Biology subjects

Buerger, P.

Publications and source records attributed to Buerger, P..

5 recordsLinked to original sources

bioRxiv2026

Heat-evolved strains of the coral symbiont Cladocopium proliferum have diverged in exon usage

Experimental evolution at 31{degrees}C produced strains of the coral symbiont Cladocopium proliferum (Symbiodiniaceae) that show increased thermal tolerance in culture, and some of them also raise the bleaching tolerance of coral. Here we investigated how exon usage and alternative splicing have diverged in the heat-evolved strains (SS3, SS5, SS8) from their wild-type cultures (WT10) by reanalysing published transcriptomes of the strains in symbiosis with Acropora kenti larvae at 27{degrees}C using limma, DEXSeq and rMATS. Exon usage separated the strains from an unselected wild-type strain, with 1,308 genes with differential exon usage for SS8, 4,931 for SS5 and 10,464 for SS3, and 59% to 72% of these genes showed no differential expression. SS8, the only strain that also raises the bleaching tolerance of coral larvae, was the closest to the wild type, while a shared set of 757 genes changed in all three heat-evolved strains together. Junction level splicing events (rMATS) did not follow this order (721, 687 and 847 events against WT10), and skipped exons were the most common type, followed by alternative 5' splice sites. Between SS8 and the non-protective strains, alternative 5' splice sites were the most common type (91 of 291 events against SS5 and 68 of 207 against SS3), and retained introns were nearly as common as skipped exons. No GO term was enriched in the shared set or the SS8 lists, but both held genes with a possible link to heat tolerance, among them a mitochondrial glutathione peroxidase in the shared set and a glutathione S-transferase in which SS8 differed from the non-protective strains. Future studies of heat-evolved symbionts should therefore include exon level and splicing analyses to resolve the fine scale differences between strains that gene level analyses miss.

evolutionary biology↗

bioRxiv2026

Rapid thermal adaptation in coral photosymbionts draws on standing variation and recombination

Bleaching tolerance in corals depends in part on the thermal tolerance of their microalgal symbionts. Laboratory evolution has increased the thermal tolerance of the symbiont Cladocopium proliferum in ~120 generations, but the genetic basis of that response was unknown. We compared single nucleotide polymorphisms in transcriptomes of three heat-evolved C. proliferum strains and one wild-type (unselected) strain from the same progenitor. We found 15,640 polymorphic loci, but no variant was both private to a strain and consistent across its replicates, which indicates that new mutations contributed little to the response in expressed sequences. Instead, allele frequencies at 350 loci differed significantly between strains, and linkage patterns indicated recombination had occurred within scaffolds both before and after the strains were separated. Selection and recombination of variation already present in the progenitor therefore underpinned the rapid thermal adaptation. Experimental evolution for reef restoration should start from genetically diverse cultures rather than single cell isolates.

evolutionary biology↗

bioRxiv2026

Conserved transcriptomic heat stress response signatures in coral recruits selectively bred from thermally distinct broodstock in a low-differentiation system

Thermal history provenancing can guide the choice of parental broodstock for selective breeding of corals from distinct reefs and has been proposed as an intervention for enhancing climate resilience. However, the genetic and molecular mechanisms underlying resultant offspring responses to heat stress, particularly during early life stages, remain poorly understood. Here, we generated Acropora tersa larvae and recruits by crossing parental colonies from the historically warmer Martin Reef and cooler Davies Reef and assessed the effects of within- and between-reef crosses on genetic diversity and transcriptional responses to heat stress. Genome-wide single nucleotide polymorphism analyses showed that broodstock from Martin and Davies Reefs were weakly differentiated (FST = 0.008) and exhibited comparable heterozygosity, as did all larval offspring groups. Transcriptomic analyses of recruits exposed to heat stress (32 {degrees}C for 36 days) revealed that both within- and between-reef offspring groups activated conserved stress-response pathways, with seven genotype-independent heat-responsive genes detected across all offspring groups. Differential expression and enrichment analyses showed induction of defence, protein homeostasis, intracellular transport, and metabolic processes alongside repression of growth- and signalling-related functions, consistent with the Type A General Coral Stress Response. Taken together, these findings suggest that the benefits of thermal history provenancing-informed selective breeding may be limited in low-differentiation systems and that targeted pre-screening of broodstock may help capture functional genetic variation relevant to restoration applications.

genomics↗

bioRxiv2024

Pushing the limits: expanding the temperature tolerance of a coral photosymbiont through differing selection regimes

Coral thermal bleaching resilience can be improved by enhancing photosymbiont thermal tolerance via experimental evolution. While successful for some strains, selection under stable temperatures was ineffective at increasing the thermal threshold of an already thermo-tolerant photosymbiont (Durusdinium trenchii). Corals from environments with fluctuating temperatures tend to have comparatively high heat tolerance. Therefore, we investigated whether exposure to temperature oscillations can raise the upper thermal limit of D. trenchii. We exposed a D. trenchii strain to stable and fluctuating temperatures profiles, which varied in oscillation frequency. After 2.1 years (54-73 generations), we characterised the adaptive responses under the various experimental evolution treatments by constructing thermal performance curves of growth from 21 to 31{degrees}C for the heat-evolved and wild-types lineages. Additionally, oxidative stress, photophysiology, photosynthesis and respiration rates were assessed under increasing temperatures. Of the fluctuating temperature profiles investigated, selection under the most frequent oscillations (diurnal) induced the greatest widening of D. trenchiis thermal niche. Continuous selection under elevated temperatures induced the only increase in thermal optimum and a degree of generalism. Our findings demonstrate how differing levels of thermal homogeneity during selection drive unique adaptative responses to heat in a coral photosymbiont.

evolutionary biology↗

bioRxiv2022

Flow cytometry-based biomarker assay for in vitro identification of heat tolerance conferring coral symbionts

Corals tolerance to high temperature stress largely depends on their symbiotic microalgae (Symbiodiniaceae). However, the contributing microalgal traits are largely unclear. Here we compare the in vitro cellular profiles of seven Cladocopium C1acro microalgal strains (derived from the same ancestral strain) during a four-week exposure to 27{degrees}C or 31{degrees}C. One was an unselected wild-type strain (WT), three were selected at 31{degrees}C for nine years and shown to confer thermal tolerance on the coral host (SS+) and three others were similarly selected but did not confer tolerance (SS-). Flow cytometry was used to measure the intracellular stress indicators reactive oxygen species (ROS), reduced glutathione (rGSH) and mitochondrial-membrane potential ({Delta}{Psi}m), as well as cell size/shape and photosynthetic pigments. Cell densities and photosynthetic efficiency ({Phi}PSII, Fv/Fm) were also measured. WT showed the highest levels of intracellular ROS and {Delta}{Psi}m, lowest rGSH and largest cell sizes at both temperatures. SS+ strains had the lowest ROS and highest rGSH values and a unique pattern of correlations among parameters at 31{degrees}C. Our results support previous reports implicating the role of microalgal ROS, {Delta}{Psi}m and rGSH in holobiont thermal tolerance and suggest flow cytometry is a useful pre-screening tool for identifying microalgal strains with enhanced thermal tolerance.

microbiology↗