Rebecca L. Cramp

Accumulation of unrepaired DNA lesions is a key mechanistic driver of mortality in organisms exposed to elevated ultraviolet-B radiation (UVBR). Recent research has found that high irradiance UVBR causes disproportionate mortality in larvae of a UV-sensitive amphibian (Limnodynastes peronii) compared with an equivalent dose of low irradiance UVBR. Here, we aimed to determine whether this irradiance-dependent effect is also reflected in the DNA damage profile of L. peronii larvae. Under laboratory conditions, we exposed larvae to one of two different UVBR irradiances over 2 days, keeping the daily dose equal by adjusting exposure duration. Larvae were sampled at set time points throughout experimental exposures for quantification of cyclobutane pyrimidine dimer (CPD) concentration. Larvae were highly susceptible to UVBR-induced CPD formation and had low rates of DNA repair, resulting in a carryover of DNA damage into the following day. Consequently, CPD concentrations accumulated to a higher level during the second day of exposure, an effect that was exacerbated by high irradiance exposure. Larvae exposed to high irradiance UVBR accumulated CPD lesions almost 3 times faster than larvae exposed at half the irradiance, causing a 47% increase in CPD concentration across sampling time points. These results demonstrate the capacity for high irradiance exposure to exacerbate UVBR-induced genomic instability, which may explain the irradiance-dependent mortality observed in this species. Given the conserved nature of DNA repair mechanisms across taxa, these findings have implications for other aquatic organisms with a larval life stage, including fish and coral, that are facing increasing UVBR levels owing to climate change.

Social living often confers substantial fitness benefits; however, close spatial association among individuals can also elevate opportunities for pathogen transmission, especially where the populations are dense. Despite this, the extent to which avoidance behaviours are expressed by wild reptiles facing fungal disease remains unclear. We examined Eastern Water Dragons (EWDs; Intellagama lesueurii ) in Roma Street Parklands, Brisbane, Australia, where a population is affected by the emerging fungal pathogen Nannizziopsis barbatae ( Nb ). Using a five-year dataset (2018-2023) spanning 146 individuals, we quantified social distance, as the minimum distance to the nearest neighbour, in relation to the number of diseased conspecifics that overlapped each individual’s seasonal core home area. Social distance decreased as diseased conspecifics became more numerous, indicating a strong crowding effect; however, this reduction was weaker for diseased individuals, which maintained larger distances than healthy individuals even under high disease pressure. Together, these patterns support partial social avoidance consistent with behavioural changes in infected individuals, suggesting that infection risk constrains density-driven proximity. Our findings provide new insights into how disease pressure shapes social spacing in reptiles and contribute to a broader understanding of behavioural responses to emerging infectious fungal diseases.

Ambient sunlight contains ultraviolet radiation (UVR), a potent genotoxic stressor, yet whether natural UVR induces DNA damage in free-living amphibian larvae remains unclear. We reared striped marsh frogs (Limnodynastes peronii) in outdoor mesocosms under low versus high ambient UVR treatments for 5 days and quantified cyclobutane pyrimidine dimers (CPDs) by ELISA. Measurable CPD levels were detected under both UVR exposures, providing direct evidence that natural sunlight induces DNA damage in amphibian larvae. Although mean CPD levels did not differ between treatments, quantile regression revealed higher levels of CPDs in both the lower (τ=0.05) and upper (τ=0.95) quantiles under high UVR. This pattern suggests that while average DNA damage levels were similar, subsets of individuals experienced disproportionately high CPD burdens under increased UVR. These results highlight the value of mesocosms as a tool to bridge laboratory and field contexts to evaluate the effects of UVR on aquatic fauna, particularly as UV environments shift with climate change.

Loss of structural habitat complexity associated with habitat degradation in marine systems may expose early life stages of fishes to harsh environmental conditions. Specifically, loss of coral cover means less suitable refuge is available for some reef fish species to lay their eggs, exposing them to pervasive stressors such as ultraviolet radiation (UVR). Here, using laboratory experiments, we exposed embryos of the clownfish Amphiprion ocellaris for 2 h daily to two UVR levels reflective of their depth at settlement; high UVR (280 µW m−2), reflective of shallow depths, and low UVR (80 µW m−2), reflective of deeper depths over their embryonic period, and then measured changes in mass, yolk sac volume, DNA damage, and survival. Despite being exposed to ecologically relevant levels of UV radiation, there was 100% mortality before hatching and inflated yolk sacs in both high and low UVR-treated animals. Exposure to UVR also resulted in DNA damage, albeit only in high UVR treatments. It is evident from our results that the protection that the reef can offer from UVR is critical for the survival of clownfish. Our results also underscore the need for future work to consider this often-neglected stressor and the role of adequate refuge for the healthy development of early-life stages of reef organisms.

Ultraviolet radiation (UVR) has a range of strong effects on freshwater ecosystems, and changing UVR is implicated in global amphibian declines. The link between UVR and amphibian declines is not well understood, largely due to limited understanding of actual UVR exposure regimes in freshwater ecosystems. Logistical challenges in measuring aquatic UVR regimes in situ have impeded progress, including the design of cost-effective radiometric monitoring tools and the measurement of UVR at ecologically relevant scales. We designed novel underwater UVR loggers and deployed them in southeast Queensland creeks to log near-continuous underwater ultraviolet index (UVI) for 11 days across four sampling events within the peak amphibian breeding season. We compared these data with solar modelling, dosimetric and handheld radiometric techniques. The dataset (2616 h from 39 UV sensors) revealed a highly heterogenous daily UVR microenvironment that showed capacity for harmful UVI exposures at both sites. Traditional cumulative or periodic UVR monitoring approaches often missed these acute high UVR exposures. Fine scale UVR data logging was proven to be a cost-effective approach for monitoring the UVR microenvironment in freshwater systems. While no single method can be considered universally optimal, our results highlight the advantages of continuous in situ UV monitoring, particularly for capturing short-duration ultraviolet fluctuations relevant to aquatic organisms.

Farmed Atlantic salmon are increasingly being challenged by rising sea surface temperature. For salmon aquaculture in Australia, the water often exceeds the thermal tolerance limit during summer, causing reduced feeding, intestinal inflammation and increased susceptibility to disease. Dietary inclusion of crystalline L‐arginine can improve gut epithelium function under heat stress in other animals, including pigs and rodents. Here, we conducted a feed trial to determine if an additional 1.5% dietary arginine above base diet requirements can improve gut function in chronically heat‐stressed Atlantic salmon. Two diets, termed ‘control’ and ‘arginine’, were fed to Atlantic salmon smolt during a 9‐week trial. After 1 week at 15°C, both treatments were ramped to 19.5°C over 5 weeks and then held at 19.5°C for 3 weeks. Following the trial, growth performance was evaluated, and the distal intestine was assessed for the effect of arginine supplementation on histopathology, intestinal permeability and tight junction gene expression. Growth performance, intestinal inflammation markers and intestinal permeability were not significantly improved by supplemental arginine in heat‐stressed Atlantic salmon. However, the distal intestine simple fold length increased, and there was a trend towards a higher daily feed intake ( p = 0.053) in salmon fed with supplemental arginine. While additional arginine did not appear to greatly improve intestinal function in heat‐stressed Atlantic salmon smolt, the results do not rule out a benefit for elevated L‐arginine for improved health.

Elevated ultraviolet radiation (UVR) is postulated as one of multiple, interrelated environmental stressors driving amphibian population declines globally. However, key knowledge gaps remain in elucidating the link between elevated UVR and amphibian declines in a changing climate, including whether timing and irradiance of UVR exposure in early life dictates the onset of detrimental carryover effects post‐metamorphosis. In this study, striped marsh frog larvae (Limnodynastes peronii) were exposed to UVR at one of two different irradiances for up to 7 days, either as hatchlings (Gosner stage 23) or as older larvae (Gosner stage 25−28). These animals were then reared to metamorphosis in the absence of UVR to examine independent and interactive carryover effects throughout development. Older larvae were more sensitive to UVR than hatchlings, with 53.1% and 15.6% mortality in larvae exposed to high and low irradiance respectively, compared with no mortality of hatchlings in either irradiance treatment. Irradiance and timing of UVR exposure had interactive effects on larval body length, causing stunted growth patterns and a lack of compensatory growth following UVR exposure, particularly in animals exposed to high irradiance UVR later in development. Timing of UVR exposure also determined the severity of carryover effects into metamorphosis, including delayed metamorphosis and the first published account (to our knowledge) of latent UVR‐induced depigmentation in an amphibian. These findings highlight how acute changes to the larval UVR exposure regime can impact on amphibian health later in life, with implications for our understanding of the effects of climate change on UVR‐related amphibian declines.

Ultraviolet radiation (UVR) is a pervasive factor that has shaped the evolution of life on Earth. Ambient levels of UVR mediate key biological functions but can also cause severe lethal and sublethal effects in a wide range of organisms. Furthermore, UVR is a powerful modulator of the effects of other environmental factors on organismal physiology, such as temperature, disease, toxicology and pH, among others. This is critically important in the context of global change, where understanding the effects of multiple stressors is a key challenge for experimental biologists. Ecological physiologists rarely afford UVR discussion or include UVR in experimental design, even when it is directly relevant to their study system. In this Commentary, we provide a guide for experimental biologists to better understand if, when, and how UVR can be integrated into experimental designs to improve the ecological realism of their experiments.

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