Photoperiodic regulation of avian physiology: From external coincidence to seasonal reproduction

Photoperiod-driven testicular DNA methylation in gonadotropin and sex steroid receptor promoters in Siberian hamsters

Seasonal cycles in breeding, often orchestrated by annual changes in photoperiod, are common in nature. Here, we studied how change in photoperiod affects DNA methylation in the testes of a highly seasonal breeder: the Siberian hamster (Phodopus sungorus). We hypothesized that DNA methylation in promoter regions associated with key reproductive genes such as follicle-stimulating hormone receptor in the testes is linked to breeding and non-breeding states. Using Oxford Nanopore sequencing, we identified more than 10 million (10,151,742) differentially methylated cytosine-guanine (CpG) sites in the genome between breeding long photoperiod and non-breeding short photoperiod conditions. ShinyGo enrichment analyses identified biological pathways consisting of reproductive system, hormone-mediated signalling and gonad development. We found that short photoperiod induced DNA methylation in the promoter regions for androgen receptor (Ar), estrogen receptors (Esr1, Esr2), kisspeptin1 receptor (kiss1r) and follicle-stimulating hormone receptor (Fshr). Long photoperiods were observed to have higher DNA methylation in promoters for basic helix-loop-helix ARNT-like 1 (Bmal1), progesterone receptor (Pgr) and thyroid-stimulating hormone receptor (Tshr). Our findings provide insights into the epigenetic mechanisms underlying seasonal adaptations in timing reproduction in Siberian hamsters and could be informative for understanding male fertility and reproductive disorders in mammals.

Timing mismatches, carryover effects, and the role of neuroendocrine mechanisms in determining birds' responses to environmental change

The neuroendocrine system plays a critical role in the synchronization of life cycle stages with variation in the environment, and in the coordination of life cycle stages with one another. When humans modify environments, these neuroendocrine mechanisms may impact how different individuals, populations, species, and even communities are affected. Here we conceptualize how endocrine mechanisms may influence the likelihood of: (1) timing mismatches between life cycle stages and environmental conditions, and (2) carryover effects within annual cycles. Timing mismatches can occur when an individual fails to synchronize a particular life cycle stage to the appropriate environmental conditions. Carryover effects occur when activities of one stage (including its timing) affect the performance in one or more subsequent stages. We suggest that there is a trade-off between timing adjustments within and across stages such that neuroendocrine mechanisms that reduce timing mismatches in temporally changing environments (e.g., strong neuroendocrine responsiveness to short-term cues, with resultant increased temporal flexibility to fine-tune the current stage to local conditions) may inherently increase the likelihood of carryover effects (e.g., through delay of a transition between stages), and vice versa. We use two examples-flexibility of the onset of photorefractoriness mediated by responsiveness to short-term cues, and sensitivity of molt to sex steroids-to illustrate these ideas, and suggest that future work should investigate the impacts of variation in these and potentially other seasonal timing mechanisms on carryover effects. The conceptual framework presented here suggests that there may be no single best set of tactics for coping with the effects of climate change; species with neuroendocrine mechanisms facilitating temporal flexibility may avoid some timing mismatches but set themselves up for deleterious carryover effects as they make temporal adjustments to environmental conditions modified by climate change.

Reproductive characteristics and methods to improve reproductive performance in goose production: A systematic review

In the past two decades, the high demand of and significance of poultry meat have promoted the development of the goose industry. Despite the continuous expansion of the goose breeding scale and the generation of large economic benefits by the goose industry, low reproductive efficiency remains a barrier to limit vigorous development of the goose industry. Poor reproductive efficiency can be attributed to breeding seasonality, strong broody behavior, and poor semen quality. Based on the reproductive endocrine regulation mechanism of geese, an overview of past studies that have developed various methods to achieve a significant improvement in goose reproductive performance including physical facilities for artificial illumination control and dietary nutrition manipulation to improve breeder reproductivity, and artificial incubation equipment and technology for better hatchability. The most recent advances utilize immunoneutralization to regulate critical hormones involved in goose reproduction. This review provides new information for industry and academic studies of goose breeding.

Endocrine and molecular regulation of seasonal avian immune function

Birds have evolved seasonal adaptations in multiple aspects of the innate and adaptive immune systems. Seasonal immunological adaptations are crucial for survival in harsh environmental conditions and in response to increased prevalence of acute and chronic diseases. Similar to other vertebrates, birds exhibit remarkable plasticity in cytokine production, chemotaxis, phagocytosis and inflammation across the year. In this review, we provide a comparative perspective on seasonal rhythms in bird immune function. We describe advances in our understanding of annual changes in immune cells and responses to innate and adaptive immune challenges. Then, the role of glucocorticoids, sex steroids, thyroid hormones (THs) and melatonin to act as immunomodulators is described. We then discuss the impact of a major and emerging disease, the high pathogenicity avian influenza, as one of the most critical seasonal diseases with significant implications for poultry and wild bird populations. The review identifies the need to enhance our knowledge of annual rhythms in immune cells and tissues in birds, at molecular, cellular and hormonal levels across the year. Moreover, there is a significant absence of information on sex-specific seasonal variation in immune function. Understanding seasonal immune system dynamics will aid in addressing the negative impacts of pathogenic diseases, minimize global economic losses and aid conservation efforts.This article is part of the Theo Murphy meeting issue 'Circadian rhythms in infection and immunity'.

Rapid changes in plasma corticosterone and medial amygdala transcriptome profiles during social status change reveal molecular pathways associated with a major life history transition in mouse dominance hierarchies

Social hierarchies are a common form of social organization across species. Although hierarchies are largely stable across time, animals may socially ascend or descend within hierarchies depending on environmental and social challenges. Here, we develop a novel paradigm to study social ascent and descent within male CD-1 mouse social hierarchies. We show that mice of all social ranks rapidly establish new stable social hierarchies when placed in novel social groups with animals of equivalent social status. Seventy minutes following social hierarchy formation, males that were socially dominant prior to being placed into new social hierarchies exhibit higher increases in plasma corticosterone and vastly greater transcriptional changes in the medial amygdala (MeA), which is central to the regulation of social behavior, compared to males who were socially subordinate prior to being placed into a new hierarchy. Specifically, the loss of social status in a new hierarchy (social descent) is associated with reductions in MeA expression of myelination and oligodendrocyte differentiation genes. Maintaining high social status is associated with high expression of genes related to cholinergic signaling in the MeA. Conversely, gaining social status in a new hierarchy (social ascent) is related to relatively few unique rapid changes in the MeA. We also identify novel genes associated with social transition that show common changes in expression when animals undergo either social descent or social ascent compared to maintaining their status. Two genes, Myosin binding protein C1 (Mybpc1) and μ-Crystallin (Crym), associated with vasoactive intestinal polypeptide (VIP) and thyroid hormone pathways respectively, are highly upregulated in socially transitioning individuals. Further, increases in genes associated with synaptic plasticity, excitatory glutamatergic signaling and learning and memory pathways were observed in transitioning animals suggesting that these processes may support rapid social status changes.

Molecular basis of photoinduced seasonal energy rheostasis in Japanese quail (Coturnix japonica)

Seasonal rhythms in photoperiod are a predictive cue used by many temperate-zone animals to time cycles of lipid accumulation. The neuroendocrine regulation of seasonal energy homeostasis and rheostasis are widely studied. However, the molecular pathways underlying tissue-specific adaptations remain poorly described. We conducted two experiments to examine long-term rheostatic changes in energy stability using the well-characterized photoperiodic response of the Japanese quail. In experiment 1, we exposed quails to photoperiodic transitions simulating the annual photic cycle and examined the morphology and fat deposition in liver, muscle, and adipose tissue. To identify changes in gene expression and molecular pathways during the vernal transition in lipid accumulation, we conducted transcriptomic analyses of adipose and liver tissues. Experiment 2 assessed whether the changes observed in Experiment 1 reflected constitutive levels or were due to time-of-day sampling. We identified increased expression of transcripts involved in adipocyte growth, such as Cysteine Rich Angiogenic Inducer 61 and Very Low-Density Lipoprotein Receptor, and in obesity-linked disease resistance, such as Insulin-Like Growth Factor Binding Protein 2 and Apolipoprotein D, in anticipation of body mass gain. Under long photoperiods, hepatic transcripts involved in fatty acid (FA) synthesis (FA Synthase, FA Desaturase 2) were down-regulated. Parallel upregulation of hepatic FA Translocase and Pyruvate Dehydrogenase Kinase 4 expression suggests increased FA uptake and inhibition of the pyruvate dehydrogenase complex. Our findings demonstrate tissue-specific biochemical and molecular changes that drive photoperiod-induced adipogenesis. These findings can be used to determine conserved pathways that enable animals to accumulate fat without developing metabolic diseases.

Mechanisms underlying reproductive responses of Japanese quails to heat stress conditions

Exposure to heat stress can cause a significant increase in the death rate and disease susceptibility of poultry birds, ultimately impacting the profitability of the poultry industry. Despite being a more economical choice, Japanese quails (Coturnix japonica) are not immune to the harmful effects of heat stress. Quails may experience negative effects on their reproductive performance due to excessive reactive molecules caused by heat stress. However, they have developed various mechanisms to maintain their reproductive abilities in such conditions. The neuroendocrine system in birds plays a vital role in regulating their reproductive responses to thermal stress, and it is also connected to other environmental factors such as photoperiod that can impact their reproductive performance. Hormones are crucial in the complex interactions necessary for sexual maturation and reproductive responses to heat stress in Japanese quails living in stressful thermal conditions.

Neural thyroid hormone metabolism integrates seasonal changes in environmental temperature with the neuroendocrine reproductive axis

We asked if environmental temperature alters thyroid hormone metabolism within the hypothalamus, thereby providing a neuroendocrine mechanism by which temperature could be integrated with photoperiod to regulate seasonal rhythms. We used immunohistochemistry to assess the effects of low-temperature winter dormancy at 4 °C or 12 °C on thyroid-stimulating hormone (TSH) within the infundibulum of the pituitary as well as deiodinase 2 (Dio2) and 3 (Dio3) within the hypothalamus of red-sided garter snakes (Thamnophis sirtalis). Both the duration and, in males, magnitude of low-temperature dormancy altered deiodinase immunoreactivity within the hypothalamus, increasing the area of Dio2-immunoreactivity in males and females and decreasing the number of Dio3-immunoreactive cells in males after 8-16 weeks. Reciprocal changes in Dio2/3 favor the accumulation of triiodothyronine within the hypothalamus. Whether TSH mediates these effects requires further study, as significant changes in TSH-immunoreactive cell number were not observed. Temporal changes in deiodinase immunoreactivity coincided with an increase in the proportion of males exhibiting courtship behavior as well as changes in the temporal pattern of courtship behavior after emergence. Our findings mirror those of previous studies, in which males require low-temperature exposure for at least 8 weeks before significant changes in gonadotropin-releasing hormone immunoreactivity and sex steroid hormones are observed. Collectively, these data provide evidence that the neuroendocrine pathway regulating the reproductive axis via thyroid hormone metabolism is capable of transducing temperature information. Because all vertebrates can potentially use temperature as a supplementary cue, these results are broadly applicable to understanding how environment-organism interactions mediate seasonally adaptive responses.

Dissociating Mechanisms That Underlie Seasonal and Developmental Programs for the Neuroendocrine Control of Physiology in Birds

Long-term programmed rheostatic changes in physiology are essential for animal fitness. Hypothalamic nuclei and the pituitary gland govern key developmental and seasonal transitions in reproduction. The aim of this study was to identify the molecular substrates that are common and unique to developmental and seasonal timing. Adult and juvenile quail were collected from reproductively mature and immature states, and key molecular targets were examined in the mediobasal hypothalamus (MBH) and pituitary gland. qRT-PCR assays established deiodinase type 2 (DIO2) and type 3 (DIO3) expression in adults changed with photoperiod manipulations. However, DIO2 and DIO3 remain constitutively expressed in juveniles. Pituitary gland transcriptome analyses established that 340 transcripts were differentially expressed across seasonal photoperiod programs and 1,189 transcripts displayed age-dependent variation in expression. Prolactin (PRL) and follicle-stimulating hormone subunit beta (FSHβ) are molecular markers of seasonal programs and are significantly upregulated in long photoperiod conditions. Growth hormone expression was significantly upregulated in juvenile quail, regardless of photoperiodic condition. These findings indicate that a level of cell autonomy in the pituitary gland governs seasonal and developmental programs in physiology. Overall, this paper yields novel insights into the molecular mechanisms that govern developmental programs and adult brain plasticity.

FSHβ links photoperiodic signaling to seasonal reproduction in Japanese quail

Annual cycles in daylength provide an initial predictive environmental cue that plants and animals use to time seasonal biology. Seasonal changes in photoperiodic information acts to entrain endogenous programs in physiology to optimize an animal's fitness. Attempts to identify the neural and molecular substrates of photoperiodic time measurement in birds have, to date, focused on blunt changes in light exposure during a restricted period of photoinducibility. The objectives of these studies were first to characterize a molecular seasonal clock in Japanese quail and second, to identify the key transcripts involved in endogenously generated interval timing that underlies photosensitivity in birds. We hypothesized that the mediobasal hypothalamus (MBH) provides the neuroendocrine control of photoperiod-induced changes in reproductive physiology, and that the pars distalis of the pituitary gland contains an endogenous internal timer for the short photoperiod-dependent development of reproductive photosensitivity. Here, we report distinct seasonal waveforms of transcript expression in the MBH, and pituitary gland and discovered the patterns were not synchronized across tissues. Follicle-stimulating hormone-β (FSHβ) expression increased during the simulated spring equinox, prior to photoinduced increases in prolactin, thyrotropin-stimulating hormone-β, and testicular growth. Diurnal analyses of transcript expression showed sustained elevated levels of FSHβ under conditions of the spring equinox, compared to autumnal equinox, short (<12L) and long (>12L) photoperiods. FSHβ expression increased in quail held in non-stimulatory short photoperiod, indicative of the initiation of an endogenously programmed interval timer. These data identify that FSHβ establishes a state of photosensitivity for the external coincidence timing of seasonal physiology. The independent regulation of FSHβ expression provides an alternative pathway through which other supplementary environmental cues, such as temperature, can fine tune seasonal reproductive maturation and involution.