Timing and tempo of early and successive adaptive radiations in Macaronesia.

The flora of Macaronesia, which encompasses five Atlantic archipelagos (Azores, Canaries, Madeira, Cape Verde, and Salvage), is exceptionally rich and diverse. Spectacular radiation of numerous endemic plant groups has made the Macaronesian islands an outstanding area for studies of evolution and speciation. Despite intensive investigation in the last 15 years, absolute age and rate of diversification are poorly known for the flora of Macaronesia. Here we report molecular divergence estimates and rates of diversification for five representative, putative rapid radiations of monophyletic endemic plant lineages across the core eudicot clade of flowering plants. Three discrete windows of colonization during the Miocene and early Pliocene are suggested for these lineages, all of which are inferred to have had a single colonization event followed by rapid radiation. Subsequent inter-archipelago dispersal events into Madeira and the Cape Verdes took place very recently during the late Pliocene and Pleistocene after initial diversification on the Canary Islands. The tempo of adaptive radiations differs among the groups, but is relatively rapid compared to continental and other island radiations. Our results demonstrate that opportunity for island colonization and successful radiation may have been constrained to discrete time periods of profound climatic and geological changes in northern African and the Mediterranean.

Molecular confirmation of the hybrid origin of the critically endangered western Mediterranean endemic Sonchus pustulatus (Asteraceae: Sonchinae).

The critically endangered composite Sonchus pustulatus Willk. despite being known from fewer than ten locations in southern Spain and northern Africa, has never been characterized in robust phylogenetic context. Here, we report molecular evidence that strongly supports a hybrid origin for S. pustulatus. Although parentage cannot be identified with certainty, analysis of DNA sequence variation from the internal transcribed spacer (ITS) region of nuclear ribosomal DNA (nrDNA) supports a phylogenetic placement of S. pustulatus close to other species in the poorly known section Pustulati, whereas examination of chloroplast DNA (cpDNA) places S. pustulatus most closely with species from the sections Sonchus and Asperi. This is one of several instances of topological non-concordance reported for the genus Sonchus. Monophyly of S. pustulatus in both gene genealogies supports the null hypothesis of a single origin, and the relatively large amount of nucleotide substitutions is indicative of an origin in the range of millions of years. A hypothesis of a northern African origin of S. pustulatus followed by dispersal to the Iberian Peninsula during the Messinian salinity crisis/later Quaternary glaciations is proposed on the basis of biogeographic patterns and calibrated estimations of molecular evolution.

Patterns of introduction and diversification of Vanilla planifolia (Orchidaceae) in Reunion Island (Indian Ocean).

The cultivated species Vanilla planifolia is a typical example of a crop introduced from its area of origin (America) to new regions where natural pollinators are absent. Although the Vanilla cultivars are exclusively vegetatively propagated, a high degree of phenotypic variation is observed among the cultivars in their introduction areas such as Reunion Island. To test several hypotheses explaining this variation-different introduction events, somatic mutations and sexual reproduction (through manual pollination)-we used AFLP markers to elucidate the patterns of introduction of V. planifolia. Most of the accessions cultivated in the world were derived from a single accession, possibly the Mexican cultivar Mansa. The patterns of diversification of this cultivated species were also studied and compared with other cultivated (V. tahitensis) and wild (V. pompona and V. bahiana) species. Except for one particular phenotype ('Aiguille'), which may come from sexual reproduction, cultivated accessions exhibit very low levels of genetic diversity. They have evolved by the accumulation of point mutations through vegetative multiplication. The genetic diversity revealed could not explain the phenotypic diversity, which may be related to epigenetics or polyploidy. This new understanding of the basis of genetic diversity of vanilla may assist to improve management of genetic resources.

Neotropical roots of a Polynesian spice: the hybrid origin of Tahitian vanilla, Vanilla tahitensis (Orchidaceae).

Absent in the wild, Tahitian vanilla (V. tahitensis) is a gourmet spice restricted in distribution to cultivated and feral stands in French Polynesia and Papua New Guinea. Its origins have been elusive. Our objective was to test the purported hybrid derivation and parentage of V. tahitensis from aromatic, neotropical progenitors. Nucleotide sequences from V. tahitensis and neotropical Vanilla were assayed for phylogenetic relatedness in two independently inherited genomic regions, the nuclear ITS region, and the trnH-psbA noncoding region of chloroplast DNA. As predicted to occur for early generation hybrids, placement of V. tahitensis was nonconcordant. All V. tahitensis clustered with V. planifolia from analysis of cpDNA sequences, suggesting V. planifolia as the maternal genome contributor. Phylogenetic reconstruction of ITS sequences showed that most V. tahitensis nested incongruently with V. odorata, but others remained sister to V. planifolia. Recovery of ITS clones in V. tahitensis related to both V. planifolia and V. odorata also supports its biphyletic origin from these two taxa. We interpret the high percentage (95%) of additive polymorphic sites in V. tahitensis relative to its parents as indication of a recent, and probably human-mediated, evolutionary origin.