Biology subjects

Cobbold, C.

Publications and source records attributed to Cobbold, C..

6 recordsLinked to original sources

bioRxiv2026

A simple method of estimating rabies outbreak sizes from phylogenies

The ability to estimate the size of a disease outbreak is beneficial both for coordinating an outbreak response and for retrospectively evaluating the effectiveness of response measures and surveillance. Methods such as seroprevalence surveys and epidemiological modelling can be used for this purpose, but are not suitable for every outbreak. We develop a simple formula to estimate the proportion of outbreak cases sequenced, using only the per-generation substitution rate and the length of a phylogenetic tree. This proportion can then be used to estimate the outbreak size. We validate this method using subsampled data from fully observed simulated outbreaks, and then apply it to an ongoing rabies outbreak in the Philippines. We find that this method produces accurate estimates of outbreak size and can be applied to outbreaks with substitution rates and R0 values within the estimated range for rabies. We estimated that approximately 19% of cases from the outbreak in the Philippines had been sequenced, suggesting better than average case detection, with a resulting outbreak size estimate consistent with previous analyses. With this method and the associated R package POSER (https://github.com/RowanDurrant/poser), we aim to make rabies outbreak size estimation more accessible, but further work is required to improve its applicability to other diseases.

genetics↗

bioRxiv2026

Phenotypic plasticity as a route to population shifts via tipping points

Environmental change has caused dramatic global declines in biodiversity, with some species showing abrupt and often irreversible changes in population abundance. These regime shifts can occur when environmental thresholds, known as tipping points, are passed. Many species can respond to environmental change via phenotypic plasticity with the expectation that strong phenotypic plasticity reduces the risk of regime shifts by enabling a species to rapidly respond to environmental change, potentially mitigating the risks of population collapse. Testing the theory that phenotypic plasticity buffers against regime shifts requires a novel whole population approach that robustly considers the feedback mechanisms between environment, phenotype and population density, common to the life-history of many species. For this purpose we develop a tractable mathematical framework, and demonstrate, counter-intuitively, that phenotypic plasticity can induce tipping points, due to the inclusion of feedback mechanisms that operate at both the level of the organism and population. Consequently, predicting the existence of potentially devastating tipping points and so understanding ecosystem collapse is more nuanced than current thinking suggests.

ecology↗

bioRxiv2026

Differences in codon usage between host-species-specific rabies virus clades are driven by UpA and purine content

Viral genes sometimes use certain codons more than others due to their nucleotide content, translational efficiency, and selection pressure from the host immune system. The rabies virus (RABV) is a negative strand RNA virus which can infect a broad range of mammalian hosts, with many of its clades circulating predominantly in specific host species. Previous work on codon usage in RABV has focused only on broader viral clades. We use publicly available RABV nucleoprotein gene sequences to investigate how dinucleotide content and codon usage biases differ between host-associated clades, and what drives these differences. We found that codon usage varies most between bat- and carnivore-associated RABV clades, and more subtly between host-species-specific minor clades within these groups. C1, GA3 and GT3 content were found to have a strong influence over codon usage patterns, and CpG content was higher in carnivore-associated RABV clades than in bat-associated clades. This, along with lower numbers of zinc-finger antiviral protein binding motifs than would be expected based on (di)nucleotide composition in bat-associated RABV sequences, suggests that bat-associated RABV clades may be under higher selection pressure from the hosts zinc-finger antiviral protein than carnivore-associated clades are, warranting further investigation of the mechanism underpinning this change.

microbiology↗

bioRxiv2023

Examining the molecular clock hypothesis for the contemporary evolution of the rabies virus

The molecular clock hypothesis assumes that mutations accumulate on an organisms genome at a constant rate over time, but this assumption does not always hold true. While modelling approaches exist to accommodate deviations from a strict molecular clock, assumptions about rate variation may not fully represent the underlying evolutionary processes. There is considerable variability in rabies virus (RABV) incubation periods, ranging from days to over a year, during which viral replication may be reduced. This prompts the question of whether modelling RABV on a per infection generation basis might be more appropriate. We investigate how variable incubation periods affect root-to-tip divergence under per-unit time and per-generation models of mutation. Additionally, we assess how well these models represent root-to-tip divergence in time-stamped RABV sequences. We find that at low substitution rates (<1 substitution per genome per generation) divergence patterns between these models are difficult to distinguish, while above this threshold differences become apparent across a range of sampling rates. Using a Tanzanian RABV dataset, we calculate the mean substitution rate to be 0.17 substitutions per genome per generation. At RABVs substitution rate, the per-generation substitution model is unlikely to represent rabies evolution substantially differently than the molecular clock model when examining contemporary outbreaks; over enough generations for any divergence to accumulate, extreme incubation periods average out. However, measuring substitution rates per-generation holds potential in applications such as inferring transmission trees and predicting lineage emergence. Author SummaryRabies is a neglected disease that kills around 60,000 people each year. After entering the body, the incubation period of the virus is usually less than one month, but can sometimes span months to years. While we normally assume a virus accumulates mutations at a constant rate, it is possible that rabies occasional long incubation periods mean that mutations accumulate at varying rates if the virus replicates (and thus mutates) more slowly during the incubation period. We compared how the rabies virus evolves over time using two simulation models where mutations either occur per unit time or per infection generation. We also calculated the mean substitution rate per infection generation, which can be useful for inferring linkage between related rabies cases. We found that at realistic substitution rates for the rabies virus, we could not distinguish between the two models. Our calculations show that in most generations no mutations are expected to occur. Thus, over a time period long enough to observe genetic divergence, occasional long incubation periods would be "cancelled out" by shorter than average incubation periods, meaning that the two models are almost equivalent. However our work suggests that modelling substitution rates per generation may be useful for epidemiological inference.

microbiology↗

bioRxiv2019

Changing environments and genetic variation: inbreeding does not compromise short-term physiological responses

O_LISelfing plant lineages are surprisingly widespread and successful in a broad range of environments, despite showing reduced genetic diversity, which is predicted to reduce long-term evolutionary potential. However, short-term capacity to respond appropriately to new conditions might not require high levels of standing genetic variation. The purpose of this study was to directly test whether mating system variation and its associated changes in genetic variability in natural populations affected responses to short-term environmental challenges.\nC_LIO_LIWe compared relative fitness and metabolome profiles of naturally outbreeding (genetically diverse) and inbreeding (genetically depauperate) populations of a long-lived perennial plant, Arabidopsis lyrata, under constant growth chamber conditions and an outdoor common garden environment outside its native range.\nC_LIO_LIWe found no effect of mating system on survival or reproductive output, although several phenological traits showed different associations with latitude for outcrossing and inbreeding populations. Natural inbreeding had no effect on the plasticity of physiological responses, using either multivariate approaches or analysis of variation in individual metabolites. Moreover, while both growing environment and time significantly affected the relative abundance of individual metabolites, inbreeding populations responded similarly to outbreeding populations, suggesting adaptation to the outdoor environment, regardless of mating system.\nC_LIO_LIWe conclude that low genetic diversity in naturally inbred populations may not compromise fitness or short-term capacity for appropriate physiological responses to environmental change. The absence of natural costs of inbreeding could help to explain the global success of clonal or asexual mating strategies for adapting to a wide range of environments.\nC_LI

evolutionary biology↗

bioRxiv2018

Application of long read sequencing to determine expressed antigen diversity in Trypanosoma brucei infections

AO_SCPLOWBSTRACTC_SCPLOWAntigenic variation is employed by many pathogens to evade the host immune response, and Trypanosoma brucei has evolved a complex system to achieve this phenotype, involving sequential use of variant surface glycoprotein (VSG) genes encoded from a large repertoire of [~]2,000 alleles. T. brucei express multiple, sometimes closely related, VSGs in a population at any one time, and the ability to resolve and analyse this diversity has been limited. We applied long read sequencing (PacBio) to VSG amplicons generated from blood extracted from batches of mice sacrificed at time points (days 3, 6, 10 and 12) post-infection with T. brucei TREU927. The data showed that long read sequencing is reliable for resolving allelic differences between VSGs, and demonstrated that there is significant expressed diversity (449 VSGs detected across 20 mice) and across the timeframe of study there was a clear semi-reproducible pattern of expressed diversity (median of 27 VSGs per sample at day 3 post infection (p.i.), 82 VSGs at day 6 p.i., 187 VSGs at day 10 p.i. and 132 VSGs by day 12 p.i.). There was also consistent detection of one VSG dominating expression across replicates at days 3 and 6, and emergence of a second dominant VSG across replicates by day 12. The innovative application of ecological diversity analysis to VSG reads enabled characterisation of hierarchical VSG expression in the dataset, and resulted in a novel method for analysing such patterns of variation. Additionally, the long read approach allowed detection of mosaic VSG expression from very few reads - this was observed as early as day 3, the earliest that such events have been detected. Therefore, our results indicate that long read analysis is a reliable tool for resolving diverse allele expression profiles, and provides novel insights into the complexity and nature of VSG expression in trypanosomes, revealing significantly higher diversity than previously shown and identifying mosaic gene formation unprecedentedly early during the infection process.

genomics↗