Reef Fish Acanthochromis Polyacanthus Research Articles

Long non-coding RNAs mediate fish gene expression in response to ocean acidification.

The majority of the transcribed genome does not have coding potential but these non-coding transcripts play crucial roles in transcriptional and post-transcriptional regulation of protein-coding genes. Regulation of gene expression is important in shaping an organism's response to environmental changes, ultimately impacting their survival and persistence as population or species face global change. However, the roles of long non-coding RNAs (lncRNAs), when confronted with environmental changes, remain largely unclear. To explore the potential role of lncRNAs in fish exposed to ocean acidification (OA), we analyzed publicly available brain RNA-seq data from a coral reef fish Acanthochromis polyacanthus. We annotated the lncRNAs in its genome and examined the expression changes of intergenic lncRNAs (lincRNAs) between A. polyacanthus samples from a natural CO2 seep and a nearby control site. We identified 4728 lncRNAs, including 3272 lincRNAs in this species. Remarkably, 93.03% of these lincRNAs were species-specific. Among the 125 highly expressed lincRNAs and 403 differentially expressed lincRNAs in response to elevated CO2, we observed that lincRNAs were either neighboring or potentially trans-regulating differentially expressed coding genes associated with pH regulation, neural signal transduction, and ion transport, which are known to be important in the response to OA in fish. In summary, lncRNAs may facilitate fish acclimation and mediate the responses of fish to OA by modulating the expression of crucial coding genes, which offers insight into the regulatory mechanisms underlying fish responses to environmental changes.

Molecular Response of the Brain to Cross-Generational Warming in a Coral Reef Fish

Ocean warming is a threat to marine biodiversity, as it can push marine species beyond their physiological limits. Detrimental effects can occur when marine poikilotherms are exposed to conditions beyond their thermal optima. However, acclamatory mechanisms, such as plasticity, may enable compensation of detrimental effects if warming is experienced during development or across generations. Studies evaluating the molecular responses of fishes to warming have mostly focused on liver, muscle, and gonads, and little is known about the effects on other vital organs, including the brain. This study evaluated the transcriptional program of the brain in the coral reef fish Acanthochromis polyacanthus, exposed to two different warming scenarios: +1.5°C and +3.0°C, across successive generations. Fish were exposed to these conditions in both developmental (F1 and F2) and transgenerational settings (F2 only), as well as a treatment with step-wise warming between generations. The largest differences in gene expression were between individuals of the first and second generation, a pattern that was corroborated by pairwise comparisons between Control F1 and Control F2 (7,500 DEGs) fish. This large difference could be associated with parental effects, as parents of the F1 generation were collected from the wild, whereas parents of the F2 generation were reared in captivity. A general response to warming was observed at both temperatures and in developmental and transgenerational treatments included protein folding, oxygen transport (i.e., myoglobin), apoptosis and cell death, modification of cellular structure, mitochondrial activity, immunity and changes in circadian regulation. Treatments at the highest temperature showed a reduction in synaptic activity and neurotransmission, which matches previous behavioral observations in coral reef fishes. The Transgenerational +3.0°C treatment showed significant activation of the gene pls3, which is known for the development of neuro-muscular junctions under heat-stress. F2 samples exposed to step-wise warming showed an intermediate response, with few differentially expressed genes compared to developmental and transgenerational groups (except for Transgenerational +1.5°C). In combination with previous studies on liver gene expression, this study indicates that warming produces a molecular signature of stress response in A. polyacanthus that is influenced both by the intensity of warming as well as the duration of exposure.

The alternative splicing landscape of a coral reef fish during a marine heatwave

Alternative splicing is a molecular mechanism that enables a single gene to encode multiple transcripts and proteins by post‐transcriptional modification of pre‐RNA molecules. Changes in the splicing scheme of genes can lead to modifications of the transcriptome and the proteome. This mechanism can enable organisms to respond to environmental fluctuations. In this study, we investigated patterns of alternative splicing in the liver of the coral reef fish Acanthochromis polyacanthus in response to the 2016 marine heatwave on the Great Barrier Reef. The differentially spliced (DS; n = 40) genes during the onset of the heatwave (i.e., 29.49°C or +1°C from average) were related to essential cellular functions such as the MAPK signaling system, Ca(2+) binding, and homeostasis. With the persistence of the heatwave for a period of one month (February to March), 21 DS genes were detected, suggesting that acute warming during the onset of the heatwave is more influential on alternative splicing than the continued exposure to elevated temperatures. After the heatwave, the water temperature cooled to ~24.96°C, and fish showed differential splicing of genes related to cyto‐protection and post‐damage recovery (n = 26). Two‐thirds of the DS genes detected across the heatwave were also differentially expressed, revealing that the two molecular mechanisms act together in A. polyacanthus to cope with the acute thermal change. This study exemplifies how splicing patterns of a coral reef fish can be modified by marine heatwaves. Alternative splicing could therefore be a potential mechanism to adjust cellular physiological states under thermal stress and aid coral reef fishes in their response to more frequent acute thermal fluctuations in upcoming decades.

Simulated coal spill causes mortality and growth inhibition in tropical marine organisms.

Coal is a principal fossil fuel driving economic and social development, and increases in global coal shipments have paralleled expansion of the industry. To identify the potential harm associated with chronic marine coal contamination, three taxa abundant in tropical marine ecosystems (the coral Acropora tenuis, the reef fish Acanthochromis polyacanthus and the seagrass Halodule uninervis) were exposed to five concentrations (0–275 mg coal l−1) of suspended coal dust (<63 μm) over 28 d. Results demonstrate that chronic coal exposure can cause considerable lethal effects on corals, and reductions in seagrass and fish growth rates. Coral survivorship and seagrass growth rates were inversely related to increasing coal concentrations (≥38 mg coal l−1) and effects increased between 14 and 28 d, whereas fish growth rates were similarly depressed at all coal concentrations tested. This investigation provides novel insights into direct coal impacts on key tropical taxa for application in the assessment of risks posed by increasing coal shipments in globally threatened marine ecosystems.

Temperature: A prolonged confounding factor on cholinesterase activity in the tropical reef fish Acanthochromis polyacanthus

Cholinesterase activity usually decreases in fish exposed to anticholinesterase compounds such as organophosphate and carbamate pesticides. Here we show that tropical reef fish Acanthochromis polyacanthus (or spiny damsel) also exhibits a decrease in ChE activity when exposed to elevated temperature from 28°C to 32°C or 34°C after 4 days. We further demonstrate that the decline persists even after 7 days of recovery at control temperature. This is the first report of a drop in ChE activity in fish as temperature increases. Our results strongly suggest the need for long-term monitoring of water temperature in the field prior to sampling A. polyacanthus for toxicology studies, as temperature is a prolonged and confounding factor for ChE activity in this species.

Climate change may affect fish through an interaction of parental and juvenile environments

Changes to tropical sea surface temperature and plankton communities are expected to occur over the next 100 years due to climate change. There is a limited understanding of how these environmental changes are likely to impact coral reef fishes, especially in terms of population replenishment through the quality of progeny produced. The present study investigated the effect that elevated sea water temperature and changes to food availability may have on the production of offspring by the reef fish Acanthochromis polyacanthus (Pomacentridae), as well as the performance of progeny in environments of varying food availability. An orthogonal design of three water temperatures and two food availabilities (high and low ration) was used, with water temperatures being the current-day average for the collection location (28.5 °C), +1.5 °C (30.0 °C) and +3.0 °C (31.5 °C), representing likely temperatures by 2100. Generally, an increase in the water temperature for adults resulted in a reduction in the size, weight and amount of yolk possessed by newly hatched offspring. Offspring whose parents were maintained under elevated temperature (30.0 °C high ration) had lower survival than offspring produced by parents at the current-day temperature (28.5 °C high ration) at 15 days post-hatching, but only when juveniles were reared under conditions of low food availability. In contrast, by 30 days post-hatching, the growth and condition of these offspring produced by parents held under elevated temperature (30.0 °C high ration) were the best of all treatment groups in all levels of juvenile food availability. This result illustrates the potential for initial parental effects to be modified by compensatory growth early in life (within 1 month) and that parental effects are not necessarily long lasting. These findings suggest that the performance of juvenile reef fish in future ocean conditions may not only depend on initial parental effects, but the interaction between their parentally mediated phenotype and their present food availability.

Thermal sensitivity does not determine acclimation capacity for a tropical reef fish

1. Short-term measures of metabolic responses to warmer environments are expected to indicate the sensitivity of species to regional warming. However, given time, species may be able to acclimate to increasing temperature. Thus, it is useful to determine if short-term responses provide a good predictor for long-term acclimation ability. 2. The tropical reef fish Acanthochromis polyacanthus was used to test whether the ability for developmental thermal acclimation of two populations was indicated by their short-term metabolic response to temperature. 3. While both populations exhibited similar short-term responses of resting metabolic rate (RMR) to temperature, fish from the higher-latitude population were able to fully acclimate RMR, while the lower-latitude population could only partially compensate RMR at the warmest temperature. These differences in acclimation ability are most likely due to genetic differences between the populations rather than differences in thermal regimes. 4. This research indicates that acclimation ability may vary greatly between populations and that understanding such variation will be critical for predicting the impacts of warming environmental temperatures. Moreover, the thermal metabolic reaction norm does not appear to be a good predictor of long-term acclimation ability.

Effects of chlorpyrifos on cholinesterase activity and stress markers in the tropical reef fish Acanthochromis polyacanthus

Tropical coastal ecosystems, including the Great Barrier Reef (GBR) of Australia are increasingly threatened by pollution; yet few studies have investigated the sensitivity of GBR species to these pollutants. Here we exposed juveniles of the tropical reef fish Acanthochromis polyacanthus (spiny damselfish) to three concentrations of the insecticide chlorpyrifos (CPF) and measured (i) muscle cholinesterase (ChE) activity; (ii) hepatic glutathione-S-transferase (GST) activity; and (iii) coenzyme Q (CoQ) redox balance, after 6h and 96h of exposure. After 96h, muscle ChE activity was significantly inhibited by 26%, 49% and 53% when fish were exposed to 1, 10 or 100μg/L CPF, respectively. Muscle ChE characterization revealed three types of ChEs, including two atypical forms. Hepatic CoQ antioxidant form significantly increased at 10μg/L after 6h of exposure, potentially demonstrating an early response to CPF-induced oxidative stress in liver. Hepatic GST was not affected by CPF exposure.

Acclimation to predicted ocean warming through developmental plasticity in a tropical reef fish

Determining the capacity of organisms to acclimate and adapt to increased temperatures is key to understand how populations and communities will respond to global warming. Although there is evidence that elevated water temperature affects metabolism, growth and condition of tropical marine fish, it is unknown whether they have the potential to acclimate, given adequate time. We reared the tropical reef fish Acanthochromis polyacanthus through its entire life cycle at present day and elevated (+1.5 and+3.0 °C) water temperatures to test its ability to thermally acclimate to ocean temperatures predicted to occur over the next 50–100 years. Fish reared at 3.0 °C greater than the present day average reduced their resting oxygen consumption (RMR) during summer compared with fish reared at present day temperatures and tested at the elevated temperature. The reduction in RMR of up to 69 mg O2 kg−1 h−1 in acclimated fish could represent a significant benefit to daily energy expenditure. In contrast, there was no acclimation to summer temperatures exhibited by fish reared at 1.5 °C above present day temperatures. Fish acclimated to +3.0 °C were smaller and in poorer condition than fish reared at present day temperatures, suggesting that even with acclimation there will be significant consequences for future populations of tropical fishes caused by global warming.

Otolith chemistry of the non-dispersing reef fish Acanthochromis polyacanthus: cross-shelf patterns from the central Great Barrier Reef

The influence of cross-shelf gradients, within and among distance strata, on the otolith chemistry of the non-dispersing reef fish Acanthochromis polyacanthus was examined on the Great Barrier Reef. Most of the variation in elemental ratios (Mg/Ca, Cu/Ca, Sr/Ca, Ba/Ca) was at the level of sites within reefs; some broad patterns of otolith chemistry were found cross-shelf. Sr/Ca and Ba/Ca ratios increased with distance from shore. Highest ratios of Mn/Ca and Cu/Ca were found at the outermost shelf sites at Myrmidon Reef, but Mn levels were generally greatest within 45 km of shore. Elevated ratios of Ba/Ca at Myrmidon Reef were persistent over 3 yr and are likely indicative of upwelling, which is known to occur in the area. The Ba/Ca ratios were the highest ever reported in marine fish otoliths, and accuracy of our estimates was confirmed in a paired laboratory test. The robustness of reef-wide chemical signatures in fish was weak, but unique signatures were found within reefs. High resolution elemental records could help to identify sites affected by upwelling and the periodicity of upwelling events.

Elevated temperature restricts growth potential of the coral reef fish Acanthochromis polyacanthus

In order to test the effect of temperature variation on the growth of a common coral-reef fish, Acanthochromis polyacanthus, juveniles, sub-adults and adults were reared on either high or low food rations at temperatures corresponding to the long-term (14 year) minimum, average and maximum summer sea-surface temperatures (26, 28 and 31°C respectively) at Orpheus Island, Great Barrier Reef, Australia. Both temperature and food supply affected the growth of juvenile and adult A. polyacanthus. Individuals grew more on high food rations, but growth declined with increasing temperature. Importantly, at 31°C, the growth of juveniles and adults on the high food ration was nearly identical to growth on the low food ration. This indicates that the capacity for growth is severely limited at higher ocean temperatures that are predicted to become the average for Orpheus Island within the next 100 years as a result of rapid climate change.

Parental condition affects early life-history of a coral reef fish

Parents can exert a range of non-genetic effects on the growth and survival of their offspring. In particular, parents may modify the size or condition of their offspring depending on the amount of energy they have available for reproduction. In this study, the body condition of breeding pairs of the coral reef fish Acanthochromis polyacanthus was experimentally manipulated to test the effects of parental condition on reproductive output and offspring life history traits. Parents in good condition commenced breeding earlier, had higher reproductive output, and their eggs exhibited increased survival during embryogenesis, compared to parents in poorer condition. Increased reproductive output was attained through more reproductive bouts over the breeding season that contained both a greater number and an increased size of eggs. The offspring from parents in good condition were larger at hatching, with larger yolk reserves and increased survival on endogenous reserves. Larger size is expected to provide benefits to offspring through reduced susceptibility to size-selective mortality. The range of offspring characteristics modified by parental condition could result in a greater proportion of offspring from good condition parents recruiting to the population.

Distribution, Abundance, and Reproductive Success in the Coral Reef Fish Acanthochromis polyacanthus

The relationships between population density, adult size, and various reproductive parameters (including summed reproductive effort and reproductive success) were examined for the planktivorous coral reef fish Acanthochromis polyacanthus. Data were based on multiple censuses conducted over a 2—yr period on One Tree Reef (southern Great Barrier Reef), at 10 sites that cover the range of habitats occupied by the species. Although several reproductive parameters varied significantly over this habitat range, between—site differences in mean reproductive effort per pair were not significant, and mean reproductive success per pair were significantly reduced at only 2 of the 10 sites. Multivariate analysis suggested that heterogeneity among sites in the mean number of broods produced per pair per spawning season is the major determinant of between—site differences in reproductive success, alone accounting for 69% of the among—site variance in reproductive success in 1979—1980, and 67% in 1980—1981. Principal components analysis of nine apparently independent population and fitness parameters over the 10 sites indicates 82.9% of the communal variance can be accounted for by three orthogonal source variables. These appear to relate to food availability, rates of predation, and, most likely, seasonal variation in water temperature. Results are consistent, overall, with the hypothesis that local populations of A. polyacanthus are equilibrial and resource limited. If this hypothesis is correct, adult density is a valid index of habitat quality. Theoretical considerations suggest that this is not likely to be true for most other small, site—attached species of reef fishes.

Brood-directed parental aggression and early brood loss in the coral reef fish, Acanthochromis polyacanthus (Pomacentridae)

Brood-directed parental aggression, in which parents attack and even kill their own young, is described for the coral reef fish Acanthochromis polyacanthus. This behaviour involves both parents, occurs on days 7–16 post-hatching, and is characteristic of all broods produced early in the spawning season. Such parental aggression appears to underlie widespread early brood loss in the species, i.e. disappearance of young before they reach an age at which they are viable in the absence of parental defence. Simultaneously, there is also a high frequency of sudden increases in the sizes of some tended broods. The data suggest that some brood-tending parents are forcibly expelling their broods from parental territories, and fostering them on to adults still tending broods. By expelling their young and re-spawning, pairs may realize a 7% increase in annual fecundity over pairs that do not expel their young, despite a low survival rate of expelled young.

Habitat Effects on Reproductive Success in the Coral Reef Fish, Acanthochromis Polyacanthus (Pomacentridae)

Current hypotheses advanced to account for the maintenance of the diversity of coral reef fishes differ fundamentally in the assumed role of competitive processes. The equilibrial hypothesis is based primarily upon an assumption of extensive competitive interactions and subsequent niche partitioning; the lottery hypothesis, instead, assumes populations limited to levels well below carrying capacity due to the high larval mortality, a large effect of chance patterns in larval recruitment, and few, if any, significant competitive interactions. To date, no direct evidence for or against the presence of such interactions has been produced, with the role of competition, if any, inferred from community characteristics. To obtain such data, reproductive success of pairs of the planktivorous reef fish Acanthochromis polyacanthus located on isolated habitat patches was recorded over a 2—yr period at One Tree Island, Great Barrier Reef. Correlations were sought between each of six measures of individual fitness and 20 physical and social characteristics of the inhabited reefs. Significant correlations were found with only four characteristics: the number of individuals of all species inhabiting the reefs, the presence of the dominant lagoonal piscivore, current strength, and, most often, the number of heterospecific planktivores inhabiting the reef. Increased numbers of these apparent food competitors correlated with delayed spawning, reduced initial brood size, and reduced adult (and possibly juvenile) rates of growth. Results of a brief series of experimental manipulations of community structure, involving selective of apparent food competitors, appear to support these observations. The results suggest that food abundance is a limiting resource for A. polyacanthus and that significant interspecific competition for food occurs. The potential therefore exists, despite possible external constraints on population size, for selection to favor niche partitioning and for resources in short supply to affect year—class success and, subsequently, community structure.