Mitochondrial DNA diversity and variability in the Adélie penguin of Antarctica : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Genetics at Massey University, Palmerston North, New Zealand
In Antarctica, there are two distinct lineages of Adélie penguin (Pygoscelis adeliae) characterised by 8.3% divergence in mitochondrial DNA hypervariable region I (mt DNA HVR I). These two lineages are known as the Antarctic and Ross Sea lineages (A and RS respectively). This study aims to characterise aspects of mutation and variation as seen in HVR I of the Adélie penguin, by sequencing the DNA of individuals from different locations around Antarctica. The geographic distribution of the two lineages was examined in greater detail. A dramatic decrease in the RS lineage was discovered on the edge of the Ross Sea region of Antarctica. Because the two lineages have different geographic distributions, and are separated by 8.3% sequence divergence, this study also investigated the possibility that these two lineages were in fact cryptic species. Sequencing of mt DNA and microsatellite genotyping proved that individuals of the two lineages mate randomly and produce offspring. Recently, a rate of evolution based on serially preserved DNA from Adélie penguins was estimated at 0.96 substitutions/site/Million years. (0.53-1.43 s/s/Myr). This rate is four to seven times higher than previous avian control region evolution rates estimated by phylogenetic methods, and is more akin to rates of mutation determined by pedigree studies in other species such as humans. In the light of this higher direct estimate of the rate of evolution in Adélie penguins, this study also begins to determine a rate of mutation in Adélie penguins based on pedigree analysis. No new mutations were found, however three cases of inherited single point heteroplasmy were detected. The inclusion of heteroplasmy in mutation rate calculation is also addressed. One of the arguments as to why pedigree studies find a higher rate of mutation than phylogenetic studies is that pedigree studies preferentially find mutations at 'hot spots' in the DNA sequence. This study also seeks to characterise the distribution of variable sites in hypervariable region I in relation to the two mt DNA lineages, and also to geographic location. While the exact sites of variation differ between the two lineages, it was seen that the regions where variation was high or low is very similar in both lineages. This could be due to underlying physical constraints on DNA sequence variation. Looking towards future work in Adélie penguin mt DNA and an expansion of the studies undertaken here, the complete mitochondrial genome of the Adélie penguin was determined. This now provides the opportunity to estimate rates of change in the entire Adélie penguin mitochondrial genome, using ancient DNA from the extremely well preserved sub-fossil bones in Antarctica.