Biology subjects

Howells, E. J.

Publications and source records attributed to Howells, E. J..

6 recordsLinked to original sources

bioRxiv2026

Localised admixture triggers parallel adaptation in a coral species trio on the Great Barrier Reef

Hybridisation can shape evolutionary trajectories and fuel rapid adaptation. Yet, whether adaptive introgression repeatedly reconfigures genomes in predictable ways remains largely unknown. Here, we show that three-way admixture drives repeatable parallel differentiation in reef-building corals in the Acropora hyacinthus species complex. Adaptive introgression is confined to the southern Great Barrier Reef, where admixture timing coincides with a recent breakdown in species barriers despite limited historical gene flow. Genome-wide introgression is characterised by numerous shared minor-parent ancestry peaks that are enriched for stress-response genes and under positive selection for parallel adaptive admixture. Our results demonstrate that introgressive hybridisation can be geographically restricted between sympatric marine species and can promote repeated rapid adaptation that transcends species boundaries.

evolutionary biology↗

bioRxiv2025

Long-distance gene flow and contrasting population structures of reef-building corals and their algal symbionts inform adaptive potential across the Western Pacific

The genetic diversity and connectivity of reef-building coral populations are key to their survival in warming oceans. Yet our understanding of corals demographic resilience and adaptive potential is complicated by cryptic species diversity, wide geographic distributions, and complex coral-algal symbioses. To address these challenges, we investigated genetic connectivity and diversity of the broadcast-spawning coral Acropora spathulata and its associated Symbiodiniaceae across 29 reefs spanning the Great Barrier Reef, the Coral Sea, and New Caledonia, using whole-genome sequencing of 1,088 colonies. We identified four genetically distinct coral populations that diverged between 0.27 and 0.65 million years ago, likely due to geographic isolation across thousands of kilometers. These populations maintained asymmetrical gene flow along major ocean currents despite demographic isolation, and sustained large local effective population sizes ([~]2,900), supported by a high dispersal range of [~]100 km per generation. In contrast, their Symbiodiniaceae partners varied over finer spatial scales, with five distinct Cladocopium taxa distributed along latitudinal and cross-shore gradients, likely driven by local environmental conditions. These results suggest that high dispersal capacity and large local population size promote demographic resilience within reef systems, while environment-specific symbioses and long-distance gene flow across reef-systems support adaptation and evolutionary rescue.

molecular biology↗

bioRxiv2024

Environmental, host, and symbiont drivers of heat tolerance in a species complex of reef-building corals

Reef-building coral populations are under unprecedented threat from climate warming. Yet, variation in coral heat tolerance exists whereby some colonies can cope with higher sea temperatures than others and thus may hold unique value for conservation and restoration. Here, we quantify variation in heat tolerance of an ecologically important tabular coral species complex across the Great Barrier Reef (GBR) while also measuring genomic variation in the coral host and symbiont partners. Coral bleaching and photochemical traits were measured in 569 colonies within the Acropora hyacinthus species complex from 17 reefs following exposure to standardized acute heat stress assays. We detected substantial variation in heat tolerance, where individual colony thermal thresholds differed by up to 7.3{degrees}C and 5.7{degrees}C among and within reefs, respectively. Sea surface temperature climatology was the strongest predictor of heat tolerance, where colonies from warmer northern and inshore reefs typically exhibited the highest thermal thresholds, while colonies from cooler southern reefs were able to tolerate greater temperature increases relative to their local summer temperatures. Heat tolerance was also positively associated with exposure to thermal stress in the weeks preceding measurements. Assignment of colonies to host genomic clusters revealed four putative species within the A. hyacinthus complex that did not vary in their responses to experimental heat stress. Symbiodiniaceae communities within colonies were comprised primarily of Cladocopium ITS2 variants that differed spatially but had minimal effect on heat tolerance. Between 36 - 80% of heat tolerance variation was explained by environmental, host, and symbiont genomic predictors, leaving 20 - 64% to be explained by additional underlying drivers such as functional genomic variation not measured here. These results may be used to inform conservation and restoration actions, including targeting heat tolerant individuals for selective breeding, and will provide a foundation for evaluating the genomic basis of heat tolerance.

ecology↗

bioRxiv2024

Quantifying the thermal tolerance traits of individual corals reveals widespread variation across the Great Barrier Reef

Adaptation of reef-building corals to global warming depends upon standing heritable variation in tolerance traits upon which selection can act. Yet limited knowledge exists on heat tolerance variation among conspecific individuals separated by meters to hundreds of kilometers. Here, we performed standardized acute heat stress assays to quantify the thermal tolerance traits of 768 colonies of Acropora spathulata from 14 reefs spanning 1060 km (9.5{degrees} latitude) of the Great Barrier Reef. Thermal thresholds for photochemical efficiency and chlorophyll retention varied considerably among individual colonies both among reefs ([~]6 {degrees}C) and within reefs ([~]3 {degrees}C). Although tolerance rankings of colonies varied between traits, the most heat tolerant corals (i.e. top 25% of each trait) were found at virtually all reefs, indicating widespread phenotypic variation. Reef-scale environmental predictors explained 12-62% of trait variation. Corals exposed to high thermal averages and recent thermal stress exhibited the greatest photochemical performance, likely reflecting local adaptation and stress pre-acclimatization, and the lowest chlorophyll retention suggesting stress pre- sensitization. Importantly, heat tolerance relative to local summer temperatures was the greatest on southern reefs suggestive of higher adaptive potential. These results can be used to identify naturally tolerant coral populations and individuals for conservation and restoration applications.

ecology↗

bioRxiv2018

Intergenerational epigenetic inheritance in reef-building corals

MainThe notion that intergenerational or transgenerational inheritance operates solely through genetic means is slowly being eroded: epigenetic mechanisms have been shown to induce heritable changes in gene activity in plants 1,2 and metazoans 1,3. Inheritance of DNA methylation provides a potential pathway for environmentally induced phenotypes to contribute to evolution of species and populations 1-4. However, in basal metazoans, it is unknown whether inheritance of CpG methylation patterns occurs across the genome (as in plants) or as rare exceptions (as in mammals) 4. Here, we demonstrate genome-wide intergenerational transmission of CpG methylation patterns from parents to sperm and larvae in a reef-building coral. We also show variation in hypermethylated genes in corals from distinct environments, indicative of responses to variations in temperature and salinity. These findings support a role of DNA methylation in the transgenerational inheritance of traits in corals, which may extend to enhancing their capacity to adapt to climate change.

genetics↗

bioRxiv2017

Genomic and transcriptomic signals of thermal tolerance in heat-tolerant corals (Platygyra daedalea) of the Arabian/Persian Gulf

Scleractinian corals occur in tropical regions near their upper thermal limits, and are severely threatened by rising ocean temperatures. Ocean warming leads to loss of symbiotic algae (Symbiodinium), reduced fitness for the coral host, and degradation of the reef. However, several recent studies have shown that natural populations of corals harbor genetic variation in thermal tolerance that may support adaptive responses to warming. Here weve extended these approaches to study heat tolerance of corals in the Persian/Arabian Gulf, where heat-tolerant local populations have adapted to warm summer temperatures (>36{degrees}C). To evaluate whether selection has depleted genetic variation in thermal tolerance, estimate the potential for future adaptive responses, and understand the functional basis for these corals unusual heat tolerance, we measured thermal tolerance using controlled crosses in the Gulf coral Platygyra daedalea. We found that heat tolerance is highly heritable in this population (0.487-0.748), suggesting substantial potential for adaptive responses to selection for thermal tolerance. To identify genetic markers associated with this variation, we conducted genomewide SNP genotyping in parental corals and tested for relationships between paternal genotype and thermal tolerance of the offspring. We found that multilocus SNP genotypes explained a large fraction of variation in thermal tolerance in these crosses (69%). To investigate the functional basis of these differences in thermal tolerance, we profiled transcriptional responses in tolerant and susceptible families, revealing substantial sire effects on transcriptional responses to thermal stress. We also studied sequence variation in these expressed sequences, identifying alleles and functional groups associated with thermal tolerance. Our findings demonstrate that corals in these populations harbor extensive genetic variation in thermal tolerance, and these heat-tolerant phenotypes differ in both gene sequences and transcriptional stress responses from their susceptible counterparts.

evolutionary biology↗