Adaptive meiotic drive in selfing populations with heterozygote advantage

The egalitarian allotment of gametes to each allele at a locus (Mendel’s law of segregation) is a near-universal phenomenon characterizing inheritance in sexual populations. As exceptions to Mendel’s law are known to occur, one can investigate why non-Mendelian segregation is not more common using modifier theory. Earlier work assuming sex-independent modifier effects in a random mating population with heterozygote advantage concluded that equal segregation is stable over long-term evolution. Subsequent investigation, however, demonstrated that the stability of the Mendelian scheme disappears when sex-specific modifier effects are allowed. Here I derive invasion conditions favoring the repeal of Mendelian law in mixed and obligate selfing populations. Oppositely-directed segregation distortion in the production of male and female gametes is selected for in the presence of overdominant fitness. The conditions are less restrictive than under panmixia in that strong selection can occur even without differential viability of reciprocal heterozygotes (i.e. in the absence of parent-of-origin effects at the overdominant fitness locus). Generalized equilibria are derived for full selfing.

Detecting differential viability selection between environments by analysis of compositional differentiation at different levels of genetic integration

Viability selection can be detected directly in an environment when the genotypes of the individuals at one ontogenetic stage (e.g. seeds) and the genotypes of the survivors at a later stage are both known, but genotypes at the earlier stage often cannot be determined. In this case, differential viability selection between environments can be detected as differences in the distributions of genetic types among survivors growing in different environments, provided that the survivors stem from random samples of seeds from the same base population (e.g. seed lot). Since commonFST-outlier methods for detecting selected gene loci use only allele frequencies, selection that affects the higher hierarchical levels of genetic integration (single- or multi-locus genotypes) without changing allele frequencies is not noticed. A new method for detecting differential viability selection at any level of genetic integration enables discovery of elementary mechanisms of selection that older methods miss. It is based on two measures of compositional differentiation between environments.δSDmeasures qualita-tive differences between distributions of genetic types at any given integration level without regarding differences in their constituent alleles, whileΔSDmeasures quantitative differences between the same distributions by additionally considering the genic differences. The difference between these measures expresses the degree to which the patterns of gene association in the genotypes differ between environments. The P-values of all measures are estimated by permutation analysis under the assumption that survivors were randomly assigned to environments. Significance indicates the occurrence of differential viability selection at the loci. As a case study, a field study of viability in juvenile beech (Fagus sylvaticaL.) for twelve enzyme loci is reanalyzed. It turns out that the significant differential selection for genotypes detected at three loci can be attributed to three combinations of selective effects: on alleles only (SKDH-A), mostly alleles but also association patterns (LAP-A); interaction of effects on alleles and association patterns that are non-significant when viewed separately (AAT-B).

Germination of cotton cultivar seeds under water stress induced by polyethyleneglycol-6000

The physiological quality of cotton cultivar seeds (Gossypium hirsutum var. latifolium L.) was evaluated in laboratory by the simulation of water potentials with polyethyleneglycol-6000 (0.0; -0.2; -0.4; -0.6; -0.8 and -1.0 MPa), at 25ºC using germitest paper as substrate. A completely randomized design in a 4 × 6 factorial scheme with four replications of 50 seeds each was used. The studied variables were: germination percentage, first count of germination, germination velocity index, accelerated aging in water, electrical conductivity, humidity, vigor classification, radicle length and radicle/shoot length ratio. The effect of water stress on seed viability and on plantlet vigor was severe at potentials below -0.4 MPa. The 'CNPA 187 8H' cultivar was the least sensitive to the tested osmotic potentials, both in terms of germination and of vigor. The 'BRS-201' cultivar was mostly affected by the viability and vigor tests under water deficit conditions. Differential viability and vigor between cultivars were observed under the water stress levels.