Stress promotes reproduction in the annual fish Austrolebias reicherti

Adult neurogenesis in the Uruguayan teleost species Austrolebias charrua and Gymnotus omarorum

Neurogenesis -the process by which new neurons are generated in the brain- is critical for nervous system development and plasticity. Adult neurogenesis underlies growth, repair, and adaptation to environmental changes. Vertebrates differ in their neurogenic and regenerative capacity, being particularly prominent in teleost as adult neurogenesis occurs throughout the rostral-caudal brain axis. This review examines adult proliferation and neurogenesis in the autochthonous Uruguayan teleost Austrolebias charrua and Gymnotus omarorum. A. charrua are annual fishes that live in temporary freshwater pools that dry up in the summer. The luminosity of the puddles varies greatly, and both vision and olfaction are crucial for the survival of this species. G. omarorum inhabits freshwater lagoons and rivers beneath dense masses of floating plants and have nocturnal habits. They rely on the electrosensory modality to navigate and communicate with conspecifics. These differences in habitats and predominant sensory modalities are reflected in the distinct brain morphotypes of G. omarorum and A. charrua. While G. omarorum is characterized by the hypertrophy of rhombencephalic cerebellum and electrosensory lateral line lobe, A. charrua has a well-developed olfactory bulb, mesencephalic tectum opticum, and torus longitudinalis. Accordingly, these regions have notorious neurogenic activity. Differences in neuroanatomy and distribution of neurogenesis in the brains of both species are discussed considering their life cycle and lifestyle. The comparison of these results with those reported in other teleost and vertebrates contributes to the understanding of the key role of neurogenesis in brain plasticity and evolution.

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

An individual's social environment can have widespread effects on their physiology, including effects on oxidative stress and hormone levels. Many studies have suggested that variation in oxidative stress experienced by individuals of different social statuses 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, and gonads) had social status-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. However, 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 statuses, 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.

Association of androgens and estrogens with agonistic behavior in the annual fish Austrolebias reicherti

Agonistic behavior governs the settlement of conflicts among conspecifics for limiting resources. Sex steroids play a critical role in the regulation of agonistic behavior which in turn may produce modulations in hormone titres. In this study we analyzed the association of androgens and estrogens with agonistic behavior in the annual fish Austrolebias reicherti. This native species inhabits temporary ponds that dry out completely during summer, having one of the shortest lifespans among vertebrates. They are highly sexually dimorphic and have a single breeding season during which they reproduce continuously. Here we measured plasma levels of 11-ketotestosterone (11KT) and 17β-estradiol (E₂) in adult males after the resolution of a social conflict and assessed the role of the aromatase conversion of testosterone (T) to E₂ in male aggression. Winners had higher levels of 11KT than losers yet; winner 11KT levels did not differ from those of males not exposed to a social challenge. E₂ levels did not show differences among winners, losers or control males. However, fights under the aromatase inhibitor Fadrozole were overall less aggressive than control fights. Our results suggest an androgen response to losing a conflict and that the conversion of T to E₂ is involved in the regulation of aggressive behavior. Annual fish extreme life history may give new insights on hormone-behavior interactions.

Biomarkers of oxidative stress in the post-embryonic characterization of the neotropical annual killifish

Annual killifish are among the most remarkable extremophile species with the shortest vertebrate life span. Few studies have reported on the oxidative balance throughout their life cycle and its association to the natural aging process of these neotropical animals in a natural environment. We standardized and analyzed physiological markers related to the redox balance of the annual killifish (Cynopoecilus fulgens) throughout the post-embryonic life cycle (enzyme activity of Superoxide Dismutase, Catalase, Glutathione Peroxidase, and Glutathione S-transferase, as well as the determination of the levels of Lipoperoxidation, Carbonylated Proteins, and Total Proteins). We tested the influence of environmental variables on these biomarkers. Individuals were collected, including juveniles, adults, and seniles, in three sampling units around the Parque Nacional da Lagoa do Peixe, located in the Coastal Plain of Rio Grande do Sul. We observed that males and females used different physiological strategies of their redox balance during their life cycle, and their oxidative balance was influenced by their reproductive period and environmental variables (water temperature, abundance of predators, abundance of another sympatric annual killifish species, and abundance of C. fulgens). The population of each temporary pond presented different physiological responses to the adaptation of their life cycle, and there was an influence of environmental component as a modulator of this cycle. Our study offers reference values that will be useful for comparison in future research with short-lived organisms.