Biology subjects

Ewart, K. M.

Publications and source records attributed to Ewart, K. M..

3 recordsLinked to original sources

bioRxiv2024

Pleistocene sea-level fluctuation shapes archipelago-wide population structure in the Endangered Lord Howe Island cockroach Panesthia lata

Studies of biogeographic processes have often centred islands as model systems, yet questions remain about the role of Pleistocene sea-level fluctuations in shaping islands biodiversity. One novel, potentially informative model system is the Lord Howe Island Group of Australia. Despite the World Heritage status of this archipelago, almost nothing is known of the biogeographic origins, evolutionary distinctiveness or genetic diversity of the ecological communities across its 28 islands. In this study, we focused on the cockroach Panesthia lata, an ecologically specialized invertebrate with one of the broadest recorded distributions of any LHIG species. To investigate the influence of Pleistocene sea-level fluctuations on LHIG fauna, we explored the phylogeography of P. lata using single-nucleotide polymorphisms and complete mitochondrial genomes. Our analyses reveal that the lineage on the permanently isolated islet Balls Pyramid is highly divergent from the remaining populations, while those on the episodically connected Lord Howe, Roach and Blackburn Islands experienced gene flow during the last glacial period. These results offer the first evidence that Pleistocene land bridges allowed for overland migration across the archipelago. Further, although P. lata was believed to have been locally extirpated by rodents on Lord Howe Island, we discovered two surviving, relict populations. We also detected high levels of inbreeding in all populations, emphasizing the need for ongoing conservation management. Finally, the combination of shallow genetic structure and low diversity suggests that genetic rescue from another island may be a viable strategy to conserve the Lord Howe Island population of P. lata, as well as other species that have been similarly impacted by rodents.

evolutionary biology↗

bioRxiv2023

Pervasive relaxed selection in termite genomes

The genetic changes that enabled the evolution of eusociality have long captivated biologists. In recent years, attention has focussed on the consequences of eusociality on genome evolution. Studies have reported higher molecular evolutionary rates in eusocial hymenopteran insects compared with their solitary relatives. To investigate the genomic consequences of eusociality in termites, we sequenced genomes from three of their non-eusocial cockroach relatives. Using a phylogenomic approach, we found that termite genomes experienced lower rates of synonymous mutations than those of cockroaches, possibly as a result of longer generation times. We identified higher rates of nonsynonymous mutations in termite genomes than in cockroach genomes, and identified pervasive relaxed selection in the former (24-31% of the genes analysed) compared with the latter (2-4%). We infer that this is due to a reduction in effective population size, rather than gene-specific effects (e.g., indirect selection of caste-biased genes). We found no obvious signature of increased genetic load in termites, and postulate efficient purging at the colony level. Additionally, we identified genomic adaptations that may underpin caste formation, such as genes involved in post-translational modifications. Our results provide insights into the evolution of termites and the genomic consequences of eusociality more broadly.

evolutionary biology↗

bioRxiv2023

The genome of a globally invasive passerine, the common myna (Acridotheres tristis)

In an era of global climate change and massive environmental disturbance, biodiversity conservation is receiving increased attention. Conservation efforts are being greatly aided by genetic tools and approaches, which seek to understand patterns of genetic diversity and how they impact species health and ability to persist under future climate regimes. Invasive species offer vital model systems in which to investigate questions around adaptive potential, with a particular focus on how changes in genetic diversity and effective population size interact with the novel selection regime of the invaded range to drive rapid evolution. The common myna (Acridotheres tristis) is a globally invasive passerine, which has undergone multiple concurrent and sequential bottlenecks across its globally invasive range, and yet has established itself across a diverse array of ecological conditions. It is therefore an excellent model species for research both into the persistence of low-diversity populations and the mechanics of biological invasion. To underpin research on the invasion genetics of this species, we present the genome assembly of the common myna, assembled using a backbone of Oxford Nanopore Technologies long reads, alongside an RNA-seq based transcriptome and genome annotation. To provide genomic context for future studies, we describe the genomic landscape of this species, including genome wide allelic diversity, methylation, repeats, and recombination rate, as well as an examination of gene family expansions and contractions. Finally, we use demographic analysis to identify that some native regions underwent a dramatic population increase between the two most recent periods of glaciation, but also reveal artefactual impacts of genetic bottlenecks on demographic analysis.

genomics↗