Talk:Natural selection
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Natural selection covers selection by survival and fertility: how differences in fitness change the genetic make-up of a population, how that change weighs against drift and migration, the selection that keeps variation, and what has been found of it in cannabis (adaptation to latitude and climate, the seed traits of plants growing outside cultivation and feral hemp in the United States). Selection by growers and breeders, and the response a breeder can expect, belong to Mass selection. The movement of alleles between populations belongs to Gene flow, the history of the crop's domestication to Domestication and the response of one genotype to different environments to Phenotypic plasticity.
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Discussion
Sources
- Felsenstein, Theoretical Evolutionary Genetics (December 2019 edition), chapters II, IV, VI, VII and IX: fitness as viability times fertility; the time selection takes to change an allele's frequency; the slow change of rare recessive alleles; overdominance and protected polymorphism; the balance of migration and selection in one population; the 2s chance that a new favourable allele survives; the 4Nes rule for when selection outweighs drift; the effective size of a population with separate sexes; natural selection working against artificial selection.
- Darwin (1859), On the Origin of Species, p. 61: the definition of natural selection and its relation to selection by people.
- Beavis and colleagues (2023), in Suza and Lamkey (eds), Quantitative Genetics for Plant Breeding, "Components of Variance": the source of phenotypic variation decides whether selection brings a heritable response.
- Bellon and colleagues (2017), Evolutionary Applications 10: 965–977: the rationale for keeping crops in cultivation under changing natural and farmer-driven selection, and its fragmentary support.
- Zhang and colleagues (2018), Frontiers in Plant Science 9: 1876: three chloroplast lineages of Chinese cannabis by latitude; mean day length as the climatic factor most closely related to them; phenology and size of 43 accessions grown together at Kunming; seed traits of wild forms.
- Chen and colleagues (2022), BMC Plant Biology 22: 371: seed weight, shattering, dormancy and flowering of wild and cultivated Chinese accessions; flowering under 18-hour days and the expression of FT-like; traits selected during domestication.
- McPartland and Small (2020), PhytoKeys 144: 81–112: divergence of Central and South Asian cannabis under different climates; the reduced fitness of Central Asian plants in monsoon conditions; wild-type seed traits; reversion of escaped hemp in Canada.
- Woods and colleagues (2023), G3 13: jkac209: whole-genome comparison of feral plants from Colorado, Kansas and Nebraska with European hemp and drug-type cannabis; loci under balancing and positive selection.
Where the sources disagree
- Wild or feral. Chen and colleagues call nine of their Chinese accessions wild, on their seed traits and the places they grew, and add that these plants derive from early cannabis ancestors whether or not they are truly wild. McPartland and Small consider that cannabis may have no surviving populations unaltered by domestication, because escaped plants revert to the wild type within a few decades.
- Association and adaptation. Zhang and colleagues measured how traits and chloroplast lineages vary with latitude and climate; Chen and colleagues measured flowering and gene expression under set day lengths. Both read the patterns as adaptation, and neither measured the fitness of plants moved from one latitude to another. The two studies come from the same institute, the Industrial Crops Research Institute of the Yunnan Academy of Agricultural Sciences, with authors in common.
- Gene functions in feral hemp. Woods and colleagues inferred what their candidate genes do from their closest matches in Arabidopsis. They name functional tests in cannabis as the next step. The functions given are those found in Arabidopsis.
Terms
- Fitness is the expected number of offspring of an individual from birth, its chance of surviving to adulthood multiplied by the offspring of a survivor. Relative fitness compares genotypes; the selection coefficient s is the difference.
- Wild type names the set of seed traits of plants growing without cultivation: small fruits that shed when ripe, a persistent mottled perianth and dormant seed.
- Feral plants descend from crops that escaped cultivation and now reproduce on their own.
- Generation. Cannabis is an annual, so a generation is a year; the 50 generations of reversion in Canada are 50 years.
- Balancing selection is used for selection that keeps more than one allele in a population, of which overdominance (an advantage to heterozygotes) is one form.
Images reserved in the article
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File:Cannabis-chloroplast-lineages-latitude-China.jpg(Adaptation to latitude and climate): a map of China with a pie chart at each of the 43 sampling sites, coloured by the three chloroplast haplogroups, high-latitude in the north, low-latitude in the south and middle-latitude between. Figure 1A of Zhang and colleagues (2018), published under the CC BY 4.0 licence, shows it.