A strong east–west Mediterranean divergence supports a new phylogeographic history of the carob tree (Ceratonia siliqua, Leguminosae) and multiple domestications from native populations

Abstract

Aim Phylogeography of fruit trees is challenging due to recurrent exchanges between domesticated and wild populations. Here we tested the eastern refugium hypothesis (ERH) for the carob tree, Ceratonia siliqua, which supports its natural and domestication origins in the eastern Mediterranean and a feral origin in the west. Location Mediterranean basin. Taxon Ceratonia siliqua L., Leguminosae. Methods A phylogenetic reconstruction based on two nuclear and one plastid sequences was performed to estimate the divergence time between the carob tree and its sister species, Ceratonia oreothauma. Variation from four plastid regions and 17 nuclear microsatellite loci were used to decipher genetic structure in the carob tree and to test coalescent‐based models by an Approximate Bayesian computation (ABC) approach. We assessed our hypotheses by examining palaeobotanical records and hindcasting the past distribution of the carob tree at Mid‐Holocene, Last Glacial Maximum (LGM) and Last Interglacial (LIG) using species distribution modelling. Results The split between C. oreothauma and C. siliqua was estimated at 6.4 Ma, and a first divergence within C. siliqua at 1.3 Ma. After a continuous presence since the Oligocene, Ceratonia was rarely found in the fossil record during the Pleistocene but present in the western and the eastern Mediterranean. Plastid and nuclear markers, characterized by low allelic richness, revealed a strong west‐east genetic structuring. ABC analyses rejected the ERH. Main conclusions Our study supports a severe population decline during LIG. The strong west–east divergence and the occurrence of four lineages within C. siliqua provided support for a new hypothesis of multiple domestications of the carob tree from native populations throughout the Mediterranean basin.

Phylogeographic sampling guided by species distribution modeling reveals the Quaternary history of the Mediterranean–Canarian Cistus monspeliensis (Cistaceae)

“…2C, 2D). This result is congruent with some other Mediterranean plants such as Olea europaea (Besnard et al, 2013), Ceratonia siliqua (Viruel et al, 2019), and Lavatera maritima (Villa‐Machío et al, 2018). The oldest long‐term persistence areas (since LIG) in the Mediterranean Basin were mainly estimated along the Atlantic shores of western Iberia (Portugal) and north‐western Africa (Morocco) (Fig.…”

Phylogeography at the crossroad: Pleistocene range expansion throughout the Mediterranean and back‐colonization from the Canary Islands in the legume Bituminaria bituminosa

“…Traits refer to the following character states: SH = shrub versus PH = tree/woody climber; FD = deciduous, semi‐deciduous or facultative deciduous versus EV = evergreen sclerophylls; LL = large‐leaved (typically >5 cm long or >5 cm 2 in size) versus SL = small leaved. (a) Bello (2015), (b) Viruel et al (2020), (c) Coello et al (2020), (d) Fernández‐Mazuecos and Vargas (2010), (e) Désamoré et al (2011), (f) Rodríguez‐Sánchez et al (2009), (g) Kondraskov et al (2015), (h) Migliore et al (2012), (i) Besnard et al (2013), (j) García‐Verdugo et al (unpublished data), (k) Mateu‐Andrés et al (2015); (l) García‐Verdugo et al (2015, 2020), (m) Vendramin et al (2008), (n) Saladin et al (2017), (o) Vitelli et al (2017), (p) Mateu‐Andrés et al (2013), (q) Chen et al (2014) and (r) Grassi et al (2006).…”

“…Hence, sclerophyllous taxa, albeit conspicuous in most plant communities, are thought to have spread across the MB under climatic conditions markedly different to those found today (i.e., colonization before the onset of the Mediterranean climate; Herrera, 1992). Because they represent iconic landscape components, this group of species has attracted a good deal of phylogeographical research (Petit et al, 2005; Rodríguez‐Sánchez et al, 2009; Viruel et al, 2020; Vitelli et al, 2017). Mediterranean plant communities are, however, functionally heterogeneous; for instance, non‐sclerophyllous, shrub species may be as common as pre‐Mediterranean tree taxa (Margaris, 1981).…”

Seasonal changes in population structure of the ambrosia beetle Xylosandrus compactus and its associated fungi in a southern Mediterranean environment

“…Unusual heavy pest infestations on large branches and trunks, associated with serious decline and wilting, have been recently observed on carob trees in Sicily (Southern Italy) [ 29 – 31 ]. Carob is a thermophilous arboreal species characteristic of the olea-lentisc and carob groups (belonging to the Oleo sylvestris-Ceratonion siliquae alliance) [ 32 ] and it is a widespread and long-living tree in Mediterranean woodland vegetation [ 33 , 34 ]. This tree species, largely diffused in dry areas of Sicily, provides to farmers several products and by-products including the flour extracted from the seeds (Locust Bean Gum, LBG) used in food industry as thickening agent (E410) [ 35 – 37 ].…”