Genetic diversity, structure and distribution of Australian Cycas

Manuel Luján, Jian Liu, Nathalie Nagalingum, California Academy of Sciences, Kunming Institute of Botany, Chinese Academy of Sciences

Rare plant species exhibit narrow geographic distribution and are often considered to have smaller populations and lower levels of genetic diversity compared to their more common relatives. The genus Cycas includes about 117 species, 32 of which are native to Australia and 20 occur only in the subtropical and tropical regions of Queensland. Most of the Queensland species of Cycas are known from only a handful of localities and their population characteristics remain to be investigated. Our main objective was to assess genetic diversity and population size of the rare species of Cycas and compare it them the more widely distributed species. We used RADseq to generate genomic data to estimate percentage of polymorphic loci (P), heterozygosity (Ho and He) and nucleotide diversity (π), and footage from unmanned aerial vehicles to estimate populations size. Our preliminary results suggest that rare species (C. terryana) have levels of genetic diversity that are comparable to more common species (C. ophiolitica and C. media). Population size of rare species (e. g. C. tuckeri) tend to be smaller than more common species (C. cairnsiana). Given that Cycas are long-lived plants, rare and small populations constituted by old plants, may be maintaining ancestral allelic variants from previously more widespread and common populations. Further study considering the populations demographic structure are needed to better understand this pattern and inform conservation efforts.