Mating Structure Research Articles

Sporidial Fusion and Infection of Maize Seedlings by the Smut Fungus Ustilago maydis

Mating and infection structures of Ustilago maydis produced in culture and on maize plants were examined with light and electron microscopy. Fusion tubes formed between low numbers of compatible haploid sporidia incubated in water for 8-16 hours. Both nuclei from paired sporidia migrated into a rapidly elongating hypha that did not differentiate further in the absence of host cells. Sporidial fusion and hyphal emergence also occurred rapidly and consistently in leaf whorls of inoculated maize seedlings, and hyphae had entered maize leaves after 12 hours. Only young leaves in the inner part of the leaf whorl were infected. Hyphae did not grow through stomatal openings, but, instead, entered epidermal cells by penetrating the cuticle and then either growing directly through the underlying cell wall or first growing between epidermal cells before penetrating an anticlinal wall of one of the cells. Invaded

Micromechanical Velcro

The authors have developed arrays of micromechanical mating structures, fabricated with silicon micromachining techniques, which act as mechanical adhesives. The microstructures are fabricated on standard silicon wafers, with an areal density of approximately 200000 per cm/sup 2/. The microstructures on two identical surfaces will self-align and interlock with each other under application of adequate external pressure. A tensile strength per unit interlocked area of 1.1 MPa, or 160 psi, has been achieved. In this work, the authors describe the design and fabrication of this micromechanical Velcro; the authors also present results of their experimental tests, a theoretical estimate of the tensile strength, and design constraints.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Silicon micro‐velcro

Silicon micromachining technology has been employed to fabricate dense, regular arrays of microstructures which act as mechanical adhesives. Structures such as that shown in the figure have potential applications in the biocompatible bonding of human tissue during surgery, their barb‐like nature preventing retraction. A second approach, using mating structures, provides precision self‐alligning, room‐temperature bonding with potential in the mounting of integrated circuit chips. magnified image

The Influence of Religious Affiliation on Surname Repetition in Marriages in Tiszaszalka, Hungary

The repeated-pairs of surnames in marriages (RP) approach is applied to the population of Tiszaszalka in north-eastern Hungary. The results indicate that: (1) lineage-like behaviour in mate choice results in population subdivision in both the Catholics and the Protestants of the village; (2) unlike in some other Tiszahat villages, the isonymous and the repeating unions in Tiszaszalka occur in different lineages so, in neither of these subpopulations are isonymous and repeating unions monopolised by a few lineages; (3) religious affilitation influences the mating structure of the population as measured by RP summary scores.

“Runaway” social evolution: Reinforcing selection for inbreeding and altruism

Kin selection theory predicts that altruistic behaviors, those that decrease the fitness of the individual performing the behavior but increase the fitness of the recipient, can increase in frequency if the individuals interacting are closely related. Several studies have shown that inbreeding therefore generally increases the effectiveness of kin selection when fitnesses are linear, additive functions of the number of altruists in the family, although with extreme forms of altruism, inbreeding can actually retard the evolution of altruism. These models assume that a constant proportion of the population mates at random and a constant proportion practices some form of inbreeding. In order to investigate the effect of inbreeding on the evolution of altruistic behavior when the mating structure is allowed to evolve, we examined a two-locus model by computer simulation of a diploid case and illustrated the important qualitative features by mathematical analysis of a haploid case. One locus determines an individual's propensity to perform altruistic social behavior and the second locus determines the probability that an individual will mate within its sibship. We assumed positive selection for altruism and no direct selection at the inbreeding locus. We observed that the altruistic allele and the inbreeding allele become positively associated, even when the initial conditions of the model assume independence between these loci. This linkage disequilibrium becomes established, because the altruistic allele increases more rapidly in the inbreeding segment of the population. This association subsequently results in indirect selection on the inbreeding locus. However, the dynamics of this model go beyond a simple "hitch-hiking" effect, because high levels of altruism lead to increased inbreeding, and high degrees of inbreeding accelerate the rate of change of the altruistic allele in the entire population. Thus, the dynamics of this model are similar to those of "runaway" sexual selection, with gene frequency change at the two loci interactively causing rapid evolutionary change.

Estimation of Genetic Parameters Using Sampled Data from Populations Undergoing Selection

In populations undergoing selection, genetic (co)variances may be altered in amounts dependent on selection intensity among parents and the mating structure. In order to estimate the genetic parameters of the unselected population, all information that led to the current population must be included in the analysis. This is often not possible due to missing information or computer limitations, and, therefore, only samples of data and pedigree information of recent generations are included in analysis, and simplified operational models are used. Biases in genetic parameters, which were estimated by multitrait derivative-free REML method, were investigated in different strategies of sampling data and pedigree. In dual purpose cattle, in which young bulls are selected for growth before being progeny tested for milk yield, heritabilities and additive genetic correlations were all unbiased when all data and all relationships were used in an animal model. Using only recent data but all relationships in an animal model also gave unbiased estimates of heritabilities. Using an animal model for growth but a sire model for milk with all data gave an unbiased estimate of heritability for milk. When only recent data were used, the heritability estimate for milk was biased downward. In single purpose dairy populations, sire models gave biased estimates of genetic parameters even when all data were included in the analysis. Treating sire effects on second crop of daughters as fixed did not overcome selection bias.

Morphology and sexual reproduction of Gonium multicoccum (Volvocales, Chlorophyta) from Nepal

Abstract Strains of Gonium (Volvocales, Chlorophyta) were isolated from a soil sample collected in Nepal. They generally produced 16- or 32-celled colonies with multipyrenoid cells, but 8-celled colonies were occasionally observed. Vegetative morphology observed by light and electron microscopy and embryogenesis indicated that this entity is referable to G. multicoccum Pocock, but differs in some respects from the original description of G. multicoccum. In addition, sexual reproduction in these Nepalese strains was unusual with regard to gametic union and zygote germination. Isogametes lacked tubular mating structures (mating papillae), which are seen in the anterior region of the gametes in other Gonium species as well as in other isogamous genera of the volvocacean and astrephomenacean algae. Plasmogamy was initiated by direct attachment between the surfaces of the two gametic protoplasts. The attaching sites were apparently randomly located on the gametic protoplasts. The germinating zygote usually gav...

Fusion-defective mutants ofChlamydomonas eugametos

Mutant strains of the unicellular green algaChlamydomonas eugametos are described which are defective in sexual fusion. All mutants are mating type plus (mt+). They are unable to fuse because none of them is capable of protruding a mating structure through the cell wall, neither during sexual agglutination nor after adding dibutyryl-cAMP or compounds that raise the intracellular calcium level, treatments that are effective in wild type cells. Evidence is presented that these mutants lack the lytic enzyme activity which is normally involved in the local hydrolysis of the cell wall to allow the protrusion of the mating structure. Furthermore, a simple light microscopic method is presented to determine the presence of activated mating structures.

FLAGELLAR APPARATUS OF THE BIFLAGELLATE ZOOSPORES OF THE ENIGMATIC MARINE GREEN ALGA BLASTOPHYSA RHIZOPUS1

ABSTRACTThe flagellar apparatus of the biflagellate zoospores from Blastophysa rhizopus Reinke has 180° rotational symmetry of the major components and counterclockwise absolute orientation. The basal bodies are connected anteriorly by a prominent striated distal fiber and posteriorly by two proximal striated bands. The C microtubules in the basal bodies terminate proximal to the transition region. Terminal caps and well‐defined proximal sheaths are absent. The four microtubular rootlets diverge at a very small angle from the basal bodies. Six to eight (usually seven) microtubules are present in the s rootlets and two microtubules in the d rootlets. Rootlet 1s is associated with the eyespot. Each d rootlet is subtended by a coarsely striated fiber. Rootlet Id also has a finely striated fiber, roughly opposite the coarsely striated fiber, associated with it. Rhizoplasts and mating structures were not observed. Ultrastructural features of B. rhizopus zoospores are essentially identical with those found in examined members of the Siphonocladales sensu lato (= Siphonocladadales/Cladophorales complex) and Dasycladales, and have relatively few features in common with motile cells of caulerpalean algae. Blastophysa rhizopus probably does not represent an intermediate between the Siphonocladadales and the Caulerpales. Its evolutionary history is different from that of other algae placed in the siphonocladalean family Chaetosiphonaceae. Whether or not Blastophysa is representative of the ancestor to the Siphonodadales and Dasycladales is unclear.

On the robustness of regular systems of inbreeding

Half-sib, first cousin, half nth cousin, and nth cousin mating systems are robust in that small deviations from the mating structure will not significantly alter the levels of genetic identity or effect qualitative distinctions between the models. Substitution of nearest kin in matings may either increase or decrease the level of homozygosity depending on the mating structure; the effect of a single error in the mating structure is not an accurate indicator of the equilibrium resulting from recurrent errors. Models of mixed half nth cousin or nth cousin mating show that the relative frequency of the lowest order inbred mating essentially determines the level of homozygosity. Any positive relative frequency of more distant matings will reduce the probability of identity by descent under half-sib or first cousin mating to less than 1.

Isolation and characterization of Chlamydomonas temperature-sensitive mutants affecting gametic differentiation under nitrogen-starved conditions

Two conditional mutants of Chlamydomonas reinhardtii, dif-1 and dif-2, affecting gametic differentiation under conditions of nitrogen (N)-starvation, have been isolated. These mutant cell remain "vegetative" at the restrictive temperature (35 degrees C) in -N medium, as defined by assays of cell body-agglutinin and cell wall lytic enzyme activities in the soluble fractions of cell homogenates. Moreover, the mutants fail to form mating structures at the restrictive temperature, but do so at the permissive temperature (25 degrees C). Temperature-shift experiments show that mutant cells which have differentiated into gametes at 25 degrees C dedifferentiate into "vegetative" cells under N-starvation conditions after transfer to 35 degrees C, but differentiate again into gametes at 25 degrees C. Genetic analyses indicate that the dif-1 and dif-2 genes are recessive and unlinked to each other or to the mating-type locus; the dif-1 phenotype cosegregates with a conditional flagellaless phenotype expressed in both +N and -N medium at the restrictive temperature.

Increase in calcium triggers mating structure activation in Chlamydomonas eugametos

For mating Chlamydomonas eugametos gametes to fuse with their partners, they must first lyse part of the anterior cell wall and protrude their mating structures. These responses can be artificially induced by compounds that raise the Ca i level, viz. InsP 3, A23187, TFP and ethanol. We conclude that calcium should be considered with cAMP to be involved in signal transduction during C. eugametos mating.

Population structure of the Jirels: Patterns of mate choice

The influence of mating practices on genetic structure has been an area of great interest for anthropologists. In this paper, the techniques of potential mates analysis are employed to explore the mating patterns observed among the Jirels, a tribal population of eastern Nepal. Genealogical, anthropometric, dermatoglyphic, and demographic data for members of seven Jirel villages are used. Potential mate pools for a sample of 268 females are enumerated by village. Age structure and the Jirel restriction against clan endogamy are found to severely limit the number of males who are potential mates for a given female. The mating structure of the population is illuminated by statistical analysis of the characteristics of 160 actual mate pairs and all corresponding potential mate pairs. Using this approach several general mate choice practices were verified: 1) biological kin tend to be avoided as mates, 2) members of the same clan are excluded as potential mates, 3) mate exchange between clans is nonrandom, 4) individuals similar in age tend to be selected as mates, and 5) mates are drawn from the natal village more often than random expectation. A multivariate phenotypic distance measure between individuals did not reveal any evidence for assortative mating for either anthropometric or dermatoglyphic characters.

Prediction of rates of inbreeding in selected populations

A method is presented for the prediction of rate of inbreeding for populations with discrete generations. The matrix of Wright's numerator relationships is partitioned into 'contribution' matrices which describe the contribution of the Mendelian sampling of genes of ancestors in a given generation to the relationship between individuals in later generations. These contributions stabilize with time and the value to which they stabilize is shown to be related to the asymptotic rate of inbreeding and therefore also the effective population size, Ne approximately 2N/(mu 2r + sigma 2r), where N is the number of individuals per generation and mu r and sigma 2r are the mean and variance of long-term relationships or long-term contributions. These stabilized values are then predicted using a recursive equation via the concept of selective advantage for populations with hierarchical mating structures undergoing mass selection. Account is taken of the change in genetic parameters as a consequence of selection and also the increasing 'competitiveness' of contemporaries as selection proceeds. Examples are given and predicted rates of inbreeding are compared to those calculated in simulations. For populations of 20 males and 20, 40, 100 or 200 females the rate of inbreeding was found to increase by as much as 75% over the rate of inbreeding in an unselected population depending on mating ratio, selection intensity and heritability of the selected trait. The prediction presented here estimated the rate of inbreeding usually within 5% of that calculated from simulation.

Mating Structure Differences Demonstrated by Freeze‐Fracture Analysis of Fusion‐Defective Chlamydomonas Gametes

ABSTRACTWhile the mating structure of unmated mating type minus (mt‐) gametes of Chlamydomonas reinhardtii has few intramembrane particles (IMPs), activation results in movement of IMPs to its center. Analysis of freeze‐fractured replicas of wild type (wt) mt‐ and 3 mt‐ fusion‐defective mutants, gam‐1, gam‐10 and gam‐11, before and after activation with wt+ flagella, provides a basis for suggesting that some of the IMPs in mt‐ mating structures, particularly a subset of particles that partitions to the E face, may be fusion‐controlling molecules. Unmated gametes of gam‐10 show a full range of images, from particle‐free to fully activated, with both the P and E face of the mating structure revealing approximately twice as many IMPs as those observed on wt. Unactivated gametes of gam‐1 and gam‐11 appear identical to wt‐. After activation, the mating structures of all of these gametes appear to have approximately the same number of IMPs. If the sizes of particles for these mutants are compared to wild type at the restrictive temperature, all 3 mutants have significantly smaller IMPs on the E face; before mating, in the plasma membrane and after mating, in the mating structure. At 34° C, the gam‐1‐II mating structure appears to be missing most of the particles from 15.5 to 16.5 nm in diameter, while all gametes with the ability to fuse have an equivalent percentage of their mating structure particles in this size range. The possibility that an IMP in this size range represents a protein that may be responsible for gamete fusion is discussed.

Cellular asymmetry in Chlamydomonas reinhardtii.

Although largely bilaterally symmetric, the two sides of the unicellular alga Chlamydomonas reinhardtii can be distinguished by the location of the single eyespot. When viewed from the anterior end, the eyespot is always closer to one flagellum than the other, and located at an angle of approximately 45 degrees clockwise of the flagellar plane. This location correlates with the position of one of four acetylated microtubule bundles connected to the flagellar apparatus. Each basal body is attached to two of these microtubule rootlets. The rootlet that positions the eyespot is always attached to the same basal body, which is the daughter of the parental/daughter basal body pair. At mitosis, the replicated basal body pairs segregate in a precise orientation that maintains the asymmetry of the cell and results in mitotic poles that have an invariant handedness. The fusion of gametic cells during mating is also asymmetric. As a result of asymmetric, but different, locations of the plus and minus mating structures, mating preferentially results in quadriflagellate dikaryons with parallel flagellar pairs and both eyespots on the same side of the cell. This asymmetric fusion, as well as all the other asymmetries described, may be necessary for the proper phototactic behavior of these cells. The invariant handedness of the spindle pole, eyespot position, and mating structure position appears to be based on the inherent asymmetry of the basal body pair, providing an example of how an intracellular pattern can be determined and maintained.

Wheat germ agglutinin induces mating reactions in Chlamydomonas eugametos by cross-linking agglutinin-associated glycoproteins in the flagellar membrane.

Species-specific binding between the flagellar surfaces of mating types plus and minus (mt+ and mt-) gametes of Chlamydomonas eugametos is mediated by mating type-specific agglutinins. Their interaction triggers several mating responses that are necessary for cell fusion, such as flagellar twitching, flagellar tip activation, redistribution of agglutinin molecules to the flagellar tip (tipping), and mating structure activation. Earlier, we reported that a monoclonal antibody (mAb 66.3) can induce mating reactions by cross-linking the agglutinins (Homan, W. L., A. Musgrave, H. de Nobel, R. Wagter, A. H. J. Kolk, D. de Wit, and H. van den Ende. 1988. J. Cell Biol. 107:177-189). Here we report that the lectin wheat germ agglutinin (WGA), which does not bind to the agglutinins, can also invoke all these mating reactions. We show, by immunofluorescence studies using anti-WGA and an agglutinin-specific monoclonal antibody (mAb 66.3), that WGA induces the redistribution of agglutinin to the flagellar tips of mt- gametes. Vice versa, when agglutinin tipping is induced by mAb 66.3, the WGA-binding glycoproteins are also tipped. Under the same conditions, the major flagellar glycoproteins are not redistributed, indicating that membrane transport is limited to a few components. We conclude that each agglutinin is associated with a WGA-binding glycoprotein. When cells lacking agglutinin or cells possessing inactive agglutinins are treated with WGA, mating responses are again elicited. The data suggest that clustering of agglutinin-containing complexes results in the production of intracellular signals, such as cAMP, and the coupling of the complex to a force generating system. In nature, the complexes are clustered via the agglutinins, but artificially they can be clustered by lectins or antibodies directed against other proteins in the complex.

Ecogenetic models, competition, and heteropatry

We develop a system of equations to analyse the existence of genetic polymorphisms under disruptive selection in heterogeneous environments. These equations have both a genetic and a population density regulation component. In the absence of the genetic component, the equations reduce to a discrete time description of competition between interacting clonal lines or species. We use these equations to demonstrate that different populations, competing along a resource spectrum, are able to dynamically coexist, as asymptotically periodic or chaotic solutions to our system of equations, despite the fact that a coexistence equilibrium—stable or unstable—does not exist. We then extend these results to environments in which several niches are explicitly defined. Our analysis of the ecological component of our model establishes that the answer to questions of coexistence among groups of individuals cannot rely on analyses of the existence of equilibria and their stability properties. In the most general model presented here, we allow for an assortative mating structure that is induced by the spatial heterogeneity of the environment. The level of assortative mating is controlled by a parameter so that at one extreme mating is panmictic, while at the other extreme individuals mate within their natal niches before dispersing to oviposit in other niches. We refer to this spatial mating structure as heteropatry. We investigate, through numerical studies, the properties of a heteropatric model containing both ecological and genetic components. First we address the question of the existence of protected genetic polymorphisms (i.e., the different allelles at a particular locus all increase in frequency when rare) under a wide range of model parameter values in a diallelic one-locus version of our model, assuming panmixis and partial dominance selection of varying direction. We make the point that establishing the instability of monomorphic population equilibria is insufficient to guarantee the existence of a protected polymorphism, since the instability may be in the population size component rather than the genetic frequency component of the monomorphic equilibrium solution. The results indicate that density dependence serves to decrease the likelihood that a protected polymorphism exists, while the degree of selection of natal habitat for oviposition purposes serves to increase this likelihood. The situation is complicated, though, since conditions which promote the existence of protected polymorphisms may actually reduce the possibility that a stable polymorphism exists. Further, the way we introduce density dependence (either by scaling the population interaction coefficients or by altering the shape of the response function) differentially affects the results. Finally, our results suggest that if individuals prefer to oviposit in their best niche (where they are most fit), rather than their natal niche (where they mature), then allele fixation very probably occurs.

Cyclic AMP enhances the sexual agglutinability of Chlamydomonas flagella.

Sexual adhesion between Chlamydomonas reinhardtii gametes elicits a rise in intracellular cAMP levels, and exogenous elevation of intracellular cAMP levels in gametes of a single mating type induces such mating responses as cell wall loss, flagellar tip activation, and mating structure activation (Pasquale, S. M., and U. W. Goodenough. 1987. J. Cell Biol. 105:2279-2292). Here evidence is presented that sexual adhesion mobilizes agglutinin to the flagellar surface, and that this mobilization can be induced by exogenous presentation of cAMP to gametes of a single mating type. It is proposed that Chlamydomonas adhesion entails a positive feedback system--initial contacts stimulate the presentation of additional agglutinin--and that this feedback is mediated by adhesion-induced cAMP generation.

Consanguinity avoidance and mate choice in Sottunga, Finland

AbstractPotential mates analysis is used to determine some of the social and demographic characteristics that influence mate choice in a small island population. Potential mate pools are defined for males in this population; characteristics such as population size and composition with respect to consanguinity are specified. Determinants of mate choice are examined in light of mate availability and potential mate pool characteristics for endogamous maters, exogamous maters, nonmaters, and males of various occupations. Random kinship is assessed from potential mate pools and compared to kinship between actual mates.The island community approximated a random mating population from 1700 to 1900 with some evidence for consanguinity avoidance intensifying in the period 1900–1950. Despite the island's small population size, kinship coefficients between random mates and actual mates are not high because of relatively high immigration rates. Having considered the contributions of various factors that influence mate choice, the significance of the island mating structure for genetic variation and the distributions of certain genetic disorders is discussed.