Biology subjects

Dijkstra, P. D.

Publications and source records attributed to Dijkstra, P. D..

7 recordsLinked to original sources

bioRxiv2026

Antioxidant modulation of stress behavior depends on stress coping style: a role for N-acetylcysteine amide

Animals experience stressors in a variety of contexts that result in activation of neuroendocrine and cellular stress responses. Release of stress hormones can disrupt or restore redox homeostasis, and the resulting changes in oxidative states, physiology and behavior vary by an individuals stress coping style. However, oxidative stress can also directly modulate neuroendocrine stress signaling. To what extent individual differences in brain antioxidant levels alter behavioral stress levels is not well understood. The present study investigated how N-acetylcysteine amide (NACA), an antioxidant and glutamate-modulating compound, regulates stress behavior across zebrafish (Danio rerio) with different stress coping styles (proactive, reactive). Following 24-hour exposure to NACA or control conditions, we quantified individual and composite stress behaviors using a Light-Dark Test (LDT). As expected, both proactive fish and NACA-treated fish showed significantly lower stress behaviors compared to reactive and control animals, respectively. Notably, stress-reducing effects of NACA were only seen in those with a reactive stress coping style. Overall, our data suggest that antioxidant mechanisms (e.g., glutathione system) may be key in facilitating the distinct behavioral and physiological responses to stressors that characterize alternative stress coping styles. The results underscore how individual differences in stress coping style and redox state can influence behavioral responses to stress.

animal behavior and cognition↗

bioRxiv2025

The effect of environmental enrichment on social dominance and welfare in a cichlid fish

Environmental enrichment can have complex, contradictory effects on aggression and animal welfare. Although increasing enrichment may reduce aggression by limiting the visibility of competitors, it may also intensify territorial defense and harm the welfare of subordinates who are the target of territorial aggression. However, it remains unclear how variation in the complexity of an enrichment structure defended by a single dominant individual influences welfare outcomes for subordinates. In the cichlid fish Astatotilapia burtoni, dominant males defend structures as mating territories, whereas subordinate males do not. To establish social hierarchies, we housed two differently sized males (larger become dominant) and six females in one compartment containing one defendable structure. We manipulated structure complexity by placing 1, 2, or 3 halves of terracotta pots clumped together. Increasing cave number did not enhance territoriality: dominant males showed similar aggression rates, relative gonad sizes, and testosterone levels across treatments. Cave number did not significantly affect mortality, body condition, growth rate, or fin damage in subordinate males. Although relative gonad size and testosterone levels were generally higher in dominants, these differences were not always significant in the 2 and/or 3-cave treatments, suggesting weaker physiological differentiation between social states. The behavioral data supported this pattern, with status-specific differences in chase rates declining with increasing cave number. Overall, increasing environmental enrichment had little effect on welfare, but resulted in reduced physiological and behavioral distinctions between dominant and subordinate males. Therefore, careful consideration of enrichment strategies is essential for accurately interpreting status-specific outcomes in laboratory settings.

animal behavior and cognition↗

bioRxiv2025

Territory proximity influences aggression and modulates the relationship between social dominance and oxidative stress in a highly social African cichlid fish

High social rank has many benefits, including priority access to mates and resources. However, maintaining high rank or social dominance can be physiologically costly, particularly in species that engage in agonistic competition to maintain their dominance status. Previous studies have rarely manipulated the intensity of agonistic competition in controlled settings to isolate the cost of social dominance. We utilized males of the cichlid fish Astatotilapia burtoni to investigate how the degree of territoriality influences patterns of oxidative stress. In this species, high-rank males compete for territories to attract mates. We housed males individually with a defendable structure and used clear tank dividers to allow visual access to a size-matched male neighbor housed in an identical setup to manipulate territoriality. Defendable structures were placed either close to the divider (proximal treatment) or further away (distal treatment). We found that males in the distal treatment expressed higher levels of territorial aggression than those in the proximal treatment. While males in the distal treatment did not display higher levels of oxidative stress, territory proximity influenced the relationships between physiological markers of dominance (i.e., testosterone, gonad size) and oxidative balance. Although our work is not consistent with higher competition increasing the physiological cost of high rank, it suggests that the level of competition influences the regulation of oxidative balance relative to social dominance characteristics. We suggest that manipulating the degree of territoriality in a controlled setting provides a unique opportunity to further our understanding of how individuals manage the trade-offs associated with high rank. Summary StatementManipulating the amount of space between territories results in variability in the degree of territorial aggression and the interaction of physiological markers of social dominance and oxidative stress.

animal behavior and cognition↗

bioRxiv2025

Background color matching influences sexual behavior, growth, and mortality rate in an African cichlid fish

Phenotypic plasticity allows organisms to adapt to changing environments within their lifetimes. The cost of plastic adaptations may constrain the persistence of plasticity over evolutionary time. One potential cost is the possibility that phenotypic adjustment to specific environments can cause correlated responses that are not necessarily adaptive. Males in the African cichlid Astatotilapia burtoni are blue or yellow, and males are able adjust their body coloration to the color of the background, presumably to increase crypsis. To test whether background color influences fitness-related traits, we raised mix-sex groups of juvenile A. burtoni to adulthood in yellow or blue tanks. We found that fish in blue tanks were darker and more bluish, whereas fish reared in yellow tanks were paler and more yellow in body coloration. Males, but not females, from blue tanks showed earlier sexual maturation than those held in yellow tanks. However, across the duration of the experiment, there was a higher frequency of females mouthbrooding in groups housed in yellow tanks than those that were housed in blue tanks. In addition, fish in blue tanks exhibited reduced growth rate but higher survivorship relative to their yellow-reared counterparts. Our data suggests that background color affects important fitness-related traits in a color polymorphic cichlid, which may influence the evolution of phenotypic plasticity.

animal behavior and cognition↗

bioRxiv2022

Variation in mate competition favors phenotypic plasticity in male coloration of an African cichlid

Sexual selection is thought to be a potent evolutionary force giving rise to diversity in sexual traits that enhance mating success, such as ornament, sexual display, and weapons. The expression of sexual traits is often influenced by environmental conditions, suggesting that phenotypic plasticity may precede and facilitate evolutionary divergence in sexual traits by sexual selection. However, the mechanisms that promote plasticity in sexual traits remain poorly understood. Using the cichlid fish Astatotilapia burtoni, we show that sexual selection may promote plasticity in sexual traits. In this species, males change between yellow and blue color and exhibit intense male contest competition over breeding territories to attract females. We found that experimentally increased competition over territories led to a higher proportion of males expressing the yellow phenotype. Furthermore, we found that expression of yellow coloration is beneficial to males in territorial disputes. Specifically, yellow males won more staged dyadic contests than blue males, and yellow males had a lower level of oxidative stress than blue males, especially when engaging in more territorial display. However, females spawned more with blue males than with yellow males, suggesting that expression of blue coloration is sexually more attractive. The ability to adjust color phenotype according to the local competitive environment could therefore promote the persistence of plastic changes in coloration. Our findings challenge the view that phenotypic plasticity sets the stage for the evolution of genetically fixed changes via sexual selection, and instead suggest that sexual selection may favor plasticity in sexual traits.

animal behavior and cognition↗

bioRxiv2022

Social rank influences relationships between hormones and oxidative stress in a cichlid fish

An individuals social environment can have widespread effects on their physiology, including effects on oxidative stress and hormone levels. Many studies have posited that variation in oxidative stress experienced by individuals of different social ranks might be due to endocrine differences, however, few studies have evaluated this hypothesis. Here, we assessed whether a suite of markers associated with oxidative stress in different tissues (blood, plasma, liver, or gonads) had social rank-specific relationships with circulating testosterone or cortisol levels in males of a cichlid fish, Astatotilapia burtoni. Across all fish, blood DNA damage (a global marker of oxidative stress) and gonadal synthesis of reactive oxygen species (as indicated by NADPH-oxidase (NOX) activity) were lower when testosterone was high. High DNA damage in both the blood and gonads was associated with high cortisol in subordinates, but low cortisol in dominants. Additionally, high cortisol was associated with greater production of reactive oxygen species (greater NOX activity) in both the gonads (dominants only) and liver (dominants and subordinates). In general, high testosterone was associated with lower oxidative stress across both social ranks, whereas high cortisol was associated with lower oxidative stress in dominants and higher oxidative stress in subordinates. Taken together, our results show that differences in the social environment can lead to contrasting relationships between hormones and oxidative stress.

physiology↗

bioRxiv2022

Social dominance and reproduction result in increased integration of oxidative state in males of an African cichlid fish

Oxidative stress is a potential cost of social dominance and reproduction, which could mediate life history trade-offs between current and future reproductive fitness. However, the evidence for an oxidative cost of social dominance and reproduction is mixed, in part because organisms have efficient protective mechanisms that can counteract oxidative insults. Further, previous studies have shown that different aspects of oxidative balance, including oxidative damage and antioxidant function, varies dramatically between tissue types, yet few studies have investigated oxidative cost in terms of interconnectedness and coordination within the system. Here, we tested whether dominant and subordinate males of the cichlid Astatotilapa burtoni differ in integration of different components of oxidative stress. We assessed 7 markers of oxidative stress, which included both oxidative damage and antioxidant function in various tissue types (total of 14 measurements). Across all oxidative stress measurements, we found more co-regulated clusters in dominant males, suggesting that components of oxidative state are more functionally integrated in dominant males than they are in subordinate males. We discuss how a high degree of functional integration reflects increased robustness or efficiency of the system (e.g. increased effectiveness of antioxidant machinery in reducing oxidative damage), but we also highlight potential costs (e.g. activation of cytoprotective mechanisms may have unwanted pleiotropic effects). Overall, our results suggest that quantifying the extent of functional integration across different components of oxidative stress could reveal insights into the oxidative cost of important life history events.

physiology↗