Behavioral differences within and among populations of an African cichlid found in divergent and extreme environments

Alteration of reproductive behaviors by aromatase inhibition is population dependent in an African cichlid fish

Although hormones are vital to an organism's ability to respond to environmental stressors, they can be directly altered by the environment and impact reproductive behavior. For example, in some fishes, aquatic hypoxia (low dissolved oxygen) inhibits the aromatase enzyme that converts testosterone to estradiol. Here, we examined the effects of short-term aromatase inhibition on reproductive behavior in male Pseudocrenilabrus multicolor, a widespread African cichlid, from one normoxic river population and one hypoxic swamp population. We further tested the response of females to treated and untreated males. We predicted that aromatase inhibition would decrease courtship and competitive behaviors, but the swamp population would be less affected given generational exposure to hypoxia. Specifically, we compared competition and courtship behavior of males treated with a short-term exposure to an aromatase inhibitor with control fish from the two populations. We found that both courtship and competitive behaviors were affected by the interaction between treatment and population. River fish performed fewer courtship and competitive behaviors under the aromatase inhibition treatment while the behavior of swamp males was unaffected. Additionally, we found that females from the swamp population preferred males from the aromatase inhibition treatment and river females preferred control males. While we found behavioral effects of short-term aromatase inhibition, we did not find any effects on male nuptial coloration. Overall, these results indicate that the effects of short-term aromatase inhibition on behavior could depend on local adaptation in response to hypoxia.

Swimming performance, but not metabolism, is related to a boldness-activity syndrome in schoolmaster snapper (Lutjanus apodus)

Commercial overexploitation and climate change can alter the physiology and behavior of marine organisms, although intraspecific phenotypic responses to such changes can vary greatly depending on the environment, species, and severity of the stressor. Under the pace-of-life syndrome (POLS) hypothesis, behavior, physiology, and life-history traits are linked, and thus, affected by selection targeting any aspect of organismal biology. However, these links are understudied in tropical marine fishes, and further work is needed to better understand the impacts of fisheries and climate change on wild stocks. Moreover, tropical regions have a greater reliance on fisheries; thus investigations should focus on species with substantial socioeconomic value to ensure benefits at the local level. This study aimed to address this need by measuring the behavior (boldness and activity), metabolism, and swimming performance (using a critical swim speed [Ucrit] test) of schoolmaster snapper Lutjanus apodus in Eleuthera, the Bahamas. We report a strong positive correlation between boldness and activity, high repeatability of these behavioral metrics, and two groupings that were consistent with "proactive" and "reactive" behavioral types. These behavioral types differed significantly in their swimming performance, with reactive individuals having a 13.1% higher mean Ucrit. In contrast, no significant differences were found in the measured metabolic parameters between behavioral types. This study is the first to investigate the intraspecific links between behavior and physiology in a snapper species, using the novel and ecologically relevant comparison of Ucrit with behavioral syndrome types. These data suggest that additional research is needed to better predict the success of proactive/reactive tropical fish if overexploited and as influenced by climate change.

Multiple stressors lead to complex responses in reproductive behaviors in an African cichlid

Exposure to multiple environmental stressors is a common occurrence that can affect organisms in predictable or unpredictable ways. Hypoxia and turbidity in aquatic environments are 2 stressors that can affect reproductive behaviors by altering energy availability and the visual environment, respectively. Here we examine the relative effects of population and the rearing environment (oxygen concentration and turbidity) on reproductive behaviors. We reared cichlid fish (the Egyptian mouthbrooder, Pseudocrenilabrus multicolor) from 2 populations (a swamp and river) until sexual maturity, in a full factorial design (hypoxic/normoxic × clear/turbid) and then quantified male competitive and courtship behaviors and female preference under their respective rearing conditions. Overall, we found that the rearing environment was more important than population for determining behavior, indicating there were few heritable differences in reproductive behavior between the 2 populations. Unexpectedly, males in the hypoxic rearing treatment performed more competitive and courtship behaviors. Under turbid conditions, males performed fewer competitive and courtship behaviors. We predicted that females would prefer males from their own population. However, under the hypoxic and turbid combination females from both populations preferred males from the other population. Our results suggest that reproductive behaviors are affected by interactions among male traits, female preferences, and environmental conditions.

Unpredictability of maternal environment shapes offspring behaviour without affecting stress-induced cortisol in an annual vertebrate

Exposure of females to stressful conditions during pregnancy or oogenesis has a profound effect on the phenotype of their offspring. For example, offspring behavioural phenotype may show altered patterns in terms of the consistency of behavioural patterns and their average level of performance. Maternal stress can also affect the development of the stress axis in offspring leading to alterations in their physiological stress response. However, the majority of evidence comes from studies utilising acute stressors or exogenous glucocorticoids, and little is known about the effect of chronic maternal stress, particularly in the context of stress lasting throughout entire reproductive lifespan. To bridge this knowledge gap, we exposed female sticklebacks to stressful and unpredictable environmental conditions throughout the breeding season. We quantified the activity, sheltering and anxiety-like behaviour of offspring from three successive clutches of these females, and calculated Intra-class Correlation Coefficients for these behaviours in siblings and half-siblings. We also exposed offspring to an acute stressor and measured their peak cortisol levels. An unpredictable maternal environment had no modifying effect on inter-clutch acute stress responsivity, but resulted in diversification of offspring behaviour, indicated by an increased between-individual variability within families. This may represent a bet-hedging strategy, whereby females produce offspring differing in behavioural phenotype, to increase the chance that some of these offspring will be better at coping with the anticipated conditions.

Each Personality Performs Its Own Function: Boldness and Exploration Lead to Differences in the Territoriality of Swimming Crabs (Portunus trituberculatus)

The boldness and exploration of animals are closely related to their territoriality, with relevant studies having important applications in wildlife conservation. The present study establishes a behavior observation system measuring the boldness and exploration of swimming crabs (Portunus trituberculatus) to clarify the relationship between boldness, exploration, and territoriality, as well as to provide a behavioral basis for the construction of marine ranching. The behavioral tests of crabs in a safe environment (predator absence), a dangerous environment (predator presence), and habitat selection (complex and simple habitat) are analyzed. A territorial behavior score is calculated as an evaluation index of territoriality. The correlation between the swimming crabs' boldness, exploration, and territoriality is analyzed. The results show that there is no boldness-exploratory behavioral syndrome. In predator absence or presence environments, boldness is dominant in territorial behavior and positively correlates with territoriality. Exploration plays a vital role in habitat selection tests but has no significant correlation with territoriality. The experimental results preliminarily show that boldness and exploration jointly develop the difference in the space utilization ability of crabs with different personalities, improving the adaptability of swimming crabs in different conditions. The results of this study supplement the behavior rules of the dominant species of typical fishery resources in marine ranches, providing a basis for achieving animal behavior management function in marine ranches.

Effects of habitat conditions on the boldness and sociability of wild-caught fish (Zacco platypus) along a river

Wild fish show consistent behavioral differences, e.g., personalities among populations, whereas the possible relationships between personality and environmental conditions have seldom been systemically examined. We aimed to test whether the personality of wild-caught fish was affected by the biotic (food resources and predation) and abiotic (temperature, dissolved oxygen level, and flow velocity) conditions of natural habitats. Six populations of pale chub (Zacco platypus) were sampled along a river longer than 1000 km, and environmental conditions and personality characteristics, such as boldness, activity, and sociability, were measured. Personality variables could be reduced to two factors by principal component analysis, boldness, and sociability factors, with the former factor having more variation among and within populations. Individuals from populations with higher food availability (plankton density) and flow velocity generally showed higher boldness factor scores, possibly due to the better energy status of higher food abundance or the low water transparency and hence decreased predation risk and fast-flow lifestyle of populations with higher water velocity populations. All populations showed high sociability as group-living species, which was positively correlated with only the phytoplankton biomass, possibly due to decreased intraspecific competition in habitats with abundant food resources. The correlations among personality variables were population-dependent, as individuals who moved more had a shorter distance to the stimulus shoal (i.e., increased shoaling tendency) within high-predation populations, whereas individuals who moved more spent less time in shoals within low-predation populations. The results suggest that alterations in habitat conditions can result in divergent natural selection that favors a particular personality; thus, human-induced alterations in habitat conditions may shape the personality of individual fish.