Local adaptation
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Local adaptation is the state in which the resident population of a place has higher fitness there than populations of the same species from elsewhere, because natural selection has favoured different genotypes in different places.[1][2] It is a genotype-by-environment interaction of a particular kind: the character is fitness and the pattern follows the origin of the plants.[3] The direct test grows plants of different origins at one another's home sites and counts their survival and reproduction.[4] Comparisons of genomes point to loci that may be involved and do not measure fitness.[4]
Cannabis has been studied through trials of many origins at one site, comparisons of genomes with the climate where seed was collected and reports of seed failure when cultivars move north.[5][6][7] These studies show inherited differences that follow latitude and climate. Their authors read them as adaptation. A comparison of resident and incoming plants at each of several home sites lies outside their designs, so a cline, the altitude of a landrace or the words "adapted to" leave local adaptation untested.
Local plants against foreign plants
A transplant experiment compares plants of two or more origins at each origin's own site. When the local plants do better than the foreign ones at both sites of a pair, their reaction norms for fitness cross. This is local adaptation in the strict sense set out by Tadeusz Kawecki and Dieter Ebert. When one population does better at both sites the norms do not cross. That result points to selection for a generalist and at least a partial lack of local adaptation.[1] A higher score at home is not enough on its own: a vigorous population may score higher everywhere.
Phenotypic plasticity is the response of one genotype to different environments, so a plant that changes when moved shows plasticity whatever its origin. A genotype-by-environment interaction is any difference among genotypes in that response, in any character.[8] A change of rank among cultivars for fibre yield is an interaction with no reference to home sites. Selection is the process and local adaptation one possible outcome, reached when selection that differs from place to place outweighs gene flow between the places.[9]
| Study | What is measured | What it can show | What it leaves open |
|---|---|---|---|
| Reciprocal transplant | Fitness of plants of each origin at each origin's site | Whether local plants do better at home, at every site tested[1] | Maternal effects of the fields the seed came from can run parallel to local adaptation[2] |
| Common garden at one site | Characters of many origins in one environment | That differences between populations are inherited and not plastic[4] | Whether any population does best at home |
| Scan for differentiated loci | Allele frequencies across populations | Candidate loci[4] | Fitness; demographic history can produce the same signal[4] |
| Association of genotype with environment | Allele frequencies against climate or soil at the collection site | Candidate loci and candidate agents of selection[4] | Fitness; neutral clines can coincide with an environmental gradient[4] |
| Cline, or altitude of origin, alone | Where a population grows | A hypothesis to test[2] | Inheritance, fitness and the loci involved |
Transplants and what they have found
Reciprocal transplants have been run since the work of Jens Clausen and colleagues, published in 1940.[4] Jon Ågren and Douglas Schemske moved Arabidopsis thaliana between a population in Sweden, near the northern edge of its native range, and one in Italy near the southern edge, over five years. Fitness was the number of fruits produced per seed or seedling planted. In eight of 10 comparisons of site and year the local population was significantly fitter, by 3.1 to 22.2 times at the southern site and 1.7 to 3.6 times at the northern one.[10]
Roosa Leimu and Markus Fischer brought together 35 studies of 32 plant species in 2008. Local plants did better than foreign ones at 71.0 per cent of sites. In the stricter comparison of a pair of origins at both their sites, local plants did better at both in 45.3 per cent of cases and one origin did better at both in 51.4 per cent. The pattern was much commoner between large populations, of more than 1,000 flowering plants, than between small ones: 52.3 against 9.3 per cent. It did not vary with distance between sites, from 3 m to 3,500 km.[1] A survey by Joe Hereford the following year put the frequency of local adaptation at 0.71 and the advantage of the native population at 45 per cent of relative fitness. A small negative correlation between fitness at home and fitness away indicated weak trade-offs.[11]
Maize landraces and altitude
Kristin Mercer, Ángel Martínez-Vásquez and Hugo Perales tested a crop in these terms. Some authors had assumed strong local adaptation in maize landraces; Eagles and Lothrop wrote in 1994 of "locally adapted landraces for every valley".[2] In 2005 Mercer's team sowed 21 landrace populations from Chiapas, seven each from lowland (690–880 m), midland (1,530–1,670 m) and highland (2,170–2,340 m) origins, in common gardens at 1,500 m and 2,150 m. Fitness combined the chance that a plant produced good seed with the mass of that seed.
Highland landraces had the highest fitness in the highland garden and were at a heavy disadvantage in the midland one, at 33 per cent of the fitness of the local plants. Lowland landraces moved up to the midland garden reached 141 per cent of it, so the midland plants held no advantage at home over plants from below. The adaptation was asymmetrical. In the highlands, midland and lowland plants reached 80 to 82 per cent of the local plants. Populations from the same altitude also varied widely: two midland populations had no fitness in the midland garden while others matched the lowland plants. Seed came directly from farmers, so the authors could not exclude maternal effects. Data from a third garden, at 700 m, were not used.[2]
Alleles behind the pattern
An allele can contribute to local adaptation in two ways. Under antagonistic pleiotropy the alleles at a locus reverse their rank in fitness between environments, which is a genetic trade-off at that locus. Under conditional neutrality an allele is favoured in one environment and neutral in the other. Jill Anderson and colleagues grew 177 recombinant inbred lines of Boechera stricta in both parental environments over two seasons. They found 2.8 per cent of the genome showing antagonistic pleiotropy and 8 per cent conditional neutrality. At one large locus for flowering time, nFT, plants homozygous for the native allele were more likely to flower in both environments. The authors warned of a bias against finding trade-offs, because the advantage must reach significance in at least two environments.[12]
Ågren and colleagues mapped fitness itself in 398 lines from the Swedish and Italian populations, across three years at the parental sites and more than 40,000 plants. Fifteen fitness quantitative trait loci emerged, of small to modest effect. A third showed evidence of trade-offs. In Sweden the local allele was often the less fit one, which the authors suggested reflects limited adaptive genetic variation there, with weaker selection letting drift fix maladaptive alleles.[13]
Genome scans
Two families of method search genomes for such loci without a transplant. One looks for loci whose differentiation among populations stands out from the rest of the genome. The other looks for allele frequencies that correlate with an environmental variable at the collection sites.[4] Their relative power depends on sampling and on the history of the populations.[14]
Population history can imitate both signals. Demographic events alone can make loci vary widely in differentiation with no selection at any of them. Expansion from a refuge can leave clines in neutral alleles that happen to run along a gradient such as temperature. Nearby populations are alike through isolation by distance while nearby environments are alike too. Tests that treat each population as independent then give many false positives. Correlated environmental variables can also credit the wrong agent. Traits with many genes of small effect may escape these scans altogether.[4]
Sean Hoban and colleagues treat each candidate locus as a hypothesis. Testing it means comparing fitness or a trait between individuals with and without the allele in a suitable environment.[4]
Measured in cannabis
Many origins in one garden
Qingying Zhang and colleagues grew 43 Chinese accessions together at Kunming in 2016. Flowering, height, stem and branching all varied with latitude of origin. High-latitude plants stayed short, branched little and finished early.[5] Because the plants shared one field, those differences point to inheritance.[4] Genetic distance in chloroplast DNA between the accessions rose with geographic distance, an isolation-by-distance pattern, beside the link between chloroplast lineage and mean day length that the authors read as adaptation to latitude.[5] Xuan Chen and colleagues grew 21 accessions at the same site. In a separate trial of four accessions under 18-hour days, expression of the flowering gene FT-like rose with latitude of origin. They concluded that cultivated cannabis has adapted to different day lengths through this gene's regulation.[15]
Mehdi Babaei and Davoud Torkamaneh grew 145 accessions from 25 Iranian landrace populations in one greenhouse. Three genetic groups emerged. One grew mainly in warmer climatic zones, one mainly in colder zones and one in all five zones. The groups differed in flowering and form. The seed came from farmers and local markets. The authors wrote that the plateau's topography and climates have "fostered local adaptation", citing work on the plateau itself; their trial measured traits at one site and mapped loci for them.[16]
Each of these trials took place at one site, away from most of the origins it compares. None grew each population at its own home.
Plants moved between latitudes
Of 14 commercial hemp cultivars at four European sites, only the early ones Fedora 17 and Markant produced seed at the most northerly site.[7] Zhang and colleagues cite earlier observations that southern cultivars fail to produce seed in the north.[5] Chen and colleagues add that high-latitude varieties grown further south shorten their growing period and yield much less fibre and seed.[15] Each of these is one half of a transplant and concerns cultivars, with no resident population at home to compare. Fibre yield measures the crop for the grower, while fitness counts offspring.
John McPartland and Ernest Small state that Central Asian plants moved to South Asian conditions suffer reduced fitness, through snapped branches under monsoon rain and grey mould in dense inflorescences. This forms part of their hypothesis of habitat isolation between the two populations. They give no figures for survival or seed.[17]
Genomes against climate
Patrick Woods and colleagues scanned the genomes of feral plants that have reproduced in the United States since the 1940s. They hypothesised that the plants' high share of derived alleles indicates local adaptation to new climates and organisms, with relaxed selection on domesticated traits. The study compares genomes and did not measure fitness.[18] Chen and colleagues' scans address domestication: genes for flowering time, seed size and germination that distinguish cultivated from wild plants.[15]
Anna Halpin-McCormick and colleagues applied environmental genomic selection to 149 samples from public data, 111 of them with collection coordinates. The method predicts a climate variable from genotype and reports the result as a genomic estimated adaptive value. Plants of the drug-type feral group scored high for rainfall, with a seasonal peak the authors linked to monsoon climates.[6] The score is calculated from genotype and the climate of the collection sites. The authors offer it for choosing parents. It involves no measure of fitness.
Altitude
Luca Giupponi and colleagues set clones of four plants of the hemp cultivar Kompolti at 1,200 m in Alagna Valsesia and at 130 m in the province of Vercelli in 2018. Plants at altitude had more terpenes in total and more cannabidiolic acid. The same genotypes grew at both sites, so the difference is plastic.[19]
Altitude also runs together with temperature and moisture.[2] A landrace's altitude of collection states where it grows. A test of adaptation to altitude takes the design Mercer's team used on maize: populations from several altitudes, gardens at those altitudes and a count of seed.
"Adapted" as a label
A common definition of a landrace is a cultivated, heterogeneous variety that has evolved in an ecogeographical area "and is therefore adapted" to its soils, climate and management.[20] Tables in Zhang and in Chen define landrace as a "domesticated, locally adapted, traditional variety".[5][15] In those tables the phrase sorts accessions before any trial. Mercer's team wrote of maize that some authors assumed strong local adaptation and that actual patterns were not well studied.[2]
The case for in situ conservation on farms rests on continued exposure to selection, a rationale Mauricio Bellon and colleagues judged to have fragmented support.[21] Small populations rarely showed local adaptation in Leimu and Fischer's survey. The authors doubted their ability to cope with changing environments.[1] Seed exchange and pollen move genes between fields. In maize landraces this gene flow can at times work against selection by growers and by the environment.[2]
See also
References
- ↑ 1.0 1.1 1.2 1.3 1.4 Leimu, R.; Fischer, M. (2008). "A meta-analysis of local adaptation in plants". PLOS ONE. 3 (12) e4010. doi:10.1371/journal.pone.0004010.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 Mercer, K.; Martínez-Vásquez, Á.; Perales, H.R. (2008). "Asymmetrical local adaptation of maize landraces along an altitudinal gradient". Evolutionary Applications. 1 (3): 489–500. doi:10.1111/j.1752-4571.2008.00038.x. PMC 3352380.
- ↑ Kawecki, T.J.; Ebert, D. (2004). "Conceptual issues in local adaptation". Ecology Letters. 7 (12): 1225–1241. doi:10.1111/j.1461-0248.2004.00684.x.
- ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 Hoban, S.; Kelley, J.L.; Lotterhos, K.E.; Antolin, M.F.; Bradburd, G.; et al. (2016). "Finding the genomic basis of local adaptation: pitfalls, practical solutions, and future directions". The American Naturalist. 188 (4): 379–397. doi:10.1086/688018. PMC 5457800.
- ↑ 5.0 5.1 5.2 5.3 5.4 Zhang, Q.; Chen, X.; Guo, H.; Trindade, L.M.; Salentijn, E.M.J.; Guo, R.; Guo, M.; Xu, Y.; Yang, M. (2018). "Latitudinal adaptation and genetic insights into the origins of Cannabis sativa L." Frontiers in Plant Science. 9 1876. doi:10.3389/fpls.2018.01876.
- ↑ 6.0 6.1 Halpin-McCormick, A.; Thomson, R.; Clarke, R.C.; Neyhart, J.; Kantar, M.B. (2026). "Dissecting genotype-environment relationships with functional implications for parental selection in Cannabis breeding". Journal of Heredity. 117 (1): 24–38. doi:10.1093/jhered/esaf048.
- ↑ 7.0 7.1 Tang, K.; Struik, P.C.; Yin, X.; Thouminot, C.; Bjelková, M.; et al. (2016). "Comparing hemp (Cannabis sativa L.) cultivars for dual-purpose production under contrasting environments". Industrial Crops and Products. 87: 33–44. doi:10.1016/j.indcrop.2016.04.026.
- ↑ Malosetti, M.; Ribaut, J.-M.; van Eeuwijk, F.A. (2013). "The statistical analysis of multi-environment data: modeling genotype-by-environment interaction and its genetic basis". Frontiers in Physiology. 4 44. doi:10.3389/fphys.2013.00044. PMC 3594989.
- ↑ Felsenstein, J. (December 2019). Theoretical evolutionary genetics. Seattle: Department of Genome Sciences, University of Washington. pp. 186–188.
- ↑ Ågren, J.; Schemske, D.W. (2012). "Reciprocal transplants demonstrate strong adaptive differentiation of the model organism Arabidopsis thaliana in its native range". New Phytologist. 194 (4): 1112–1122. doi:10.1111/j.1469-8137.2012.04112.x.
- ↑ Hereford, J. (2009). "A quantitative survey of local adaptation and fitness trade-offs". The American Naturalist. 173 (5): 579–588. doi:10.1086/597611.
- ↑ Anderson, J.T.; Lee, C.-R.; Rushworth, C.A.; Colautti, R.I.; Mitchell-Olds, T. (2013). "Genetic trade-offs and conditional neutrality contribute to local adaptation". Molecular Ecology. 22 (3): 699–708. doi:10.1111/j.1365-294X.2012.05522.x. PMC 3492549.
- ↑ Ågren, J.; Oakley, C.G.; McKay, J.K.; Lovell, J.T.; Schemske, D.W. (2013). "Genetic mapping of adaptation reveals fitness tradeoffs in Arabidopsis thaliana". Proceedings of the National Academy of Sciences. 110 (52): 21077–21082. doi:10.1073/pnas.1316773110. PMC 3876199.
- ↑ Lotterhos, K.E.; Whitlock, M.C. (2015). "The relative power of genome scans to detect local adaptation depends on sampling design and statistical method". Molecular Ecology. 24 (5): 1031–1046. doi:10.1111/mec.13100.
- ↑ 15.0 15.1 15.2 15.3 Chen, Xuan; Guo, Hong-Yan; Zhang, Qing-Ying; Wang, Lu; Guo, Rong; Zhan, Yi-Xun; Lv, Pin; Xu, Yan-Ping; Guo, Meng-Bi; Zhang, Yuan; Zhang, Kun; Liu, Yan-Hu; Yang, Ming (2022). "Whole-genome resequencing of wild and cultivated cannabis reveals the genetic structure and adaptive selection of important traits". BMC Plant Biology. 22 (1) 371. doi:10.1186/s12870-022-03744-0.
- ↑ Babaei, M.; Torkamaneh, D. (2026). "Genetic architecture of phenological, morphological, and phytochemical traits in Cannabis landraces". The Plant Genome. 19 (2) e70243. doi:10.1002/tpg2.70243.
- ↑ McPartland, J.M.; Small, E. (2020). "A classification of endangered high-THC cannabis (Cannabis sativa subsp. indica) domesticates and their wild relatives". PhytoKeys. 144: 81–112. doi:10.3897/phytokeys.144.46700.
- ↑ Woods, P.; Price, N.; Matthews, P.; McKay, J.K. (2023). "Genome-wide polymorphism and genic selection in feral and domesticated lineages of Cannabis sativa". G3. 13 (2) jkac209. doi:10.1093/g3journal/jkac209.
- ↑ Giupponi, L.; Leoni, V.; Pavlovic, R.; Giorgi, A. (2020). "Influence of altitude on phytochemical composition of hemp inflorescence: a metabolomic approach". Molecules. 25 (6) 1381. doi:10.3390/molecules25061381.
- ↑ Casañas, F.; Simó, J.; Casals, J.; Prohens, J. (2017). "Toward an evolved concept of landrace". Frontiers in Plant Science. 8 145. doi:10.3389/fpls.2017.00145.
- ↑ Bellon, M.R.; Dulloo, E.; Sardos, J.; Thormann, I.; Burdon, J.J. (2017). "In situ conservation: harnessing natural and human-derived evolutionary forces to ensure future crop adaptation". Evolutionary Applications. 10 (10): 965–977. doi:10.1111/eva.12521.