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

Abstract

Strong geographical isolation within the distribution of a species may result in differentiated lineages exhibiting conspicuous phenotypic differences. In the present paper, we investigate whether plastid and phenotypic variation is geographically structured within the Olea europaea complex in Macaronesia, which comprises three subspecies separated by oceanic barriers: maroccana (south-west Morocco), guanchica (Canary Islands) and cerasiformis (Madeira archipelago). Plastid variation showed a significant pattern of geographical structure (NST > GST = 0.56), because of the lack of shared haplotypes among subspecies and the presence of a single and private haplotype in the eastern Canary Islands. Such a clear molecular structure, however, was not reflected in a congruent pattern of phenotypic differentiation among taxa in leaf morpho-functional traits. Despite the substantial genetic differentiation observed between the subspecies from Madeira and the Canary Islands, they displayed both higher leaf size (leaf area) and specific leaf area (leaf surface area-to-mass ratio) than their continental counterparts, probably as a result of oceanic conditions in subtropical environments. Unlike most of the plant groups previously studied in the Macaronesian region, the lineages of Olea illustrate how low phenotypic differentiation can be also related to a clear molecular differentiation in oceanic island enclaves. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 162, 54–63.