Biology subjects

Millar, C. D.

Publications and source records attributed to Millar, C. D..

3 recordsLinked to original sources

bioRxiv2020

Ancient and modern genomes reveal microsatellites maintain a dynamic equilibrium through deep time

Microsatellites are widely used in population genetics, but their evolutionary dynamics remain poorly understood. It is unclear whether microsatellite loci drift in length over time. We identify more than 27 million microsatellites using a novel and unique dataset of modern and ancient Adelie penguin genomes along with data from 63 published chordate genomes. We investigate microsatellite evolutionary dynamics over two time scales: one based on the Adelie penguin samples dating to approximately 46.5 kya, the other dating to the diversification of chordates more than 500 Mya. We show that the process of microsatellite allele length evolution is at dynamic equilibrium; while there is length polymorphism among individuals, the length distribution for a given locus remains stable. Many microsatellites persist over very long time scales, particularly in exons and regulatory sequence. These often retain length variability, suggesting that they may play a role in the maintenance of evolutionary plasticity.

evolutionary biology↗

bioRxiv2018

Fishing for Mitochondrial DNA in The Egyptian Sacred Ibis Mummies

The long-term preservation of DNA requires a number of optimal conditions, including consistent exposure to cool, dry, and dark environments. As a result, the successful recovery of ancient DNA from material from warmer climates such as those in Egypt has often been met with scepticism. Egypt has an abundance of ancient mummified animals and humans, whose genetic analyses would offer important insights into ancient cultural practices. To date, the retrieval of complete genomes from ancient Egyptian remains of humans or other animals has been largely unsuccessful. To test for the presence of even short DNA sequences in Egyptian material, we performed second-generation shotgun sequencing of DNA libraries constructed from ancient Sacred Ibis mummies. Since most of the resulting Illumina libraries were shown to contain extremely low levels (less than 0.06%) of endogenous mitochondrial DNA, we aimed to enrich these samples using targeted in-solution hybridisation methods. Using biotinylated RNA baits designed to Sacred Ibis complete mitochondrial sequences, we trialled a number of conditions and parameters and achieved up to 4705-fold enrichment. We also found that a combination of hybridisation temperature and the use of the polymerase KAPA HiFi significantly increased both the efficiency of targeted hybridisation and post-hybridisation amplification respectively. Furthermore, improved enrichment was accompanied with only minor increases in clonality. Our method enabled us to reconstruct the first complete mitochondrial genomes from ancient Egyptian sub-fossil material.

genomics↗

bioRxiv2017

Genetic structure of the grey side-gilled sea slug (Pleurobranchaea maculata) in coastal waters of New Zealand

Pleurobranchaea maculata is a rarely studied species of the Heterobranchia found throughout the south and western Pacific - and recently recorded in Argentina - whose population genetic structure is unknown. Interest in the species was sparked in New Zealand following a series of dog deaths caused by ingestions of slugs containing high levels of the neurotoxin tetrodotoxin. Here we describe the genetic structure and demographic history of P. maculata populations from five principle locations in New Zealand based on extensive analyses of 12 microsatellite loci and the COI and CytB regions of mitochondrial DNA (mtDNA). Microsatellite data showed significant differentiation between northern and southern populations with population structure being associated with previously described regional variations in tetrodotoxin concentrations. However, mtDNA sequence data did not support such structure, revealing a star-shaped haplotype network with estimates of expansion time suggesting a population expansion in the Pleistocene era. Inclusion of publicly available mtDNA sequence from Argentinian sea slugs did not alter the star-shaped network. We interpret our data as indicative of a single founding population that fragmented following geographical changes that brought about the present day north-south divide in New Zealand waters. Lack of evidence of cryptic species supports data indicating that differences in toxicity of individuals among regions are a consequence of differences in diet.

genetics↗