A Hydraulic Conductivity Model Points to Post-Neogene Survival of the Mediterranean Olive

Abstract

Research on the subfossil record and paleoecology of Olea europaea suggests a new interpretation of its history and ecology with reference to the Mediterranean climate since the Neogene. New results are based on the wood anatomy of ancient and extant Olea and a model estimating hydraulic conductance established for wild forms belonging to Olea europaea subsp. europaea. These suggest that during glacial periods wild olive populations survived in protected microenvironments, particularly riparian habitats. Thereafter, the postglacial expansion of olive associated with climatic warming took place from these refuge areas. This new evidence suggests that the continued existence of Olea in Mediterranean areas since the Neogene was made possible either by preferential survival of Olea lineages adaptable to the Holocene climate or from enhanced adaptation to extreme environmental variation, a trait possibly originating from Tertiary predecessors and maintained in postglacial olive populations.

Parallel evolution of insular Olea europaea subspecies based on geographical structuring of plastid DNA variation and phenotypic similarity in leaf traits

“…Contemporary expression of functional traits such as leaf size, SLA (analysed in the present study), leaf scales (Besnard et al. , 2009) and vessel conductivity (Terral et al. , 2004) support the hypothesis that mainland subspecies adapted progressively to environmental conditions less favourable than those experienced by insular taxa.…”

“…, 2009). Most of the Macaronesian islands had already emerged at that period, offering populations of Olea an oceanic climate buffered against long‐term climatic extremes and close to the original subtropical environments experienced by the ancestors of O. europaea (Terral et al. , 2004).…”

Plastid and nuclear DNA polymorphism reveals historical processes of isolation and reticulation in the olive tree complex (Olea europaea)

“…, 2002). This clear‐cut phylogeographical structure is congruent with palaeobotanical evidence for evolution of ‘modern’ lineages during the Plio‐Pleistocene (Terral et al. , 2004b).…”

Olea europaea L. in the North Mediterranean Basin during the Pleniglacial and the Early–Middle Holocene

“…However, at Cueva de Nerja (6), a continuous Olea wood-charcoal curve is detected as early as the end of the Pleistocene and throughout the Holocene sequence (Badal, 1998). The presence of Olea wood-charcoal has also been documented during the Pleistocene/Holocene transition at Cova de Santa Maira (13) (Aura et al, 2006) and during the Early Holocene at Boquete de Zafarraya (3) (Terral et al, 2005) ( (Badal, 1999).…”

“…The origins and the natural distribution of wild olive populations have been a focus of multidisciplinary research largely on aspects of its domestication and cultivation (Liphschitz et al, 1991;Terral, 1996;Zohary and Hopf, 2000;Contento et al, 2002;Besnard et al, 2002;Terral et al, 2004Terral et al, , 2005Breton et al, 2006). The cultivation of the olive tree since late prehistory, in the Bronze Age, has turned it into an emblematic and genuine plant of the Mediterranean cultures that has both domestic and symbolic uses.…”