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A geographical pattern of Antirrhinum (Scrophulariaceae) speciation since the Pliocene based on plastid and nuclear DNA polymorphisms

Authors


*Pablo Vargas, Real Jardín Botánico de Madrid, Consejo Superior de Investigaciones Científicas (CSIC), Plaza de Murillo 2, 28014 Madrid, Spain. E-mail: vargas@rjb.csic.es

Abstract

Aim  To infer phylogenetic relationships among Antirrhinum species and to reconstruct the historical distribution of observed sequence polymorphism through estimates of haplotype clades and lineage divergence.

Location Antirrhinum is distributed primarily throughout the western Mediterranean, with 22 of 25 species in the Iberian Peninsula.

Methods  Plastid (83 trnS-trnG and 83 trnK-matK) and nuclear (87 ITS) sequences were obtained from 96 individuals representing 24 of the 25 Antirrhinum species. Sequences were analysed using maximum parsimony, Bayesian inference and statistical parsimony networking. Molecular clock estimates were obtained for plastid trnK-matK sequences using the penalized likelihood approach.

Results  Phylogenetic results gave limited support for monophyletic groups within Antirrhinum. Fifty-one plastid haplotypes were detected and 27 missing haplotypes inferred, which were all connected in a single, star-like network. A significant number of species shared both the same haplotypes and the same geographical areas, primarily in eastern Iberia. Furthermore, many species harboured populations with unrelated haplotypes from divergent haplotype clades. Plastid haplotype distribution, together with nucleotide additivity in 59 of the 86 nuclear ribosomal ITS sequences, is interpreted as evidence of extensive hybridization. Lineage divergence estimates indicated that differentiation within Antirrhinum post-dates the Miocene, when the Mediterranean climate was established.

Main conclusions  Incongruence between plastid sequences, nuclear sequences and taxonomic delimitation is interpreted as strong evidence of limited cladogenetic processes in Antirrhinum. Rather, extensive nucleotide additivities in ITS sequences in conjunction with haplotype and haplotype-clade distributions related to geographical areas support both recent and ancient hybridization. This geographical pattern of Antirrhinum speciation, particularly in eastern Iberia, is congruent with isolation–contact–isolation processes in the Pleistocene.

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