Levels of genetic polymorphism: marker loci versus quantitative traits

Species are the units used to measure ecological diversity and alleles are the units of genetic diversity. Genetic variation within and among species has been documented most extensively using allozyme electrophoresis. This reveals wide differences in genetic variability within, and genetic distances among, species, demonstrating that species are not equivalent units of diversity. The extent to which the pattern observed for allozymes can be used to infer patterns of genetic variation in quantitative traits depends on the forces generating and maintaining variability. Allozyme variation is probably not strictly neutral but, nevertheless, heterozygosity is expected to be influenced by population size and genetic distance will be affected by time since divergence. The same is true for quantitative traits influenced by many genes and under weak stabilizing selection. However, the limited data available suggest that allozyme variability is a poor predictor of genetic variation in quantitative traits within populations. It is a better predictor of general phenotypic divergence and of postzygotic isolation between populations or species, but is only weakly correlated with prezygotic isolation. Studies of grasshopper and planthopper mating signal variation and assortative mating illustrate how these characters evolve independently of general genetic and morphological variation. The role of such traits in prezygotic isolation, and hence speciation, means that they will contribute significantly to the diversity of levels of genetic variation within and among species

The analysis of quantitative variation in natural populations with isofemale strains

Isofemale strains are having an increasing role in the analysis of variability of ecological and behavioural traits in natural populations. This paper therefore considers the association between heritability and phenotypic variation within and between isofemale strains. Heritability from an isofemale strain analysis approximates narrow heritability over a wide range of dominance values, particularly when genes contributing to variation in a trait are at intermediate frequencies. Meaningful heritability estimates require that isofemale strains are maintained at a population size greater than 50 and tested within 5 generations after establishment. Values of heritabilities for morphological traits in Drosophila melanogaster were similar to those estimated from a conventional sib analysis. Published data on isofemale strains can therefore be put into a theoretical framework. The contribution of isofemale strain analyses to the debate about the number of loci affection variation in quantitative traits is briefly discussed

Phenotypic and genetic variability of morphometrical traits in natural populations of Drosophila melanogaster and D simulans. II. Within-population variability

International audienc

Phenotypic plasticity, global change, and the speed of adaptive evolution

International audienc

Genetic variability of host-parasite relationship traits: utilization of isofemale lines in a Drosophila simulans parasitic wasp

International audienc