencies, infection levels (by Centrocestus sp.), and snail densities of four natural populations of sexual and asexual Melanoides tuberculata snails. The results obtained provide no evidence of either prediction of the Red Queen hypothesis. We found partial support for reproductive assurance in a single population, and could not discriminate between the three hypotheses in another population. The remaining two populations did not support any of the hypotheses in question.

Reproductive stem cell research and its application to urology

Germ cells are defined by their innate potential to transmit genetic information to the next generation through fertilization. Males produce numerous sperm for long periods to maximize chances of fertilization. Key to the continuous production of large numbers of sperm are germline stem cells and their immediate daughter cells, functioning as transit amplifying cells. Recently, it has become possible to expand germline stem cells of rodents in vitro. In addition, multipotent stem cells, which are functionally the same as embryonic stem cells, have been established from neonatal mouse testes. These stem cells derived from the testis should contribute to biological research and technologies. On the other hand, the nature of human spermatogenesis is largely unknown due to the lack of an appropriate experimental system. However, the prevailing testicular sperm extraction procedure unraveled hitherto unknown facets of human spermatogenesis. The establishment of a culturing method for human spermatogonial stem cells in hopefully the near future would be a great benefit for achieving further insight into human spermatogenesis and should lead to more sophisticated diagnostic and therapeutic clinical measures for male infertility.

Regulation of sperm storage and movement in the mammalian oviduct

The oviduct plays a vital role in ensuring successful fertilization and normal early embryonic development. The male inseminates many thousands or even millions of sperm, but this alone does not ensure that fertilization will be successful. The female tract, particularly the oviduct, provides filters that select for normal vigorously motile sperm. In conjunction with molecules in the seminal plasma and on sperm, the female tract regulates how and when sperm pass though the tract to reach the site of fertilization. Various regulatory processes control sperm passage into and through the oviduct. In some species, the uterotubal junction opens and closes to regulate when sperm may enter; furthermore, passage through the junction requires certain proteins on the sperm surface. Most of the sperm that manage to enter the oviduct soon become trapped and held in a reservoir. In marsupials and insectivores, this involves trapping sperm in mucosal crypts; while in most other mammalian species, this involves binding sperm to the oviductal epithelium. As the time of ovulation approaches, the sperm in the reservoir undergo capacitation, including motility hyperactivation. Capacitating sperm shed proteins that bind them to the mucosal epithelium, while hyperactivation assists the sperm in pulling off of the epithelium and escaping out of mucosal pockets. The process of sperm release is gradual, reducing chances of polyspermic fertilization. Released sperm may be guided towards the oocyte by secretions of the oviduct, cumulus cells, or oocyte. Hyperactivation likely assists sperm in penetrating the cumulus matrix and is absolutely required for penetrating the oocyte zona pellucida and achieving fertilization.

Exploring Cyanobacterial Mutualisms

Cyanobacterial symbioses with eukaryotes are ancient associations that are widely distributed in aquatic and terrestrial environments. Cyanobacteria are a significant driving force in the evolution of their hosts, providing a range of services including photosynthesis, nitrogen fixation, UV protection, and defensive toxins. Although widespread, cyanobacteria occur in a limited range of hosts. Terrestrial symbioses are typically restricted to lichens and early evolved plants, and aquatic symbioses to sessile or slow-moving organisms. This review examines the underlying evolutionary processes that may have lead to these patterns. It also examines the facts that the degree of integration between symbiont and host, and the mode of transmission of the symbiont, do not appear to be an indication of how old the symbiosis is or how important it is to host well-being. Biparental transmission of symbionts may prolong the survival of gametes that persist in the environment, increasing chances of fertilization.

Mating behaviour of the marine snail Littoraria flava (Mollusca:Caenogastropoda) on a boulder shore of south-east Brazil

The mating pattern of Littoraria flava, a typical grazer snail of the supralittoral zone and sometimes the midlittoral zone of boulder shores in tropical and sub-tropical regions, was examined to determine the occurrence of size-assortative mating and sexual selection on size. We also evaluated its reproductive behavioural mechanisms, as well as their implications for the evolution of the species. The population was investigated from May 2001 through April 2002, on an artificial rocky shore composed of a boulder wall at Flexeira Beach, Itacuruçá Island, Rio de Janeiro, Brazil (22°56′S 43°53′W). The current study showed that: (1) copulating pairs were observed only from November through March, indicating seasonal reproduction of the population; (2) linear correlation between sizes of copulating mates were weak but significant, characterizing assortative mating by size; (3) there was sexual selection for female size, i.e. large females were favoured as mating partners over small ones; however, sexual selection on size was not observed among males; (4) there were significant positive correlations between male and female shell sizes and the copulation time; (5) there were significant differences in copulation time among different types of copulating pairs; and (6) mating females were significantly larger than non-mating females, while there were no differences between the sizes of mating and non-mating males, indicating differential sexual selection between sexes. These findings may contribute to the evolution of sexual dimorphism in this species. Male choice behaviour plausibly explains the assortative mating and sexual selection on female size of Littoraria flava. As males chose larger mates because they benefit reproductively therefore large females have increased chances of mating and fertilization (sexual selection for size). Further evidence suggests that large females are more successful than small females in carrying out mating, because large females remain in copulation for a longer time than do small females.