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PubMed2005

Nuclear fusion occurs during mating in Candida albicans and is dependent on the KAR3 gene.

It is now well established that mating can occur between diploid a and alpha cells of Candida albicans. There is, however, controversy over when, and with what efficiency, nuclear fusion follows cell fusion to create stable tetraploid a/alpha cells. In this study, we have analysed the mating process between C. albicans strains using both cytological and genetic approaches. Using strains derived from SC5314, we used a number of techniques, including time-lapse microscopy, to demonstrate that efficient nuclear fusion occurs in the zygote before formation of the first daughter cell. Consistent with these observations, zygotes micromanipulated from mating mixes gave rise to mononuclear tetraploid cells, even when no selection for successful mating was applied to them. Mating between different clinical isolates of C. albicans revealed that while all isolates could undergo nuclear fusion, the efficiency of nuclear fusion varied in different crosses. We also show that nuclear fusion in C. albicans requires the Kar3 microtubule motor protein. Deletion of the CaKAR3 gene from both mating partners had little or no effect on zygote formation but reduced the formation of stable tetraploids more than 600-fold, as determined by quantitative mating assays. These findings demonstrate that nuclear fusion is an active process that can occur in C. albicans at high frequency to produce stable, mononucleate mating products.

Base Sequence↗

PubMed2005

Candida albicans MTLalpha tup1Delta mutants can reversibly switch to mating-competent, filamentous growth forms.

Candida albicans strains that are homozygous at the mating type locus (MTLa or MTLalpha) can spontaneously switch from the normal round-to-oval yeast cell morphology to an elongated, so-called opaque cell form that can mate with opaque cells of the opposite mating type. In response to environmental signals, C. albicans also undergoes a transition from yeast to filamentous growth, which is negatively regulated by the general repressor Tup1p. Therefore, C. albicans mutants in which the TUP1 gene is inactivated grow constitutively in the filamentous form. We found that tup1Delta mutants of the MTLalpha strain WO-1 are still able to undergo phenotypic switching. Although the mutants had lost the capacity to grow in the normal yeast (white) or opaque forms, they could still reversibly switch between four different cell and colony phenotypes (designated as fuzzy, frizzy, wrinkled and smooth) at a frequency of about 10(-3) to 10(-4). Deletion of TUP1 resulted in deregulated expression of phase-specific genes. While the white-specific WH11 gene was constitutively expressed in all four cell types, the opaque-specific SAP1 gene remained repressed and the opaque-specific OP4 gene was weakly induced in all phase variants. In spite of the loss of white- and opaque-specific cell morphology and gene expression, the tup1Delta mutants retained an important characteristic of their wild-type parent, the ability to switch to a mating-competent form. The three filamentous phase variants (fuzzy, frizzy and wrinkled) all were able to mate and produce recombinant progeny with opaque cells of an MTLa strain at frequencies that were somewhat lower than those of normal opaque cells, whereas the smooth phase variant was unable to do so. Therefore, although deletion of TUP1 in C. albicans MTLalpha cells affects cellular morphology and gene expression patterns, the mutants can still reversibly switch between mating-competent and -incompetent cell types and mate with a partner of the opposite mating type.

Blotting, Southern↗

PubMed2005

The evolution of repeated mating under sexual conflict.

In insects, repeated mating by females may have direct effects on female fecundity, fertility, and longevity. In addition, a female's remating rate affects her fitness through mortality costs of male harassment and ecological risks of mating such as predation. We analyse a model where these female fitness factors are put into their life-history context, and traded against each other, while accounting for limitations because of mate availability. We solve analytically for the condition when female multiple mating will evolve. We show that the probability that a female mates with a courting male decreases with increases in population density. The extent of conflict between the sexes thus automatically becomes larger at higher densities. However, because at higher densities females meet males at a higher rate, the resulting ESS female remating rate is independent of population density. The female remating probability is in conflict with male adaptations that increase male mating rate by persuading or forcing females to mate, and also in conflict with male adaptations for protecting the own sperm from being removed by future female mates. We show that the relative importance of these conflicts depends on population density.

Animals↗

PubMed2006

Theoretical influence of female mating status and remating propensity on male sperm allocation patterns.

Theoretical models predict that males should allocate more sperm in matings where the immediate risk of sperm competition is high. It has therefore often been argued that males should invest less sperm in matings with virgin females compared with matings with already mated females. However, with relatively polyandrous females, high sperm competition risk will covary with high sperm competition intensity leading to more unpredictable conditions, as high competition intensity should favour smaller ejaculates. With the use of a genetic algorithm, we found that males should allocate more sperm in matings with virgin females when female mating frequency is relatively high, whereas low remating rates will select for higher effort in matings with nonvirgin females. At higher remating rates, first male sperm precedence favours larger ejaculates in matings with virgin females and second male precedence favours the reverse. These results shed some light on several findings that have been difficult to explain adaptively by the hitherto developed theory on sperm allocation.

Algorithms↗

PubMed2007

Reinforcement of mate preference among hybridizing Heliconius butterflies.

Recent models of mate preference evolution suggest that direct selection on alleles at preference loci and correlated evolution of preference with locally adapted mating cues are more likely to drive the evolution of assortative mate preference than reinforcement. Mate preference evolution in mimetic Heliconius butterflies has been attributed to all three forms of selection, but here we show that reinforcement has been critical. By examining geographical variation in assortative mating and male mate preference among seven populations of three hybridizing Heliconius species from Costa Rica, we found pronounced character displacement of preference such that sexual isolation was enhanced in areas of interspecific contact. Of the different explanations for the evolution of assortative mate preference, only reinforcement is dependent on interspecific contact in this system. Thus, the observed pattern of reproductive character displacement of mate preference is best explained as a product of indirect selection generated by natural selection against nonmimetic hybrids.

Animals↗

PubMedDate not supplied

Specific and common epitopes in mating pheromones of Euplotes raikovi revealed by monoclonal antibodies.

Polypeptide mating pheromones Er-1 and Er-2, purified from the supernatant of Euplotes raikovi cultures of mating type I and mating type II, respectively, were used to immunize mice and obtain monoclonal antibodies. Five hybridoma clones producing antibodies specific to the mating pheromones were selected. They were analyzed for immunospecificity by immunoperoxidase assay, immunoblotting, and for their efficacy in inhibition of mating pheromone activity. Monoclonal antibodies from two hybridoma clones recognized only the mating pheromone used as antigen: those from the other three clones reacted, to comparable extents, with both mating pheromones. On the basis of these results it was assumed that two immunogenic sites exist in Er-1 and Er-2, one specific and the other common to both mating pheromones.

Animals↗

PubMed1998

Identification of the mgc1 mutation which affects mating-pheromone-induced morphogenesis in the yeast Saccharomyces cerevisiae.

Cells of the yeast Saccharomyces cerevisiae undergo morphogenesis in response to the mating pheromones a- and alpha-factors. The 'shmoo' morphology involves localized cell surface projection formation and cytoskeleton protein synthesis. This polarization is presumed to be a prelude to mating between mating partners with opposite mating types, a and alpha. To identify genes involved in pheromone-induced morphogenesis, a system in which a gpa1 fus3 double mutant was used as a parent strain was developed, and mutants which showed altered morphogenesis in response to mating pheromone were identified. The mutation was designated mgc1 for morphogenesis control by mating pheromones. The mgc1 mutant arrested cell division in response to alpha-factor and mated with cells of the opposite mating type, but did not form a typical projection in response to pheromones.

Ethyl Methanesulfonate↗

PubMed2002

Maintenance of mating cell integrity requires the adhesin Fig2p.

Fungal adhesins represent a large family of serine/threonine-rich secreted glycoproteins. Adhesins have been shown to play roles in heterotypic and homotypic cell-cell adhesion processes, morphogenetic pathways and invasive/pseudohyphal growth, frequently in response to differentiation cues. Here we address the role of the Saccharomyces cerevisiae mating-specific adhesin Fig2p. Cells lacking FIG2 possess a variety of mating defects that relate to processes involving the cell wall, including morphogenetic defects, cell fusion defects, and alterations in agglutination activities. We found that mating-specific morphogenetic defects caused by the absence of FIG2 are suppressible by increased external osmolarity and that, during mating, fig2delta cells display reduced viability relative to wild-type cells. These defects result from alterations in signaling activated by the mating and cell integrity pathways. Finally, we show that fig2delta zygotes also have defects in zygotic spindle positioning that are osmoremedial, whereas the requirements for FIG2 in normal cell-cell agglutination and cell fusion during mating are insensitive to changes in the extracellular osmotic environment. We conclude that FIG2 performs distinct functions in the mating cell wall that are separable with respect to their ability to be suppressed by changes in external osmolarity and that a fundamental role of FIG2 in mating cells is the maintenance of cell integrity.

Cell Adhesion↗

PubMed2003

Cell biology of mating in Candida albicans.

It was recently demonstrated that strains homozygous for either of the mating type-like loci MTLa and MTLalpha of Candida albicans undergo white-opaque switching and that expression of the opaque-phase phenotype greatly enhances mating between strains. Exploiting the latter property to obtain high-frequency mating, we have characterized the cell biology of the mating process of C. albicans. Employing continuous videomicroscopy, computer-assisted three-dimensional reconstruction of living cells, and fluorescence microscopy, we have monitored the mating-associated processes of conjugation, tube formation, fusion, budding, septum formation, and daughter cell development and the spatial and temporal dynamics of nuclear migration and division. From these observations, a model for the stages in C. albicans mating is formulated. The stages include shmooing, chemotropism of conjugation tubes, fusion of tubes and nuclear association, vacuole expansion and nuclear separation in the conjugation bridge, asynchronous nuclear division in the zygote, bud growth, nuclear migration into the daughter cell, septation, and daughter cell budding. Since there was no cytological indication of karyogamy, genetic experiments were performed to assess marker segregation. Recombination was not observed, suggesting that mating takes place in the absence of karyogamy between naturally occurring, homozygous a and alpha strains. This study provides the first description of the cell biology of the mating process of C. albicans.

Candida albicans↗

PubMed2005

Unique aspects of gene expression during Candida albicans mating and possible G(1) dependency.

Taking advantage of the high frequency of conjugation tube formation in mating mixtures and alpha-pheromone-treated a/a cells derived from saturation phase cultures of opaque cells of Candida albicans, 56 up-regulated and 30 down-regulated genes were identified employing microarray and Northern analyses. Combining these results with previous profiling studies of pheromone-induced cells, a more comprehensive transcript profile was developed for comparison with Saccharomyces cerevisiae. This comparison revealed the following: (i) that while a majority of mating-associated genes are regulated similarly between the two species, a significant minority are regulated dissimilarly; (ii) that filamentation genes are uniquely up-regulated and opaque-specific genes uniquely down-regulated during C. albicans mating; and (iii) that a newly identified class of genes is selectively down-regulated in opaque, but not white, cells that have entered saturation phase in a growth culture and then are up-regulated by pheromone. The observations that opaque cells are uniquely mating competent, that saturation phase facilitates mating, and that a newly identified group of genes is down-regulated only in opaque cells that have entered saturation phase led us to hypothesize that entering saturation phase may be requisite for mating. A test of this hypothesis revealed, however, that cells, whether in the exponential or saturation phase, may simply have to be in G(1) of the cell cycle to respond to pheromone and that the response includes G(1) arrest. These results add to the lists of similarities and dissimilarities between the mating processes of C. albicans and S. cerevisiae and underscore the unique regulation of filamentation and switching genes in the C. albicans mating process.

Candida albicans↗

PubMed2001

The KlGpa1 gene encodes a G-protein alpha subunit that is a positive control element in the mating pathway of the budding yeast Kluyveromyces lactis.

The cloning of the gene encoding the KlGpa1p subunit was achieved by standard PCR techniques and by screening a Kluyveromyces lactis genomic library using the PCR product as a probe. The full-length open reading frame spans 1,344 nucleotides including the stop codon. The deduced primary structure of the protein (447 amino acid residues) strongly resembles that of Gpa1p, the G-protein alpha subunit from Saccharomyces cerevisiae involved in the mating pheromone response pathway. Nevertheless, unlike disruption of Gpa1 from S. cerevisiae, disruption of KlGpa1 rendered viable cells with a reduced capacity to mate. Expression of a plasmidic KlGpa1 copy in a DeltaKlgpa1 mutant restores full mating competence; hence we conclude that KlGpa1p plays a positive role in the mating pathway. Overexpression of the constitutive subunit KlGpa1p(K(364)) (GTP bound) does not induce constitutive mating; instead it partially blocks wild-type mating and is unable to reverse the sterile phenotype of DeltaKlgpa1 mutant cells. K. lactis expresses a second Galpha subunit, KlGpa2p, which is involved in regulating cyclic AMP levels upon glucose stimulation. This subunit does not rescue DeltaKlgpa1 cells from sterility; instead, overproduction of KlGpa2p slightly reduces the mating of wild-type cells, suggesting cross talk within the pheromone response pathway mediated by KlGpa1p and glucose metabolism mediated by KlGpa2p. The DeltaKlgpa1 DeltaKlgpa2 double mutant, although viable, showed the mating deficiency observed in the single DeltaKlgpa1 mutant.

Amino Acid Sequence↗

PubMed1999

Mate choice in tree crickets and their kin.

Mate choice theory has become a major field of research in behavioral ecology. Tree crickets provide excellent opportunities for studying the diversity and variability of mate choice. The evidence for female mate choice in tree crickets is reviewed, and broad comparisons with other orthopteran groups are made. The evidence shows that female choice may occur during several different stages of mating and may target several different criteria. Song preferences are perhaps dominated by stabilizing preferences for the cues of species recognition, but there is a growing body of evidence for directional preferences based on sensory biases or mate quality. Mate rejection during courtship and forms of postcopulatory choice may favor males, based both on phenotypic quality and on the amount of nutritious courtship gifts they provide, and may differ with the value of mating incentives. Understanding the balance and trade-offs between different forms of mate choice may help in understanding their evolutionary causes.

Journal Article↗

PubMed1999

Mating vocalizations of female frogs: control and evolutionary mechanisms.

Vocalization behaviors of anuran amphibians are universally sexually dimorphic. Usually, only male frogs give an advertisement call, while female frog calls are limited to a soft and simple release call which is specifically suppressed at mating. In a very few species, however, female frogs also give mating vocalizations. We examined possible mechanisms for control of this rare heterotypical behavior. At the peripheral level, most differences in temporal and spectral characteristics between female mating calls and the calls of conspecific males related directly to sexual dimorphisms in laryngeal and oblique muscle morphology. At the neural and hormonal level, we first developed an integrated model for control of vocalizations, based primarily on male frog data. When this model is applied to females, female mating vocalizations were most similar to male advertisement calls, rather than being modified release calls. Females may have conscripted preexisting androgen-sensitive neural pathways typically used only by males but present in both sexes. Female mating calls have been heard only during courtship and amplexus. Androgen levels in females at this time are significantly higher than even those levels in males. Because this situation is common in frogs, female mating vocalizations likely evolved independently multiple times. Character optimization suggests that mate location is the most common biological role for female mate calling, but the particular aspects of reproductive biology vary widely across species.

Animals↗

PubMed1998

Androgen receptors and estrogen receptors are colocalized in male rat hypothalamic and limbic neurons that express Fos immunoreactivity induced by mating.

Conversion of testosterone into estradiol is important for male rat sexual behavior, and both steroids probably contribute to mating. The distributions of neurons containing androgen receptors (AR) and estrogen receptors (ER) overlap, and many AR-immunoreactive (AR-ir) neurons express Fos immunoreactivity (Fos-ir) induced by mating. Because mating-induced Fos-ir in the male rat occurs mainly in AR-ir neurons, and because both steroids are important for mating, we hypothesized that (i) AR-ir and ER-ir are colocalized and that (ii) some of these neurons are activated during mating. We examined, in adjacent sections from the medial preoptic area (MPN) through the central tegmental field (CTF), the expression of ER-ir in: (i) AR-ir-containing neurons, and (ii) Fos-ir-expressive neurons. PG21 anti-AR, OA-11-824 anti-c-fos, H222 or 1D5 anti-ER primary antibodies were visualized, respectively, with cyanine-conjugated, fluorescein- or cyanine-conjugated, and fluorescein-conjugated secondary antibodies in male rats which were killed 1 h after ejaculating with a receptive female. In MPN, bed nucleus of the stria terminalis (BNST), and medial amygdala (MEA), 80-90% of ER-ir labeling occurred in AR-ir-positive neurons but only about 30% of AR-ir neurons were ER-ir-positive. No ER-ir was found in the CTF. This suggests the presence of three types of brain neurons sensitive to gonadal steroid hormones: neurons sensitive to androgens only, neurons sensitive to both androgens and estrogens, and neurons sensitive to estrogens only. About 50% of ER-ir labeling occurred in cells expressing mating-induced Fos-ir but only about 30% of Fos-ir neurons were ER-ir-positive. These findings suggest that, in the MPN, at least two different neuronal populations are activated during mating: the first contains AR-ir only and the second contains AR-ir and ER-ir. In the BNST and MEA, at least three hormonally sensitive populations are activated during mating: the two described above plus a third population which expresses ER-ir only.

Animals↗

PubMed1992

Sex difference in the effect of mating on c-fos expression in luteinizing hormone-releasing hormone neurons of the ferret forebrain.

The pulsatile secretion of LH was previously found to rise in female ferrets after receipt of an intromission, whereas in males that achieved an intromission, both LH and testosterone secretion were either reduced or unchanged. We sought to determine whether this sexually dimorphic pattern of LH secretion reflects a sex difference in the effect of mating on the activity of forebrain neurons that secrete LHRH. Immunocytochemical methods were used to localize the nuclear protein product of the immediate early gene, c-fos, as an index of increased neuronal activity after mating. Nuclear FOS immunoreactivity (FOS-IR) was monitored in LHRH-IR neurons as well as other non-LHRH forebrain neurons. In confirmation of previous reports, LHRH-IR perikarya in ferrets of both sexes were located medially along the base of the brain at rostral, medial, and caudal levels of the preoptic-hypothalamic continuum. In each of these regions a significantly higher percentage of LHRH-IR neurons was colabeled with nuclear FOS-IR in mated than in unpaired females. By contrast, an equivalent low percentage of LHRH-IR neurons was colabeled with FOS-IR in mated and unpaired male ferrets. Significantly more FOS-IR neurons (not colabeled with LHRH) were detected in the bed nucleus of the stria terminalis, the medial preoptic area, the dorsal-medial hypothalamus, and the medial amygdala (MA) of mated vs. unpaired females. By contrast, mating significantly augmented FOS-IR only in the MA of male ferrets. The results suggest that the sexually dimorphic pattern of LH secretion that occurs in ferrets after mating reflects a selective activation of LHRH neurons in the female forebrain. This sex-specific increase in the responsiveness of LHRH neurons to mating may depend on input from a limbic circuit which includes the medial amygdala, bed nucleus of the stria terminalis, and medial preoptic area.

Animals↗

PubMed2002

Light wavelength dependency of mating activity in the Drosophila melanogaster species subgroup.

The action spectra of mating activity among the six species of the Drosophila melanogaster species subgroup were compared to understand how light wavelength affects mating activity. The species fell into three groups with respect to the action spectrum of mating activity. We chose one representative species from each of the three types for detailed study: D. melanogaster, D. sechellia and D. yakuba. The mating activities were investigated under three different light intensities of three monochromatic lights stimulus. Each species showed a unique spectral and intensity response. To know the evolutionary meaning of the light wavelength dependency of mating activity, we superimposed the type of action spectrum of mating activity in these six species on a cladogram. Mating inhibition under UV was conserved in evolution among these species. Furthermore we clarified that D. melanogaster showed low mating activity under UV because males courted less under UV.

Animals↗

PubMed2005

Divergent selection and the evolution of signal traits and mating preferences.

Mating preferences are common in natural populations, and their divergence among populations is considered an important source of reproductive isolation during speciation. Although mechanisms for the divergence of mating preferences have received substantial theoretical treatment, complementary experimental tests are lacking. We conducted a laboratory evolution experiment, using the fruit fly Drosophila serrata, to explore the role of divergent selection between environments in the evolution of female mating preferences. Replicate populations of D. serrata were derived from a common ancestor and propagated in one of three resource environments: two novel environments and the ancestral laboratory environment. Adaptation to both novel environments involved changes in cuticular hydrocarbons, traits that predict mating success in these populations. Furthermore, female mating preferences for these cuticular hydrocarbons also diverged among populations. A component of this divergence occurred among treatment environments, accounting for at least 17.4% of the among-population divergence in linear mating preferences and 17.2% of the among-population divergence in nonlinear mating preferences. The divergence of mating preferences in correlation with environment is consistent with the classic by-product model of speciation in which premating isolation evolves as a side effect of divergent selection adapting populations to their different environments.

Adaptation, Biological↗

PubMed1993

[Hypothalamo-pituitary-ovarian function in female Japanese monkeys (Macaca fuscata) in the non-mating season].

We investigated the mechanism of reduction of hypothalamo-pituitary-ovarian function in female Japanese monkeys in the non-mating season. We administered PMSG and LH-RH to 19 females in the non-mating and in the mating season. When PMSG was administered every day for 12 to 14 days to seven monkeys in the non-mating season, follicle development was observed together with an increase in serum estradiol-17 beta (E2), but there was no rise in serum LH in two animals and little increase in five others. Follicle involution began about ten days after PMSG administration, and no ovulation occurred. These findings show that secretion of LH by the pituitary in response to positive feedback by the E2 secreted by the follicles which had developed was in adequate to induce ovulation. Serum LH levels increased markedly in five females after a single iv injection of LH-RH in the mating season, but not at all in the non-mating season, even when five-times the dose was administered. These data show that the LH-secreting function of the pituitary is definitely reduced in the non-mating season. When LH-RH was administered to seven monkeys following PMSG administration, an LH surge was observed in all animals, and ovulation occurred in four animals. These findings suggest that one reason for the reduction in pituitary-ovarian function in the non-mating season was a decline in LH-RH secretion by the hypothalamus.

Animals↗