Genetic differentiation in Eurasian populations of the postfire ascomycete Daldinia loculata

The genetic population structure of the postfire ascomycete Daldinia loculata was studied to test for differentiation on a continental scale. Ninety-six samples of spore families, each comprising mycelia from six to 10 spores originating from single perithecia, were sampled from one Russian and six Fennoscandian forest sites. Allelic distribution was assayed for six nuclear gene loci by restriction enzyme analyses of polymerase chain reaction (PCR)-amplified gene fragments. In addition, the full sequence of the gene fragment was analysed for a subset of haploid single-ascospore isolates in a multiallelic approach. A third data set was generated by using arbitrary-primed PCR with the core sequence of the phage M13 as primer. Although there was a reduction in heterozygosity in the total population from what would have been expected at random mating, the levels of genetic differentiation among the Eurasian subpopulations of D. loculata were low. All subpopulations were found to be in Hardy-Weinberg equilibrium and gametic equilibrium was observed between all investigated nuclear gene loci. The results obtained by the different markers were consistent; we confirmed low levels of genetic differentiation among the Eurasian subpopulations of D. loculata. The differentiation did not increase with distance; the Russian subpopulation, sampled more than 7000 km from the Fennoscandian subpopulations, was only moderately differentiated from the others (FST = 0.00-0.14). In contrast, one of the Swedish populations was the most highly differentiated from the others, with FST and GST values of 0.10-0.16. The results suggest that D. loculata consists of a long-lived background Eurasian population of latent mycelia in nonburned forests, established by sexual ascospores dispersed from scattered burned forest sites. Local differentiation is probably due to founder effects of populations in areas with low fire frequency. A tentative life cycle of D. loculata is presented.     

Structure and mating system of the graminicolous fungal epibiont Echinodothis tuberiformis (Clavicipitales)

The developmental morphology and mating system of the epibiont Echinodothis tuberiformis is investigated. The structure of conidial stromata, conidia, perithecial stromata, asci, and ascospores is documented. Crosses involving transfer of conidia between stromata resulted in formation of perithecia, indicating a heterothallic mating system. Comparisons are made to other members of the Clavicipitales that are presently classified in the tribe Balansieae. It is suggested that this epibiont bears a closer relationship to the grass endophytes classified in the genus Epichloë (Fr.) Tul. than to several other members of the Balansieae.     

Performance of non-motile male gametes in the sea: analysis of paternity and fertilization success in a natural population of a red seaweed,Gracilaria gracilis

In haploid–diploid red seaweeds, the dispersal of male gametes is presumed limited due to their lack of flagella. It has been suggested that this group suffers from sperm limitation and, consequently, that fertilization is relatively inefficient. Fertilization in most floridean rhodophytes results in the formation a cystocarp, a swelling on the haploid female thallus housing the diploid zygote and its thousands of diploid daughter spores. To study the performance of non-motile male gametes in the sea, we evaluated both female and male fertilization success in a natural population of the red marine alga Gracilaria gracilis. Female fertilization success, estimated by cystocarp yield per unit female thallus, was evaluated with respect to the availability of male gametes. Male fertilization success, estimated by the individual contribution of different males to zygotes, was assessed by paternity analyses on 350 cystocarps produced in one reproductive season using two microsatellite loci. The results show that cystocarp yield is not sperm limited and that the large variation in male fertilization success cannot be solely explained by the distance travelled by the male gamete to find a mate. Taken together, the results suggest that, not only is fertilization efficient, but that male–male competition and/or female choice may play a role in shaping population mating patterns.     

Non-random mating in controlled multiple-donor crosses in Gracilaria gracilis (Gracilariaceae,Rhodophyta)

Crosses were performed to identify the sources of variation in zygote production (via cystocarp production) in Gracilaria gracilis, a red haploid-diploid seaweed. First, because male gametes are short-lived (<6?h), the rate of gamete encounters was evaluated in a time-course experiment. Second, the effect of water motion on gamete encounters was assessed by introducing turbulent eddies in the crossing tank and by comparing fertilization rates with and without this added turbulence. Third, variation due to individual performance was explored by performing multiple-donor crosses using 12 males and 12 females from three populations. Paternity of cystocarps produced in these crosses was determined using microsatellite markers. The results show that cystocarp yield increased with exposure time: fertilization occurred in as little as 15?min after the introduction of male branches into the crossing tank and maximum cystocarp production values were observed at 6?h. There were no significant differences in cystocarp production between the two turbulence levels. On the other hand, cystocarp production was highly influenced by male and female parental identities and to a lesser degree by an interaction between the male and female parents. The variation in cystocarp production according to male and female identity was not due to population origin as there was no difference between intra- and inter-population crosses. Thus nonrandom mating occurs in controlled conditions and arises from differential performance in G. gracilis. There was a strong deviation from equality of male performance, implicating post-adhesion events and/or male gamete production as important in generating non-random mating. Consequently, non-random mating may play a role in the evolution of mating patterns in G. gracilis.     

The developments between gametogenesis and fertilization: ovulation and female sperm storage in Drosophila melanogaster

In animals with internal fertilization, ovulation and female sperm storage are essential steps in reproduction. While these events are often required for successful fertilization, they remain poorly understood at the developmental and molecular levels in many species. Ovulation involves the regulated release of oocytes from the ovary. Female sperm storage consists of the movement of sperm into, maintenance within, and release from specific regions of the female reproductive tract. Both ovulation and sperm storage elicit important changes in gametes: in oocytes, ovulation can trigger changes in the egg envelopes and the resumption of meiosis; for sperm, storage is a step in their transition from being "movers" to "fertilizers." Ovulation and sperm storage both consist of timed and directed cell movements within a morphologically and chemically complex environment (the female reproductive tract), culminating with gamete fusion. We review the processes of ovulation and sperm storage for Drosophila melanogaster, whose requirements for gamete maturation and sperm storage as well as powerful molecular genetics make it an excellent model organism for study of these processes. Within the female D. melanogaster, both processes are triggered by male factors during and after mating, including sperm and seminal fluid proteins. Therefore, an interplay of male and female factors coordinates the gametes for fertilization.     

“Pollination” of a fungus by a fly

Summary The mechanism resulting in fertilization of Epichloë typhina, a heterothallic ascomycete that is an endophytic pathogen of grasses, has now been discovered. Conidia of one mating type are produced in stromata and are then transferred by insects to individuals of the opposite mating type. One insect, Phorbia phrenione, is a particularly important vector of conidia. Once conidia of the opposite mating type have been transferred to a stroma, the life cycle continues with the formation of perithecia.     

Sexual Reproduction in Aspergillus flavus Sclerotia: Acquisition of Novel Alleles from Soil Populations and Uniparental Mitochondrial Inheritance

Aspergillus flavus colonizes agricultural commodities worldwide and contaminates them with carcinogenic aflatoxins. The high genetic diversity of A. flavus populations is largely due to sexual reproduction characterized by the formation of ascospore-bearing ascocarps embedded within sclerotia. A. flavus is heterothallic and laboratory crosses between strains of the opposite mating type produce progeny showing genetic recombination. Sclerotia formed in crops are dispersed onto the soil surface at harvest and are predominantly produced by single strains of one mating type. Less commonly, sclerotia may be fertilized during co-infection of crops with sexually compatible strains. In this study, laboratory and field experiments were performed to examine sexual reproduction in single-strain and fertilized sclerotia following exposure of sclerotia to natural fungal populations in soil. Female and male roles and mitochondrial inheritance in A. flavus were also examined through reciprocal crosses between sclerotia and conidia. Single-strain sclerotia produced ascospores on soil and progeny showed biparental inheritance that included novel alleles originating from fertilization by native soil strains. Sclerotia fertilized in the laboratory and applied to soil before ascocarp formation also produced ascospores with evidence of recombination in progeny, but only known parental alleles were detected. In reciprocal crosses, sclerotia and conidia from both strains functioned as female and male, respectively, indicating A. flavus is hermaphroditic, although the degree of fertility depended upon the parental sources of sclerotia and conidia. All progeny showed maternal inheritance of mitochondria from the sclerotia. Compared to A. flavus populations in crops, soil populations would provide a higher likelihood of exposure of sclerotia to sexually compatible strains and a more diverse source of genetic material for outcrossing.     

The effect of alternative mating tactics on the fertilization success of a hermaphroditic seabass

In the simultaneously hermaphroditic marine fish, Serranus subligarius, male role individuals are known to pair spawn, group spawn and streak spawn. While the effects of these common mating tactics on mating success in the male role have been well studied, their consequences for the reproductive success of the individuals taking the female role have received little attention. To investigate those consequences, I observed mating behaviors and quantified fertilization success in natural and experimental settings during the summers of 2005-2008 at three sites with different local population densities. I observed focal individuals in 15-min increments and recorded the total number of spawns, number of streak spawns, size of participating spawners, and fertilization rate. The occurrence of small-sized individuals in the local population is associated with higher frequencies of streaking behavior; these small fish are most often first-year individuals reaching sexual maturity late in the spawning season (August/September). Spawns that included one or more streak spawners had a significantly lower average fertilization rate (89?%) than pair spawns without a streak spawner (97?%). This pattern was confirmed with a field manipulation experiment in which spawning events that included streakers again showed lower fertilization rates (93?%) than spawning events that did not include streakers (98?%). These lower fertilization rates occurred despite the fact that spawns that included multiple males produced, on average, 20?% more sperm than produced in spawns with only a single male. These results indicate that females incur a significant fitness cost when streakers invade a spawning event, a cost not attributable to sperm limitation or any direct effects on the female.     

Studies in the life cycle of Allomyces javanicus Kniep

Summary The life cycle of Allomyces javanicus was studied with the hanging drop method under laboratory conditions. The isolate has a life cyrle similar to that already described in A. javanicus and A. arbuscula. Planonts from resistant sporangia do not germinate directly to produce gametophytic plants, but on the contrary, the latter germinate to produce plants like their immediate parents. Female and male gametes growing in the gametangia of relatively young sexual mycelia develop into asexual mycelia after conjugation, but some of the female gametes after germination develop into asexual mycelia without conjugation.     

从天然蛹虫草不同部位分离菌株特性比较

以采集自泰山地区的6株野生蛹虫草为研究对象,分别通过菌核、子座组织分离和子囊孢子分离法共获得18个菌株,经ITS鉴定均为蛹虫草菌株后,进一步对18个菌株进行了菌丝生长速度、菌落形态、出草试验、主要活性物质（虫草素、腺苷、虫草多糖、β-类胡萝卜素、叶黄素）和交配型的测定分析。结果表明：在菌丝长势、出草产量和整齐度方面,从子囊孢子分离得到的菌株普遍优于组织分离菌株;而在活性物质含量方面,从子囊孢子和子座分离得到的菌株普遍优于菌核分离菌株。通过交配型测定发现,从菌核、子座和子囊孢子分离得到的18个菌株均不存在交配型缺失现象。     

GENDER VARIATION IN BARTSIA ALPINA (SCROPHULARIACEAE), A SUBARCTIC PERENNIAL HERMAPHRODITE

Maternal and paternal effects on seed size and reproductive success (RS) were studied in a subarctic population of Bartsia alpina L. (Scrophulariaceae), a hemiparasitic perennial herb forming dense clones in open habitats. The impact of environmental factors was assessed in fertilization and defoliation experiments, and gender specialization of individual genets was investigated in a series of diallel experiments (reciprocal crossings) in the field. Maternal effects on seed weight were much larger than paternal effects, and seed weight was also strongly influenced by resource availability (especially nitrogen). The highest seed weights were usually found when genets were associated with Astragalus frigidus, which seems to be the optimal host species in the population, but similar results were achieved with NPK (nitrogen-phosphorus-potassium) fertilization. Defoliation experiments revealed an innate minimum seed weight, below which seed number was affected by resource deprivation. The reciprocal crossing program indicated a high level of gender specialization in individual genets (clones), ranging continuously from almost pure males to almost pure females. Early-flowering genets showed the highest average male RS, whereas female RS increased in late-flowering genets. Phenological separation of the genets into ‘early’ and ‘late’ revealed an inverse correlation between male and female performance. Numerous characters contributing to phenotypic gender were measured in the genets, but these characters and functional gender calculations from the diallel experiment were only weakly correlated. It is concluded that simultaneous measures of both male and female RS are needed for a reliable assessment of gender variation.     

A test of host specialization by insect vectors as a mechanism for reproductive isolation among entomophilous fungal species

Epichloë species are self incompatible (heterothallic) fungi that must be fertilized by spermatia from individuals of opposite mating type for successful sexual reproduction to occur. Female flies of the genus Botanophila act as vectors of the fungi by ingesting and defecating spermatia (gametes) onto fungal stromata (fruiting bodies) after oviposition. Larvae feed and develop on the stromata and thus maintain a symbiotic relationship with Epichloë fungi. We hypothesized that sole dependence on fertilized stromata as a food source would promote specialization by flies to single compatible host species and that this specialization would promote reproductive isolation among Epichloë species. Analysis of progeny of ascospores from experimental field plots in Zurich, Switzerland, indicated prevalence of specific matings between stromata of the same host, and thus was consistent with the hypothesis that flies are species-specific in their visitation behaviour. Genetic analyses of spermatia contained in the faeces of individual flies also gave some support for this hypothesis. We recovered spermatia of 4 different Epichloë species from fly faeces. Comparison of spermatia found in fly faeces to those available from stromata showed flies avoided Epichloë clarkii and may have preferred Epichloë typhina . Interestingly, these are the only two Epichloë species known to be interfertile with one another. Individual flies tended to carry spermatia predominantly from one fungal species. Thus, flies may adopt a type of "majoring" and "minoring" behaviour when visiting fungi. Yet, Botanophila flies are not monolectic and often visited all hosts that were available within screened cages. In addition to any reproductive isolation flies may provide to some fungal species, differences in competitiveness among spermatia of different species deposited on the same stroma may favor intraspecific matings.     

Molecular diversity of ericoid mycorrhizal endophytes isolated from Woollsia pungens

One hundred and sixty-eight sterile endophytic mycelia were isolated from roots of four Woollsia pungens (Cav.) F. Muell. (Epacridaceae) plants collected from a field site in New South Wales, Australia. All isolates formed typical ericoid mycorrhizal structures when inoculated onto roots of Vaccinium macrocarpon Ait. (Ericaceae). Microsatellite-primed PCR fingerprints generated using the primers (GTG)₅ and (GACA)₄ indicated that considerable genetic diversity exists within the endophyte population. It was estimated that a minimum of 43 genetically distinct mycelial genets were present in the root systems of the sampled W. pungens population, with most genets confined to individual plants. Two genets, however, were present within the root systems of two adjacent plants. While most genets were represented by less than eight isolates, three genets contained up to 41 isolates, suggesting that root system colonization by some endophytic mycelia might be extensive.     

Epigenetic reprogramming in plant reproductive lineages

Monoecious flowering plants produce both microgametophytes (pollen) and megagametophytes (embryo sacs) containing the male and female gametes, respectively, which participate in double fertilization. Much is known about cellular and developmental processes giving rise to these reproductive structures and the formation of gametes. However, little is known about the role played by changes in the epigenome in dynamically shaping these defining events during plant sexual reproduction. This has in part been hampered by the inaccessibility of these structures-especially the female gametes, which are embedded within the female reproductive tissues of the plant sporophyte. However, with the recent development of new cellular isolation technologies that can be coupled to next-generation sequencing, a new wave of epigenomic studies indicate that an intricate epigenetic regulation takes place during the formation of male and female reproductive lineages. In this mini review, we assess the fast growing body of evidence for the epigenetic regulation of the developmental fate and function of plant gametes. We describe how small interfereing RNAs and DNA methylation machinery play a part in setting up unique epigenetic landscapes in different gametes, which may be responsible for their different fates and functions during fertilization. Collectively these studies will shed light on the dynamic epigenomic landscape of plant gametes or 'epigametes' and help to answer important unresolved questions on the sexual reproduction of flowering plants, especially those underpinning the formation of two products of fertilization, the embryo and the endosperm.     

Photographs of Fertilization in the Smaller Species of Trichonympha

SYNOPSIS. The photographs illustrate male and female gametes before fertilization, several progressive stages in the entrance of the male gamete into the cytoplasm of the female, cytoplasmic fusion of gametes, loss of extranuclear organelles of male gamete, retention of extranuclear organelles of female gamete, movement of pronucleus of male gamete to that of female, progressive stages in fusion of pronuclei, and the formation of the zygote which possesses the extranuclear organelles of the female gamete. Some abortive attempts at fertilization, resulting from failure of gametes to differentiate, are shown.     

Male-by-female interactions influence fertilization success and mediate the benefits of polyandry in the sea urchin Heliocidaris erythrogramma

Numerous studies have reported that females benefit from mating with multiple males (polyandry) by minimizing the probability of fertilization by genetically incompatible sperm. Few, however, have directly attributed variation in female reproductive success to the fertilizing capacity of sperm. In this study we report on two experiments that investigated the benefits of polyandry and the interacting effects of males and females at fertilization in the free-spawning Australian sea urchin Heliocidaris erythrogramma. In the first experiment we used a paired (split clutch) experimental design and compared fertilization rates within female egg clutches under polyandry (eggs exposed to the sperm from two males simultaneously) and monandry (eggs from the same female exposed to sperm from each of the same two males separately). Our analysis revealed a significant fertilization benefit of polyandry and strong interacting effects of males and females at fertilization. Further analysis of these data strongly suggested that the higher rates of fertilization in the polyandry treatment were due to an overrepresentation of fertilizations due to the most compatible male. To further explore the interacting effects of males and females at fertilization we performed a second factorial experiment in which four males were crossed with two females (in all eight combinations). In addition to confirming that fertilization success is influenced by male x female interactions, this latter experiment revealed that both sexes contributed significant variance to the observed patterns of fertilization. Taken together, these findings highlight the importance of male x female interactions at fertilization and suggest that polyandry will enable females to reduce the cost of fertilization by incompatible gametes.     

Gametic behavior in a marine green alga, Monostroma angicava: an effect of phototaxis on mating efficiency

The role of phototactic behavior of gametes was tested experimentally in the slightly anisogamous marine green alga Monostroma angicava Kjellman, and the effect of phototaxis on mating efficiency was discovered. Both male and female gametes showed positive phototaxis in response to a white light source. In contrast, they did not respond to a red light source. Their swimming velocity did not differ between these two illuminating light sources. It was, therefore, suggested that the search ability of the gamete itself might not vary between phototactic and non-phototactic conditions. The number of zygotes formed during the mating process may be expressed as the product of the number of encounters between male and female gametes and the fraction of encounters that result in sexual fusion. In this study, with high densities of male and female gametes mixed in test tubes, almost all minor (fewer in number) gametes fused sexually within 10 min. After dilution of the gamete suspensions by half, mating efficiency in test tubes illuminated by white light from above was higher than that in dark controls. This suggests that male and female gametes gathered at the water surface through their positive phototaxis, thus increasing the rate of encounters. Mating efficiency also decreased if the test tubes were illuminated from above by white light and also shaken. Since negative phototaxis is clearly shown in planozygotes, we suggest that positive phototaxis of male and female gametes in M. angicava is an adaptive trait for increasing the rate of gametic encounters rather than for the dispersal of zygotes as previously reported for zoospores of some marine algae. Received: 12 February 1999 / Revision accepted: 24 May 1999     

具有无色子囊孢子的木霉属两新种

报道了采自我国安徽省金寨县天堂寨的木霉属 Trichoderma 两个新种。新种天堂寨木霉T. tiantangzhaiense位于Hypocreanum分支,子座黄褐色至淡褐色,平垫状至盘状,子囊孢子相对较小;新种余氏木霉T. yui与沃格玛木霉T. voglmayrii亲缘关系较近,具有橙褐色至金棕色子座,褐色至红褐色孔口区和绿色分生孢子。本文提供了这两种木霉宏观和微观特征的详细描述及图示,并探讨了其分类地位。     

Effects of gamete behavior and density on fertilization success in marine green algae: insights from three-dimensional numerical simulations

We developed a numerical simulation of mating experiment to study effects of phototactic gamete behavior and density on fertilization success, using the C++ programming language, and pseudo-parallelization methods with input parameters based on experimental data. In our experiments, we found that gametes with positive phototaxis are favored, particularly in shallow water, because they can search for potential mates on the two-dimensional (2-D) water surface rather than randomly in three dimensions. We also found evidence that sperm (male gametes) limitation might not be the dominant selective force in the evolution of isogamous or slightly anisogamous marine green algae because almost all of female gametes can be fertilized on the 2-D water surface meaning they might not be under sperm limited conditions. Gamete density also appears to affect mating success seriously. These findings were produced by some technical progress made recently to rapidly and correctly count the numbers of zygotes formed calculating the locations of huge numbers of male and female gametes in the test tank. Both gamete behavior and density might be determined by environmental conditions of habitat, particularly the depth of water.     

Multiple Paternity in Norway Lobster (<Emphasis Type="Italic">Nephrops norvegicus</Emphasis> L.) Assessed with Microsatellite Markers

We investigated genetic diversity and the mating system of the Norway lobster (Nephrops norvegicus) in a wild population off the Portuguese coast. Approximately 100 individuals were screened for 2 microsatellite loci. For 11 ovigerous lobsters both the female and a sample of her offspring (24 eggs) were genotyped. High genetic diversity was observed for the 2 markers in the population. Paternity within broods was analyzed by comparing multilocus genotypes of each egg with the corresponding mother, and the male parent contribution was then deduced. Multiple paternity was observed in 6 of the 11 broods studied. In those cases, 2 to 3 male parents were likely to have contributed to the fertilization of the eggs. When multiple paternity was involved, the comparative reproductive success of the male parents was quite even. This is the first report of multiple paternity in the Norway lobster. Comparisons with other taxa are presented, and consequences of multiple paternity are discussed.