Phylogenomics yields new systematic and taxonomical insights for Lissotriton newts, a genus with a strong legacy of introgressive hybridization.

Abstract

The ease with which genome-wide data can nowadays be collected allows complicated phylogenetic questions to be re-evaluated. Phylogenetic relationships among newts have often proven difficult to resolve due to the prevalence of incomplete lineage sorting and introgressive hybridization. For the newt genus Lissotriton, phylogenetic relationships are not settled and there is controversy surrounding the species status of several taxa. We obtain c. 7 k nuclear DNA markers with target enrichment by sequence capture and conduct a concatenated analysis with RAxML, gene-tree summarization with ASTRAL, and species tree estimation with SNAPPER. We explore introgression between evolutionary lineages with TreeMix and Dsuite and compare how introgression events influence the different phylogenetic tools employed. We retrieve tree topologies that are discordant with previous mtDNA-based attempts, particularly concerning the phylogenetic placement of L. italicus and the L. vulgaris species complex. Yet, we also observe deviations between the phylogenetic hypotheses resulting from the different analyses. We interpret the placement of L. montandoni deep within the L. vulgaris species complex by SNAPPER, rather than as the sister taxon to the remainder of the L. vulgaris species complex according to RAxML and ASTRAL, as an artifact of introgression - well-documented in previous work and backed up by TreeMix and Dsuite analyses. Our analyses allow us to make some taxonomical recommendations: we confirm the recently proposed species status of L. kosswigi and L. graecus and propose that L. v. lantzi and L. v. schmidtleri had better be treated as subspecies. Our work also highlights areas for further taxonomic research: range-wide phylogenomic data are required to disentangle the L. boscai - L. maltzani species complex and the northern and southern lineages of L. v. vulgaris. Our study illustrates the power of target enrichment by sequence capture in tackling longstanding questions in taxa with an extensive history of hybridization and introgression.