Talk:Fitness (biology)

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Fitness (biology) covers fitness as genetics measures it: viability and fertility, absolute and relative fitness, selection coefficients, fitness in populations with overlapping generations, fitness that varies in time and space, mean fitness and adaptive landscapes, how fitness is measured, and the fitness components measured in cannabis. How selection changes allele frequencies over time, and how it weighs against drift and migration, belongs to Natural selection. The change in the mean of a selected trait belongs to Response to selection, the loss of fitness in the offspring of relatives to Inbreeding depression, the superiority of hybrids to Heterosis, heterozygote advantage at one locus to Overdominance, fitness at home and away to Local adaptation, and the trace a favoured allele leaves in DNA to Selective sweep.

Data verification

Record source conflicts, figures that differ between studies and sources not used here. Keep narrative content on the article.

Discussion

Sources

• Felsenstein (2019), Theoretical evolutionary genetics, chapter II: absolute fitness as viability times fertility, relative fitness and population density, selection coefficients, the continuous-time model, the product rule for fertilities, and mean fitness with Fisher's theorem.
• Orr (2009), Nature Reviews Genetics: fitness components, individual fitness and genotype fitness, absolute and relative fitness, Malthusian fitness, fitness that varies in time and space, the fundamental and secondary theorems, fitness landscapes and the ways fitness is measured.
• Younginger and colleagues (2017), Applications in Plant Sciences: how 170 studies estimated plant fitness, and whether biomass can stand in for it.
• Ågren and colleagues (2013), Proceedings of the National Academy of Sciences: fitness measured as fruits per seedling planted in Arabidopsis thaliana in Italy and Sweden.
• Wizenberg, Dang and Campbell (2022), PLOS ONE: non-abortion rate and germination of pollen in the hemp cultivar CFX-2.
• Wizenberg, Muir-Guarnaccia and Campbell (2023), Plants: flowering, pollen output and pollen germination in male and cosexual plants of CFX-2.
• Punja and Holmes (2020), Frontiers in Plant Science: hermaphroditic flowers, seed set and seed germination in drug-type strains grown indoors.

Where the sources disagree

• The standard genotype. Felsenstein takes any genotype as the standard and writes relative fitnesses either as 1 + s and 1 or as 1 and 1 − s. Orr divides by the fitness of the fittest genotype, which gives the second form only. The two values of s differ slightly: 0.01 in favour of one allele equals about 0.0099 against the other.
• The standing of Fisher's theorem. Felsenstein describes the theorem as an approximation in continuous time, unclear about which measure of fitness increases, and less fundamental than its name. Orr treats it as a special case of the secondary theorem of Robertson and Price, and notes a mathematical literature that finds an interpretation under which it holds strictly.
• "Viability". In population genetics viability is the probability that an individual survives to adulthood. Wizenberg and colleagues use the word for the share of pollen grains that germinate in a medium.
• Silver and pollen germination. Wizenberg, Muir-Guarnaccia and Campbell found much lower germination in pollen from plants treated with colloidal silver. They note that Flajšman and colleagues (2021), who also used colloidal silver, found no fall in germination, and suggest that the earlier study found none because it did not compare the treated plants with male plants.
• How long pollen keeps an intact nucleus. Wizenberg, Dang and Campbell found most grains still non-aborted after 12 weeks at room temperature and 96 weeks in a freezer. They note that this differs from earlier work on the species by Choudhary and colleagues, and suggest differences in method or genotype.

How far the evidence goes

• No study cited here measures the lifetime fitness of cannabis plants, the number of offspring a plant leaves in a population. Each measures one component: pollen output, the state of pollen grains, pollen germination in a medium, seed number or seed germination.
• The two pollen studies used one hemp cultivar, CFX-2, under fluorescent lamps. The 2022 study took pollen from five early-flowering male plants. The 2023 study compared male plants with seven drought-induced and twelve silver-treated cosexual plants, and its authors give the small number of drought-induced plants as a limit on their statistics.
• Fresh pollen in the 2022 study germinated at no more than 42.4 per cent. The authors suggest that the medium could be improved, and that germination in a medium serves only as a relative indicator of performance.
• The seed counts of Punja and Holmes come from three inflorescences, and the seeds were germinated in potting medium. Their figure of 5 to 10 per cent of plants with hermaphroditic flowers comes from visual inspection of about 1,000 plants of three strains.
• The review of Younginger and colleagues drew its 170 studies at random from one literature database; most concerned annual or perennial herbs, and two had an agricultural focus.
• The figures in the article's table on population density are an illustration in Felsenstein's text, not measurements.

Terms

• Absolute fitness (Darwinian fitness): the expected number of offspring of an individual of a genotype, counted from birth.
• Relative fitness: absolute fitness divided by that of a standard genotype.
• Selection coefficient: the difference in relative fitness between two genotypes, written s.
• Fitness component: one part of fitness, such as survival, mating success or fecundity.
• Malthusian parameter: the rate of increase of a genotype, its birth rate less its death rate, used as fitness where generations overlap.
• Hard and soft selection: selection in which a region's contribution of adults follows the mean fitness of its residents (hard) or is fixed whatever their fitness (soft).
• Cosexual: bearing both female and male flowers; here, genetically female cannabis plants that formed male flowers.
• Non-abortion rate: the share of pollen grains with an intact nucleus, shown by a stain.