Image analysis of Moroccan carob seeds (Ceratonia siliqua L.) revealed substantial intraspecific variations depending on climate and geographic origin

Abstract

Background The carob tree (Ceratonia siliqua L.) is one of the most iconic tree species of the Mediterranean region, with valuable economic, ecological and cultural value. Carob has been exploited around the Mediterranean region since antiquity and has been regarded as an important component of natural habitats and traditional agroecosystems. Several studies have focused on its morphological, biochemical, and genetic diversity. However, less is known about the intraspecific variation of seed traits. In this regard, and as an overall objective, we intend to evaluate the amplitude and the expression of intraspecific variations of carob seed traits at different ecological scales ranging from individual trees to different geographical landscapes. In addition, we investigated how the climate along the study area affects the extent of carob seed variability. Using image analysis techniques, we measured seven traits related to the size and the shape of 1740 seeds collected from 18 populations of spontaneous C. siliqua distributed along a latitudinal transect in Morocco under different bioclimatic conditions. Results The morphometric analysis of carob seed showed the effectiveness of adopted approach to highlight the amount and the amplitude of intraspecific variation according to geographic and climatic factors. Seed trait analysis revealed high intraspecific variability, explained by differences between and among carob populations and geographic zones. Seed area, perimeter, length, and width showed the largest variability between geographic zones. However, circularity, aspect ratio, and seed roundness showed higher variability at the tree level. Finally, our results show that seed traits vary depending on altitude and climate condition. Conclusions Revealing the amount and the structure of intraspecific traits variability of carob seed provides interesting insights to understand the mechanisms underlying trees adaptation to various environmental and ecological conditions. Therefore, intraspecific variation of seed traits should be integrated into trait-based functional ecology to assess plant species responses to environmental changes.

Effects of climate change on the distribution of the native Carob tree (Ceratonia siliqua L.) in Morocco

“…Occurrence data of Ceratonia siliqua were collected through eld surveys recording each presence points with GPS coordinates. In addition, we extracted additional occurrence data from the Global Biodiversity Information Facility-GBIF (2020) and from previous published studies dealing with carob presence in Morocco (e.g., Baumel et al 2018;Viruel et al 2019;Kassout et al 2022bKassout et al , 2023. In this study, we considered only occurrence data within natural conditions.…”

“…1). As a biodiversity hotspot (Médail and Diadema 2009), the study region presents a wide range of phytogeographic and phytoecological units including forests, matorrals and shrub-lands (Taleb and Fennane 2019), with an important variation in climatic conditions (Kassout et al 2019(Kassout et al , 2022b(Kassout et al , 2023.…”

“…In Morocco, carob communities show signi cant differentiation between the North, characterized by a thermo-Mediterranean vegetation under sub-humid and semi-arid climate, and the South region communities characterized by a quasi-steppic vegetation under semi-arid climate (Baumel et al 2018; Taleb and Fennane 2019; Kassout et al 2022bKassout et al , 2023. Despite their interest, the carob tree populations show a declining trend (Rankou et al 2017), mainly due to the multiple threats from the rapid global warming and anthropogenic pressures.…”

“…Ceratonia siliqua L. (Leguminosae) is an evergreen, thermophilous and dioecious Mediterranean fruit tree (Batlle and Tous 1997;Baumel et al 2018), with some rare hermaphrodite and monoecious cases (Batlle and Tous 1997). The carob (C. siliqua) is slow-growing and long-lived tree dotted with high resistance to drought with limited resistance to extreme cold (Batlle and Tous,1997), thus it shows important genetic diversity (Viruel et al 2019) and phenotypic variability (Kassout et al 2022b(Kassout et al , 2023. The carob tree has been exploited around the Mediterranean region since antiquity as food and forage source (Zohary 2002), thus, it represents an important component of its semi-natural and traditional agroecosystems (Ramón-Laca and Mabberley 2004; Viruel et al 2019).…”

“…However, our results show that the precipitationrelated variables have greater in uence on the geographical distribution of C. siliqua compared to temperature-related variables. The low contribution of temperature variables might be explained by the thermophilous nature of C. siliqua and its distribution under various climatic conditions form sub-humid to semi-arid climates(Baumel et al 2018;Kassout et al 2022b). Hence, the weak sensitivity of suitable habitat models to temperatures could be interpreted as an adaptation form of the carob tree.…”