Article

Contrasting Patterns in Crop Domestication and Domestication Rates: Recent Archaeobotanical Insights from the Old World

Institute of Archaeology, University College London, 31-34 Gordon Square, London WC1H 0PY, UK.
Annals of Botany (Impact Factor: 3.3). 12/2007; 100(5):903-24. DOI: 10.1093/aob/mcm048
Source: PubMed

ABSTRACT Archaeobotany, the study of plant remains from sites of ancient human activity, provides data for studying the initial evolution of domesticated plants. An important background to this is defining the domestication syndrome, those traits by which domesticated plants differ from wild relatives. These traits include features that have been selected under the conditions of cultivation. From archaeological remains the easiest traits to study are seed size and in cereal crops the loss of natural seed dispersal.
The rate at which these features evolved and the ordering in which they evolved can now be documented for a few crops of Asia and Africa. This paper explores this in einkorn wheat (Triticum monococcum) and barley (Hordeum vulgare) from the Near East, rice (Oryza sativa) from China, mung (Vigna radiata) and urd (Vigna mungo) beans from India, and pearl millet (Pennisetum glaucum) from west Africa. Brief reference is made to similar data on lentils (Lens culinaris), peas (Pisum sativum), soybean (Glycine max) and adzuki bean (Vigna angularis). Available quantitative data from archaeological finds are compiled to explore changes with domestication. The disjunction in cereals between seed size increase and dispersal is explored, and rates at which these features evolved are estimated from archaeobotanical data. Contrasts between crops, especially between cereals and pulses, are examined.
These data suggest that in domesticated grasses, changes in grain size and shape evolved prior to non-shattering ears or panicles. Initial grain size increases may have evolved during the first centuries of cultivation, within perhaps 500-1000 years. Non-shattering infructescences were much slower, becoming fixed about 1000-2000 years later. This suggests a need to reconsider the role of sickle harvesting in domestication. Pulses, by contrast, do not show evidence for seed size increase in relation to the earliest cultivation, and seed size increase may be delayed by 2000-4000 years. This implies that conditions that were sufficient to select for larger seed size in Poaceae were not sufficient in Fabaceae. It is proposed that animal-drawn ploughs (or ards) provided the selection pressure for larger seeds in legumes. This implies different thresholds of selective pressure, for example in relation to differing seed ontogenetics and underlying genetic architecture in these families. Pearl millet (Pennisetum glaucum) may show some similarities to the pulses in terms of a lag-time before truly larger-grained forms evolved.

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    • "On the other hand, herbivores feeding on larger fruit can be more likely to escape parasitism, such as the apple maggot fly, Rhagoletis pomonella (Walsh), which are parasitized less on the larger apple fruit than on fruit of their native hawthorn trees (Feder, 1995). Grain and legume plants have been repeatedly selected for larger seeds (Evans, 1993; Fuller, 2007; Schmutz et al., 2014). It has been proposed that seed size evolved as a trade-off between the probability of survival after germination and the number of seeds. "
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    • "During their domestication, plants acquire a set of morphological and physiological traits that differentiate them from their wild progenitors, a process called the domestication syndrome (Harlan 1992; Doebley et al. 2006). This process includes, among other aspects, loss of dispersal seed, loss of seed dormancy, development of photoperiod insensitivity, and an increase in fruit size (Hammer 1984; Pickersgill 2007; Fuller 2007). Fundamental goals to elucidate the origin and domestication of plants are (1) identifying the wild ancestors of domesticated plants, (2) documenting the geographic location of wild relatives that gave rise to the domesticated, and (3) determining the number of times and the regions of domestication for that crop (Zeder et al. 2006). "
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    • "Archeobotanical evidence (Willcox, 2004; Fuller, 2007), as well as experimental data from the current study (Fig. 1) and other studies (Abbo et al., 2014b) indicate that, in general, domesticated wheat has larger grains than its wild progenitor. The grain of domesticated wheat is usually wider and shorter, traits which are associated with heavier grain weight, while wild wheat has longer and narrower grains (Figs 1, 2). "
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