Genetic Sampling Strategy
Camcore collects seeds from trees of threatened or endangerd species and plants them elsewhere to conserve the genetic base ex situ. How do we know how many trees to sample per population and how many populations to sample across a species’ geographic range? We have studied the genetic diversity within a population using both chemical and molecular markers and have used this information plus results from field trials (provenance tests) to develop in situ and ex situ conservation strategies.
As an example, we looked at how gene frequencies varied within a small (5 hectare) and large (200 hectare) population of Pinus tecunumanii in Guatemala. Even though the two populations were separated by 65 km, we found that the two populations carried a number of the same major genes. Where they differed was in their composition of rare genes, better known as alleles. Once we knew the frequency of major and minor alleles, we conducted statistical probability simulations to determine how many trees we would need to sample in the large and small population, using actual allele counts from our study, in order to sample all alleles at frequency of 5% or greater. We found that in the small populations we would need to collect open-pollinated seed from about 20 trees, and in the large populations from only 10 trees to conserve most of the genetic diversity.
In Indonesia, we used microsatellite and chloroplast DNA markers to assess the evolutionary history and genetic diversity of Eucalyptus urophylla, which occurs on only seven islands. We found that populations on the islands of Timor and Wetar were the most diverse and that it appears the species migrated from east to west across the islands.
Camcore samples approximately 20 to 50 trees per population in its field work in natural stands. This is because we are interested in both tree breeding (field testing) and ex situ conservation. We also sample a number of populations throughout the species’ geographic range to ensure that we are also maintaining broad adaptability.