Phylogenomic analyses of the Austral podocarps (Podocarpus: Podocarpaceae) support hybrid ancestry of a New Zealand species

Hybridisation is widespread in plants and can generate novel evolutionary lineages. Here, we develop a phylogenetic hypothesis for the Austral podocarps (Podocarpus), a monophyletic group of six species distributed in Tasmania, mainland Australia, New Zealand and New Caledonia, and identify a putative hybrid lineage. Using a targeted capture approach to generate DNA sequence data, we find discordance between nuclear and plastid derived phylogenetic estimates and in particular, the relationships of the New Zealand species Podocarpus nivalis and Australian P. lawrencei are significantly discordant. Species network analyses largely resolve this incongruence and suggest that P. nivalis is a hybrid lineage, with P. laetus (New Zealand) and P. lawrencei as parents. We hypothesise that P. nivalis has arisen following trans-Tasman dispersal of P. lawrencei, and shows eco-geographic divergence from P. laetus, which could facilitate reproductive isolation. We suggest that introgression from P. laetus to colonising P. lawrencei could significantly reduce founder effects while cold tolerance inherited from P. lawrencei has enabled P. nivalis to occupy alpine environments. These findings highlight the importance of reticulate evolution in generating diversity among insular floras and demonstrate the value of phylogenomic approaches for resolving recent and complex radiations.