Insights into the historical biogeography of the date palm (Phoenix dactyliferaL.) using geometric morphometry of modern and ancient seeds

Abstract

Aim The main purpose of this work is to understand the origin, history, historical biogeography and mechanisms of date palm (Phoenix dactylifera L.) domestication.Location Seeds of uncultivated Phoenix individuals from isolated Oman populations, cultivated date palm varieties of various geographical origins and other related Phoenix species were analysed. Additionally, well‐preserved seeds from Egyptian archaeological sites (14th century bc to 8th century ad) were compared with the morphometric reference model based on the analysis of modern material.Methods Elliptic Fourier transforms (EFT), a morphometric method applied to shape outline analysis, were used to characterize seed shape and to quantify morphological diversity in P. dactylifera and related species.Results Analysis of seed outlines by EFT (1) showed that P. dactylifera can be differentiated from other Phoenix species and (2) enabled the quantification of patterns of shape differentiation in the genus Phoenix at different taxonomic, geographical and chronological levels. Date palm agrobiodiversity, partitioned in distinct morphotypes, appeared to be complex in terms of geographical structure. Allocation of archaeological seeds to different modern Phoenix forms and date palm morphotypes allowed us to reveal ancient forms consumed and/or exploited in Egypt and finally to determine spatial and temporal changes in agrobiodiversity.Main conclusions Based on the morphological diversity quantified in P. dactylifera and related species, we characterized ancestral seed shape features present in uncultivated populations. The geographical distribution pattern of seed shapes points to human dispersal routes that spread cultivation from one or more initial ‘domestication centres’. Finally, this work provides a powerful tool to identify ancient forms as demonstrated by the analysis of well‐preserved Egyptian archaeological seeds, dating from the 14th century bc to the 8th century ad. Results open new and fascinating perspectives on the investigation of the origins and chrono‐geographical fluctuation of date palm agrobiodiversity.

Identification of inter- and intra-species variation in cereal grains through geometric morphometric analysis, and its resilience under experimental charring

“…The manner in which this is achieved depends on whether there are many features present that can be landmarked, or 100 whether curves, outlines and surfaces are the shapes' main homologous features. Recently, application of geometric morphometrics to archaeobotanical material has proven helpful to aid species identification (García-Granero et al, 2016) and, beyond this, to examine variation within species (Burger et al, 2011;Newton et al, 2006;Orrù et al, 2013;Pagnoux et al, 2014;Ros et al, 2014;Terral et al, 2012Terral et al, , 2010Terral et al, , 2004Ucchesu et al, 2016). Studies 105 to date have, however, focused on fruit stones such as grape and olive, while the application of geometric morphometrics to cereal grains has been treated with caution due to the known shape distortion caused by charring of starch-rich grain compared with the relative shape stability of woody fruit stones.…”

Biodiversity, Genetic Diversity, and Genetic Resources of Date Palm

“…It is argued that conditions of a hot, dry land with wet, saline soils to which date palms are adapted are found precisely in this part of Arabia Deserta . This viewpoint is supported by paleobotanical data and archaeological, historical, and cultural information (Meyer et al 2012 ;Terral et al 2012 ).…”

“…Recent genetic data suggest that the cultivated date derives from wild populations of P. dactylifera ; however, gene fl ow from cultivated to wild date palms could complicate the identifi cation of true wild P. dactylifera populations. The geometric morphometry of modern and ancient seed differentiated Phoenix species (e.g., P. dactylifera, P. canariensis, P. reclinata, P. sylvestris, and P. theophrasti ) at different taxonomic, geographic, and chronological levels (Terral et al 2012 ).…”

First complete mitochondrial genome of Phoenix dact ylifera var. Khanezi

“…Date palm is a perennial, monocotyledon (2n ¼ 36), dioecious, cross-pollinated tree that has been widely cultivated (Barrow 1998;Terral et al 2012;Cherif et al 2013). Morphological variations, which are heavily dependent on environmental factors and data variety, do exist among cultivars.…”