Physiological parameters of a plover during nonbreeding and breeding in Patagonia, Argentina

Migratory shorebirds are of the most threatened avian species due to effects of human activities and climate change. Physiological parameters are useful to evaluate the health status of free-living animals. Here we investigated lymphocytes, heterophils, heterophils/lymphocytes, and glucose for female and male Two-banded plovers (TBPLs), Charadrius falklandicus (Latham, 1790) during nonbreeding (body moult) and breeding (incubation), in coastal areas of northern Patagonia Argentina. We also measured corticosterone for first time for the species during breeding. Nonbreeding TBPLs were more likely to have higher physiological measurements that were not dependent on body moult nor body condition, being similar between sexes. Differences found in glucose are likely related to recent feeding in nonbreeding birds compared with fasting during incubation. The gregarious nonbreeding behaviour in comparison with the isolated breeding pairs, would increase the risk of acquiring parasites and /or pathogens inducing a response of the immune system reflected in higher values of lymphocytes. Baseline corticosterone during breeding was similar between sexes and were lower compared with other values reported for breeding plovers. TBPLs undergo energetically demanding physiological changes during the nonbreeding stage, strengthening the idea that conservation of the environmental resources at these locations may be more important than previously thought.

Are individuals consistent? Endocrine reaction norms under different ecological challenges

Quantifying organismal capacity for compensatory mechanisms is essential to forecast response to environmental change. Despite accumulating evidence for individual variation in physiological plasticity, the causes and consequences of this variation remain unclear. An outstanding question is whether individual reaction norms are consistent across different environmental challenges, i.e., whether an individual that is responsive to one environmental variable will be equally responsive to a different environmental variable. Additionally, are these reaction norms themselves consistent over time, i.e., repeatable? Here, we quantified individual baseline glucocorticoid responses in house sparrows, Passer domesticus, to sequential manipulations of temperature, wind speed, and food unpredictability that were repeated in discrete blocks of sampling under both control and stressor-exposed conditions. Individuals significantly decreased their baseline corticosterone levels and increased their mass during treatment exposure. This response was consistent across environmental challenge types. There was high repeatability in the intercept and slope of the baseline corticosterone reaction norm between environmental challenges but broad credible intervals in the repeatability of the reaction norm slope, suggesting that although glucocorticoid levels during baseline conditions are repeatable, among-individual variation in the shape of the glucocorticoid response may be higher than within-individual variation. Within-subject variation in baseline corticosterone levels was mainly explained by within-individual variation in body mass during stressor exposure. Despite the high lability in physiological traits, endocrine plasticity is repeatable across environmental challenges and may be able to evolve due to genetic accommodation, in which selection acts on genetic variation of reaction norms.

Foraging in Urban Environments Increases Bactericidal Capacity in Plasma and Decreases Corticosterone Concentrations in White Ibises

As humans continue to infringe on natural habitats, more animals are exposed to urbanization and its associated challenges. It is still unclear, however, whether the movement of animals into urban habitats negatively influences the health and/or survival of those animals, however those animals often experience shifts in resource availability, diet composition, and exposure to stimuli that are new and potentially stressful. Recently, white ibises (Eudocimus albus) have become increasingly common in urban habitats where they forage in close proximity to humans and even interact with them, collecting food handouts. We hypothesized that foraging in urban habitats would negatively impact measures of health, impair innate immunity, trigger elevated concentrations of corticosterone, and depress physiological responses to stressors in white ibises. We found that plasma from birds captured from urban sites had higher bactericidal capacity against Escherichia coli than those captured in natural sites. Additionally, adults captured in urban habitats had a significantly lower baseline corticosterone concentrations during the post-breeding season, and corticosterone responses to a handling challenge were lower for birds captured from urban sites during year 2 of the study. These results indicate that exposure to urban habitats impacts ibis health, though in the opposite direction of what was predicted.

Developmental programming of the adrenocortical stress response by yolk testosterone depends on sex and life history stage

ABSTRACTDevelopmental exposure of embryos to maternal hormones such as testosterone in the avian egg influences the expression of multiple traits, with certain effects being sex specific and lasting into adulthood. This pleiotropy, sex dependency and persistency may be the consequence of developmental programming of basic systemic processes such as adrenocortical activity or metabolic rate. We investigated whether experimentally increased in ovo exposure to testosterone influenced hypothalamus–pituitary–adrenal function, i.e. baseline and stress-induced corticosterone secretion, and resting metabolic rate (RMR) of adult male and female house sparrows (Passer domesticus). In previous experiments with this passerine bird we demonstrated effects of embryonic testosterone exposure on adult agonistic and sexual behavior and survival. Here we report that baseline corticosterone levels and the stress secretion profile of corticosterone are modified by in ovo testosterone in a sex-specific and life history stage-dependent manner. Compared with controls, males from testosterone-treated eggs had higher baseline corticosterone levels, whereas females from testosterone-treated eggs showed prolonged stress-induced corticosterone secretion during the reproductive but not the non-reproductive phase. Adult RMR was unaffected by in ovo testosterone treatment but correlated with integrated corticosterone stress secretion levels. We conclude that exposure of the embryo to testosterone programs the hypothalamus–pituitary–adrenal axis in a sex-specific manner that in females depends, in expression, on reproductive state. The modified baseline corticosterone levels in males and stress-induced corticosterone levels in females may explain some of the long-lasting effects of maternal testosterone in the egg on behavior and could be linked to previously observed reduced mortality of testosterone-treated females.

Neuroendocrine and behavioral measures of negative valence in male sign-tracker and goal-tracker rats

Cues, or stimuli in the environment, attain the ability to guide behavior via learned associations. As predictors, cues can elicit adaptive behavior and lead to valuable resources (e.g., food). For some individuals, however, cues are transformed into incentive stimuli and can elicit maladaptive behavior. The goal-tracker/sign-tracker animal model captures individual differences in cue-motivated behaviors, with reward-associated cues serving as predictors of reward for both goal-trackers and sign-trackers, but becoming incentive stimuli only for sign-trackers. While these distinct phenotypes are characterized based on Pavlovian conditioned approach behavior, they exhibit differences on a number of behaviors of relevance to psychopathology. To further characterize the neurobehavioral endophenotype associated with individual differences in cue-reward learning, we investigated neuroendocrine and behavioral profiles associated with negative valence in male goal-trackers, sign-trackers, and intermediate responders. We found that baseline corticosterone increases with Pavlovian learning, and that this increase is positively associated with the development of sign-tracking. We did not observe significant differences between goal-trackers and sign-trackers in behavior during an elevated plus maze or open field test, nor did we see differences in the corticosterone response to the open field test or physiological restraint. We did, however, find that sign-trackers have greater glucocorticoid receptor mRNA expression in the ventral hippocampus, with no phenotypic differences in the dorsal hippocampus. These findings suggest that goal-trackers and sign-trackers do not differ on indices of negative valence; rather, differences in neuroendocrine measures between these phenotypes can be attributed to distinct cue-reward learning styles.Significance StatementWhile the goal-tracker/ sign-tracker animal model derives from individual differences in Pavlovian conditioned approach behavior, other traits, including some of relevance to addiction and post-traumatic stress disorder, have been shown to co-exist with the propensity to sign-track. The extent to which this model encompasses differences in negative valence systems, however, remains largely unexplored. Here we show that behavioral and corticosterone response to paradigms associated with negative valence do not differ between goal-trackers and sign-trackers; but baseline corticosterone levels appear to be linked to the development of sign-tracking, as do differences in glucocorticoid receptor expression in the ventral hippocampus. These findings suggest that neuroendocrine measures typically associated with negative valence may, in fact, play an important role in positive valence systems.

Baseline and stress-induced corticosterone levels across birds and reptiles do not reflect urbanization levels

Rates of human-induced environmental change continue increasing with human population size, potentially altering animal physiology and negatively affecting wildlife. Researchers often use glucocorticoid concentrations (hormones that can be associated with stressors) to gauge the impact of anthropogenic factors (e.g. urbanization, noise and light pollution). Yet, no general relationships between human-induced environmental change and glucocorticoids have emerged. Given the number of recent studies reporting baseline and stress-induced corticosterone (the primary glucocorticoid in birds and reptiles) concentrations worldwide, it is now possible to conduct large-scale comparative analyses to test for general associations between disturbance and baseline and stress-induced corticosterone across species. Additionally, we can control for factors that may influence context, such as life history stage, environmental conditions and urban adaptability of a species. Here, we take a phylogenetically informed approach and use data from HormoneBase to test if baseline and stress-induced corticosterone are valid indicators of exposure to human footprint index, human population density, anthropogenic noise and artificial light at night in birds and reptiles. Our results show a negative relationship between anthropogenic noise and baseline corticosterone for birds characterized as urban avoiders. While our results potentially indicate that urban avoiders are more sensitive to noise than other species, overall our study suggests that the relationship between human-induced environmental change and corticosterone varies across species and contexts; we found no general relationship between human impacts and baseline and stress-induced corticosterone in birds, nor baseline corticosterone in reptiles. Therefore, it should not be assumed that high or low levels of exposure to human-induced environmental change are associated with high or low corticosterone levels, respectively, or that closely related species, or even individuals, will respond similarly. Moving forward, measuring alternative physiological traits alongside reproductive success, health and survival may provide context to better understand the potential negative effects of human-induced environmental change.