cycads

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.

Date Recorded: 
Wednesday, September 11, 2019

Christy Powell, Brian Dorsey, San Diego Zoo Global, Huntington Botanical Garden

As the most endangered group of plants on the planet, cycads (Cycadales) face a number of threats to their continued existence. Efforts to preserve these iconic plants (in situ reserves and ex situ collections) could benefit greatly from a better understanding of population genetic dynamics and recent demographic history. We have shown that within the genus Dioon most species likely diverged between 30-80 kya. This very recent divergence along with long generation times suggests the possibility of shared polymorphisms across species and potentially incomplete speciation between accepted taxa. Conversely, the distribution of populations and the pollination/dispersal system suggests that migration rates may be quite low. Determining the relative influence of these processes will better inform conservation efforts. Given the nearly 50 Gb genomes of this group, we are using a hybrid of two RADseq methods to produce high coverage/highly multiplexed reduced representation data sets to assess connectivity, historical demography, and genetic diversity. While data for Dioon is still coming in, we have a pilot study using the same technique to assess the genetic diversity among Encephalartos latifrons plants held in botanical gardens in the USA, which we plan to extend to include wild populations with similar goals.

Contributing Author(s): 
Date Recorded: 
Tuesday, September 10, 2019