Biology subjects

Harper, A.

Publications and source records attributed to Harper, A..

6 recordsLinked to original sources

bioRxiv2026

Hurricane-induced structural disturbance amplifies forest vulnerability to subsequent heatwaves

Sequential hurricane-heatwave events threaten forest resilience via understudied legacy effects. Using Bayesian Structural Time Series, piecewise Structural Equation Modeling, and a 21-event global synthesis, we quantify how structural degradation non-linearly amplifies productivity loss during subsequent heatwaves. Our Hurricane Michael (2018) case study reveals significant negative GPP legacy effects during the 2019 heatwave. Intact, tall and diverse canopies buffer microclimates and moderate thermal sensitivity. Hurricane-induced structural simplification removes this protection, exposing temperature-sensitive shaded leaves to extreme stress. We identified a context-dependent hydraulic trade-off: structural complexity provides shading but exacerbates forest sensitivity to water deficits during peak heat, the vulnerability of which reverses during the recovery phase. Globally, these legacy effects are triggered by heatwave intensity and modulated by soil type, with loamy-soil forests most vulnerable. These findings highlight the critical role of forest structure in forest responses to compound disturbances. Neglecting structural legacies in Earth System Models likely underestimates risks to global carbon sinks.

ecology↗

bioRxiv2025

Pre-cheliceral region patterning in a spider provides new insights into the development and evolution of arthropod neurosecretory centres

Comparing head development among arthropods has helped identify ancestral aspects of brain patterning and structure in these animals and more broadly. Most understanding of arthropod head patterning has been learned from insects and the myriapod Strigamia maritima. Chelicerates represent an outgroup to mandibulate arthropods and can provide a valuable perspective to arthropod evolution and development. We assayed the expression of key markers of head patterning and neurosecretory centres in mandibulates in the pre-cheliceral region of embryos of the spider Parasteatoda tepidariorum. We found that, like mandibulates, this spider likely has a pars intercerebralis, marked by six3.2 and visual system homeobox/chx. We also found some evidence for another neurosecretory centre, the pars lateralis, marked by six3.2 and fasciclin 2. Furthermore, we identified anterior-medial cells in the spider pre-cheliceral region that express six3.2, foxQ2, and collier1, suggesting they may be pioneer neurons. However, these spider cells do not appear to be equivalent to the central pioneer neuronal cells identified in S. maritima because they lack expression of other key markers. Taken together, our study of spider pre-cheliceral region patterning adds a new chelicerate perspective to understanding the development and evolution of the arthropod head.

developmental biology↗

bioRxiv2023

Development and patterning of a highly versatile visual system in spiders

Visual systems provide a key interface between organisms and their surroundings, and have evolved in many forms to perform diverse functions across the animal kingdom. Spiders exhibit a range of visual abilities and ecologies, the diversity of which is underpinned by a highly versatile, modular visual system architecture. This typically includes eight eyes of two developmentally distinct types, but the number, size, location, and function of the eyes can vary dramatically between lineages. Previous studies of visual system development in spiders have confirmed that many components of the retinal determination gene (RDG) network are conserved with other arthropods, but so far, comparative studies among spiders are lacking. We characterised visual system development in eight species of spiders representing a range of morphologies, visual ecologies, and phylogenetic positions, to determine how these diverse configurations are formed, and how they might evolve. Combining synchrotron radiation tomography, transcriptomics, in situ hybridisation, and selection analyses, we characterise the repertoires and expression of key RDGs in relation to adult morphology. We identify key molecular players, timepoints, and developmental events that may contribute to adult diversity, in particular the molecular and developmental underpinnings of eye size, number, position, and identity across spiders.

developmental biology↗

bioRxiv2022

An atlas of spider development at single-cell resolution provides new insights into arthropod embryogenesis

Spiders are a diverse order of chelicerates that diverged from other arthropods over 500 million years ago. Research on spider embryogenesis, particular studies using the common house spider Parasteatoda tepidariorum, has made important contributions to understanding the evolution of animal development, including axis formation, segmentation, and patterning. However, we lack knowledge about the cells that build spider embryos, their gene expression profiles and fate. Single-cell transcriptomic analyses have been revolutionary in describing these complex landscapes of cellular genetics in a range of animals. Therefore, we carried out single-cell RNA sequencing of P. tepidariorum embryos at stages 7, 8 and 9, which encompass the establishment and patterning of the body plan, and initial differentiation of many tissues and organs. We identified 20 cell clusters, from 18.5k cells, which were marked by many developmental toolkit genes, as well as a plethora of genes not previously investigated. There were differences in the cell cycle transcriptional signatures, suggestive of different proliferation dynamics, which related to distinctions between endodermal and some mesodermal clusters, compared with ectodermal clusters. We found many Hox genes were markers of cell clusters, and Hox gene ohnologs often were present in different clusters. This provided additional evidence of sub- and/or neo-functionalisation of these important developmental genes after the whole genome duplication in the arachnopulmonate ancestor (spiders, scorpions, and allies). We also examined the spatial expression of marker genes for each cluster to generate a comprehensive cell atlas of these embryonic stages. This revealed new insights into the cellular basis and genetic regulation of head patterning, hematopoiesis, limb development, gut development, and posterior segmentation. This atlas will serve as a platform for future analysis of spider cell specification and fate, and studying the evolution of these processes among animals at cellular resolution.

developmental biology↗

bioRxiv2020

The evolution of Sox gene repertoires and regulation of segmentation in arachnids

The Sox family of transcription factors regulate many processes during metazoan development, including stem cell maintenance and nervous system specification. Characterising the repertoires and roles of these genes can therefore provide important insights into animal evolution and development. We further characterised the Sox repertoires of several arachnid species with and without an ancestral whole genome duplication (WGD), and compared their expression between the spider Parasteatoda tepidariorum and the harvestman Phalangium opilio. We also found that most Sox families have been retained as ohnologs after WGD and evidence for potential subfunctionalisation and/or neofunctionalization events. Our results also suggest that Sox21b-1 likely regulated segmentation ancestrally in arachnids, playing a similar role to the closely related SoxB gene, Dichaete, in insects. We previously showed that Sox21b-1 is required for the simultaneous formation of prosomal segments and sequential addition of opisthosomal segments in P. tepidariorum. We studied the expression and function of Sox21b-1 further in this spider and found that while this gene regulates the generation of both prosomal and opisthosomal segments, it plays different roles in the formation of these tagmata reflecting their contrasting modes of segmentation and deployment of gene regulatory networks with different architectures.

developmental biology↗

bioRxiv2019

Enhanced prediction of gene and missense rare-variant pathogenicity by joint analysis of gene burden and amino-acid residue position

BackgroundAlthough rare-missense variants in Mendelian disease-genes have been noted to cluster in specific regions of proteins, it is not clear how to consider this information when evaluating the pathogenicity of a gene or variant. Here we introduce methods for gene-association and variant-interpretation that utilise this powerful signal. MethodsWe present a case-control rare-variant association test, ClusterBurden, that combines information on both variant-burden and variant-clustering. We then introduce a data-driven modelling framework to estimate mutational hotspots in genes with missense variant-clustering and integrate further in-silico predictors into the models. ResultsWe show that ClusterBurden can increase statistical power to scan for putative disease-genes, driven by missense variants, in simulated data and a 34-gene panel dataset of 5,338 cases of hypertrophic cardiomyopathy. We demonstrate that data-driven models can allow quantitative application of the ACMG criteria PM1 and PP3, to resolve a wide range of pathogenicity potential amongst variants of uncertain significance. A web application (Pathogenicity_by_Position) is accessible for missense variant risk prediction of six sarcomeric genes and an R package is available for association testing using ClusterBurden. ConclusionThe inclusion of missense residue position enhances the power of disease-gene association and improves rare-variant pathogenicity interpretation.

genetics↗