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Bolder individuals have greater access to food sources and reproductive partners but are also at increased risk of predation. Boldness is believed to be consistent across time and contexts, but few studies have investigated the stability of this trait across variable environments, such as varying stress loads or long periods of time. Moreover, the underlying molecular components of boldness are poorly studied. Here, we report that boldness of 1154 European sea bass, evaluated using group risk-taking tests, is consistent over seven months and for individuals subjected to multiple environments, including a chronically stressful environment. Differences in risk-taking behaviour were further supported by differences observed in the responses to a novel environment test: shy individuals displayed more group dispersion, more thigmotaxic behaviour and lower activity levels. Transcriptomic analyses performed on extreme phenotypes revealed that bold individuals display greater expression for genes involved in social and exploration behaviours, and memory in the pituitary, and genes involved in immunity and responses to stimuli in the head kidney. This study demonstrates that personality traits come with an underpinning molecular signature, especially in organs involved in the endocrine and immune systems. As such, our results help to depict state–behaviour feedback mechanisms, previously proposed as key in shaping animal personality. [ABSTRACT FROM AUTHOR]

In most animals, sex determination occurs at conception, when sex chromosomes are segregated following Mendelian laws. However, in multiple reptiles and fishes, this genetic sex can be overridden by external factors after fertilization or birth. In some species, the genetic sex may also be governed by multiple genes, further limiting our understanding of sex determination in such species. We used the European sea bass (Dicentrarchus labrax) as a model and combined genomic (using a single nucleotide polymorphism chip) and transcriptomic (RNA-Sequencing) approaches to thoroughly depict this polygenic sex determination system and its interaction with temperature. We estimated genetic sex tendency (eGST), defined as the estimated genetic liability to become a given sex under a liability threshold model for sex determination, which accurately predicts the future phenotypic sex. We found evidence that energetic pathways, concerning the regulation of lipids and glucose, are involved in sex determination and could explain why females tend to exhibit higher energy levels and improved growth compared to males. Besides, early exposure to high temperature up-regulated sox3, followed by sox9a in individuals with intermediate eGST, but not in individuals showing highly female-biased eGST, providing the most parsimonious explanation for temperature-induced masculinization. This gonadal state was maintained likely by DNA methylation and the up-regulation of several genes involved in histone modifications, including jmjd1c. Overall, we describe a sex determination system resulting from continuous genetic and environmental influences in an animal. Our results provide significant progress in our understanding of the mechanisms underlying temperature-induced masculinization in fish. [ABSTRACT FROM AUTHOR]

Temperature‐dependent sex determination (TSD) can be observed in multiple reptile and fish species. It is adaptive when varying environmental conditions advantage either males or females. A good knowledge of the thermosensitive period is key to understand how environmental changes may lead to changes in population sex ratio. Here, by manipulating temperature during development, we confirm that cold temperature (16°C) increases the proportion of fish that develop as females in European sea bass (Dicentrarchus labrax) until 56 days posthatching, but show that it has an opposite effect at later stages, with the proportion of males reaching ~90% after 230 days at 16°C. This is the first observation of opposite effects of temperature at different time periods on the sex ratio of a vertebrate. Our results highlight the potential complexity of environmental effects on sex determination. [ABSTRACT FROM AUTHOR]

Clear evidence for a physiological role of the mineralocorticoid-like hormone 11-deoxycorticosterone (DOC) and the mineralocorticoid receptor (MR) in fish is still lacking. Efforts to demonstrate an osmoregulatory role for this hormone has so far not been conclusive, while a few scattered studies have indicated a role for DOC in development and reproduction. In this study, we investigate the onset of de novo DOC synthesis in parallel with endogenous corticosteroid receptor mRNA production from fertilization to the swim-up stage in rainbow trout. Whole egg DOC content decreased from fertilization until hatching followed by an increase to pre-fertilization levels just after hatching. Onset of de novo transcription of corticosteroid receptor mRNA’s was observed shortly after the midblastula transition; initially glucocorticoid receptor 2 (GR2) followed by MR and then GR1. Non-invasive introduction of DOC or cortisol at fertilization resulted in altered corticosteroid receptor regulation and accelerated hatching date, suggesting a regulatory role in trout ontogenesis of both hormones through MR signaling pathway. The results presented in this study suggest a possible physiological role of the DOC-MR signaling pathway during fish ontogenesis, at fertilization and just after hatching. [ABSTRACT FROM AUTHOR]

Nature-based tourism is gaining extensive popularity, increasing the intensity and frequency of human-wildlife contacts. As a consequence, behavioral and physiological alterations were observed in most exposed animals. However, while the majority of these studies investigated the effects of punctual exposure to tourists, the consequences of constant exposition to humans in the wild remains overlooked. This is an important gap considering the exponential interest for recreational outdoor activities. To infer long-term effects of intensive tourism, we capitalized on Odontostilbe pequira , a short-lived sedentary Tetra fish who spends its life close to humans, on which it feeds on dead skin. Hence, those fish are constantly exposed to tourists throughout their lifecycle. Here we provide an integrated picture of the whole phenomenon by investigating, for the first time, the expression of genes involved in stress response and neurogenesis, as well as behavioral and hormonal responses of animals consistently exposed to tourists. Gene expression of the mineralocorticoid (and cortisol) receptor (mr) and the neurogenic differentiation factor (NeuroD) were significantly higher in fish sampled in the touristic zone compared to those sampled in the control zone. Additionally, after a simulated stress in artificial and controlled conditions, those fish previously exposed to visitors produced more cortisol and presented increased behavioral signs of stress compared to their non-exposed conspecifics. Overall, nature-based tourism appeared to shift selection pressures, favoring a sensitive phenotype that does not thrive under natural conditions. The ecological implications of this change in coping style remain, nevertheless, an open question. [ABSTRACT FROM AUTHOR]

1. As nature-based tourism grows, its impacts on aquatic ecosystems follow, requiring effective management techniques to conserve river integrity. Nevertheless, strong indicators of tourism impacts are scarce and have seldom been studied for many species. 2. This study evaluated whether microhabitat use and activity period of a variety of fish species are effective for assessing tourism impacts in a headwater stream in which recreation (snorkelling) occurs. Microhabitat use and activity period of the most representative fish were observed in river stretches used for recreation and compared with reference stretches. 3. Fish neither altered microhabitat use nor became more cryptic owing to tourism, maybe because they have evolved to occupy a certain microhabitat and cannot inhabit others, thus making habitat use a poor indicator of tourism impact. 4. Fish respond to the presence of tourists by changing the promptness to begin and end activity, making the time of activity a good indicator of tourism impact, which can be easily assessed by tourism managers or government agencies and used to control the environmental impact of recreation involving fish. 5. It is suggested that aquatic conservation protocols should include local indicators, and that behavioural indicators (activity period) might be more relevant than ecological indicators (microhabitat use) for early recognition of tourism impacts. These findings can be extended to the conservation of other fish communities subject to intensive tourism and with a strong circadian rhythm, such as coral reef fishes. [ABSTRACT FROM AUTHOR]

Kleptoparasitism refers to either interspecific or intraspecific stealing of food already procured by other species or individuals. Within a given species, individuals might differ in their propensity to use such a tactic, in a similar manner to which they differ in their general level of aggressiveness. Standard metabolic rate is often viewed as a proxy for energy requirements. For this reason, it should directly impact on both kleptoparasitism and aggressiveness when individuals have to share the same food source. In the present study we first assessed the standard metabolic rate (SMR) of 128 juvenile European eels ( Anguilla anguilla ) by the determination of oxygen consumption. We then tested how the SMR could influence agonistic behavior of individuals competing for food in three distinct trials evenly distributed over three months. We demonstrate that SMR positively correlates with attacks (sum of bite and push events) in all trials. Similarly SMR correlated positively with kleptoparasitism (food theft), but this was significant only for the third trial (month 3). To our knowledge, the present study is the first reporting a link between kleptoparasitism and SMR in a fish species. This has ecological implications owing to the fact that this species is characterized by an environmental sex determination linked to early growth rate. We discuss theses findings in the light of the producer-scrounger foraging game. [ABSTRACT FROM AUTHOR]

Behavioural syndrome, which refers to a suite of correlated behaviours across differing situations, has been identified in numerous animals, including fish. The presence and conservation of a behavioural syndrome throughout evolutionary times suggests it confers various advantages at a population level. In eels, such as the European eel (Anguilla anguilla), activity and aggressiveness are important factors in their life history, since both traits influence dispersal and territoriality. In the present study we investigated whether these behavioural traits were consistent at both the nychtemeral scale (24 h) and over a long time period (7 months). In addition, we investigated if aggressiveness and activity were positively correlated. Both activity and aggressiveness were significantly repeatable, indicating that both behavioural traits could be considered as personality traits. Interestingly, nocturnal activity was correlated to diurnal activity, indicating that this personality trait was highly stable at the circadian scale. Both aggressiveness and activity were correlated in the course of the experiment, underlining the presence of a behavioural syndrome. The detection of two behaviourally distinct groups in juvenile eels: aggressive and active individuals versus their counterpart have implications in the understanding of the colonization profile of the watershed. We discuss these findings in relation to the ecology of this species. [ABSTRACT FROM AUTHOR]

- Social interactions impact growth rate of animals in different ways such as direct or indirect competition for food and/or territories. In this study, behaviour of glass eels and elvers was described throughout three trials of 9 days spread out over 3 months. The impact of recruitment season (spring and autumn runs) and glass eels' propensity to migrate (assessed thanks to an experimental sorting) on individual growth was studied. Overall, spring elvers were more aggressive and active than autumn elvers while autumn fish were more gregarious and reached a higher specific growth rate than spring fish. At the individual level, gregariousness and swimming, respectively, promote and impair growth rate. In addition, skinny individuals and individuals with high motivation to get food achieved better growth rate suggesting catch-up growth processes. These findings may help in clarifying the complex relations between behaviour, growth, river basin colonisation and future sex (which is environmentally determined in eel) and then contribute to the urgent need of scientific knowledge to guide the stocking programme of this endangered species. [ABSTRACT FROM AUTHOR]