Conservation genetics of the endemic root holoparasite, Dactylanthus taylorii : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Plant Biology at Massey University, Palmerston North, New Zealand
Dactylanthus taylorii is a New Zealand endemic root holoparasite in the family Balanophoraceae. The vegetative body is extremely reduced and the majority of the plant grows underground attached to its host root. Flowers are dioecious and are pollinated by the short tail bat; a native seed disperser is unknown. Pollen records indicate D. taylorii was formerly more widespread over the North Island of New Zealand but habitat fragmentation and browsing by introduced mammals is thought to have severely reduced population sizes. The species is classified as nationally vulnerable and conservation management is overseen by the New Zealand Department of Conservation. Here, a conservation genetics approach was taken in order to understand the genetic variation and structure of D. taylorii populations.
Previously, the genetic structure of 17 populations had been studied using randomly amplified polymorphic DNAs (RAPDs) and a broad geographical pattern was identified, but was not suitable for conservation management. Alternative molecular markers are microsatellites, which have many favourable attributes for use in conservation genetic studies. Microsatellites allow for estimates of allele frequencies and therefore can be used to determine heterozygosity and their high mutation rate can be used to detect more recent changes in the genetic structure of populations. Next-generation sequencing was used in order to develop microsatellite markers as this method does not require cloning. From the 62,000 sequences obtained, 4,000 microsatellites were identified and primers were able to be designed for 750 repeats. From this primer pool, 72 were chosen to be screened and ten microsatellite loci were found to be polymorphic and consistently amplifiable. These ten were used to genotype 241 D. taylorii individuals from 31 populations.
Across all populations a high number of alleles were identified, although a high percentage of these were private alleles. Within-population assessment of genetic variation indicated that many populations have low levels of genetic diversity and a high proportion of homozygotes. A high degree of genetic differentiation was detected and was found to be strongly correlated to geographic distance between populations. Also, populations grouped into two, three or eight clusters that were reflective of geography. Possible explanations for the geographic pattern observed include
volcanism, mountains as physical barriers to gene flow, habitat availability and gene flow mediated by the short tail bat.
This information suggests that although populations are secure from environmental risks such as habitat loss or herbivory, there is a genetic threat to extinction. In order to increase genetic variation within-populations, translocation of genetic variation (i.e. pollen or seed) is suggested between geographically adjacent populations.