Teratogenic Effects of Larval Low-Salinity Experience in Development of the Juvenile Body in Acanthaster sp.

The environmental experiences of marine invertebrate larvae can affect their later life stage performance, subsequently influencing population regulation, as posited for the crown-of-thorns sea star (CoTS; Acanthasterspp.) by the terrestrial runoff hypothesis (TRH). The TRH proposes that eutrophic river runoff plumes boost larval phytoplankton food levels, enhancing metamorphic success to the juvenile to seed outbreaks. However, runoff plumes also freshen seawater which can be deleterious to sea star larvae. For settlement-ready brachiolaria larvae of CoTS, the impact of decreased salinity (17-34 ‰) across a range of exposure durations on survival and normal development were assessed. Salinity performance curves were generated to identify salinity levels with deleterious effects (tipping points, 50% normal development and survival). Decreasing salinity and prolonged exposure significantly reduced larval survival and morphology, with salinity ranges optimal for survival and normal morphology decreasing with exposure time. To examine carryover effects on metamorphosis and juvenile production, competent larvae exposed to salinities seen in runoff plumes (25-34 ‰) on the Great Barrier Reef (GBR) were induced to settle. Juvenile production was highest in slightly reduced (30 ‰) and control (34 ‰) salinity treatments, with faster transition to the juvenile under extended 30 ‰ exposures. However by 5-days post settlement juveniles produced by larvae that had experienced 30‰ were smaller indicating the presence of negative carry over traits that reduce juvenile quality. This highlights the need to consider metamorphic transitions when evaluating the TRH, particularly as climate change intensifies low-salinity events on the GBR.

Key factors influencing the occurrence and frequency of ciguatera

Population irruptions of the western Pacific crown-of-thorns sea star (Acanthaster sp.) are a perennial threat to coral reefs and may be initiated by fluctuations in reproductive or settlement success. However, the processes dictating their early life history, particularly larval settlement, remain poorly understood given limitations in sampling larvae and newly settled juveniles in the field. Here, we introduce an innovative method to measure crown-of-thorns sea star settlement, using artificial settlement collectors and droplet digital polymerase chain reaction based on crown-of-thorns sea star-specific mitochondrial DNA primers. This study demonstrated the utility of this method and explored temporal and spatial patterns of crown-of-thorns sea star settlement on the Great Barrier Reef from 2016 to 2020. Settlement varied considerably between sampling periods at Rib Reef and peaked between October 2016 and January 2017. Our results further suggest that crown-of-thorns sea star larvae readily settle in shallow reef environments, with no preferential settlement detected between depths tested (4-12 m). Substantial variation between Great Barrier Reef regions was revealed in 2019-2020, because collectors deployed on reefs in the central Great Barrier Reef were >10 times as likely to record newly settled crown-of-thorns sea stars as reefs in the northern Great Barrier Reef near Lizard Island. The trends reported here add to our understanding of this critical life-history stage; however, further method validation and larger-scale studies are needed to address pertinent information gaps, such as the stock-recruitment dynamics of this species. Most importantly, fluctuations in crown-of-thorns sea star settlement can now be detected using this sampling protocol, which demonstrates its utility in heralding new and renewed population irruptions of this destructive sea star.

Carryover effects are widespread in nature and can link early-life experiences to the regulation of populations. However, for organisms with complex life cycles, it is unclear whether offspring can overcome negative early-life experiences when provided with abundant post-metamorphic resources. We tested this by rearing larvae of the keystone sea star Asterias forbesi, under high or low food conditions, and then reared the juveniles for 2–3 weeks under one of four food treatments. Larvae reared under low food conditions took longer to reach metamorphosis and settled as smaller juveniles with fewer spines. For early settlers (mean age at settlement = 24.0 d), carryover effects of low larval food significantly reduced post-metamorphic size, mussel consumption and growth. However for late settlers (mean age at settlement = 29.3 d), there were no carryover effects of larval food availability detected post-metamorphosis. The differences between early and late settlers may indicate a trade-off between larval duration and the presence of carryover effects. Our data suggest that carryover effects mediated by body size at settlement could determine post-metamorphic survival, growth, and performance, ultimately impacting the recruitment of this keystone predator.

Crown-of-thorns sea stars (Acanthaster sp.) are among the most studied coral reef organisms, owing to their propensity to undergo major population irruptions, which contribute to significant coral loss and reef degradation throughout the Indo-Pacific. However, there are still important knowledge gaps pertaining to the biology, ecology, and management of Acanthaster sp. Renewed efforts to advance understanding and management of Pacific crown-of-thorns sea stars (Acanthaster sp.) on Australia's Great Barrier Reef require explicit consideration of relevant and tractable knowledge gaps. Drawing on established horizon scanning methodologies, this study identified contemporary knowledge gaps by asking active and/or established crown-of-thorns sea star researchers to pose critical research questions that they believe should be addressed to improve the understanding and management of crown-of-thorns sea stars on the Great Barrier Reef. A total of 38 participants proposed 246 independent research questions, organized into 7 themes: feeding ecology, demography, distribution and abundance, predation, settlement, management, and environmental change. Questions were further assigned to 48 specific topics nested within the 7 themes. During this process, redundant questions were removed, which reduced the total number of distinct research questions to 172. Research questions posed were mostly related to themes of demography (46 questions) and management (48 questions). The dominant topics, meanwhile, were the incidence of population irruptions (16 questions), feeding ecology of larval sea stars (15 questions), effects of elevated water temperature on crown-of-thorns sea stars (13 questions), and predation on juveniles (12 questions). While the breadth of questions suggests that there is considerable research needed to improve understanding and management of crown-of-thorns sea stars on the Great Barrier Reef, the predominance of certain themes and topics suggests a major focus for new research while also providing a roadmap to guide future research efforts.

Failure of medical treatments can hamper responses to subsequent treatments. It has been suggested that changing the route of drug administration could reduce such negative carry-over effects, but direct evidence for this approach is lacking. We therefore investigated in 211 healthy volunteers whether changes in drug administration route reduce such carry-over effects. A positive or negative treatment history with topical analgesic treatments was induced experimentally in a mock clinical trial setting. Subsequently, a different inert drug was introduced via the same (topical) or another (oral) route of administration and its analgesic efficacy was tested. Changing the route of drug administration induced expectations of positive treatment effects in the subjects but did not actually counteract the negative carry-over effects on treatment efficacy. These findings indicate that learned carry-over effects generalize over time and across routes of drug administration-independent of conscious expectations. Other strategies are needed to prevent negative carry-over effects of treatment failure from influencing the results of subsequent treatment attempts.

<p>Salinity, temperature and ultraviolet-B (UV-B) radiation are common environmental stressors in coastal habitats. These stressors are likely to increase in intensity due to the effects of climate change and can have important impacts on population and community dynamics for early development in gastropods that deposit egg masses on rocky shores. The aim of this study was to identify the effects of single and multiple stressors on the development of intertidal and shallow subtidal gastropods with encapsulated embryos. In manipulative experiments I exposed egg masses of the gastropod species Siphonaria australis, Ercolania felina, Pleurobranchaea maculata, Aplysia juliana and Doris wellingtonensis to realistic levels of either salinity, temperature or UV-B radiation, or to a combination of stressors, for different lengths of time. Embryos were then subjected to the most stressful levels of each stressor at either early or late stages of development and at different days of embryonic development. Further, egg masses were exposed to sublethal salinity, temperature and UV-B radiation stress simultaneously, simulating tide pool conditions on a warm sunny summer day. Larvae hatching from stressed and unstressed egg masses were subsequently periodically subjected to increased temperature and UV-B radiation and examined over 10 days to detect possible carry-over effects of exposure to stress in the egg mass. The results revealed that for individual stressors, low salinity (20‰), high temperature (25°C) and high UV-B (1.7 W m ⁻ ² s ⁻ ¹, i.e. a level similar to a sunny NZ summer day) all caused the highest embryonic mortality. The response to stressors was species-specific but overall the intertidal species had lower embryonic mortality than the subtidal species. Generally, chronic exposure had higher impacts on the development of embryos than periodic exposure and early embryonic development stages were most vulnerable to stress. UV-B radiation had particularly damaging effects on embryonic and larval stages for the intertidal pulmonate limpet Siphonaria australis. Further, multiple stressors had synergistic effects and caused high embryonic mortality in the egg mass as well as impacting on the vulnerability of larvae to stressors. This study revealed that stress experienced during embryonic stages can result in sub-lethal damage that increases vulnerability to temperature and decreases vulnerability to UV-B radiation experienced in the larval stage. In total, my results suggest that (1) the effects of different environmental stressors on early development of intertidal and subtidal gastropods are complex and depend on the intensity, duration and time of stress, and are generally species-specific; (2) multiple stressors can act synergistically to affect early development and (3) sublethal exposure to stress in the egg mass can have negative carry-over effects on later larval stages.</p>

<p>Salinity, temperature and ultraviolet-B (UV-B) radiation are common environmental stressors in coastal habitats. These stressors are likely to increase in intensity due to the effects of climate change and can have important impacts on population and community dynamics for early development in gastropods that deposit egg masses on rocky shores. The aim of this study was to identify the effects of single and multiple stressors on the development of intertidal and shallow subtidal gastropods with encapsulated embryos. In manipulative experiments I exposed egg masses of the gastropod species Siphonaria australis, Ercolania felina, Pleurobranchaea maculata, Aplysia juliana and Doris wellingtonensis to realistic levels of either salinity, temperature or UV-B radiation, or to a combination of stressors, for different lengths of time. Embryos were then subjected to the most stressful levels of each stressor at either early or late stages of development and at different days of embryonic development. Further, egg masses were exposed to sublethal salinity, temperature and UV-B radiation stress simultaneously, simulating tide pool conditions on a warm sunny summer day. Larvae hatching from stressed and unstressed egg masses were subsequently periodically subjected to increased temperature and UV-B radiation and examined over 10 days to detect possible carry-over effects of exposure to stress in the egg mass. The results revealed that for individual stressors, low salinity (20‰), high temperature (25°C) and high UV-B (1.7 W m ⁻ ² s ⁻ ¹, i.e. a level similar to a sunny NZ summer day) all caused the highest embryonic mortality. The response to stressors was species-specific but overall the intertidal species had lower embryonic mortality than the subtidal species. Generally, chronic exposure had higher impacts on the development of embryos than periodic exposure and early embryonic development stages were most vulnerable to stress. UV-B radiation had particularly damaging effects on embryonic and larval stages for the intertidal pulmonate limpet Siphonaria australis. Further, multiple stressors had synergistic effects and caused high embryonic mortality in the egg mass as well as impacting on the vulnerability of larvae to stressors. This study revealed that stress experienced during embryonic stages can result in sub-lethal damage that increases vulnerability to temperature and decreases vulnerability to UV-B radiation experienced in the larval stage. In total, my results suggest that (1) the effects of different environmental stressors on early development of intertidal and subtidal gastropods are complex and depend on the intensity, duration and time of stress, and are generally species-specific; (2) multiple stressors can act synergistically to affect early development and (3) sublethal exposure to stress in the egg mass can have negative carry-over effects on later larval stages.</p>

Carry-over effects from one stage of the annual cycle to subsequent stages can have profound effects on individual fitness. In migratory birds, much research has been devoted to examining such effects from the nonbreeding to the breeding period. We investigated potential carry-over effects influencing spring body condition, breeding phenology, and performance for 3 species of sympatric, declining Nearctic–Neotropical migratory swallows: Bank Swallow (Riparia riparia), Barn Swallow (Hirundo rustica), and Cliff Swallow (Petrochelidon pyrrhonota). To examine carry-over effects, we used structural equation modeling and several intrinsic markers, including stable isotope (δ 2H, δ 13C, and δ 15N) and corticosterone (CORTf) values from winter molted-feathers, and changes in telomere length between breeding seasons. We found support for carry-over effects for all 3 species, however, the specific relationships varied between species and sexes. Effects leading to lower breeding performance were only observed in male Bank, female Barn, and female and male Cliff Swallows. In most cases, carry-over effects were attributed to differences in stable isotope values (most commonly with δ 2H) presumably related to differences in winter habitat use, but, for Cliff Swallows, negative carry-over effects were also linked to higher CORTf values and greater rates of telomere shortening. This work provides further support for the potential role of nonbreeding conditions on population declines, and indicates how multiple intrinsic markers can be used to provide information on ecological conditions throughout the annual cycle.

Multi-omics analysis of sea urchin (Strongylocentrotus intermedius) adaptation to salt stress reveals epigenetic regulatory mechanisms

Genome-wide methylome and transcriptome dynamics provide insights into epigenetic regulation of kidney functioning of large yellow croaker (Larimichthys crocea) during low-salinity adaption

Surface-based constraints on target selection and distractor rejection: Evidence from preview search

Evidence for inhibitory processes in visual search comes from studies using preview conditions, where responses to new targets are delayed if they carry a featural attribute belonging to the old distractor items that are currently being ignored-the negative carry-over effect (Braithwaite, Humphreys, & Hodsoll, 2003). We examined whether inhibition was applied in the same manner across different types of displays or whether the inhibitory weighting applied to different features varied with their utility for the search task. To test this, we present the first empirical investigation of negative carry-over effects under the ecologically valid conditions of dynamic visual search. Experiment 1 investigated preview search using dynamic moving and static displays. Detection was very poor when new targets carried the color of the old distractors, and this negative carry-over effect was significantly exaggerated with moving, compared with static, displays. Experiments 2a and 2b demonstrated that this effect could not be attributed to an increased role of preattentive grouping between new and old items for dynamic displays. Collectively, the findings suggest that feature-based inhibition contributes strongly to preview search through dynamic displays, and this leads to an amplified attentional blindness to new targets. The data specifically indicate that inhibitory processes in search differentially weight color and location in moving and static displays, and that feature-based inhibition may underlie many instances of sustained inattentional blindness in everyday life.

Salinity levels and drought status of coastal wetlands may be strongly affected by climate change, and changes in the nitrogen cycle of mangrove wetlands may also be affected. We established combinations of three salinity and water levels with applied stable isotope 15N to study the δ15N distributions in the sediment and plants of a greenhouse-based simulated mangrove Aegiceras corniculatum wetland system. The stable isotope 13C and 15N, C and N contents and the C:N ratio were determined. Results showed that increasing in salinity significantly increased the δ13C value in plant organs. The δ15N value of plant organs increased with increasing water level in low salinity (10‰) and medium salinity (20‰) treatment groups but not in the high salinity (30‰) treatment group. This may attributed to A. corniculatum adjusting the δ15N distribution in different organs in response to high salinity stress. Compared to the δ13C, the δ15N values of plant were strongly affected by salinity and water level treatments, indicating that the behavior of N cycle was somewhat different than the C cycle, and affected by the combined effects of both salinity and water level. Most of 15N absorbed by plant tissues were in leaves except for the highest salinity and high water level treatment, showing at increasing water level, the proportion of 15N increased in root. Overall, the measured indicators exhibited different responses to salinity level and water level, suggesting that the changes in salinity and water levels have an impact on N cycling processes of wetland systems.

Oilseed rape (Brassica napus L.), an important oil crop of the world, suffers various abiotic stresses including salinity stress during the growth stage. While most of the previous studies paid attention to the adverse effects of high salinity stress on plant growth and development, as well as their underlying physiological and molecular mechanisms, less attention was paid to the effects of moderate or low salinity stress. In this study, we first tested the effects of different concentrations of NaCl solution on the seedling growth performance of two oilseed rape varieties (CH336, a semi-winter type, and Bruttor, a spring type) in pot cultures. We found that moderate salt concentrations (25 and 50 mmol L−1 NaCl) can stimulate seedling growth by a significant increase (10~20%, compared to controls) in both above- and underground biomasses, as estimated at the early flowering stage. We then performed RNA-seq analyses of shoot apical meristems (SAMs) from six-leaf-aged seedlings under control (CK), low (LS, 25 mmol L−1), and high (HS, 180 mmol L−1) salinity treatments in the two varieties. The GO and KEGG enrichment analyses of differentially expressed genes (DEGs) demonstrated that such a stimulating effect on seedling growth by low salinity stress may be caused by a more efficient capacity for photosynthesis as compensation, accompanied by a reduced energy loss for the biosynthesis of secondary metabolites and redirecting of energy to biomass formation. Our study provides a new perspective on the cultivation of oilseed rape in saline regions and new insights into the molecular mechanisms of salt tolerance in Brassica crops. The candidate genes identified in this study can serve as targets for molecular breeding selection and genetic engineering toward enhancing salt tolerance in B. napus.