Possible hybrid speciation for two Malagasy species of Piper L. (Piperaceae)

Two new species of genus Piper L. from Madagascar: Piper malgassicum Papini, Palchetti, M. Gori & Rota Nodari and Piper tsarasotrae Papini, Palchetti, M. Gori & Rota Nodari, were analyzed to investigate their phylogenetic position and evolutionary history. Both plastidial and nuclear markers were used for sequencing. The plastidial markers (ndhF and trnL intron) showed a close relationship between the two species with respect to the other species of Piper. Both species appeared phylogenetically related to the African P. guineense and the Malagasian/Mascarenhas endemic P. borbonense. The nuclear marker (G3pdh) amplification produced two separate sets of sequences: “long” sequences and “short” sequences, characterized by some long deletions. Analyzing together the nuclear sequences, we observed that the “long” sequence of P. tsarasotrae had a stricter relationship to the African accessions of P. guineense, while the accession of P. malgassicum was more strictly related to P. borbonense. On the contrary both “short” sequences of P. malgassicum and P. tsaratsotrae resulted phylogenetically related to Asian accessions and more distantly related to the formerly cited species. This unexpected result was tentatively explained with a more ancient hybridization event between an ancestor of P. malgassicum and P. tsarasotrae (and possibly P. borbonense) and an Asian species of Piper. The Asian contribution would have produced the ancestors carrying the “short” sequences. A more recent hybridization event would have led to the separation of P. malgassicum from P. tsarasotrae with an African pollen-derived genome contribution from P. guineense or, more probably, an ancestor thereof, to an ancestor of P. tsarasotrae. The chromosome numbers of P. tsarasotrae (2n = about 38) and P. malgassicum (2n = about 46), were more similar to the Asian species than to the American species. Unfortunately, no chromosome number of the African species P. guineense is currently available, to compare the chromosomal numbers.two new species of genus Piper L. from Madagascar: Piper malgassicum Papini, Palchetti, M. Gori & Rota Nodari and Piper tsarasotrae Papini, Palchetti, M. Gori & Rota Nodari, were analyzed to investigate their phylogenetic position and evolutionary history. Both plastidial and nuclear markers were used for sequencing. The plastidial markers (ndhF and trnL intron) showed a close relationship between the two species with respect to the other species of Piper. Both species appeared phylogenetically related to the African P. guineense and the Malagasian/Mascarenhas endemic P. borbonense. The nuclear marker (G3pdh) amplification produced two separate sets of sequences: “long” sequences and “short” sequences, characterized by some long deletions. Analyzing together the nuclear sequences, we observed that the “long” sequence of P. tsarasotrae had a stricter relationship to the African accessions of P. guineense, while the accession of P. malgassicum was more strictly related to P. borbonense. On the contrary both “short” sequences of P. malgassicum and P. tsaratsotrae resulted phylogenetically related to Asian accessions and more distantly related to the formerly cited species. This unexpected result was tentatively explained with a more ancient hybridization event between an ancestor of P. malgassicum and P. tsarasotrae (and possibly P. borbonense) and an Asian species of Piper. The Asian contribution would have produced the ancestors carrying the “short” sequences. A more recent hybridization event would have led to the separation of P. malgassicum from P. tsarasotrae with an African pollen-derived genome contribution from P. guineense or, more probably, an ancestor thereof, to an ancestor of P. tsarasotrae. The chromosome numbers of P. tsarasotrae (2n = about 38) and P. malgassicum (2n = about 46), were more similar to the Asian species than to the American species. Unfortunately, no chromosome number of the African species P. guineense is currently available, to compare the chromosomal numbers.