Relationships of the Macaronesian and Mediterranean floras: molecular evidence for multiple colonizations into Macaronesia and back‐colonization of the continent in Convolvulus (Convolvulaceae)

Abstract

A molecular phylogenetic analysis of the Macaronesian endemic species of Convolvulus was undertaken using data from the nuclear ribosomal internal transcribed spacer (ITS) regions. The results of the analysis support two introductions into Macaronesia from distantly related clades within Convolvulus and a subsequent back-colonization to the continent from within one of the clades. Hypothesized relationships between Macaronesian species and New World taxa and between the Canarian endemic C. caput-medusae and the Moroccan C. trabutianus are refuted. Both Macaronesian clades are shown to have Mediterranean sister groups although one is predominantly western Mediterranean and the other predominantly eastern Mediterranean in distribution. The patterns of colonization into Macaronesia demonstrated by Convolvulus and also by other multiple colonizing genera conform to either a pattern of phylogenetic distinctiveness or a checkerboard distribution of island lineages. Both are consistent with the hypothesis that niche preemption is responsible for the limited number of colonizations into the region. A review of sister group relationships demonstrates that, in common with Convolvulus, most Macaronesian groups have sister groups distributed in the near-continent (i.e., western Mediterranean). Disjunct sister group relationships (including Eastern Mediterranean disjunctions) occur in only 18% of groups.

Are islands the end of the colonization road?

“…In our literature survey of clades with suitable molecular phylogenies, about one-third of those involving terrestrial animals provide evidence of over-water dispersal from islands to continental regions. Based on morphological and molecular observations, several cases of reverse colonization have also been found in Macaronesia flora [49], and the author of this study considers that such events might be 'far more frequent than presently considered' (J. Caujapé -Castells, pers. comm.…”

“…First, island-to-continent colonization accounted for less than 10% of colonization events reported for the endemic Macaronesian flora [49], compared to 38% for animal taxa. Relative frequency of reverse colonizations also differed between animal groups, being lower in insects and mammals compared to birds, reptiles and amphibians.…”

Δ6-Desaturase sequence evidence for explosive Pliocene radiations within the adaptive radiation of Macaronesian Echium (Boraginaceae)

“…The Macaronesian archipelagos (the Azores, Madeira, the Canary Islands, and Cape Verde) were subjects of numerous early molecular studies aimed at interpreting patterns of dispersal and colonization, as well as the acquisition of particular characteristics (see Carine et al, 2004;Vargas, 2007, for revision). The Sonchus alliance (Kim et al, 1996), the Aeonium alliance (Mort et al, 2002), Argyranthemum , and the Echium group (Böhle et al, 1996), with over 25 species each, provide opportunities to investigate multiple patterns of evolution.…”

“…A traditional hypothesis is that woodiness originated in the continent and was maintained exclusively in the Canary Islands after climatic changes in the Tethyan-Tertiary (Lems, 1960;Bramwell, 1972). Many phylogenetic studies, however, reveal that remarkable shifts from herbaceous to bush and tree-like species across different plant groups (taxonomic families) is the predominant pattern (see revisions in Carine et al, 2004;Vargas, 2007). Among the 1062 genera of Macaronesian vascular plants, secondary acquisition of woodiness has been documented by means of molecular phylogenetics in Sonchus (Kim et al, 1996), Pericallis (Panero et al, 1999), the Aeonium alliance (Mort et al, 2002), Sideritis (Barber et al, 2002), Tolpis (Moore et al, 2002), and Convolvulus (Carine et al, 2004).…”

“…Many phylogenetic studies, however, reveal that remarkable shifts from herbaceous to bush and tree-like species across different plant groups (taxonomic families) is the predominant pattern (see revisions in Carine et al, 2004;Vargas, 2007). Among the 1062 genera of Macaronesian vascular plants, secondary acquisition of woodiness has been documented by means of molecular phylogenetics in Sonchus (Kim et al, 1996), Pericallis (Panero et al, 1999), the Aeonium alliance (Mort et al, 2002), Sideritis (Barber et al, 2002), Tolpis (Moore et al, 2002), and Convolvulus (Carine et al, 2004). Remarkably, significant morphological diversity (as exemplified by growth habits), is found in 28 Macaronesian Echium species (Böhle et al, 1996), surpassing that of the remaining 40 continental relatives.…”