Single nucleotide polymorphism analysis in Leptospermum scoparium (Myrtaceae) supports two highly differentiated endemic species in Aotearoa New Zealand and Australia

Leptospermum scoparium is the basis of a flourishing honey industry in Aotearoa New Zealand (NZ) and Australia. The genetic structure of L. scoparium across its range in NZ and Australia was previously assessed using pooled, whole genome sequencing; however, only one sampling site in Tasmania was included. Here, we used a single nucleotide polymorphism (SNP) array for genotyping samples of L. scoparium collected in natural stands around Tasmania and NZ, to determine the genetic relationship between L. scoparium individuals from the two regions. In total, 2069 high quality, polymorphic SNP markers were applied across the sample set of 504 individuals, revealing that Tasmanian L. scoparium are genetically distinct from NZ manuka, confirming the observation from the pooled whole genome sequencing project. F-ST and discriminant analysis of principal components confirmed that the Tasmanian populations are well differentiated genetically from NZ populations, suggesting that they should be recognised as a separate, endemic Australian species. Within NZ, eight geographic groups are distinguished with genotypic variation exhibiting north to south landscape scale patterns with regional genetic clusters. We found support for isolation by distance, and this was reflected in the range of pairwise F-ST values estimated between NZ genetic clusters (0.056 to 0.356); however, each geographic genetic group exhibits geneflow and is only weakly differentiated from neighbouring clusters as evidenced by low population differentiation (low pairwise F-ST). These data provide little support for taxonomic revision and subdividing L. scoparium into segregate species within NZ.

Automated summary

Leptospermum scoparium is the basis of a flourishing honey industry in Aotearoa New Zealand and Australia. Genetic analysis shows that Tasmanian L. scoparium has distinct genetic traits from NZ manuka, suggesting that it should be recognized as a separate, endemic Australian species. However, within NZ, L. scoparium exhibits genotypic variation with a north to south landscape pattern, indicating support for isolation by distance and minimal genetic differentiation between geographic groups.