DNA is found in the cells of all living organisms and it provides a blueprint of their history over different time frames. We can use DNA signatures to investigate relatedness between family members, within populations, and how populations are connected to each other. At higher levels we can use DNA to identify species and how these species are related to other organisms. Project Manta is a part of the Molecular Fisheries Laboratory at UQ and employs DNA methods to investigate several of these questions, with particular focus on population size and structure.
Research methods
To conduct DNA analysis we require a small amount of tissue from the manta ray. The best way to obtain this tissue from live manta rays is to use a hand biopsy spear. The biopsy plug is a cylindrical stainless steel tube with a cutting edge at one end and some divots cut in along the side to trap the tissue. The plug is attached to a hand spear which a diver uses to approach the manta under water and shoots the plug into the muscle tissue towards the wing tip of the manta. This causes little interference to the manta rays who often resume their behaviour before the biopsy occurred (such as circling cleaning stations) within a matter of minutes.
Taking a biopsy. Photo credit: Michaela Rathbone
Back in the laboratory, DNA is extracted from the tissue and then examined for different types of genetic markers. The DNA markers we use include mitochondrial and nuclear markers. The mitochondrial genome is a small circular genome found in every cell. It is passed down from mother to offspring directly without much change between generations so is useful for addressing questions of population structure and phylogenetic relatedness. We also examine the more rapidly evolving DNA markers from the nuclear genome: microsatellites and single nucleotide polymorphisms (SNPs). These nuclear markers are inherited from both parents so change frequently between generations. This variation is useful for examining population structure as well as the genetic diversity within populations and relatedness among individuals.
Research directions
Project Manta PhD Student Amelia Armstrong is utilising DNA to address two primary questions:
How interconnected are the populations around Australia, and how connected are these Australian populations with our immediate neighbours such as Indonesia, New Caledonia and Papua New Guinea?
What is the genetic effective population size (Ne) of the main aggregation sites within Australian waters? Ne is a useful tool that gives an estimate of the number of breeding adults in a population. Ne is gaining interest for direct use in fisheries and conservation management and has shown parallels with census size estimates of breeding adults for a manta ray population in Japan (Kashiwagi 2014).
