, Volume 121, Issue 4, pp 357-364
Date: 20 May 2008

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

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Abstract

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.