Biology subjects

Cassidy, D.

Publications and source records attributed to Cassidy, D..

4 recordsLinked to original sources

bioRxiv2026

Juveniles exhibit lower heatwave tolerance than adults in a reef-building coral

Marine heatwaves cause widespread coral bleaching and mortality, yet thermal responses often differ between adult and juvenile corals, with the latter frequently being more tolerant. Whether the observed enhanced tolerance of juveniles reflects intrinsic physiological differences across life stages or simply reduced environmental stress due to shaded microhabitats occupied by juveniles, or a combination of both factors, remains unclear. To test whether colony size determines thermal responses and if a threshold size exists for tolerance, we exposed 89 colonies of the reef-building coral Acropora aff. digitifera to a 6-week, 32.5 C simulated marine heatwave under controlled light conditions, with cumulative stress reaching 20 C-weeks. Contrary to expectations, ~2 C-weeks less heat stress was required to trigger bleaching and mortality in coral juveniles compared to adults. Mortality divergence across colony sizes was greatest at ~10 C-weeks, when the smallest corals exceeded 80% mortality, whereas the largest colonies showed <10% mortality. A breakpoint in survival odds was apparent at 13.4 cm diameter, corresponding to the size at onset of sexual maturity in the native wild population for this species. These results indicate an ontogenetic shift in physiological heat tolerance, with larger reproductively mature colonies showing enhanced tolerance. The apparent survival advantage of juveniles in the reef frequently reported during bleaching events could be more likely due to micro-environmental buffering than intrinsic physiological tolerance. Our findings suggest that juvenile corals may be more vulnerable to climate change than previously thought, particularly as declining habitat complexity could reduce microhabitat refugia on future reefs.

ecology↗

bioRxiv2026

ACC1-Dependent De Novo Lipogenesis Sustains Hematopoietic Stem Cell Quiescence and Self-Renewal

Certain aspects of lipid metabolism are known to regulate hematopoietic stem cell (HSC) function, including fatty acid oxidation and lipid uptake, but there is a limited understanding of the contribution of de novo fatty acid synthesis to HSC homeostasis. Here, we show that endogenous fatty acid synthesis is essential for HSC function. Conditional deletion of Acaca, the gene that encodes the rate-limiting enzyme for de novo fatty acid synthesis, acetyl-CoA carboxylase 1 (ACC1), in hematopoietic cells profoundly reduces HSC function, marked by a reduced ability to reconstitute irradiated mice after competitive transplantation. ACC1 deficiency reduced quiescence, increased uptake of extracellular lipids, and increased reactive oxygen species in HSCs. The loss of HSC function is partly caused by increased fatty acid oxidation as deletion of CPT1a, which is required for long-chain fatty acid oxidation, partially rescued HSC function. A balance between fatty acid synthesis and fatty acid oxidation is thus critical for the maintenance of HSC function.

cell biology↗

bioRxiv2025

Accessible AI Enhances Monitoring of Coral Seeding Devices in Reef Restoration

1. Coral seeding devices (CSDs) - tools designed to deliver sexually propagated corals to target locations - offer a promising means to increase coral abundance on degraded reefs. However, evaluating CSD effectiveness for coral reef restoration across wide areas and over many years is limited by the lack of robust and efficient monitoring approaches. Large-area reef imagery offers an attractive potential solution, but manual detection of CSDs within imagery is slow and limits the scalability of CSD monitoring. 2. We investigated whether machine learning classifiers could accurately detect CSDs in reef orthoimages and tested the performance of classifiers created following minimal manual annotation effort. Using freely available software, we first evaluated classifier performance in a single-site experiment using an orthoimage containing 989 CSDs deployed in Palau. We then also evaluated performance in a multi-site experiment using orthoimages containing a different CSD design deployed across seven sites in the central Great Barrier Reef, Australia. 3. In Experiment 1, classifiers trained on just 30 CSDs annotated within 10 minutes achieved mean recall and precision of 96.7% and 97.1% respectively, reducing manual annotation time by 95.6% whilst still detecting 98.8% of the number of devices found manually. Larger training sets yielded less reliable classifiers and required more manual effort. In Experiment 2, classifiers trained on 30 CSD annotations from one site performed excellently across seven orthoimages from multiple reefs, achieving mean recall and precision of 99.2% and 93.3%. 4. We present evidence that CSD classifiers can be highly effective across both single- and multi-site CSD deployments. In using a free and user-friendly software, we also demonstrate their accessibility to reef restoration practitioners. To facilitate wider uptake of CSD monitoring, we provide a step-by-step protocol for implementing CSD classifiers. By improving access to efficient, direct assessment of intervention outcomes, this method can play a vital role in guiding the enhancement of approaches aiming to restore coral reefs.

ecology↗

bioRxiv2024

Ascorbate depletion increases quiescence and self-renewal potential in hematopoietic stem cells and multipotent progenitors

Ascorbate (vitamin C) limits hematopoietic stem cell (HSC) function and suppresses leukemia development by promoting the function of the Tet2 tumor suppressor. In humans, ascorbate is obtained from the diet while in mice it is synthesized in the liver. In this study, we show that deletion of the Slc23a2 ascorbate transporter severely depleted ascorbate from hematopoietic cells. Slc23a2 deficiency increased HSC reconstituting potential and self-renewal potential upon transplantation into irradiated mice. Slc23a2 deficiency also increased the reconstituting and self-renewal potential of multipotent hematopoietic progenitors (MPPs), conferring the ability to long-term reconstitute irradiated mice. Slc23a2-deficient HSCs and MPPs divided much less frequently than control HSCs and MPPs. Increased self-renewal and reconstituting potential were observed particularly in quiescent Slc23a2-deficient HSCs and MPPs. The effect of Slc23a2 deficiency on MPP self-renewal was not mediated by reduced Tet2 function. Ascorbate thus regulates quiescence and restricts self-renewal potential in HSCs and MPPs such that ascorbate depletion confers MPPs with long-term self-renewal potential. KEY POINTSO_LIDeletion of the ascorbate transporter, Slc23a2, increases quiescence and self-renewal potential in HSCs and multipotent progenitors C_LIO_LIAscorbate depletion is sufficient to confer long-term self-renewal potential upon multipotent hematopoietic progenitors C_LI

cell biology↗