Fernando Ribeiro Gomes

The tiger shark is a highly migratory apex predator with distinct populations in the Atlantic and Indo-Pacific regions. Regional analyses in the western Atlantic Ocean have revealed additional genetic differentiation between northern (Caribbean) and southern (Brazilian) populations, particularly in maternally inherited mitochondrial DNA. The eastern Atlantic Ocean, however, remains understudied, leaving connectivity between American and African populations unresolved. Using a fin-mounted satellite transmitter, we document the complete eastward transatlantic movement of a female tiger shark (2.9 m total length), tracked from Fernando de Noronha Archipelago, Brazil, to the coastal waters of Sierra Leone, West Africa. Following an initial prolonged residency of around Fernando de Noronha, the individual undertook a 6,764 km migration across the Atlantic over 116 days (mean ~58 km day ^-1 ). Surfacing behavior differed significantly between the residency and migration phases, shifting from predominantly nocturnal to predominantly diurnal detections. This movement corroborates previous findings that female tiger sharks can disperse across basin scales and suggests that equatorial migration may facilitate genetic connectivity between the western and eastern Atlantic. In the absence of genetic data from West Africa, the demographic and genetic consequences of such movements remain undetermined, underscoring the need to integrate telemetry with expanded population genetic sampling to better understand connectivity in highly mobile marine predators.

Amphibians face threats from emerging bacterial, viral, and fungal pathogens, and their innate immune response plays a key role in early defense. The liver is a central immune organ that produces acute-phase proteins (APPs) and complement system proteins, which are essential for early pathogen neutralization and a positive disease outcome. Here, we investigated the temporal dynamics of hepatic gene expression for APPs [C-reactive protein (CRP), serum amyloid A (SAA), fibrinogen-like protein 1 (FGL1)] and complement components (C1s, C3, C4, C5, C9) in Rhinella diptycha toads injected with lipopolysaccharide (LPS) or saline. Using RT-qPCR at four time points post-injection (1h, 3h, 6h, and 18h), we detected a significant effect of LPS on C1s expression and a treatment x time interaction for C4, C5, and C9, indicating time-dependent activation of different complement proteins. In contrast, we found no evidence for LPS-induced changes in APPs expression. However, several APPs were positively correlated with complement components, suggesting coordinated regulation even in the absence of differential expression. Our findings provide a temporal analysis of hepatic acute-phase responses to LPS in Rhinella diptycha toads, unraveling a complex network of complement system activation. By showing that complement components, rather than APPs, dominate the early hepatic response to a bacterial antigen in a widespread Neotropical toad species, our study provides a temporal and mechanistic baseline for future investigations of amphibian innate immunity and underscores the need for future work to determine how these early pathways respond to different pathogens and contribute to variation in disease outcomes among amphibians.

Recent studies have shown that acute physiological increases in endogenous glucocorticoid levels have immunostimulatory effects. Although post-acute stress immunosuppressive effects have also been described, the difference between enhancing and suppressing the immune response seems mediated by the stressor's duration, intensity, and the immune component under analysis. To elicit physiologically relevant corticosterone levels that can be found in Rhinella icterica toads after stressful events (e.g., restraint or captivity) and understand how acute increased glucocorticoid levels of different intensities affect corticosterone and testosterone plasma levels and immune parameters (in vitro plasma bacterial killing ability, neutrophil-to-lymphocyte ratio, and in vivo phagocytosis of peritoneal leukocytes), we submitted toads to the transdermal application of two corticosterone doses (1 and 10 μg). Corticosterone transdermal application increased corticosterone plasma levels with different intensities: 3 times for 1 μg and fourteen times for 10 μg, compared to the vehicle, and the neutrophil-to-lymphocyte ratio increased regardless of the corticosterone dose. However, there was no effect on testosterone levels and bacterial killing ability. Interestingly, both corticosterone doses promoted immunosuppression, decreasing peritoneal leukocytes' phagocytosis activity by 60% for toads receiving the dose of 1µg and 40% for those receiving 10 μg. Our results show the complexity of the relationship between increased corticosterone levels and immunomodulation. The different corticosterone doses promoted increases of distinct magnitudes in corticosterone plasma levels, with the less intense increase in corticosterone levels generating greater cell-mediated immunosuppression. Future studies using different corticosterone doses to achieve and compare physiological vs. pharmacological hormone levels are imperative to understanding these interrelationships between corticosterone and immune response.

This paper reviews several aspects of immunoendocrinology and ecoimmunology in Brazilian species of anurans under investigation for more than a decade, including (1) patterns of annual covariation of circulating steroids, calling behavior and innate immunity, (2) endocrine and immune correlates of calling performance, (3) behavioral and physiological correlates of parasite load, (4) thermal sensitivity of immune function, and (5) endocrine and immunomodulation by experimental exposure to acute and chronic stressors, as well as to endocrine manipulations and simulated infections. Integrated results have shown an immunoprotective role of increased steroid plasma levels during reproductive activity in calling males. Moreover, a higher helminth parasite load is associated with changes in several behavioral and physiological traits under field conditions. We also found anuran innate immunity is generally characterized by eurythermy, with maximal performance observed in temperatures close to normal and fever thermal preferendum. Moreover, the aerobic scope of innate immune response is decreased at fever thermal preferendum. Experimental exposure to stressors results in increased corticosterone plasma levels and immune redistribution, with an impact on immune function depending on the duration of the stress exposure. Interestingly, the fate of immunomodulation by chronic stressors also depends in part on individual body condition. Acute treatment with corticosterone generally enhances immune function, while prolonged exposure results in immunosuppression. Still, the results of hormonal treatment are complex and depend on the dose, duration of treatment, and the immune variable considered. Finally, simulated infection results in complex modulation of the expression of cytokines, increased immune function, activation of the Hypothalamus-Pituitary-Interrenal axis, and decreased activity of the Hypothalamus-Pituitary-Gonadal axis, as well as reduced melatonin plasma levels, suggesting that anurans have a functional Immune-Pineal axis, homologous to that previously described for mammals. These integrated and complementary approaches have contributed to a better understanding of physiological mechanisms and processes, as well as ecological and evolutionary implications of anuran immunoendocrinology.

Mammals show immune up-regulation and increased plasma and local (gastrointestinal tract) concentrations of some immunoregulatory hormones, such as corticosterone and melatonin, after feeding. However, little is known about the endocrine and immune modulation in the postprandial period of ectothermic animals. This study investigated the effects of feeding on endocrine and immune responses in the bullfrog (Lithobates catesbeianus). Frogs were fasted for 10 days and divided into two groups: fasted and fed with fish feed (5% of body mass). Blood and gastrointestinal tract tissues (stomach and intestine) were collected at 6, 24, 48, 96 and 168 h to measure neutrophil/lymphocyte ratio, plasma bacterial killing ability, phagocytosis of blood leukocytes, plasma corticosterone and melatonin, and stomach and intestine melatonin. Feeding increased plasma corticosterone at 24 h and decreased it at 168 h, and increased neutrophil/lymphocyte ratio at 6, 24 and 96 h. We also observed decreased bacterial killing ability 48 h after feeding. Stomach melatonin increased after 17 days of fasting. We show that feeding activates the hypothalamic–pituitary–interrenal axis and promotes transient immunosuppression, without stimulating an inflammatory response. Increased corticosterone may mobilize energy to support digestive processes and melatonin may protect the stomach during fasting. We conclude that feeding modulates secretion of immunoregulatory hormones, initially increasing plasma corticosterone levels, followed by a decrease at the end of meal digestion, and causes systemic immune cell redistribution, increasing neutrophil/lymphocyte ratio for almost the entire period of meal digestion in bullfrogs. Also, fasting modulates secretion of melatonin in the stomach.

Increased plasma glucocorticoids (corticosterone – CORT, in amphibians) and melatonin (MEL) are associated with the daily activity phase and with environmental darkness, respectively. Besides, CORT and MEL also play pivotal immunomodulatory roles in several vertebrates. Herein we described the daily profile of plasma MEL and CORT for Rhinella icterica toads in captivity. Thereafter, we investigated the effects of lipopolysaccharide (LPS)-induced systemic inflammation on the production of CORT and MEL in the R. icterica. Captive toads showed CORT and MEL diurnal variation typical of nocturnal species, with increased values for CORT at ZT12 (18 h) and MEL peak at ZT18 (24 h). LPS-induced hormonal changes included increased plasma CORT and decreased ocular and plasma MEL when compared to those from toads treated with saline 2 h post-injection. Our results demonstrated the presence of a diurnal CORT and MEL variation in toads. We also showed the crosstalk between CORT and MEL during the toad’s systemic inflammation in response to an immune challenge with LPS. Additionally, our results demonstrated that anuran eyes’ MEL production might be regulated during the inflammatory processes.