Biology subjects

Dijkstra, P. D.

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

3 recordsLinked to original sources

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↗