Reticulate or tree-like chloroplast DNA evolution in Sileneae (Caryophyllaceae)?

Abstract

Despite sampling of up to 25kb of chloroplast DNA sequence from 24 species in Sileneae a number of nodes in the phylogeny remain poorly supported and it is not expected that additional sequence sampling will converge to a reliable phylogenetic hypothesis in these parts of the tree. The main reason for this is probably a combination of rapid radiation and substitution rate heterogeneity. Poor resolution among closely related species are often explained by low levels of variation in chloroplast data, but the problem with our data appear to be high levels of homoplasy. Tree-like cpDNA evolution cannot be rejected, but apparent incongruent patterns between different regions are evaluated with the possibility of ancient interspecific chloroplast recombination as explanatory model. However, several major phylogenetic relationships, previously not recognized, are confidently resolved, e.g. the grouping of the two SW Anatolian taxa S. cryptoneura and S. sordida strongly disagrees with previous studies on nuclear DNA sequence data, and indicate a possible case of homoploid hybrid origin. The closely related S. atocioides and S. aegyptiaca form a sister group to Lychnis and the rest of Silene, thus suggesting that Silene may be paraphyletic, despite recent revisions based on molecular data.