Domestication Genetic changes in plant (or animal) populations as a response to selective pressures of cultivation and harvest by humans. [from Domus Latin – home]

Domestication: animals Wolves  Dogs

Domestication: animals Aurochs  Cattle

Maize / CornTeosinte

Crop Domestication human influence  change in genetics of plant population  leads to “Adaptive syndrome of domestication” may be deliberate or not (“unconscious” or “incidental”) due to change in selective environment and control over reproduction (e.g., harvesting grains with sickle, sowing saved seeds)

Domesticated Pearl Millet Pennisetum glaucum Images on right by Laura Lewis Archaeology: >4000-year old millet in South Asia, & now 4500–year old domesticated pearl millet recently reported from Mali Images on right by Laura Lewis

Domesticated Pearl Millet Pennisetum glaucum better seed recovery and yield, but less able to survive in natural conditions compared to wild progenitor. more apical dominance (less branching) compact growth habit flowering at same time (rather than spread over long period) larger spikes non-shattering spikelets loss of bristles & glumes around grains larger seeds non-dormant seeds germinate at same time

Domesticated Pearl Millet Pennisetum glaucum better seed recovery and yield, but less able to survive in natural conditions compared to wild progenitor. more apical dominance (less branching) compact growth habit flowering at same time (rather than spread over long period) larger spikes non-shattering spikelets loss of bristles & glumes around grains larger seeds non-dormant seeds germinate at same time wheat spikelet wild and domesticated pearl millet

Barley Hordeum vulgare

domesticated barley Barley brittle and non-brittle spikes wild Barley Barley Hordeum vulgare Domestication syndrome Loss of natural dissemination classical example: non-shattering rachis of grains

wild emmer and Durum wheat, Triticum turgidum classical example: non-shattering rachis of grains Domestication syndrome Loss of natural dissemination source: openi.nlm.nih.gov/detailedresult.php?img= _jexboterr206f01_3c&req=4

Domestication syndrome Loss of natural dissemination Grains: –non-shattering rachis. selection through harvesting and re-sowing – “unconscious selection,” automatic. dependent on humans for seed dispersal 1-2 genes Legumes: –one gene for opening of pod sutures (others control extent) Other examples: –Brassica (mustard seed, canola) –poppies (opium vs. breadseed) burma-all.com/ / Canola = rapeseed bred for low erucic acid and glucosinolate

Domestication syndrome Loss of seed germination inhibition (seed dormancy) loss of dormancy, so that all seeds germinate when sown What is the advantage of extended dormancy in wild plants? Why is this not an advantage in cultivated plants? –seed coat thickness –chemical inhibitors of germination, including anthocyanins –light trigger

B. Smith, the Emergence of Agriculture, © Scientific American Library Domesticated crops divert more biomass toward human use e.g., larger seeds, fruits, inflorescences, roots, tubers, bulbs, or whatever parts we use.

Domestication syndrome Reallocate biomass for human use More efficient metabolism and photosynthesis: increase leaf surface, decrease root system, increase leaf longevity Grains: more fertile florets, larger inflorescence OR number of ears  different ways to get more seed Larger seeds (automatic vs. deliberate selection) Oil plants: increased oil content or more seed Fiber plants: long, strong fibers

Increased in domesticate seed germination determinate growth longer pods bigger (heavier) seeds earliness harvest index (seed yield/biomass) Decreased in domesticate seed dispersal seed dormancy twining number of nodes length of internode number of pods photoperiod sensitivity Common Bean Phaseolus vulgaris © Paul Gepts

Domestication syndrome Reduced defenses Reduced competitiveness in natural environment: Loss of bitter or toxic compounds (but not always!) –cucurbitacins in squashes (vs. wild gourds) –hydrocyanic acid (HCN) released in cassava, yams, lima beans –mustard oils Loss of mechanical protection –plant hairs and spines –coarse thick seed coat in wild legume seeds –reduce number awns, glume thickness, husks of grains

Domestication syndrome Reproductive changes (in different directions: may reduce or increase sexual reproduction in different crops) reproduction shift from sexual reproduction to vegetative propagation (genetically identical clones) –rooted cuttings and offshoots [olive, grape, fig, date, etc.] –grafting later [apple, pear, plum, cherry] –parthenocarpic fruits (seedless) –loss of sexual reproduction in some yams BUT ALSO: breakdown of self-incompatibility increases fertility grains: restore fertility to all spikelets (all female) – example maize

Domestication syndrome Photoperiod response (in different directions) Photoperiod response (“daylength sensitivity”) – the length of the night cues plants to flower, make tubers, go dormant, etc., at a certain time of year –different directions in different cases: decrease in daylength sensitivity as moved into temperate regions increase in daylength sensitivity to promote uniformity in grain maturation

Domestication syndrome Photoperiod response (in different directions) How does this relate to movement of crops around the world? –think Jared Diamond’s hypothesis (Guns, Germs and Steel)

Domestication syndrome One species may be selected for several traits: Beta vulgaris L. beetroot, Swiss chard, sugar beet – – –

J.R. Harlan 1976 Sci. American Divergent selection for different purposes Brassica oleracea cabbage, broccoli, cauliflower, kale, romanesco, collards, kohrabi, brussels sprouts

–Beta vulgaris - beetroot, Swiss chard, sugar beet –Brassica oleracea - cabbage, cauliflower, kale, kohlrabi, collards, broccoli –Linum usitatissimum - flax, linseed oil: selection for oil vs. fiber –Cannabis sativa - fiber, oil, THC Domestication syndrome One species may be selected for several traits:

Loss of seed dissemination mechanism Loss of seed germination inhibition (reduced seed dormancy) –(the 2 above apply only if crop is propagated by seed) Reallocate biomass for human use Reduced defenses (usually, but not always) Reproductive changes (either way) Photoperiod response (either down or up) Different varieties (cultivars) of one species may be selected for several different traits Domestication syndrome summary