The history of extant Ilex species (Aquifoliaceae): Evidence of hybridization within a Miocene radiation

The history and diversification of the genus Ilex (Aquifoliaceae), based on 108 different species (116 specimens), are inferred from the analysis of two nuclear (ITS and nepGS) and three plastid (rbcL, trnL-F and atpB-rbcL) sequences. Nuclear and plastid trees are highly incongruent and the nuclear tree is more compatible with current taxonomic classifications than the plastid one. The most recent common ancestor (MRCA) of extant species is dated from the Miocene, although the Ilex stem lineage can be traced back to the late Cretaceous, according to fossil records. This suggests extensive lineage extinctions between the Cretaceous and Miocene and may also explain the difficulties encountered in defining the relationships between Ilex and its closest relatives. The MRCA ancestral area was identified as being in the North Hemisphere (North America and/or East Asia). Several bidirectional North America/East Asia and North America/South America dispersal events are proposed to explain observed geographic and phylogenetic patterns. Hybridization and introgression events between distantly related lineages are also inferred, indicating weak reproductive barriers between species in Ilex.

Graphical abstractA complex scenario of hybridization and chloroplast capture among Ilex species.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► The most recent common ancestor of extant Ilex species is dated from the Miocene. ► This suggests extensive lineage extinctions between the Cretaceous ‘and Miocene. ► Past and present hybridizations indicate weak reproductive barriers between species.