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At least 253 records · Page 14Linked to original sources
PubMed2005

The Yeast Systems Biology Network: mating communities.

Systems biology requires model organisms that allow detailed studies to be performed rapidly, accurately and reproducibly. Such model systems are important driving forces for elucidating the principle properties of biomolecules, for developing general concepts for the quantitative description of living cells, and for generating the computational tools for systems analyses. The yeast Saccharomyces cerevisiae serves as an excellent model system. To coordinate efforts and to bring the yeast research and systems biology communities together, the Yeast Systems Biology Network has recently been started.

Computer Simulation↗
PubMed2003

Sex-biased movement in the guppy (Poecilia reticulata).

The movement strategies of birds and mammals are often closely linked to their mating system, but few studies have examined the relationship between mating systems and movement in fishes. We examined the movement patterns of the guppy ( Poecilia reticulata) in the Arima river of Trinidad and predicted that sexual asymmetry in reproductive investment would result in male-biased movement. Since male guppies maximize their reproductive success by mating with as many different females as possible, there should be strong selection for males to move in search of mates. In agreement with our prediction, the percentage of fish that emigrated from release pools was higher for males than females (27.3% vs. 6.9%, respectively). Sex ratio was highly variable among pools and may influence a male's decision to emigrate or continue moving. We also detected a positive relationship between body length and the probability of emigration for males and a significant bias for upstream movement by males. Among the few females that did emigrate, a positive correlation was observed between body length and distance moved. Sex-biased movement appears to be related to mating systems in fishes, but the evidence is very limited. Given the implications for ecology, evolution, and conservation, future studies should explicitly address the influence of sex and mating systems on movement patterns.

Animals↗
PubMed2006

Consequences of vegetative herbivory for maintenance of intermediate outcrossing in an annual plant.

Given the occurrence of mixed mating systems among plants, a general mechanism explaining the evolution and maintenance of this condition is needed. Although numerous theoretical models predict mixed mating to be evolutionarily stable, conditions favoring intermediate selfing are often stringent and have limited applicability. Here we investigated the role of vegetative herbivory, a ubiquitous biotic factor limiting plant reproduction, in the mating system expression of Impatiens capensis (Balsaminaceae), a species with an obligate mixed-mating system (individuals produce both selfing, cleistogamous, and facultatively outcrossing, chasmogamous flowers). Herbivory reduced proportional chasmogamous reproduction partially, but not entirely, through a reduction in plant size and the strength of this effect varied among replicates. Herbivory decreased geitonogamous selfing in chasmogamous flowers via several mechanisms including reduced chasmogamous flower display size and pollinator visitation rate and altered pollinator composition. Overall, herbivory caused a decrease in whole-plant outcrossing, indicating that the effects of herbivory on proportional chasmogamous reproduction, which favor selfing, outweigh the effects on chasmogamous outcrossing rate, which favor outcrossing. Not only do our findings unravel the mechanisms underlying herbivore-mediated changes in the mating system, but they also point to the role of natural enemies in contributing to the maintenance of a mixed mating system.

Animals↗
PubMed2000

Intratetrad mating, heterozygosity, and the maintenance of deleterious alleles in Microbotryum violaceum (=Ustilago violacea).

The mating system of Microbotryum violaceum was investigated in populations that are polymorphic for mating-type bias, where individuals produce viable haploids of only one of the two required mating types. The cause of mating-type bias was identified as deleterious recessive alleles linked to mating type. Maintenance of the deleterious alleles was promoted by early conjugation among products of single meioses, such that the duration of the free-living haploid stage is minimized. This development was also observed in nonbiased isolates. As a consequence, the mating system tends toward mating within the tetrad, which might be expected to reduce heterozygosity. However, complete centromere linkage of mating type ensures conjugation between first division meiotic products, such that mating in M. violaceum is analogous to forms of meiotic parthenogenesis with first division restitution (i.e. automixis with central fusion). This fungus was used to test the prediction that this mating system would maintain heterozygosity in regions of the genome linked to centromeres. Therefore, populations were screened for additional heterozygous lethal recessive alleles linked to centromeres, and several examples were found. Furthermore, the occurrence of intratetrad mating in M. violaceum provides an explanation for low variation among individuals within populations, inconsistent estimates of outcrossing rates, low levels of mating between tetrads of one diploid individual, and high frequencies of haplo-lethal alleles in natural populations.

Alleles↗
PubMed2006

The hyper-systemizing, assortative mating theory of autism.

The hyper-systemizing theory of autism proposes that the systemizing mechanism is set too high in people with autism. As a result, they can only cope with highly lawful systems, and cannot cope with systems of high variance or change (such as the social world of other minds). They appear 'change-resistant'. This proposal extends the extreme male brain theory of autism. Finally, evidence is reviewed for autism being the genetic result of assortative mating of two high systemizers.

Asperger Syndrome↗
PubMed2005

Evolutionary pathways in shorebird breeding systems: sexual conflict, parental care, and chick development.

Sexual selection, mating opportunities, and parental behavior are interrelated, although the specific nature of these relationships is controversial. Two major hypotheses have been suggested. The parental investment hypothesis states that the relative parental investment of the sexes drives the operation of sexual selection. Thus, the sex that invests less in offspring care competes more intensely and monopolizes access to mates. The sexual conflict hypothesis proposes that sexual selection (the competition among both males and females for mates), mating opportunities, and parental behavior are interrelated and predicts a feedback loop between mating systems and parental care. Here we test both hypotheses using a comprehensive dataset of shorebirds, a maximum-likelihood statistical technique, and a recent supertree of extant shorebirds and allies. Shorebirds are an excellent group for these analyses because they display unique variation in parental care and social mating system. First, we show that chick development constrains the evolution of both parental care and mate competition, because transitions toward more precocial offspring preceded transitions toward reduced parental care and social polygamy. Second, changes in care and mating systems respond to one another, most likely because both influenced and are influenced by mating opportunities. Taken together, our results are more consistent with the sexual conflict hypothesis than the parental investment hypothesis.

Animals↗
PubMed2000

An association between a floral trait and inbreeding depression.

Inbreeding depression is a general phenomenon that is well documented in many plants and animals. Furthermore, it is generally considered to be the driving force behind mating-system evolution. Traditionally, the focus has been on the mean level of inbreeding depression in populations. However, more recently, the variation in inbreeding depression among individuals within populations has been shown to be influential in mating-system evolution. One set of theories predicts that genetic associations will develop between a mating-system locus and loci causing inbreeding depression, whereas another suggests either that no such association will occur or that it will be difficult to detect empirically. Here, we focus on variation in inbreeding depression among individuals and present empirical evidence of a genetic association between genes causing inbreeding depression and a floral trait influencing the mating system (i.e., selfing rate). We found a positive association between inbreeding depression and herkogamy (the degree to which the stigma and anthers are separated) in an annual plant, Gilia achilleifolia. These results are consistent with theory predicting that an individual's history of inbreeding will affect its level of inbreeding depression and highlight the potential importance of genetic associations between selfing-modifier traits and viability in mating-system evolution.

California↗
PubMed1997

Mating type in filamentous fungi.

Mating type genes regulate sexual compatibility and sexual reproduction in fungi. This review focuses on recent molecular analyses of well-characterized mating systems from representative ascomycete (Neurospora crassa, Podospora anserina) and basidiomycete (Ustilago maydis, Coprinus cinereus, Schizophyllum commune) fungi. These mating systems include many conserved components, such as gene regulatory polypeptides and pheromone/receptor signal transduction cascades, as well as conserved processes, like self-nonself recognition and controlled nuclear migration. The components' structures and their genetic arrangements in the mating system vary greatly in different fungi. Although similar components and processes are also found in ascomycete yeasts (Saccharomyces cerevisiae and Schizosaccharomyces pombe), the filamentous systems exhibit properties not encountered in yeast. Mating type genes act within, and control the development of, spatially differentiated fruiting bodies. The complex mating systems of basidiomycetes, unlike ascomycete systems, involve novel one-to-many specificity in both pheromone-receptor and homeodomain protein interactions.

Ascomycota↗
PubMed1990

On the classification of regular systems of inbreeding.

Regular systems of inbreeding are defined as those with discrete, nonoverlapping generations and with the same number of individuals and mating pattern in every generation. Given the number of individuals in a generation, there are many possible regular mating systems. A notion of when two such mating systems are equivalent is introduced, and several necessary conditions are given for such an equivalence. The use of these conditions is illustrated for N = 2, 3, 4 and 5 individuals, and a complete enumeration has been found for these cases: the numbers of inequivalent mating systems are 1, 5, 57 and 858, respectively. The maximal eigenvalue of the matrix q that specifies the recursion relations satisfied by the probabilities of identity have also been found for these cases. For N = 3 and 4 (and 2 trivially), circular mating gives the slowest rate of approach to genetic uniformity of those systems that do evolve to uniformity, but for N = 5 there are two other mating systems that have a slower rate of convergence, and for N = 6 partial results show that there are many such examples.

Animals↗
PubMed2005

Genomic compatibility occurs over a wide range of parental genetic similarity in an outcrossing plant.

The theory of inbreeding and outbreeding suggests that there is a hump-shaped relationship between the genetic similarity of sexually reproducing parents and the performance of their offspring. Inbreeding depression occurs when genetic similarity is high, whereas hybrid breakdown is expected when genetic similarity is low. Between these extremes, the effect of genetic similarity on fitness is unclear. We studied the shape of this relationship by crossing 65 target genotypes of the clonal, self-incompatible Ranunculus reptans with partner genotypes spanning a broad scale of genetic similarity, ranging from crosses within populations to between-population crosses and hybridisation with a closely related species. Offspring were raised in outdoor tubs. Results revealed a quadratic relationship between parental genetic distance and offspring performance, with the clonal component of fitness more strongly hump-shaped than the sexual component. Optimal genetic similarity encompassed a broad range of within-population and between-population crosses. This pattern of genomic compatibility has important implications for the evolution of mating systems and mate choice.

Analysis of Variance↗
PubMed2001

Microsatellite determination of male reproductive success in a natural population of the territorial ornate dragon lizard, Ctenophorus ornatus.

It is now evident that the genetic mating system can be very different to the observed mating system. However, it is less well known what makes particular individuals more (or less) successful than expected from the observed system. In this study the observed territorial structure of a field population of the agamid lizard, Ctenophorus ornatus, was compared with the mating system as evidenced by microsatellite parentage assignment. This study also investigated whether any male traits predicted reproductive success. Sixty-five per cent of clutches were sired at least partially by a male other than the main territory-holding male and 35% of clutches were sired by a male with no overlap of the female's territory. Multiple paternity was moderately frequent at 25% of clutches. Male chest patch size predicted territory size and the number of females in the territory, but did not predict reproductive success. Instead, male head depth and body size were independently related to the number of offspring sired. As male head depth also predicted the number of females in a territory, these males are likely to be gaining increased reproductive success as a consequence of the higher number of females in their territories. Larger body size males, however, did not have a greater number of females in their territory and instead had more extra-territorial copulations. Whether these extra-territorial copulations are due to female choice or success in male competition is unknown.

Animals↗
PubMed2005

Genetic quality and sexual selection: an integrated framework for good genes and compatible genes.

Why are females so choosy when it comes to mating? This question has puzzled and marveled evolutionary and behavioral ecologists for decades. In mating systems in which males provide direct benefits to the female or her offspring, such as food or shelter, the answer seems straightforward--females should prefer to mate with males that are able to provide more resources. The answer is less clear in other mating systems in which males provide no resources (other than sperm) to females. Theoretical models that account for the evolution of mate choice in such nonresource-based mating systems require that females obtain a genetic benefit through increased offspring fitness from their choice. Empirical studies of nonresource-based mating systems that are characterized by strong female choice for males with elaborate sexual traits (like the large tail of peacocks) suggest that additive genetic benefits can explain only a small percentage of the variation in fitness. Other research on genetic benefits has examined nonadditive effects as another source of genetic variation in fitness and a potential benefit to female mate choice. In this paper, we review the sexual selection literature on genetic quality to address five objectives. First, we attempt to provide an integrated framework for discussing genetic quality. We propose that the term 'good gene' be used exclusively to refer to additive genetic variation in fitness, 'compatible gene' be used to refer to nonadditive genetic variation in fitness, and 'genetic quality' be defined as the sum of the two effects. Second, we review empirical approaches used to calculate the effect size of genetic quality and discuss these approaches in the context of measuring benefits from good genes, compatible genes and both types of genes. Third, we discuss biological mechanisms for acquiring and promoting offspring genetic quality and categorize these into three stages during breeding: (i) precopulatory (mate choice); (ii) postcopulatory, prefertilization (sperm utilization); and (iii) postcopulatory, postfertilization (differential investment). Fourth, we present a verbal model of the effect of good genes sexual selection and compatible genes sexual selection on population genetic variation in fitness, and discuss the potential trade-offs that might exist between mate choice for good genes and mate choice for compatible genes. Fifth, we discuss some future directions for research on genetic quality and sexual selection.

Animals↗
PubMed1999

To store or mature spermatozoa? The primary role of the epididymis.

The function of the epididymis is considered in the context that it is necessary to transport spermatozoa for internal fertilization, but is also an adaptation involved in the competition between males to achieve paternity. Post-testicular sperm maturation and storage occur in lower vertebrates, such as the chondrichthyes, in which sperm storage is essential due to the slow rate of spermatogenesis. These roles persist in higher vertebrates, including mammals. However, they are less important in certain birds, in which the rate of sperm production by the testes is sufficient to supply enough spermatozoa to cope with the demands of a competitive mating system. There is no evidence for mammals, other than humans, that spermatozoa can achieve the capacity to fertilize an ovum without passing through some of the proximal epididymis. Storage of spermatozoa in the epididymis is probably not essential for a male to achieve conception in a protected mating system, but is very important in a competitive mating system. There is some variation between species in the magnitude of the epididymal storage region. This is related to the descent of the epididymides (and testes) into a scrotal sac in some species and/or the demands of the mating system in other species. The claims that humans are not dependent on post-testicular sperm maturation and storage need to be qualified, as they are based on studies of abnormal tracts and tests of fertility which are not rigorous. Nevertheless, the claims are of considerable clinical significance and may indicate that humans are less dependent on post-testicular sperm maturation and storage than other mammals. This may be an adaptation of the testes and epididymides to the scrotal conditions of modern man or a response to changing environmental factors.

Animals↗
PubMed2003

Outcrossing rate and inbreeding depression in the herbaceous autotetraploid, Campanula americana.

Polyploidy in angiosperms is frequently associated with an increase in self-compatibility. Self-fertilization can enhance polyploid establishment, and theory predicts reduced inbreeding depression in polyploids relative to diploids. Therefore, we may expect mating systems that promote self-fertilization or mixed-mating in polyploid species. However, few studies have measured polyploid mating systems and inbreeding depression. We report the outcrossing rate and inbreeding depression for Campanula americana, a self-compatible protandrous herb. Allozyme genotypes suggest that C. americana is an autotetraploid with tetrasomic inheritance. We found that the multilocus outcrossing rate, t(m)=0.938, did not differ from unity. This result was unexpected since previous work demonstrated that pollinators frequently move from male- to female-phase flowers on the same plant, that is, geitonogamy. Self and outcross pollinations were conducted for three populations. Offspring were germinated in controlled conditions and grown to maturity in pots in nature. Inbreeding depression was not significant for most seed and germination characters. However, all later life traits except flowering date differed between inbred and outcrossed individuals resulting in a 26% reduction in cumulative fitness for inbred plants. Limited early- and moderate later-life inbreeding depression suggest that it is buffered by the higher levels of heterozygosity found in an autotetraploid. C. americana appears to have a flexible mating system where within flower protandry and/or cryptic self-incompatibility result in a high outcrossing rate when pollinators are abundant, but self-compatibility and limited inbreeding depression maintain reproductive success when mates are limited.

Campanulaceae↗
PubMed1994

Sexual selection and genital anatomy of male primates.

Correlations between mating system and various aspects of genital anatomy suggest a strong influence of sexual selection on genital morphology. We test the generality of the influence by examining whether primate taxa in which there might be enhanced sexual selection (those with multi-male mating systems) possess, as expected, relatively more spinous penises than do taxa with other mating systems. As most prosimians, but few anthropoids (monkeys and apes), possess penile spines, and because the predominant mating systems of the two taxa differ, taxonomic constraints are taken into account. Sexual selection apparently does not act on penile spines in the same manner as on other aspects of genital anatomy: spinosity is not greatest in multi-male taxa of either prosimians or anthropoids. In some taxa, spines might stimulate reproductive readiness and synchrony in situations in which the sexes live apart and do not have other means of communicating reproductive state (dispersed social systems and 'stolen' extra-pair copulations), but problems exist with the hypothesis, as they do with the idea that spines are involved with scent marking. It seems that either penile spines have several functions, or penile spinosity in primates, and other orders, remains to be explained.

Animals↗
PubMed2003

Delayed selfing and resource reallocations in relation to mate availability in the freshwater snail Physa acuta.

We study the influence of mate availability on the mating behavior of the self-fertile, preferentially outcrossing freshwater snail Physa acuta. Previous optimization theory indicated that mating system interacts with life-history traits to influence the age at first reproduction, providing three testable predictions. First, isolated individuals should reproduce later than individuals with available mates in the expectancy of finding a partner and avoiding the cost of inbreeding. Second, resource reallocation to future fecundity is needed for such reproductive delays to evolve. Third, the reproductive delay can be optimized with respect to life-history traits (e.g., survival, growth) and the mating system (inbreeding depression). Our results largely validate these predictions. First, reproduction is significantly delayed in isolated individuals ("selfers") as compared with individuals frequently exposed to mates ("outcrossers"). Second, delayed reproduction is associated with reallocation to future growth, survival, and fecundity, although fecundity is also affected by the mating system (selfing vs. outcrossing). Third, the reproductive delay found (approximately 2 wk) is consistent with quantitative predictions from optimization models. The delay is largely heritable, which might be partly explained by among-family differences in the amount of inbreeding depression (mating system) but not growth or survival.

Animals↗
PubMed2005

The evolution of self-fertilization and inbreeding depression under pollen discounting and pollen limitation.

We model the evolution of plant mating systems under the joint effects of pollen discounting and pollen limitation, using a dynamic model of inbreeding depression, allowing for partial purging of recessive lethal mutations by selfing. Stable mixed mating systems occur for a wide range of parameter values with pollen discounting alone. However, when typical levels of pollen limitation are combined with pollen discounting, stable selfing rates are always high but less than 1 (0.9<s<1 in most cases); in this situation, complete selfing does not evolve because pollen discounting becomes very large at high selfing rates, so that the automatic advantage of selfing changes to a disadvantage. These results suggest that mixed mating systems with high selfing rates can be maintained by selection, whereas mixed mating systems with low to moderate selfing rates are more likely attributable to unavoidable geitonogamous selfing.

Biological Evolution↗
PubMed1997

Quantitative trait loci differentiating the outbreeding Mimulus guttatus from the inbreeding M. platycalyx.

Theoretical predictions about the evolution of selfing depend on the genetic architecture of loci controlling selfing (monogenic vs. polygenic determination, large vs. small effect of alleles, dominance vs. recessiveness), and studies of such architecture are lacking. We inferred the genetic basis of mating system differences between the outbreeding Mimulus guttatus and the inbreeding M. platycalyx by quantitative trait locus (QTL) mapping using random amplified polymorphic DNA and isozyme markers. One to three QTL were detected for each of five mating system characters, and each QTL explained 7.6-28.6% of the phenotypic variance. Taken together, QTL accounted for up to 38% of the variation in mating system characters, and a large proportion of variation was unaccounted for. Inferred QTL often affected more than one trait, contributing to the genetic correlation between those traits. These results are consistent with the hypothesis that quantitative variation in plant mating system characters is primarily controlled by loci with small effect.

Chromosome Mapping↗