Events that shape genomes

The invention and development of Next Generation Sequencing has opened up new possibilities for exploring the genomes of non-model organisms. For this thesis, a diverse range of non-model species from both plants and animals were used to identify and answer questions of evolutionary interest in four case studies. In doing so, a wide assortment of methodologies were used and developed, taking full advantage of the versatility that whole genome sequencing can provide. The genome of the Natal Long Fingered Bat, Miniopterus natalensis, was assembled to investigate the genetic mechanisms responsible for the evolution of the bat wing. The assembled genome was required to facilitate RNA-seq and ChIP-seq analysis. In addition to the genome assembly and annotation, dN/dS analysis and lncRNA prediction were also conducted. This resulted in a high quality genome assembly with just over 24000 genes being annotated and 227 putative lncRNAs being identified. None of the genetic pathways highlighted by the RNA-seq analysis showed any elevated dN/dS signal, suggesting this was not the loci of evolutionary change. The Amboseli National Park in Kenya has a local population of Yellow baboons (Papio cynocephalus) that has recently come into contact and hybridised with a population of Olive baboons (Papio anubis). A genome assembly of P. cynocephalus was created and used to align low coverage sequencing from 45 baboons, including admixed individuals along with unadmixed individuals from each species. By identifying SNPs that were predictive of the species, hybrid individuals were confirmed and evidence for previous admixture events discovered, such as P. anubis SNPs already at fixation in the P. cynocephalus population at Amboseli. The Ruschioideae are a clade of plants that encompasses the prolific tribe, the Ruschieae, which is comprised of approximately 1500 recently diverged species. An exploratory analysis sequenced two Ruschieae genomes (Polymita steenbokensis and Faucaria felina) along with a sister taxon (Cleretum herrei) from a neighbouring tribe (Dorotheantheae). The three plants were compared to each other in order to try and identify any genetic signatures that could be influencing the rapid speciation. The two Ruschieae species were found to have increased levels of non-tandem duplication within the genome as well as on going transposable element activity when compared to C. herrei. Xerohpyta humilis is a desiccation tolerant plant. In order to further facilitate research into how this is possible, the genome was sequenced and assembled. Irregular data led to the discovery that the plant had a genome duplication as well as a large amount of somatic mutations in its genome. Further analysis confirmed that this pattern of somatic mutations was only present in plants that had undergone multiple cycles of desiccation and rehydration. These apparently disparate topics explored the possibilities and limitations for whole genome sequencing in the study of non-model organisms. Mechanisms of genetic change were examined at the genomic scale, from adaptation and hybridisation to various forms of duplication and mutation. In this way, a large variety of events responsible for the evolutionary change of genomes in plants and animals were analysed in a diverse set of systems

Mendelian nightmares: The germline-restricted chromosome of songbirds

Germline-restricted chromosomes (GRCs) are accessory chromosomes that occur only in germ cells. They are eliminated from somatic cells through programmed DNA elimination during embryo development. GRCs have been observed in several unrelated animal taxa and show peculiar modes of non-Mendelian inheritance and within-individual elimination. Recent cytogenetic and phylogenomic evidence suggests that a GRC is present across the species-rich songbirds, but absent in non-passerine birds, implying that over half of all 10,500 bird species have extensive germline/soma genome differences. Here, we review recent insights gained from genomic, transcriptomic, and cytogenetic approaches with regard to the genetic content, phylogenetic distribution, and inheritance of the songbird GRC. While many questions remain unsolved in terms of GRC inheritance, elimination, and function, we discuss plausible scenarios and future directions for understanding this widespread form of programmed DNA elimination

Vegetative desiccation tolerance in the resurrection plant Xerophyta humilis has not evolved through reactivation of the seed canonical LAFL regulatory network

It has been hypothesised that vegetative desiccation tolerance in resurrection plants evolved via reactivation of the canonical LAFL (i.e. LEC1, ABI3, FUS3 and LEC2) transcription factor (TF) network that activates the expression of genes during the maturation of orthodox seeds leading to desiccation tolerance of the plant embryo in most angiosperms. There is little direct evidence to support this, however, and the transcriptional changes that occur during seed maturation in resurrection plants have not previously been studied. Here we performed de novo transcriptome assembly for Xerophyta humilis, and analysed gene expression during seed maturation and vegetative desiccation. Our results indicate that differential expression of a set of 4205 genes is common to maturing seeds and desiccating leaves. This shared set of genes is enriched for gene ontology terms related to abiotic stress, including water stress and abscisic acid signalling, and includes many genes that are seed-specific in Arabidopsis thaliana and targets of ABI3. However, while we observed upregulation of orthologues of the canonical LAFL TFs and ABI5 during seed maturation, similar to what is seen in A. thaliana, this did not occur during desiccation of leaf tissue. Thus, reactivation of components of the seed desiccation program in X. humilis vegetative tissues likely involves alternative transcriptional regulators.The University of Cape Town, the National Research Foundation via Incentive Funding (UID 103423) and a National Bioinformatics Functional Genomics grant (UID 93697).https://onlinelibrary.wiley.com/journal/1365313xam2020BiochemistryGeneticsMicrobiology and Plant Patholog

Diagnostic testing in influenza and pertussis related paediatric intensive care unit admissions,Queensland, Australia, 1997-2013

Severe respiratory infections make up a large proportion of Australian paediatric intensive care unit (ICU) admissions each year. Identification of the causative pathogen is important and informs clinical management. We investigated the use of polymerase chain reaction (PCR) in the ICU-setting using data collated by the Australian and New Zealand Paediatric Intensive Care (ANZPIC) Registry from five ICUs in Queensland, Australia. We describe diagnostic testing use among pertussis and influenza-related paediatric ICU admissions between 01 January 1997 and 31 December 2013

Songbird germline-restricted chromosome as a potential arena of genetic conflicts

Genetic conflicts can arise between components of the genome with different inheritance strategies. The germline-restricted chromosome (GRC) of songbirds shows unusual mitotic and meiotic transmission compared with the rest of the genome. It is excluded from somatic cells and maintained only in the germline. It is usually present in one copy in the male germline and eliminated during spermatogenesis, while in the female germline, it usually occurs in two copies and behaves as a regular chromosome. Here, we review what is known about the GRC's evolutionary history, genetic content, and expression and discuss how it may be involved in different types of genetic conflicts. Finally, we interrogate the potential role of the GRC in songbird germline development, highlighting several unsolved mysteries

Genomewide ancestry and divergence patterns from low‐coverage sequencing data reveal a complex history of admixture in wild baboons

Naturally occurring admixture has now been documented in every major primate lineage, suggesting its key role in primate evolutionary history. Active primate hybrid zones can provide valuable insight into this process. Here, we investigate the history of admixture in one of the best-studied natural primate hybrid zones, between yellow baboons (Papio cynocephalus) and anubis baboons (Papio anubis) in the Amboseli ecosystem of Kenya. We generated a new genome assembly for yellow baboon and low-coverage genomewide resequencing data from yellow baboons, anubis baboons and known hybrids (n = 44). Using a novel composite likelihood method for estimating local ancestry from low-coverage data, we found high levels of genetic diversity and genetic differentiation between the parent taxa, and excellent agreement between genome-scale ancestry estimates and a priori pedigree, life history and morphology-based estimates (r(2)  = 0.899). However, even putatively unadmixed Amboseli yellow individuals carried a substantial proportion of anubis ancestry, presumably due to historical admixture. Further, the distribution of shared vs. fixed differences between a putatively unadmixed Amboseli yellow baboon and an unadmixed anubis baboon, both sequenced at high coverage, is inconsistent with simple isolation-migration or equilibrium migration models. Our findings suggest a complex process of intermittent contact that has occurred multiple times in baboon evolutionary history, despite no obvious fitness costs to hybrids or major geographic or behavioural barriers. In combination with the extensive phenotypic data available for baboon hybrids, our results provide valuable context for understanding the history of admixture in primates, including in our own lineage

Genomewide ancestry and divergence patterns from low‐coverage sequencing data reveal a complex history of admixture in wild baboons

Naturally occurring admixture has now been documented in every major primate lineage, suggesting its key role in primate evolutionary history. Active primate hybrid zones can provide valuable insight into this process. Here, we investigate the history of admixture in one of the best-studied natural primate hybrid zones, between yellow baboons (Papio cynocephalus) and anubis baboons (Papio anubis) in the Amboseli ecosystem of Kenya. We generated a new genome assembly for yellow baboon and low coverage genome-wide resequencing data from yellow baboons, anubis baboons, and known hybrids (n=44). Using a novel composite likelihood method for estimating local ancestry from low coverage data, we found high levels of genetic diversity and genetic differentiation between the parent taxa, and excellent agreement between genome-scale ancestry estimates and a priori pedigree, life history, and morphology-based estimates (r(2)=0.899). However, even putatively unadmixed Amboseli yellow individuals carried a substantial proportion of anubis ancestry, presumably due to historical admixture. Further, the distribution of shared versus fixed differences between a putatively unadmixed Amboseli yellow baboon and an unadmixed anubis baboon, both sequenced at high coverage, are inconsistent with simple isolation-migration or equilibrium migration models. Our findings suggest a complex process of intermittent contact that has occurred multiple times in baboon evolutionary history, despite no obvious fitness costs to hybrids or major geographic or behavioral barriers. In combination with the extensive phenotypic data available for baboon hybrids, our results provide valuable context for understanding the history of admixture in primates, including in our own lineage

Rapid gene content turnover on the germline-restricted chromosome in songbirds

Abstract The germline-restricted chromosome (GRC) of songbirds represents a taxonomically widespread example of programmed DNA elimination. Despite its apparent indispensability, we still know very little about the GRC’s genetic composition, function, and evolutionary significance. Here we assemble the GRC in two closely related species, the common and thrush nightingale. In total we identify 192 genes across the two GRCs, with many of them present in multiple copies. Interestingly, the GRC appears to be under little selective pressure, with the genetic content differing dramatically between the two species and many GRC genes appearing to be pseudogenized fragments. Only one gene, cpeb1, has a complete coding region in all examined individuals of the two species and shows no copy number variation. The acquisition of this gene by the GRC corresponds with the earliest estimates of the GRC origin, making it a good candidate for the functional indispensability of the GRC in songbirds