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

Dorian Q Fuller

doi:10.1007/s00334-017-0659-2

Abstract

This paper asks whether we can identify a recurrent domestication syndrome for tree crops (fruits, nuts) and track archaeologically the evolution of domestication of fruits from woody perennials. While archaeobotany has made major contributions to documenting the domestication process in cereals and other annual grains, long-lived perennials have received less comparative attention. Drawing on examples from across Eurasia, comparisons suggest a tendency for the larger domesticated fruits to contain seeds that are proportionally longer, thinner and with more pointed (acute to attenuated) apices. Therefore, although changes in flavour, such as increased sweetness, are not recoverable, seed metrics and shape provide an archaeological basis for tracking domestication episodes in fruits from woody perennials. Where available, metrical data suggest length increases, as well as size diversification over time, with examples drawn from the Jomon of Japan (Castanea crenata), Neolithic China (Prunus persica) and the later Neolithic of the Near East (Olea europaea, Phoenix dactylifera) to estimate rates of change. More limited data allow us to also compare Mesoamerica avocado (Persea americana) and western Pacific Canarium sp. nuts and Spondias sp. fruits. Data from modern Indian jujube (Ziziphus mauritiana) are also considered in relation to seed length:width trends in relation to fruit contents (flesh proportion, sugar content). Despite the long generation time in tree fruits, rates of change in their seeds are generally comparable to rates of phenotypic evolution in annual grain crops, suggesting that gradual evolution via unconscious selection played a key role in initial processes of tree domestication, and that this had begun in the later Neolithic once annual crops had been domesticated, in both west and east Asia.

Highlights

The archaeobotanical documentation of plant domestication has made significant progress in the studying of the domestication of annual grain crops, including several cereals, pulses and some of the pseudo-cereals and oilseeds (Fuller et al 2014)
Can we identify recurrent features that might be classified as a domestication syndrome for long-lived perennial fruit crops and how does this compare to the better documented domestication syndrome of annual seed crops? Goldschmidt (2013) argued that increasing productivity, reduction of juvenile period and reduced inter-annual variability in yield would all have been selected for in tree fruit domestication, this cannot be directly determined archaeologically, except for the potential yield value per fruit, i.e. fruit size
The comparative data presented in this paper highlight that morphological evolution of tree fruits can be documented through archaeobotanical evidence using simple metrics and when large time series are available

Summary

Introduction

The archaeobotanical documentation of plant domestication has made significant progress in the studying of the domestication of annual grain crops, including several cereals, pulses and some of the pseudo-cereals and oilseeds (Fuller et al 2014). Recent insights from archaeobotany include recognition that the domestication process was protracted and that change to non-shattering Dispersal) and grain size increase were both gradual over 2,000–4,000 years (Tanno and Willcox 2012; Fuller et al 2012, 2014), but that domestication processes and rates of evolution show many parallels across crops and between geographical centres of origin (Fuller et al 2014). 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 present paper aims to explore the potential of large datasets of fruit and nut measurements to identify evolutionary processes of domestication, suggesting both a

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