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Maternal hormones in avian egg yolks may signal and prepare offspring for the prevailing conditions. However, this adjustment requires some degree of flexibility in regulating yolk hormone deposition. The Greater Rhea (Rhea americana) has a particular mating system that combines mixed polygyny and polyandry, communal nesting, and exclusive paternal care of chicks. In this species, we previously found that yolk hormone deposition varies among eggs of different captive populations and could influence chicks' physiology and behavior. However, it is still unknown whether females can modify yolk hormone deposition in a changing social environment. Using a captive population of Greater Rheas, in this study, we quantified yolk hormone levels before and after a reduction in the number of females present in the population. We found that females deposited on average higher yolk corticosterone and lower yolk progesterone after the change in their social environment. Since corticosterone deposited into the yolk comes exclusively from the female's plasma, our results suggest that females had, on average, higher plasma corticosterone levels. The change in the number of females may increase the events of male-male competitions, courtships, and matings, leading to an increase of corticosterone in the females' plasma and then into their eggs. Since we previously found that higher yolk corticosterone and lower yolk progesterone were associated with the production of chicks that have an attenuated stress response, the present study results suggest that yolk hormone deposition is mediated by flexible mechanisms that could adjust development to the prevailing conditions., (© 2022 Wiley Periodicals LLC.)

Maternal corticosterone in avian eggs may modify offspring phenotype in order to increase survival in poor environments. In the Greater Rhea (Rhea americana), we previously found that yolk immunoreactive corticosterone is influenced by the quality of the maternal environment: eggs laid by females of the intensive rearing system (IRS), living in poor captive conditions, had higher yolk immunoreactive corticosterone than those produced by females of the semi-extensive rearing system (SRS), living in better conditions. Here, we evaluate if these different hormone levels are associated with the production of different phenotypes. We collected eggs from the IRS and SRS for hormonal quantification and artificial incubation. Then, half of the chicks selected from each environment were exposed to a capture and restraint protocol, and the rest remained undisturbed and were used as controls. In the IRS, we found that higher yolk immunoreactive corticosterone was associated with the production of chicks that had reduced hatchability, lower hatchling mass and higher baseline fecal glucocorticoid metabolites (FGM) than those produced by SRS females. Moreover, after capture and restraint, IRS chicks did not modify their FGM nor their behaviors compared to their controls, while SRS chicks increased their FGM and spent more time ambulating and less time pecking, compared to their controls. These results indicate that yolk immunoreactive corticosterone could modify offspring phenotype. Although future studies are needed to elucidate their implications for fitness, our results suggest that yolk corticosterone could be mediating an adaptive maternal effect that allows individuals to better cope with poor conditions., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The Greater Rhea (Rhea americana) is an endemic ratite to South America, whose wild populations have undergone a remarkable decrease due to habitat degradation and fragmentation by the expansion of the agricultural frontier, poaching and predation by dogs. Anthropogenic perturbations in wild environments, as well as the management in captivity, can generate different stress responses in this species, thus, the monitoring of adrenocortical and behavioral activities are considered primary assessment tools with both conservation and welfare implications. In this review we analyze and integrate the different measurements of glucocorticoids (in plasma, feces, and yolk) carried out in different captive and wild populations, taking into account the diverse predictable and unpredictable conditions to which the Greater Rhea responds in each of those environments. In addition, the translocation of this bird is presented as an application of stress physiology in field ecology for conservation purposes, in which we evaluated how this species responds when it is released into a novel environment. Our results indicate that this ratite has a striking high sensitivity of the hypothalamic-pituitary-adrenal (HPA) axis compared to that of other bird species and shows a wide variety of adrenocortical responses depending on the environment in which it lives. This suggests that its HPA axis has a phenotypic plasticity that enables the rhea to cope with the environmental challenges. In this sense, we propose that one of the routes of this plasticity could be mediated by the maternal transfer of steroid hormones to the egg. Finally, we discuss the importance of integrating the monitoring of the adrenocortical response along with the environmental variables that define the life history of the species, in management and conservation programs ex-situ and in situ., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Progesterone is the most concentrated maternal yolk steroid characterized to date in birds; however, no information about it is available in ratite eggs. We collected freshly laid eggs from zoo-housed Greater Rhea females (Rhea americana) bred under similar rearing conditions during two breeding seasons to characterize concentration and distribution of maternal yolk progesterone. After high-performance liquid chromatography analysis, yolk hormone was measured using a commercial electrochemiluminescence immunoassay. Progesterone concentrations were found to vary significantly among the yolk layers, supporting a follicular origin for this steroid in Greater Rhea eggs. Additionally, highly similar mean absolute yolk progesterone concentrations were detected between 2013 and 2015 breeding seasons (1,332.98 ± 82.59 and 1,313.59 ± 85.19 ng/g, respectively). These values are also comparable to those found in some domestic carinate species. Findings suggest that at population level, when rearing conditions are similar, mean absolute yolk maternal progesterone concentrations also appear bounded. Future research on the factors and mechanisms that regulate progesterone deposition in Greater Rhea eggs is needed to better understand whether its levels depend on different rearing conditions., (© 2017 Wiley Periodicals, Inc.)

Many environmental conditions elevate plasma corticosterone in laying birds, leading to elevated hormone accumulation in the egg. We investigated whether maternal yolk corticosterone levels in Greater Rheas differ between fresh eggs collected from an intensive (IRS) and a semi-extensive (SRS) rearing system. After HPLC validation, yolk corticosterone was measured using a corticosterone (125) I radio-immunoassay kit. Results (mean ± SE) showed that eggs collected from the IRS exhibited a significantly higher corticosterone concentration than eggs from SRS (89.88 ± 8.93 vs. 45.41 ± 5.48 ng/g yolk, respectively). Our findings suggest that rearing conditions under an intensive scheme (e.g., small pens with bare ground, no direct foraging and handling) might be perceived as more stressful for Greater Rhea females than semi-extensive rearing conditions (e.g., low animal density distributed in extensive areas and direct foraging), which would result in the transfer of higher yolk corticosterone levels. A better understanding of environmental conditions and female traits that affect yolk corticosterone deposition provides a background for future studies concerning the roles of maternal corticosterone on offspring development. Zoo Biol. 35:246-250, 2016. © 2016 Wiley Periodicals, Inc., (© 2016 Wiley Periodicals, Inc.)

Purpose: The vertebrate inner retina has a subset of intrinsically photosensitive retinal ganglion cells (ipRGCs) that express the nonvisual photopigment melanopsin. The intrinsically photosensitive retinal ganglion cells send light information from the environment to the brain to control, among other parameters, the amount of energy entering the eyes through the pupillary light reflex (PLR). A daily variation in the PLR in both mice and humans has recently been shown, indicating circadian control of this response. In a previous work involving the sensitivity spectra for the PLR, we showed that blind chickens (GUCY1*) display the highest sensitivity to light of 480 nm. The aim of the present study was to evaluate the potential circadian control of PLRs in blind birds under scotopic conditions., Methods: Circadian PLR was performed on GUCY1* chickens with lights of different wavelengths (white or blue light of 475 nm) under scotopic conditions., Results: We found a significant daily variation in the PLRs of chickens exposed to white or blue light of 475 nm, with increased sensitivity at circadian time 6 during the subjective day., Conclusions: Our observations clearly point to circadian control of PLRs even in blindness, strongly indicating that both the entry of light into the eyes and its quality are differentially regulated during the day in diurnal animals., (Copyright 2015 The Association for Research in Vision and Ophthalmology, Inc.)

Seasonal rhythm in sex hormones has been extensively studied in birds, as well as its relationship with the type of mating system. The Greater Rhea (Rhea americana), a South American ratite species, reproduces seasonally and has a complex mating system: female-defense polygyny and sequential polyandry. The present study aimed at analyzing the endocrine basis of reproduction in this species and its relationship with its mating system. We used HPLC and electrochemiluminescence techniques to identify and measure plasma testosterone and estradiol levels. Annual oscillations in sex hormones, testosterone and estradiol, in adult males and females were observed. Lower levels of these hormones were exhibited during the non reproductive season (February to July), whereas their maximum values were reached in September for males and November-December for females. These fluctuations reflect the seasonal changes in gonadal function. By contrast, no significant sex hormones oscillations were observed in juvenile males and females (negative control of seasonal changes). Greater rheas maintain high testosterone and estradiol levels throughout the reproductive period. The high testosterone levels during incubation and chick rearing did not inhibit parental behavior in males, which appears not to conform to the "Challenge Hypothesis". In females, the high estradiol levels throughout the reproductive season would be needed to sustain their long egg-laying period.

Animal transport is an indispensable practice in species that need to be moved for management or commercial purposes. However, transport may have negative effects on individuals' welfare. The aims of the present work were to determine if the behavioral responses of adult Greater Rheas (Rhea americana) bred in captivity are sensitive to short-term transport and if males and females differ in their posttransport behavioral activity and recovery. Eight males and 8 females were placed in individual pens and allowed 6 d to habituate (d 1 to 6) before transport procedure. On the transport day (d 7), half of the birds (4 males and 4 females) were randomly assigned to a transport group that was captured and handled to be placed into the crates, exposed to a 30-min transport stressor, and immediately returned to their pens. Four transports with 1 different male and female each time were performed. The other half remained undisturbed and were used as controls. Behavior of all individuals was video-recorded during habituation days, after transport on d 7, and on the 2 following days (d 8 and 9) to evaluate pre- and posttransport behavioral activity for 2 h per day. No significant behavioral changes were observed during the last 2 d of the habituation period (d 5 and 6), suggesting that Greater Rheas were adapted to the housing conditions before transport. After transportation, several behaviors were affected: transported males and females showed null resting, transported females also showed reduced preening and increased vigilance (P < 0.05), whereas transported males showed increased drinking (P < 0.05) compared with their respective control groups. The results suggest that behavioral responses of captive-bred Greater Rheas are sensitive to short-term transport (which includes handling) and that males and females differ in their posttransport behavioral activity, recovering their overall basal levels on the third day posttransportation.

The effect of transport stress on blood corticosterone levels in captive Greater Rheas was investigated. Twelve adult individuals (7 males; 5 females) were loaded in pairs inside wooden crates and transported along a paved road for 30 min. Blood samples were taken before the individuals were introduced into the crate (baseline value) and immediately after they were unloaded (30 min after capture). To assess whether corticosterone levels were affected by the blood sampling procedure per se, another 6 (nontransport) control birds (3 males; 3 females) were also captured and sampled at the same times as their transported counterparts. Plasma corticosterone concentrations were measured using a commercially available corticosterone (125)I radio-immunoassay kit. Baseline corticosterone levels were similar in the control and transported birds (9.0 ± 1.6 and 10.4 ± 0.8 ng/mL, respectively). Transportation induced a highly significant (P < 0.001), more than 40-fold increase in the corticosterone levels (433.6 ± 35.4 ng/mL) that was about 5 times higher (P < 0.001) than in their nontransported counterparts (88.4 ± 14.8 ng/mL). The present findings suggest that Greater Rhea is a species highly sensitive to stressful manipulations. Both blood sampling and transportation induced highly significant adrenocortical responses. Considering that transportation is one of the unavoidable common practices in the management of Greater Rheas and, as shown in the present study, that it induces a significant 40-fold corticosterone stress response, efforts should focus on helping to generate management transport standards for optimization of the welfare of this ratite.