Evolutionary significance of long-distance dispersal and hybridisation in the New Zealand endemic genus Hoheria (Malvaceae)

Abstract

Parsimony and SplitsTree analyses of ITS and 5′ trnK/matK sequence data were used to assess the extent of hybridisation and its evolutionary significance in the New Zealand endemic genus Hoheria A.Cunn. The seven species of Hoheria form a monophyletic group along with the New Zealand endemic genus Plagianthus J.R.Forst. & G.Forst. and the Australian endemics Asterotrichion Klotzsch. and Gynatrix Alef. This strongly supported clade is sister to a clade of Australian species of Lawrencia Hook. The inferred evolutionary history of Hoheria suggests that the extant species are derived from a common ancestor that arrived in New Zealand by long-distance dispersal. There was little divergence among the species of Hoheria in either their ITS or trnK/matK sequences. Two known Hoheria hybrids exhibited overlapping heteromorphic nucleotides at virtually all of the variable positions. Approximately 40% of the other Hoheria accessions in our study retain similar heteromorphic sites. These polymorphisms were shared among the deepest branches in the ITS phylogeny, which potentially suggests that hybridisation has occurred throughout the evolutionary history of Hoheria. The phylogenetic structure of the ITS phylogeny completely collapsed in the strict consensus tree, and there was significant conflict between the biparentally inherited ITS phylogeny and the maternally inherited trnK/matK phylogeny. However, the removal of known and suspected hybrids resulted in parsimony trees that were more resolved. SplitsTree analyses revealed incompatible signals in the data, but recovered well supported groups that diverged from a central boxy network. Although the species of Hoheria are isolated by their ecological preferences or geographical distributions, interspecific hybrids are common in urban areas where the species are often planted.