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

Abstract

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 mānuka, confirming the observation from the pooled whole genome sequencing project. FST 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 FST 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 FST). These data provide little support for taxonomic revision and subdividing L. scoparium into segregate species within NZ.

Leptospermum tairawhitiense (Myrtaceae), a new species from Aotearoa / New Zealand, segregated from Leptospermum scoparium s. l.

“…Species rank has been accorded where tag name entities are widespread, sympatric, and even syntopic with accepted Leptospermum species, and exist as morphologically discrete and stable units (Schmid et al, 2023). Both genetic studies (Koot et al, 2022;Chagné et al, 2023) recovered a distinct genetic entity centred on the East Coast of the North Island. When plotted on linear discriminants axes, the East Coast plants form the most isolated genetic cluster among New Zealand Leptospermum (Chagné et al, 2023), and in dendrograms East Coast plants form a distinct cluster sister to other central North Island populations (Koot et al, 2022).…”

“…Both genetic studies (Koot et al, 2022;Chagné et al, 2023) recovered a distinct genetic entity centred on the East Coast of the North Island. When plotted on linear discriminants axes, the East Coast plants form the most isolated genetic cluster among New Zealand Leptospermum (Chagné et al, 2023), and in dendrograms East Coast plants form a distinct cluster sister to other central North Island populations (Koot et al, 2022). In ancestry analyses East Coast plants are recovered as forming their own ancestral population, with limited evidence for admixture with geographically proximate populations (Koot et al, 2022;Chagné et al, 2023).…”

“…Formal taxonomic recognition has been informed by investigations of genetic variation within New Zealand Leptospermum (Koot et al, 2022;Chagné et al, 2023). Insights into genetic structure from those studies have been synthesised with observational data from field work, plant collection, cultivation of wild-collected plants, and herbarium-based investigations to inform species circumscriptions that explain the distribution of character data from these data sources.…”

“…When plotted on linear discriminants axes, the East Coast plants form the most isolated genetic cluster among New Zealand Leptospermum (Chagné et al, 2023), and in dendrograms East Coast plants form a distinct cluster sister to other central North Island populations (Koot et al, 2022). In ancestry analyses East Coast plants are recovered as forming their own ancestral population, with limited evidence for admixture with geographically proximate populations (Koot et al, 2022;Chagné et al, 2023). In splits networks, however, the East Coast plants are nested among central North Island plants (Buys et al, 2019;Koot et al, 2022;Chagné et al, 2023).…”

A phosphatase gene is linked to nectar dihydroxyacetone accumulation in mānuka (Leptospermum scoparium)

“…The Leptospermum genus is concentrated in Australia, and its species are found in a range of habitats, with Leptospermum scoparium (J.R. Forst et G. Forst) growing naturally in south-eastern Australia (Thompson, 1989). Leptospermum scoparium is also widespread throughout Aotearoa-NZ and is the only indigenous Leptospermum species (Koot et al, 2022;Chagn e et al, 2023). Recent modelling suggests that within L. scoparium, two clades diverged c. 9-12 million yr ago and that Aotearoa-NZ L. scoparium (m anuka) is genetically distant from the Australia population and contains five geographically distinct gene pools (Koot et al, 2022).…”