fitness variation
Charlesworth B 2015 Causes of natural variation in fitness: evidence from studies of Drosophila populations. PNAS 112:1662-1669.
- there is too much genetic variability in fitness in many populations of D. melanogaster to be explained by the mutation selection balance hypothesis
- the first of these conclusions casts doubt on the frequently used method of estimating the mean of hi from the regression of the viability of chromosomal heterozygotes on the mean viability of homozygotes for the two parental chromosomes
- this assumes mutation selection balance
- the genetic variance in viability for the small fourth chromosome of D. melanogaster appears to be approximately one-half of that for the second chromosome
- this finding strongly suggests the maintenance of variability by balancing selection
- this conclusion should not be taken to mean that balancing selection is ubiquitous across the genome
- population genomics results provide little evidence for balancing selection, suggesting only a scattering of loci across the genome with alleles that have been maintained at intermediate frequencies by selection for periods of time that are much larger than the mean neutral coalescence time
- such loci contribute disproportionately to the genetic variance
- the vast majority of individual variants affecting fitness were kept at low frequencies by purifying selection
