Seasonal changes in plasma levels of sex hormones in the greater Rhea (Rhea americana), a South American Ratite with a complex mating system

Experimentally Elevated Levels of Testosterone Advance Daily Onset of Activity in Short-Day Housed Male House Sparrows (Passer domesticus)

Seasonal changes in sleep/wake cycles and behaviors related to reproduction often co-occur with seasonal fluctuations in sex hormones. Experimental studies have established that fluctuations in circulating testosterone mediate circadian rhythms. However, most studies are performed under constant lighting conditions and fail to investigate the effects of testosterone on the phenotypic output of circadian rhythms, that is, chronotype (daily activity patterns under light:dark cycles). Here, we experimentally elevated testosterone with implants during short nonbreeding daylengths in male house sparrows (Passer domesticus) to test if observed seasonal changes in chronotype are directly in response to photoperiod or to testosterone. We fitted individuals with accelerometers to track activity across treatment periods. Birds experienced three treatments periods: short day photoperiods before manipulation (SD), followed by testosterone implants while still on short days (SD + T). Implants were then removed. After a decrease in cloacal protuberance size, an indicator of low testosterone levels, birds were then photostimulated on long days (LD). Blood samples were collected at night, when testosterone peaks, to compare testosterone levels to daily onset/offset activity for experimental periods. Our results indicate that experimentally elevated testosterone under short nonbreeding photoperiods significantly advanced daily onset of activity and total daily activity relative to daylength. This suggests that testosterone, independent of photoperiod, is responsible for seasonal shifts in chronotypes and daily activity rhythms. These findings suggest that sex steroid hormone actions regulate timing of daily behaviors, likely coordinating expression of reproductive behaviors to appropriate times of the day.

Review of the Effects of Enclosure Complexity and Design on the Behaviour and Physiology of Zoo Animals

The complexity of the habitat refers to its physical geometry, which includes abiotic and biotic elements. Habitat complexity is important because it allows more species to coexist and, consequently, more interactions to be established among them. The complexity of the habitat links the physical structure of the enclosure to the biological interactions, which occur within its limits. Enclosure complexity should vary temporally, to be able to influence the animals in different ways, depending on the period of the day and season and throughout the year. In the present paper, we discuss how habitat complexity is important, and how it can positively influence the physical and mental states of zoo animals. We show how habitat complexity can ultimately affect educational projects. Finally, we discuss how we can add complexity to enclosures and, thus, make the lives of animals more interesting and functional.

Seasonal variations on semen quality attributes in turkey and egg type chicken male breeders

A biological experiment was carried out in twenty-four adult healthy breeder males each in turkey (Beltsville small white) and egg type chicken (White Leghorn Babcock) in order to assess the seasonal influence on semen production and quality. The birds were maintained in individual cages under uniform husbandry conditions throughout the year. The birds were fed with breeder ration and water ad libitum was offered with a constant photoperiod of 14 h/day. Physical and biochemical characteristics of semen, serum hormones (testosterone and thyroxine), and antioxidant activity (catalase and lipid peroxidation) were evaluated throughout the year (January-December). Based on the THI calculations, the observations were classified under three different seasons, namely, winter (November-February), spring (March, April, and October), and summer (May-September). Semen physical parameters, sperm concentration, motility, live sperm percentage, and sperm plasma membrane integrity were superior during the winter season. In seminal plasma, biochemical parameters (phosphorus, ALT, ALP, AST, and uric acid) had a significant (P < 0.05) difference between seasons. There was a significant difference (P < 0.05) among serum hormones (testosterone and thyroxine) that were higher during the winter season. Significant variation was observed in catalase and lipid peroxidation antioxidant enzyme activities (seminal and blood plasma) in winter than in the other two seasons. Both the turkey and egg type chicken breeders exhibited superior seminal characteristics, sex hormone profile, and antioxidant enzyme activity during winter seasons.

An updated look at the mating system, parental care and androgen seasonal variations in ratites

Androgens modulate multiple key aspects of male reproduction, from morphology to mating behavior. Across animals the seasonal patterns of androgens are tightly linked to many of the species' life-history traits and their evolution. One popular framework to address this issue has been the Challenge Hypothesis, which proposed a testosterone-mediated trade-off between mating and parental care in males. Given the lack of empirical support, especially in birds, this hypothesis has been recently revisited (Challenge Hypothesis 2.0), integrating aspects such as male-female interactions and the diversity of reproductive systems in birds. Ratites constitute the most basal avian group (Palaeognathae: ratites together with Tinamiformes) and have certain characteristics that make them unique. They are flightless and generally have promiscuous mating systems with communal nests and male-only parental care (nest building, incubation and chick rearing). Furthermore, male testosterone concentrations remain high during the entire parental care period. Here we review the reproductive biology of ratites, integrating information on seasonal variations in parental care, social interactions and androgen levels across the group, in light of the Challenge Hypotheses and the Challenge Hypothesis 2.0 (there are no seasonal hormonal data for Tinamiformes, therefore they are not included in this review). We also discuss the constraints that could explain the lack of experimental approaches in behavioral endocrinology across ratites. I hope this review will motivate further research on this basal group of birds and further our understanding of the evolution of the mechanisms in the endocrine system that underly reproductive behavior across birds.

Reproduction in the Eared Dove: An exception to the classic model of seasonal reproduction in birds?

In avian species living at high altitudes and latitudes, reproductive events are largely controlled by photoperiod, with changes being perceived mainly through encephalic photoreceptors located in the hypothalamus. It is known that during long day periods (reproductive periods), the information transmitted by brain photoreceptors triggers the production of thyroid hormones that regulate GnRH secretion, inducing secretion of pituitary gonadotropins. As a result, gonads develop and grow and the production of gonadal sex hormones, testosterone and estradiol increases (classic gonadal cycle). During short day periods (non-reproductive periods) on the other hand, the gonads regress, and plasma gonadal steroid levels are low. By means of this mechanism, birds synchronize their physiology and reproductive behaviors with seasonal changes in the environment. However, it appears that not all avian species comply with this general reproductive pattern. For example, the Eared Dove (Zenaida auriculata), a South American opportunistic breeding columbiform, has been reported to successfully reproduce throughout the year, making it an interesting avian system for studying the endocrine basis of avian reproduction. In view of a clear lack of seasonal variability in testicular weight and size (the classic gonadal regression/recrudescence cycle) in the male Eared Dove, we examined whether their reproductive aseasonality could be the result of being in a continuous state of reproductive preparedness. Our results show that despite the absence of a marked gonadal cycle in terms of gonadal volume, plasma testosterone levels in males were minimal during autumn-winter, reaching maximum values during spring-summer. This indicates that male gonad function is not seasonal in terms of spermatogenesis but that circulating testosterone levels are correlated with photoperiod, demonstrating an exception to the classic model of reproduction in birds.

State of the art knowledge in adrenocortical and behavioral responses to environmental challenges in a threatened South American ratite: Implications to in situ and ex-situ conservation

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.

Aspects of spermatogenesis and microscopic testicular morphology in Greater Rhea, Rhea americana (Linnaeus, 1758)

ABSTRACT: The purpose of this study was to study the microscopic morphology of the testicular parenchyma of Rhea americana birds. Fifty-four 2.5±0.5 year-old male adults bred in captivity. were used. During commercial slaughter, samples of testis were collected in November/2005, December/2006 and May/2007, in order to compare possible differences. The samples underwent optical microscopy analysis and measurements of seminiferous tubule (ST) total diameters, lumen, epithelium thickness and the relative volume of parenchyma. The ST had circular form in transverse cross sections. November/2005 and December/2006 samples had many types of germinative cells and spermatozoa in lumen, but in May/2007 the samples of epithelium were poor regarding meiotic and mitotic pictures, and it was difficult to find any spermatozoon; in many tubules the lumen was inexistent or diminished. In December/2006 and May/2007 the averages were: tubule diameter 110.3 and 5.3mμ, lumen 52.4 and 4.5mμ, epithelium thickness 57.8 and 0.7mμ respectively. The volumetric proportions were: seminiferous epithelium 75.6 and 75.9, cysts in epithelium 2.1 and 1.0, ST 93.3 and 84.0, interstitium 6.2 and 15.6 respectively. The sperm reserves were: 19.7±2 and 0±0 x109 sperm cells in December 2006 and May 2007 respectively. Microscopic measures of seminiferous tubules, spermatic cells and diameter of the nuclei were presented. These data confirm reproductive seasonality, with breeding season in spring-summer with sperm production. A great variation n parenchyma, when compared breeding was noticeable.

Sex hormones establish a reserve pool of adult muscle stem cells

Quiescent satellite cells, known as adult muscle stem cells, possess a remarkable ability to regenerate skeletal muscle following injury throughout life. Although they mainly originate from multipotent stem/progenitor cells of the somite, the mechanism underlying the establishment of quiescent satellite cell populations is unknown. Here, we show that sex hormones induce Mind bomb 1 (Mib1) expression in myofibres at puberty, which activates Notch signalling in cycling juvenile satellite cells and causes them to be converted into adult quiescent satellite cells. Myofibres lacking Mib1 fail to send Notch signals to juvenile satellite cells, leading to impaired cell cycle exit and depletion. Our findings reveal that the hypothalamic-pituitary-gonadal axis drives Mib1 expression in the myofibre niche. Moreover, the same axis regulates the re-establishment of quiescent satellite cell populations following injury. Our data show that sex hormones establish adult quiescent satellite cell populations by regulating the myofibre niche at puberty and re-establish them during regeneration.

Influence of breeding season on fecal glucocorticoid levels in captive Greater Rhea (Rhea americana)

Sex hormones and stress-related changes can be seasonally influenced. We investigate whether fecal glucocorticoid metabolite (FGM) levels can differ between male and female captive Greater Rheas during the breeding and non-breeding seasons. Over a 3-year-period, fresh fecal samples from 10 individuals (five of each sex) were collected during the breeding months (October, November, and December) and non-breeding months (April and June). A total of 960 samples were assayed using a commercial radioimmunoassay. Results showed that FGM levels (mean ± SE) were affected by the breeding season in a sex-dependent way. Male Greater Rheas showed significantly higher FGM levels in the breeding months than in the non-breeding months (13.44 ± 0.37 vs. 7.92 ± 0.1 ng/g feces, respectively). By contrast, females did not show FGM seasonal changes throughout the same sampling periods (7.55 ± 0.14 vs. 7.26 ± 0.73 ng/g feces). Moreover, during the breeding season months, males showed higher average FGM levels than females (13.44 ± 0.37 vs. 7.55 ± 0.14 ng/g feces, respectively), and no differences were found between sexes during the non-breeding season (7.92 ± 0.1 vs. 7.26 ± 0.73 ng/g feces, respectively). Our findings suggest that male Greater Rheas have a higher adrenocortical activity during the breeding season, which is probably indirectly related to the increased testosterone levels and agonist interactions that are also observed during that phase. Studies aimed to determine the appropriate sex ratio for captive rearing should be developed to minimize male agonist encounters and therefore improve welfare of the captive group.