Genomic comparisons in an Austral-Pacific sandalwood (Santalaceae)
complex highlights novel clades, divergent groups, and the conservation
dynamics of critically endangered and non-threatened lineages
Abstract
Understanding the genetic processes underlying divergence and
connectivity among species is crucial for identifying evolutionary
histories and informing conservation strategies. The Santalum genus,
exhibits distinct genetic variations across the complex geographic
regions of Australia, Asia, and the Pacific Islands. This study
leveraged genome-wide SNP markers to explore the genetic relationships
within critically endangered and non-threatened species in an
Austral-Pacific sandalwood complex, including Santalum lanceolatum, S.
leptocladum, and S. macgregorii. Our findings revealed significant
geographic partitioning and genetic divergence mostly aligned with
current taxonomic classifications. However notably, we showed S.
macgregorii populations in Papua New Guinea (PNG) were divided into two
distinct genetic groups: one in the Central and Gulf provinces and
another in the Western Province, which shows a closer genetic
relationship with S. lanceolatum from Australia’s Northern Peninsula
Area (NPA). This genetic connection suggests a history of secondary
contact and potential hybridization, influenced by historical land
bridges and geological events. Our study highlighted that the sandalwood
trees from the Western Province may represent a divergent lineage of S.
lanceolatum, the S. macgregorii populations in the Central and Gulf
provinces display vicariant divergence due to geographic isolation.
These insights underscore the evolutionary complexity of sandalwoods and
emphasise the need for tailored conservation strategies. Our results
advocate for genetic rescue programs involving NPA S. lanceolatum to
enhance reproductive success in threatened sandalwood populations,
offering crucial guidance for conservation and management efforts in
Australasia.