Convergent evolution and parallelism in plant domestication revealed by an expanding archaeological record

Abstract

Recent increases in archaeobotanical evidence offer insights into the processes of plant domestication and agricultural origins, which evolved in parallel in several world regions. Many different crop species underwent convergent evolution and acquired domestication syndrome traits. For a growing number of seed crop species, these traits can be quantified by proxy from archaeological evidence, providing measures of the rates of change during domestication. Among domestication traits, nonshattering cereal ears evolved more quickly in general than seed size. Nevertheless, most domestication traits show similarly slow rates of phenotypic change over several centuries to millennia, and these rates were similar across different regions of origin. Crops reproduced vegetatively, including tubers and many fruit trees, are less easily documented in terms of morphological domestication, but multiple lines of evidence outline some patterns in the development of vegecultural systems across the New World and Old World tropics. Pathways to plant domestication can also be compared in terms of the cultural and economic factors occurring at the start of the process. Whereas agricultural societies have tended to converge on higher population densities and sedentism, in some instances cultivation began among sedentary hunter-gatherers whereas more often it was initiated by mobile societies of hunter-gatherers or herder-gatherers.D omestication offers an ideal laboratory for understanding evolution because it is a recent phenomenon in terms of geological time scales and because the selection pressures that affect harvestability by humans are often known (1). Domestication is a product of human behaviors that regulate or increase food supply, but may also inadvertently lock humans into an increased reliance on managed taxa (2). Archaeological research provides a fossil record of past organisms undergoing domestication, often accompanied by cultural artifacts associated with habitat management or niche construction (3, 4). The effects of agriculture in terms of intensifying land productivity to support larger populations has been fundamental to the development of civilizations and the ongoing impact on and management of ecosystems (5, 6). Domestications have occurred separately on different continents and in different cultural traditions, and thus represent a set of parallel experiments from which to infer recurrent processes (Fig. 1). In some cases this represents parallelism of phylogenetically related organisms that have been subjected to similar selection pressures and developed identical or similar adaptations in different places. In others, we can consider domestication as convergent evolution, in as much as similar adaptations have evolved across crops in different plant families. These parallel adaptations have been defined as the "domestication syndrome" (7, 8). A distinction can be made between true convergence, in which analogous states have been reached from very different and unrelated starting points, versus parallelism...

Pathways of Rice Diversification across Asia

“…3). In the Lower Yangtze region these indicate a chronologically protracted evolutionary process over 3000-4000 years Fuller et al 2014), reaching the domesticated non-shattering state by ca. 3800 BC.…”

Ecology in an anthropogenic biosphere

“…2012, Fuller et al 2014. Through early forms of agriculture, horticultural societies reached much greater scales of population and cultural accumulation than those of hunter-gatherers, and this led to further population growth, the spread of agricultural populations into new areas and the displacement of hunter-gatherers, and to more and more complex forms of farming and other technologies, including manuring, terracing, and the development of smelting to produce nonferrous metal ornaments, weapons, and later other tools including farm implements (Bellwood 2004, Bocquet-Appel 2011, Gignoux et al 2011.…”

Long and attenuated: comparative trends in the domestication of tree fruits

“…However, this can perhaps be understood as partly due a key difference in selection mechanism. For the most part it appears likely that grain size increase in annual seed crops evolved gradually through a process of unconscious selection (Fuller 2007;Fuller et al 2014). In addition the level of selection was kept somewhat low by the problem that the cost of selection is additive across all traits under selection and very strong selection increases the risk of population extinction (Allaby et al 2016).…”

“…Recent insights from archaeobotany include recognition that the domestication process was protracted and that change to non-shattering (loss of wild-type seed dispersal) and grain size increase were both gradual over 2,000-4,000 years (Tanno and Willcox 2012;Fuller et al 2012Fuller et al , 2014, but that domestication processes and rates of evolution show many parallels across crops and between geographical centres of origin . Archaeobotany confirms parallel evolution towards a recurrent domestication syndrome in seed crops (Smith 2006;Fuller and Allaby 2009), including increasing grain size, which makes the recording of measurements on archaeobotanical specimens meaningful to studies of crop domestication.…”

“…The approach taken in the present study derives from recent assessments of domestication in annual grain crops by plotting time series data of size, identifying episodes of largely directional change and estimating rates of phenotypic evolution in terms of haldanes (Purugganan and Fuller 2011;Fuller et al 2012Fuller et al , 2014. The haldane rate [hereafter h] represents the shift in the normal statistical distribution of a trait, taking into account not just the mean but the range of the standard deviation (Gingerich 2009).…”