Neural effects of elevated CO2 in fish may be amplified by a vicious cycle

Maladaptive behavioural disturbances have been reported in some fishes and aquatic invertebrates exposed to projected future CO2 levels. These disturbances have been linked to altered ion gradients and neurotransmitter function in the brain. Still, it seems surprising that the relatively small ionic changes induced by near-future CO2 levels can have such profound neural effects. Based on recent transcriptomics data, we propose that a vicious cycle can be triggered that amplifies the initial disturbance, explaining howsmall pH regulatory adjustments in response to ocean acidification can lead to major behavioural alterations in fish and other water-breathing animals. The proposed cycle is initiated by a reversal of the function of some inhibitory GABA(A) receptors in the direction of neural excitation and then amplified by adjustments in gene expression aimed at suppressing the excitation but in reality increasing it. In addition, the increased metabolic production of CO2 by overexcited neurons will feed into the cycle by elevating intracellular bicarbonate levels that will lead to increased excitatory ion fluxes through GABA(A) receptors. We also discuss the possibility that an initiation of a vicious cycle could be one of the several factors underlying the differences in neural sensitivity to elevated CO2 displayed by fishes

Neuro-molecular characterization of fish cleaning interactions

Coral reef fish exhibit a large variety of behaviours crucial for fitness and survival. The cleaner wrasse Labroides dimidiatus displays cognitive abilities during interspecific interactions by providing services of ectoparasite cleaning, thus serving as a good example to understand the processes of complex social behaviour. However, little is known about the molecular underpinnings of cooperative behaviour between L. dimidiatus and a potential client fish (Acanthurus leucosternon). Therefore, we investigated the molecular mechanisms in three regions of the brain (Fore-, Mid-, and Hindbrain) during the interaction of these fishes. Here we show, using transcriptomics, that most of the transcriptional response in both species was regulated in the Hindbrain and Forebrain regions and that the interacting behaviour responses of L. dimidiatus involved immediate early gene alteration, dopaminergic and glutamatergic pathways, the expression of neurohormones (such as isotocin) and steroids (e.g. progesterone and estrogen). In contrast, in the client, fewer molecular alterations were found, mostly involving pituitary hormone responses. The particular pathways found suggested synaptic plasticity, learning and memory processes in the cleaner wrasse, while the client indicated stress relief

Probing SWATH‐MS as a tool for proteome level quantification in a nonmodel fish

Quantitative proteomics via mass spectrometry can provide valuable insight into molecular and phenotypic characteristics of a living system. Recent mass spectrometry developments include data-independent acquisition (SWATH/DIA-MS), an accurate, sensitive and reproducible method for analysing the whole proteome. The main requirement for this method is the creation of a comprehensive spectral library. New technologies have emerged producing larger and more accurate species-specific libraries leading to a progressive collection of proteome references for multiple molecular model species. Here, for the first time, we set out to compare different spectral library constructions using multiple tissues from a coral reef fish to demonstrate its value and feasibility for nonmodel organisms. We created a large spectral library composed of 12,553 protein groups from liver and brain tissues. Via identification of differentially expressed proteins under fish exposure to elevated pCO2 and temperature, we validated the application and usefulness of these different spectral libraries. Successful identification of significant differentially expressed proteins from different environmental exposures occurred using the library with a combination of data-independent and data-dependent acquisition methods as well as both tissue types. Further analysis revealed expected patterns of significantly up-regulated heat shock proteins in a dual condition of ocean warming and acidification indicating the biological accuracy and relevance of the method. This study provides the first reference spectral library for a nonmodel organism. It represents a useful guide for future building of accurate spectral library references in nonmodel organisms allowing the discovery of ecologically relevant changes in the proteome

Proteomic Responses to Ocean Acidification in the Brain of Juvenile Coral Reef Fish

Elevated CO₂ levels predicted to occur by the end of the century can affect the physiology and behavior of marine fishes. For one important survival mechanism, the response to chemical alarm cues from conspecifics, substantial among-individual variation in the extent of behavioral impairment when exposed to elevated CO₂ has been observed in previous studies. Whole brain transcriptomic data has further emphasized the importance of parental phenotypic variation in the response of juvenile fish to elevated CO₂. In this study, we investigate the genome-wide proteomic responses of this variation in the brain of 5-week old spiny damselfish, Acanthochromis polyacanthus. We compared the accumulation of proteins in the brains of juvenile A. polyacanthus from two different parental behavioral phenotypes (sensitive and tolerant) that had been experimentally exposed to short-term, long-term and inter-generational elevated CO₂. Our results show differential accumulation of key proteins related to stress response and epigenetic markers with elevated CO₂ exposure. Proteins related to neurological development and glucose metabolism were also differentially accumulated particularly in the long-term developmental treatment, which might be critical for juvenile development. By contrast, exposure to elevated CO₂ in the parental generation resulted in only three differentially accumulated proteins in the offspring, revealing potential for inter -generational acclimation. Lastly, we found a distinct proteomic pattern in juveniles due to the behavioral sensitivity of parents to elevated CO₂, even though the behavior of the juvenile fish was impaired regardless of parental phenotype. Our data shows that developing juveniles are affected in their brain protein accumulation by elevated CO₂, but the effect varies with the length of exposure as well as due to variation of parental phenotypes in the population

The time course of molecular acclimation to seawater in a euryhaline fish

The Arabian pupfish, Aphanius dispar, is a euryhaline fish inhabiting both inland nearly-freshwater desert ponds and highly saline Red Sea coastal lagoons of the Arabian Peninsula. Desert ponds and coastal lagoons, located respectively upstream and at the mouths of dry riverbeds ("wadies"), have been found to potentially become connected during periods of intense rainfall, which could allow the fish to migrate between these different habitats. Flash floods would therefore flush Arabian pupfish out to sea, requiring a rapid acclimation to a greater than 40 ppt change in salinity. To investigate the molecular pathways of salinity acclimation during such events, a Red Sea coastal lagoon and a desert pond population were sampled, with the latter exposed to a rapid increase in water salinity. Changes in branchial gene expression were investigated via genome-wide transcriptome measurements over time from 6 h to 21 days. The two natural populations displayed basal differences in genes related to ion transport, osmoregulation and immune system functions. These mechanisms were also differentially regulated in seawater transferred fish, revealing their crucial role in long-term adaptation. Other processes were only transiently activated shortly after the salinity exposure, including cellular stress response mechanisms, such as molecular chaperone synthesis and apoptosis. Tissue remodelling processes were also identified as transient, but took place later in the timeline, suggesting their importance to long-term acclimation as they likely equip the fish with lasting adaptations to their new environment. The alterations in branchial functional pathways displayed by Arabian pupfish in response to salinity increases are diverse. These reveal a large toolkit of molecular processes important for adaptation to hyperosmolarity that allow for successful colonization to a wide variety of different habitats

Species-specific molecular responses of wild coral reef fishes during a marine heatwave

The marine heatwave of 2016 was one of the longest and hottest thermal anomalies recorded on the Great Barrier Reef, influencing multiple species of marine ectotherms, including coral reef fishes. There is a gap in our understanding of what the physiological consequences of heatwaves in wild fish populations are. Thus, in this study, we used liver transcriptomes to understand the molecular response of five species to the 2016 heatwave conditions. Gene expression was species specific, yet we detected overlap in functional responses associated with thermal stress previously reported in experimental setups. The molecular response was also influenced by the duration of exposure to elevated temperatures. This study highlights the importance of considering the effects of extreme warming events when evaluating the consequences of climate change on fish communities

Hologenome analysis of two marine sponges with different microbiomes

Background: Sponges (Porifera) harbor distinct microbial consortia within their mesohyl interior. We herein analysed the hologenomes of Stylissa carteri and Xestospongia testudinaria, which notably differ in their microbiome content. Results: Our analysis revealed that S. carteri has an expanded repertoire of immunological domains, specifically Scavenger Receptor Cysteine-Rich (SRCR) like domains, compared to X. testudinaria. On the microbial side, metatranscriptome analyses revealed an overrepresentation of potential symbiosis-related domains in X. testudinaria. Conclusions: Our findings provide genomic insights into the molecular mechanisms underlying host-symbiont coevolution and may serve as a roadmap for future hologenome analyses

Challenges in marine ecology: genomic investigations of dispersal patterns and phenotypic plasticity in Mediterranean Fishes = Desafíos en ecología marina: investigaciones genómicas de los patrones de dispersión y de la plasticidad fenotípica en peces del Mediterráneo

[spa] Uno de los retos más importantes en ecología marina es la comprensión de las capacidades de dispersión de las especies. En consecuencia, las decisiones sobre la conservación correcta de nuestros ecosistemas marinos deben incluir datos de genética de poblaciones y procesos oceanográficos, así como medidas directas de la dispersión larvaria para una comprensión más completa sobre la dinámica poblacional de las especies. Por lo tanto, en esta tesis evalúo la estructura poblacional, la dispersión larvaria y expresión génica en varias especies de peces del mar Mediterráneo. El primer análisis se centra en la conservación de la especie amenazada Epinephelus marginatus para dar indicaciones sobre el estado de la especie, así como la información genética de las poblaciones para la gestión adecuada de la especie. Se demuestra que los procesos oceanográficos, como frentes y corrientes, influyen en la estructura genética de las poblaciones, se procede a un análisis más multidisciplinar de la estructuración genética de Serranus cabrilla, una especie común de peces del Mediterráneo. El enfoque incluye la comparación de los datos genéticos con simulaciones de partículas oceanográficos y da indicaciones del grado de influencia que el entorno físico puede tener en una distribución de una especie. En el próximo capítulo investigo la base molecular de las diferencias entre tipos de machos con tácticas reproductivas alternativas mediante la evaluación de las diferencias en la expresión génica. Este es el primer estudio de una especie no-modelo con estrategias de apareamiento alternativas y proporciona información esencial sobre la base molecular de la dominación social. El ultimo capitulo trata con el desarrollo de marcadores SNPs de datos de ultra secuenciación para Tripterygion delaisi explorando un protocolo óptimo que permite el desarrollo de SNPs en especies no -modelos. Finalmente, he usado SNPs para explorar los patrones de conectividad mediante el uso de análisis de paternidad. La evidencia directa de la dispersión requiere una gran cantidad de muestras, pero puede proporcionar información muy importante y es esencial para la comprensión de los patrones de conectividad actuales en diferentes hábitats marinos.[eng] One of the most important challenges in marine ecology is understanding the dispersal capabilities of species. Connectivity, if from en evolutionary perspective or a more current ecological perspective, is highly important in determining the natural regulation of populations. By considering both time scales, it is possible to estimate the persistence of a species and its populations. Hence, correct management decisions on conservation issues should include genetic population data combined with oceanographic processes as well as direct measurements of larval dispersal for the full understanding of the population dynamics of species. Therefore, in this thesis I evaluated the population structure, larval dispersal and gene expression in several fish species from the Mediterranean Sea. In this thesis, I approach a variety of ecological and evolutionary challenges from different angles. In chapter 3.1 I analyze the genetic population structure of two different Mediterranean fish species. The first analysis focuses on the conservation of the endangered species Epinephelus marginatus and attempts to give indications on the status of the species as well as population genetic information for the correct design of management strategies. As it becomes clear that oceanographic processes, such as fronts and currents, are important factors in influencing genetic population structure, I proceed with a more multi-disciplinary analysis of the genetic structuring of Serranus cabrilla, a common Mediterranean fish species. The approach includes the comparison of genetic data with oceanographic particle simulations and can give indications on the degree of influence that the physical environment can have on a species genetic distribution. In chapter 3.2 I move from a population approach to the individual level approach. The development, physiology and behavior of an organism determine the life history traits as well as the adaptability to changing conditions. I investigate this by evaluating the differences in gene expression and function for males displaying alternative reproductive tactics as well as females. This is the first genome-wide study for a non-molecular model species in the context of alternative mating strategies and provides essential information on the molecular basis of social dominance. With the production of a de novo transcriptome assembly in chapter 3.2, it can be possible to identify in silico single nucleotide polymorphism markers from this type of data. I start in chapter 3.3 with the development of such markers in Tripterygion delaisi exploring for an optimal protocol allowing future SNP developments in non-model species. This type of genetic markers permits a more time and resource-efficient genotyping for a large amount of samples. Therefore, I used SNPs to explore connectivity patterns by using paternity analysis. The direct evidence of dispersal requires a large amount of individuals, but can provide very important insights and is essential to understanding current connectivity patterns in different marine habitats. This study especially complements the investigations in chapter 3.1 granting a wholesome understanding of population connectivity on evolutionary as well as ecological time scales