Are Macaronesian islands refugia of relict plant lineages?: A molecular survey

Abstract

From a historical biogeographical perspective, Macaronesia has been considered as an island system where relict plants formerly distributed in Europe and northern Africa found appropriate ecological conditions for survival. In this context, and using previously published data on the Macaronesian flora, three basic relictualism concepts (geographic, taxonomic, and lineage relicts) are evaluated. A significant number of the 88 critically endangered species on the Canary Islands may stem from ongoing range reductions on each island (geographic relicts). Macrofossil evidence supports the occurrence of subtropical angiosperms in Europe in the Tertiary and subsequent extinction of genera and species on the continent, whereas they were sheltered in Macaronesia (taxonomic relicts). Using parsimony-based reconstructions, thirty angiosperm and two gymnosperm phylogenies are used to determine the number of stem-based versus crown-based lineages. In 18 plant groups,16 unequivocal stem-based lineages (lineage relicts) were established in Macaronesia earlier than closely-related lineages differentiated on the mainland. In contrast, 13 lineages display a relatively more recent differentiation in Macaro-nesia as shown by unequivocal sister-group relationships with respect to their continental siblings. When introducing a time scale, some of these 13 crown-based lineages are found to have evolved in Macaronesia since the Tertiary. Relict status of ancient versus stem-based lineages is discussed and a fourth concept of lineage relictualism (ancient lineage) considered in terms of absolute timing. All stem-based lineages plus some crownbased lineages predate the Quaternary and are thus considered to be ancient lineages. Association between endo-zoochory and multiple colonizations is observed. Eight plant groups, out of a total of 29 properly sampled, underwent multiple colonizations, of which four tree groups (Hedera, Ilex, Juniperussect. Juniperus, Olea) display endozoochorous syndromes. Endozoochory may have been crucial to recurrent long-distance dispersal of fleshy-fruited plants to Macaronesia and the establishment of ancient lineages in the Tertiary.