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Title: A global perspective on the origins of agriculture : the importance of unconscious selection
Author: Kluyver, Thomas
ISNI:       0000 0004 2744 7910
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2013
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The protracted model of agricultural origins proposes that farming developed gradually in broad regions, rather than being invented and adopted rapidly in small 'core areas'. This view points to an important role for unconscious selection in the evolution of crop plants, wherein humans unintentionally modified the environment of plants in cultivation, setting up selection pressures different from those acting in the wild. This thesis examines the role of unconscious selection on seed mass and photosynthesis, especially in grass and legume crops. Domestication is known to have increased seed mass in many seed crops, while studies that have compared photosynthetic rate have mostly, but not universally, found no difference between wild and domestic forms. An important aspect of this work has been making comparisons among a range of crop species and geographic regions. This is not to presume that the same processes were acting in these different cases: it is important to study each crop and each region individually. However, it is also natural to look for larger patterns. Agriculture in widely separated parts of the world appears to have started more-or-less simultaneously, and in many cases to have used plants from the same families, especially the grasses and the legumes. I have therefore chosen to examine how far these similarities extend, and how great the differences between the regions and crop species are. Analysing seed mass data shows that crop progenitors already have large seeds in comparison to other wild species, but only the centre of agricultural origins in Western Asia has an unusual abundance of large-seeded species. A variety of vegetable crops, including vegetatively propagated species, have larger seeds than their wild progenitors, providing evidence that unconscious selection has acted on seed mass; the difference, however, is smaller than that seen in seed crops. A comparative experiment tested the hypothesis that seed burial and the need to emerge from deeper in the soil drove the evolution of larger seeds, the results of which support this mechanism in some, but not all, of the grain legume species tested. Finally, photosynthetic rate has not changed in domestication in any of a range of grass and legume crops; possible explanations for this are discussed. In summary, I find broad taxonomic and geographic patterns in the seed mass of crop progenitors, increased seed mass in both seed and vegetable crops, and no change in photosynthesis during domestication, while the effect of seed mass on emergence depth differs among species, and the availability of wild large-seeded grass and legume species differs markedly among regions.
Supervisor: Osborne, Colin P. ; Jones, Glynis ; Charles, Michael Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available