Seed Dispersal and Crop Domestication: Shattering, Germination and Seasonality in Evolution Under Cultivation

Abstract

The transition between wild plant forms and domesticated species can be considered an evolutionary adaptation by plants in response to a human driven ecology. Evidence from archaeobotany and genetics is providing deeper insight into this evolutionary process in terms of its scale, mechanism and parallelism between species. The evidence indicates that the timescale of this evolution was considerably longer than previously supposed, raising questions about the mode of human mediated selection pressure and increasing the importance of the role of pre‐domestication cultivation. Different selection pressures were chronologically separated into at least three stages, each important at different points of the evolutionary process affecting different traits. Early selection pressures were ultimately driven by the pre‐domestication sowing activities affecting the polygenically controlled germination and seed size traits. Later, in the second stage, release of natural selection pressures of dispersal requirements led to modification of architecture such as awns loss of awns and increase in dispersal unit size. The loss of dispersal requirement combined with positive pressure through harvesting practice led to the typically monogenically controlled non‐shattering phenotypes. At the tertiary stage new selection pressures were imposed with changing climate caused by movement of the crops into different latitudes, resulting in typically monogenically controlled aseasonal phenotypes. The genetic evidence shows in most cases that genetically similar mechanisms have been affected in different plant species implying an evolutionary convergence in response to adaptation to human ecology. These adaptations can be considered various types of heterochrony; a mechanism of major importance generally in plant evolution.

How Could the Use of Crop Wild Relatives in Breeding Increase the Adaptation of Crops to Marginal Environments?

“…Selection attributes according to the crop objective are related to classical domestication traits, such as reduced seed and fruit dispersal, changes in plant structure, plant phenology, seed dormancy, palatability, or acquisition of modified fruit size and shape in vegetable crops ( Alonso-Blanco et al, 2009 ; Sakuma et al, 2011 ; Meyer et al, 2012 ; Zohary et al, 2012 ; Abbo et al, 2014 ; Fuller and Allaby, 2018 ; Ogutcen et al, 2018 ; Smýkal et al, 2018 ; Iqbal et al, 2020 ). Much progress has been made in the most widely grown and intensively selected crops (rice, wheat, soybean, sugarcane, tomato and potato), but improvement using CWR is more recently ( Hajjar and Hodgkin, 2007 ; Shelef et al, 2017 ; Zhang et al, 2018 ; Zsögön et al, 2018 ; Fernie and Yan, 2019 ).…”

Idiosyncratic shifts in life‐history traits at species' geographic range edges

“…In miner's lettuce, significant differences in germination rate persisted even after one generation in the common garden, indicating a putative genetic basis. One plausible explanation may be that marginal populations were founded by escapees from cultivation and that seed dormancy was selected against in cultivated populations, as commonly observed in crops (Fuller and Allaby 2009). These seed traits translate into a much higher fitness for marginal miner's lettuce populations, consistent with theoretical and empirical studies on expanding species (Burton et al 2010, Colautti and Barrett 2013, Lustenhouwer et al 2018).…”

Phenotypic evolution of agricultural crops

“…Nonshattering became dominant in the agricultural stands of cereals, even though it is maladaptive in the wild. In fact, nonshattering fruits is a diagnostic trait that has been used to distinguish wild from domesticated plant remains (Fuller & Allaby, 2009). This is because domesticates, by definition, are populations which reproduction is under the control of the domesticator to a large degree (Purugganan, 2022).…”