Reinforcement and sex linkage

We present a general model for the effect of sex linkage on the evolution of reinforcement of mating preferences on an island. We find that the level of reinforcement can vary up to 80% depending on the mode of inheritance of the female preference and male trait. When reinforcement is driven mainly by selection in the male trait and intrinsic hybrid incompatibilities are weak, sex-linked preferences and autosomal male traits are the most conducive to reinforcement, whereas autosomal preferences and X-linked traits are the least. Surprisingly, the effect of mode of inheritance on reinforcement is poorly predicted by its effect on the genetic correlation between the male trait and female preference. Sex-linkage of genetic incompatibility loci increases reinforcement, though this is not due solely to the occurrence of Haldane's rule. We find that reinforcement can lead to complete reproductive isolation in some cases but not others and that the mode of inheritance can determine which outcome occurs.     

Food or sex; pollinator–prey conflict in carnivorous plants

Carnivorous plants potentially trap their own pollinators and it has been argued that considerable spatial separation of flowers and traps has evolved to protect pollinators. We investigated flower-trap separation of Drosera and Utricularia . Short Drosera had a greater element of floral–trap separation than tall Drosera . Such a relationship is unexpected for plants whose peduncles were evolved to protect their pollinators. Utricularia can not trap pollinators but this genus still produces exceptionally long peduncles. We propose that flower-trap separation evolved because carnivorous plants are often short and need to project their flowers well above ground level to make them more attractive to pollinators.     

Sexual selection and sex linkage

Some animal groups, such as birds, seem prone to extreme forms of sexual selection. One contributing factor may be sex linkage of genes affecting male displays and female preferences. Here we show that sex linkage can have substantial effects on the genetic correlation between these traits and consequently for Fisher's runaway and the good-genes mechanisms of sexual selection. Under some kinds of sex linkage (e.g. Z-linked preferences), a runaway is more likely than under autosomal inheritance, while under others (e.g., X-linked preferences and autosomal displays), the good-genes mechanism is particularly powerful. These theoretical results suggest empirical tests based on the comparative method.     

Pathogens and sex in plants

Summary Extant theories that attribute the evolution of sex to pathogen attack depend on the assumption that pathogens are narrowly specialized, so that high fitness on one host genotype results in poor fitness on hosts with other allele combinations. This assumption is necessary in order for frequency-dependent selection to produce sustained cycling of gametic disequilibrium across the host's disease resistance loci, which makes recombination advantageous. However, a review of numerous genetic studies on plant disease resistance failed to uncover a single example consistent with this assumption. Instead, the empirical results provide strong support for a different pattern of pathogen specificity, in which adaptation by pathogens to one resistance allele does not preclude high fitness on alternate host genotypes lacking that allele. Modification of traditional models for pathogen-mediated evolution of sex showed that for conditions close to the empirical pattern of genotypic specificity, sex is almost never favoured. For plants, these results cast doubt on current theories arguing that pathogens are the primary selective agent responsible for sexual reproduction.     

Labile sex expression in plants

The range of environmental sex determination and sex changes throughout plant taxa from bryophytes and pteridophytes to spermatophytes is reviewed. Lability in sex expression occurs in many plant taxa but only in homosporous pteridophytes is labile sex the rule. Among angiosperms, labile sex appears to be more common among dioecious and monoecious plants than among hermaphrodites. However, hermaphrodites can control allocation to male and female functions by varying the relative emphasis on pollen and ovules. A majority of plants with labile sex expression are perennials, which indicates that flexibility in sex is more important for species with long life cycles. Environmental stress, caused by less-than-optimal light, nutrition, weather or water conditions, often favours maleness. The extreme lability in the sex expression of homosporous pteridophytes is suggested to be related primarily to the mating systems.     

Mammalian sex hormones in plants

The occurrence of mammalian sex hormones and their physiological role in plants is reviewed. These hormones, such as 17beta-estradiol, androsterone, testosterone or progesterone, were present in 60-80% of the plant species investigated. Enzymes responsible for their biosynthesis and conversion were also found in plants. Treatment of the plants with sex hormones or their precursors influenced plant development: cell divisions, root and shoot growth, embryo growth, flowering, pollen tube growth and callus proliferation. The regulatory abilities of mammalian sex hormones in plants makes possible their use in practice, especially in plant in vitro culture.     

Heterozygosity of genes on the sex chromosome regulates Candida albicans virulence

In the mouse model for systemic infection, natural a/alpha strains of C. albicans are more virulent and more competitive than their spontaneous MTL-homozygous offspring, which arise primarily by loss of one chromosome 5 homologue followed by duplication of the retained homologue (uniparental disomy). Deletion of either the a or alpha copy of the MTL locus of natural a/alpha strains results in a small decrease in virulence, and a small decrease in competitiveness. Loss of the heterozygosity of non-MTL genes along chromosome 5, however, results in larger decreases in virulence and competitiveness. Natural MTL-homozygous strains are on average less virulent than natural MTL-heterozygous strains and arise by multiple mitotic cross-overs along chromosome 5 outside of the MTL region. These results are consistent with the hypothesis that a competitive advantage of natural a/alpha strains over MTL-homozygous offspring maintains the mating system of C. albicans.     

The zygotic algebra for sex linkage

Summary The zygotic algebra for sex linkage with multiple alleles contains an idealB which is a baric algebra. This ideal possesses at least one idempotent with non negative coefficients. For the mutation case and the case of simple Mendelian inheritance in the female sex convergence theorems are proved for the sequence of plenary powers of a normalized element. For these two cases it is shown that the idealB is a special train algebra.     

植物性别决定的研究进展

通过回顾近年来以多种植物为材料进行的性染色体观察,性别决定基因及调控方式的研究,对植物性别决定的机制进行了初步探讨,从而可以看出不同植物具有不同的性别决定机制：对于有性染色体的植物而言,目前已经从Y染色体上分离和鉴定了许多与雄性发育紧密相关的基因;部分性别决定基因和调控序列已利用构建减法文库,诱导突变体等方法从一些植物中获得。此外,还有研究表明,DNA脱甲基化,以及某些激素(如赤霉素、乙烯、Ace)都对植物的性别决定有重要作用。     

Predation-associated differences in sex linkage of wild guppy coloration

Evolutionary theory predicts that the sex linkage of sexually selected traits can influence the direction and rate of evolutionary change, and also itself be subject to selection. Theory abounds on how sex-specific selection, mate choice, or other phenomena should favor different types of sex-linked inheritance, yet evidence in nature remains limited. Here, we use hormone assays in Trinidadian guppies to explore the extent to which linkage of male coloration differs among populations adapted to varying predation regimes. Results show there is consistently higher degree of X- and autosomal linkage in body coloration among populations adapted to low-predation environments. More strikingly, analyses of an introduced population of guppies from a high- to a low-predation environment suggest that this difference can change in 50 years or less.