Biology subjects

Pearman, W. S.

Publications and source records attributed to Pearman, W. S..

6 recordsLinked to original sources

bioRxiv2024

Joint consideration of selection and microbial generation count provides unique insights into evolutionary and ecological dynamics of holobionts

The relationship between, and joint selection on, a host and its microbes - the holobiont - can impact evolutionary and ecological outcomes of the host and its microbial community. Here we present a novel agent-based modelling framework for understanding the ecological dynamics of hosts and their microbiomes. Our model explicitly incorporates numerous microbial generations per host generation allowing for selection on both host and microbe. We apply our model to explore community fitness and diversity in the face of rapid environmental change. We demonstrate that multiple microbial generations can buffer changes experienced across host lifetimes by smoothing environmental transitions. Our simulations reveal that microbial fitness and host fitness may be at odds with each other when considering the impact of vertical inheritance of microbial communities from a host to its offspring - where high values favour microbial fitness, while low values favour host fitness - these tradeoffs are minimized when microbial generation count per host generation is high. We suggest that these results arise from cross-generational priority effects which maintain diversity within the community and can subsequently be acted upon by selection. Our model is readily extensible into new areas of holobiont research and provides novel insights into holobiont evolution under variable environmental conditions.

microbiology↗

bioRxiv2024

A Cry For Kelp: Evidence for Polyphenolic Inhibition of Oxford Nanopore Sequencing of Brown Algae

Genomic resources for macroalgae are increasingly important for conservation and commercial management, however the generation of such resources continues to be hampered by difficulties in the isolation of suitable DNA. Even when DNA has been isolated that otherwise appears high quality, such samples may not perform well during the sequencing process. We here compare Oxford Nanopore long-read sequencing results for three species of macroalgae to those of non-macroalgal species and find that macroalgal samples tend to lead to rapid decline in the number of available sequencing pores resulting in reduced sequencing yield. LC-MS analysis of macroalgal DNA that would be considered suitable for sequencing reveals that DNA derived from dried macroalgae is enriched for polyphenol-DNA adducts - which may lead to sequencing inhibition. Our findings have wide-ranging implications for the generation of genomic resources from macroalgae, for example long read sequencing of dried herbarium specimens, and suggest a need to use fresh tissue wherever possible for genome sequencing.

molecular biology↗

bioRxiv2023

Differences in density: taxonomic but not functional diversity in seaweed microbiomes affected by an earthquake

Host-associated microbial communities can make important contributions to host health, and are shaped by a range of different factors ranging from host condition, environmental conditions, and other microbes. Disentangling the roles of these factors can be particularly difficult as many variables are correlated. Here, we leveraged earthquake-induced changes in host density to identify the influence of host density on microbiome composition. A large (7.8 magnitude) earthquake in New Zealand in 2016 led to widespread coastal uplift of up to ~6m, sufficient to locally extirpate some intertidal kelp populations. These uplifted populations are slowly recovering, but intertidal kelps remain at much lower densities than at nearby, less uplifted sites. By comparing the microbiome of the low and high density sites using 16S amplicon sequencing, we observed that low density populations had higher beta-diversity than high density populations with regards to taxonomic variability, while no beta-diversity differences were observed between functional categories. Using phylogenetic and taxonomic turnover approaches, we determined that dispersal limitation shapes low density populations to a greater extent, while homogeneous selection shapes high density populations to a greater extent. Our findings shed light on microbiome assembly processes, particularly highlighting that large-scale disturbances that affect host density can dramatically influence microbiome structure.

microbiology↗

bioRxiv2021

Long read sequencing reveals atypical mitochondrial genome structure in a New Zealand marine isopod

Most animal mitochondrial genomes are small, circular, and structurally conserved. However, recent work indicates that diverse taxa possess unusual mitochondrial genomes. In Isopoda, species in multiple lineages have atypical and rearranged mitochondrial genomes. However, more species of this speciose taxon need to be evaluated to understand the evolutionary origins of atypical mitochondrial genomes in this group. In this study, we report the presence of an atypical mitochondrial structure in the New Zealand endemic marine isopod, Isocladus armatus. Data from long and short read DNA sequencing, suggests that I. armatus has two mitochondrial chromosomes. The first chromosome consists of two mitochondrial genomes that have been inverted and fused together in a circular form, and the second chromosome consists of a single mitochondrial genome in a linearized form. This atypical mitochondrial structure has been detected in other isopod lineages, and our data from an additional divergent isopod lineage (Sphaeromatidae) lends support to the hypothesis that atypical structure evolved early in the evolution of Isopoda. Additionally, we find that a heteroplasmic site previously observed across many species within Isopoda is absent in I. armatus, but confirm the presence of two heteroplasmic sites recently reported in two other isopod species.

genomics↗

bioRxiv2021

Commonly used Hardy-Weinberg equilibrium filtering schemes impact population structure inferences using RADseq data

Reduced representation sequencing (RRS) is a widely used method to assay the diversity of genetic loci across the genome of an organism. The dominant class of RRS approaches assay loci associated with restriction sites within the genome (restriction site associated DNA sequencing, or RADseq). RADseq is frequently applied to non-model organisms since it enables population genetic studies without relying on well-characterized reference genomes. However, RADseq requires the use of many bioinformatic filters to ensure the quality of genotyping calls. These filters can have direct impacts on population genetic inference, and therefore require careful consideration. One widely used filtering approach is the removal of loci which do not conform to expectations of Hardy-Weinberg equilibrium (HWE). Despite being widely used, we show that this filtering approach is rarely described in sufficient detail to enable replication. Furthermore, through analyses of in silico and empirical datasets we show that some of the most widely used HWE filtering approaches dramatically impact inference of population structure. In particular, the removal of loci exhibiting departures from HWE after pooling across samples significantly reduces the degree of inferred population structure within a dataset (despite this approach being widely used). Based on these results, we provide recommendations for best practice regarding the implementation of HWE filtering for RADseq datasets.

evolutionary biology↗

bioRxiv2020

Population Structure in a Direct-Developing Marine Isopod

Marine organisms generally exhibit one of two developmental modes: biphasic, with distinct adult and larval morphology, and direct development, in which larvae resemble adults. Developmental mode is thought to significantly influence dispersal, with direct developers expected to have much lower dispersal potential. However, in contrast to our relatively good understanding of dispersal and population connectivity for biphasic species, comparatively little is known about direct developers. In this study, we use a panel of 8,020 SNPs to investigate population structure and gene flow for a direct developing species, the New Zealand endemic marine isopod Isocladus armatus. On a small spatial scale (20 kms), gene flow between locations is extremely high and suggests an island model of migration. However, over larger spatial scales (600km), populations exhibit a clear pattern of isolation-by-distance. Because our sampling range is intersected by two well-known biogeographic barriers (the East Cape and the Cook Strait), our study provides an opportunity to understand how such barriers influence dispersal in direct developers. Our results indicate that I. armatus exhibits significant migration across these barriers, and suggests that ocean currents associated with these locations do not present a barrier to dispersal. Interestingly, we do find evidence of a north-south population genetic break occurring between M[a]hia and Wellington, two locations where there are no obvious biogeographic barriers between them. We conclude that developmental life history largely predicts dispersal in intertidal marine isopods. However, localised biogeographic processes can disrupt this expectation.

ecology↗