The bird of time: cognition and the avian biological clock

Parallel and convergent evolution in genes underlying seasonal migration

Seasonal migration has fascinated scientists and natural historians for centuries. While the genetic basis of migration has been widely studied across different taxa, there is little consensus regarding which genomic regions play a role in the ability to migrate and whether they are similar across species. Here, we examine the genetic basis of intraspecific variation within and between distinct migratory phenotypes in a songbird. We focus on the Common Yellowthroat (Geothlypis trichas) as a model system because the polyphyletic origin of eastern and western clades across North America provides a strong framework for understanding the extent to which there has been parallel or convergent evolution in the genes associated with migratory behavior. First, we investigate genome-wide population genetic structure in the Common Yellowthroat in 196 individuals collected from 22 locations across breeding range. Then, to identify candidate genes involved in seasonal migration, we identify signals of putative selection in replicate comparisons between resident and migratory phenotypes within and between eastern and western clades. Overall, we find wide-spread support for parallel evolution at the genic level, particularly in genes that mediate biological timekeeping. However, we find little evidence of parallelism at the individual SNP level, supporting the idea that there are multiple genetic pathways involved in the modulation of migration.

Sex-Specific Methylomic and Transcriptomic Responses of the Avian Pineal Gland to Unpredictable Illumination Patterns

In the production environment of chickens, exposure to unpredictable light patterns is a common painless stressor, widely used to influence growth rate and egg production efficiency. The pineal gland, a key regulator of circadian rhythms through melatonin secretion, responds to environmental light cues, and its function is modulated by epigenetic mechanisms. In this study, we investigated how the pineal gland methylome and transcriptome (including micro-RNAs) interact to respond to a rearing exposure to unpredictable illumination patterns, with a particular focus on sex differences. We conducted an integrative multi-omic analysis-including methylomic (MeDIP-seq), transcriptomic (RNA-seq), and miRNA expression profiling-on the pineal gland of Hy-Line White chickens (n = 34, 18 females, 16 males) exposed to either a standard 12:12 light-dark cycle (control) or a randomized, unpredictable light schedule from Days 3 to 24 post-hatch. Our findings reveal that unpredictable light exposure alters the pineal gland methylome and transcriptome in a sex-specific manner. However, while transcriptomic differences between sexes increased due to the stress, methylomic differences decreased, particularly on the Z chromosome. These changes were driven by females (the heterogametic sex in birds), which became more male-like in their pineal methylome after exposure to the illumination stress, leading to reduced epigenetic sexual dimorphism while maintaining differences at the gene expression level. Further, we implemented a fixed sex effect model as a biological proof of concept, identifying a network of 12 key core genes interacting with 102 other genes, all linked to circadian regulation and stress adaptation. This network of genes comprises a core regulatory framework for circadian response. Additionally, tissue-specific expression analysis and cell-type specific expression analysis revealed enrichment in brain regions critical for circadian function, including neuronal populations involved in circadian regulation and the hypothalamic-pituitary-thyroid axis. Together, these findings provide strong evidence of sex-specific epigenetic transcriptomic responses of the pineal gland upon illumination stress and offer valuable insights into the interplay of different omic levels in relation to circadian response.

Nocturnal playback experiments: The response of two European species of birds to singing of foreign male at night

Recent studies have shown that nocturnal singing in diurnal birds is a common phenomenon, however, the understanding of the mechanisms, functions and consequences of this behaviour has been lacking. We focused on the night singing of two diurnal songbirds-the yellowhammer and the common chaffinch that are widely distributed in Europe. We conducted day and night playback experiments, during which we broadcast songs of an unfamiliar male to the territory holder at two different stages of the breeding season, to examine whether the night singing in species which normally do not sing at night elicits responses from their conspecifics. We hypothesized that if nocturnal singing had no function, birds would ignore the night-time playback and respond only to the daytime intrusion. Otherwise, a response to the night-time playback would suggest that night singing may increase reproductive success but is limited by ecological factors. We found that, in contrast to the diurnal experiment, neither species responded vocally to the nocturnal playback. In yellowhammers, the probability of flights was higher during and after the playback than before it. This pattern was similar both during the day and night and did not differ between the stages of the season. For the common chaffinches, the probability of flight was low at night and constant across treatments, in contrast to the day when we observed more flights during the playback stage than before and after it. The playback of either species' songs at night caused the approach of predators, which was not observed during the day. The observed discrepancy in the probability of flights between the species suggests that nocturnal singing is a functional trait that affects other individuals in a specific context. Nocturnal singing does not seem to be a simple behaviour that extends during the day; it is a complex mechanism potentially dependent on specific conditions related to intraspecific communication, predatory pressure, local female access, or species' evolutionary history. We emphasise that those ecological and evolutionary factors need to be taken into account to understand this phenomenon widely.

Phenotypic correlates between clock genes and phenology among populations of Diederik cuckoo, Chrysococcyx caprius

The Diederik cuckoo, Chrysococcyx caprius, is a small Afrotropical bird in the family Cuculidae. It is taxonomically related to 13 other species within the genus Chrysococcyx and is migratory in sub-Saharan Africa. It has a unique breeding behaviour of being a brood parasite: Breeding pairs lay their eggs in the nests of a host species and hatchlings expel the eggs of the host species. The aim of the present study was to investigate diversity in two circadian clock genes, Clock and Adcyap1, to probe for a relationship between genetic polymorphisms and their role in circannual timing and habitat selection (phenology) in intra-African migrants. DNA extracted from blood was used for the PCR amplification and sequencing of clock genes in 30 Diederik cuckoos. Three alleles were detected for Clock with similar genotypes between individuals from the Northern and Southern breeding ranges while 10 alleles were detected for Adcyap1, having shorter alleles in the North and longer alleles in the South. Population genetic analyses, including allele frequency and zygosity analysis, showed distinctly higher frequencies for the most abundant Clock allele, containing 10 polyglutamine repeats, as well as a high degree of homozygosity. In contrast, all individuals were heterozygous for Adcyap1 and alleles from both regions showed distinct differences in abundance. Comparisons between both clock genes and phenology found several phenotypic correlations. This included evidence of a relationship between the shorter alleles and habitat selection as well as a relationship between longer alleles and timing. In both instances, evidence is provided that these effects may be sex-specific. Given that these genes drive some of the synchronicity between environments and the life cycles of birds, they provide valuable insight into the fitness of species facing global challenges including climate change, urbanisation and expanding agricultural practices.

Constant light and pinealectomy disrupt daily rhythm in song production and negatively impact reproductive performance in zebra finches

We assessed the circadian clock control of singing and reproductive performance in zebra finches. Experiment 1 examined changes in body mass, testis size, and plasma corticosterone and testosterone levels in male birds exposed to constant light (LL, 100 lx) and constant darkness (DD, 0.5 lx), with controls on 12L:12D (L = 100 lx, D = 0.5 lx). There was a significant increase in the body mass and testis size under LL and a decrease in testis size under the DD. Using a similar design, experiment 2 assessed the persistence of the circadian rhythm in singing along with activity-rest pattern in cohort I birds that were entrained to 12L:12D and subsequently released in DD or LL, and in cohort II birds that were entrained to 12L:12D and following pinealectomy were released in DD. Both activity and singing patterns were synchronized with the light phase under 12L:12D, free-ran with a circadian period under DD, and were arrhythmic under the LL. There was an overall decreased and increased effect on singing under DD and LL, respectively, albeit with differences in various song parameters. The pinealectomy disrupted both activity and singing rhythms but did not affect singing or the overall song features. Pinealectomized bird pairs also exhibited a significant reduction in their nest-building and breeding efforts, resulting in a compromised reproductive performance. These results suggest a circadian clock control of singing and more importantly demonstrate a role of the pineal clock in breeding behaviors, leading to a compromised reproductive performance in diurnal zebra finches.

Mate calling alters expression of neuropeptide, cocaine- and amphetamine- regulated transcript (CART) in the brain of male frog Microhyla nilphamariensis

Croaking is a unique component of reproductive behaviour in amphibians which plays a key role in intraspecies communication and mate evaluation. While gonadal hormones are known to induce croaking, central regulation of sound production is less studied. Croaking is a dramatic, transient activity that sets apart an animal from non-croaking individuals. Herein, we aim at examining the profile of the neuropeptide cocaine- and amphetamine-regulated transcript (CART) in actively croaking and non-croaking frog Microhyla nilphamariensis. In anurans, this peptide is widely expressed in the areas inclusive of acoustical nuclei as well as areas relevant to reproduction. CART immunoreactivity was far more in the preoptic area (POA), anteroventral tegmentum (AV), ventral hypothalamus (vHy), pineal (P) and pituitary gland of croaking frog compared to non-croaking animals. On similar lines, tissue fragments collected from the mid region of the brain inclusive of POA, vHy, AV, pineal and pituitary gland of croaking frog showed upregulation of CART mRNA. However, CART immunoreactivity in the neuronal perikarya of raphe (Ra) was completely abolished during croaking activity. The data suggest that CART signaling in the brain may be an important player in mediating croaking behaviour in the frog.

Past and future: Urbanization and the avian endocrine system

Urban environments are evolutionarily novel and differ from natural environments in many respects including food and/or water availability, predation, noise, light, air quality, pathogens, biodiversity, and temperature. The success of organisms in urban environments requires physiological plasticity and adjustments that have been described extensively, including in birds residing in geographically and climatically diverse regions. These studies have revealed a few relatively consistent differences between urban and non-urban conspecifics. For example, seasonally breeding urban birds often develop their reproductive system earlier than non-urban birds, perhaps in response to more abundant trophic resources. In most instances, however, analyses of existing data indicate no general pattern distinguishing urban and non-urban birds. It is, for instance, often hypothesized that urban environments are stressful, yet the activity of the hypothalamus-pituitary-adrenal axis does not differ consistently between urban and non-urban birds. A similar conclusion is reached by comparing blood indices of metabolism. The origin of these disparities remains poorly understood, partly because many studies are correlative rather than aiming at establishing causality, which effectively limits our ability to formulate specific hypotheses regarding the impacts of urbanization on wildlife. We suggest that future research will benefit from prioritizing mechanistic approaches to identify environmental factors that shape the phenotypic responses of organisms to urbanization and the neuroendocrine and metabolic bases of these responses. Further, it will be critical to elucidate whether factors affect these responses (a) cumulatively or synergistically; and (b) differentially as a function of age, sex, reproductive status, season, and mobility within the urban environment. Research to date has used various taxa that differ greatly not only phylogenetically, but also with regard to ecological requirements, social systems, propensity to consume anthropogenic food, and behavioral responses to human presence. Researchers may instead benefit from standardizing approaches to examine a small number of representative models with wide geographic distribution and that occupy diverse urban ecosystems.

Role of Melatonin in Daily Variations of Plasma Insulin Level and Pancreatic Clock Gene Expression in Chick Exposed to Monochromatic Light

To clarify the effect of monochromatic light on circadian rhythms of plasma insulin level and pancreatic clock gene expression and its mechanism, 216 newly hatched chicks were divided into three groups (intact, sham operation and pinealectomy) and were raised under white (WL), red (RL), green (GL) or blue (BL) light for 21 days. Their plasma and pancreas were sampled at six four-hour intervals. For circadian rhythm analysis, measurements of plasma melatonin, insulin, and clock gene expression (cClock, cBmal1, cBmal2, cCry1, cCry2, cPer2, and cPer3) were made. Plasma melatonin, insulin, and the pancreatic clock gene all expressed rhythmically in the presence of monochromatic light. Red light reduced the mesor and amplitude of plasma melatonin in comparison to green light. The mesor and amplitude of the pancreatic clock gene in chickens exposed to red light were dramatically reduced, which is consistent with the drop in plasma melatonin levels. Red light, on the other hand, clearly raised the level of plasma insulin via raising the expression of cVamp2, but not cInsulin. After the pineal gland was removed, the circadian expressions of plasma melatonin and pancreatic clock gene were significantly reduced, but the plasma insulin level and the pancreatic cVamp2 expression were obviously increased, resulting in the disappearance of differences in insulin level and cVamp2 expression in the monochromatic light groups. Therefore, we hypothesize that melatonin may be crucial in the effect of monochromatic light on the circadian rhythm of plasma insulin level by influencing the expression of clock gene in chicken pancreas.

Characterization of Chicken α2A-Adrenoceptor: Molecular Cloning, Functional Analysis, and Its Involvement in Ovarian Follicular Development

Adrenoceptors are suggested to mediate the functions of norepinephrine (NE) and epinephrine (EPI) in the central nervous system (CNS) and peripheral tissues in vertebrates. Compared to mammals, the functionality and expression of adrenoceptors have not been well characterized in birds. Here, we reported the structure, expression, and functionality of chicken functional α_2A-adrenoceptor, named ADRA2A. The cloned chicken ADRA2A cDNA is 1335 bp in length, encoding the receptor with 444 amino acids (a.a.), which shows high amino acid sequence identity (63.4%) with its corresponding ortholog in humans. Using cell-based luciferase reporter assays and Western blot, we demonstrated that the ADRA2A could be activated by both NE and EPI through multiple signaling pathways, including MAPK/ERK signaling cascade. In addition, the mRNA expression of ADRA2A is found to be expressed abundantly in adult chicken tissues including thyroid, lung, ovary and adipose from the reported RNA-Seq data sets. Moreover, the mRNA expression of ADRA2A is also found to be highly expressed in the granulosa cells of 6–8 mm and F5 chicken ovarian follicles, which thus supports that ADRA2A signaling may play a role in ovarian follicular growth and differentiation. Taken together, our data provide the first proof that the α_2A-adrenoceptor is functional in birds involving avian ovarian follicular development.

Effects of Night Illumination on Behavior, Body Mass and Learning in Male Zebra Finches

An increase in artificial night lighting has blurred the boundaries of day and night and transformed the natural day-night environment with alteration in the temporal niche of the animals. Male zebra finches were exposed to a dim light at night (dLAN) protocol (Light: dLAN, 12L = 200 lux: 12dLAN = 5 lux) with controls on darkness at night (Light: dark, 12L = 200 lux: 12D = 0 lux) for six weeks. We assayed sleep-wake, daily behaviors, mood, and cognition, as well as changes in physiological parameters. Dim light at night increased sleep frequency, delayed sleep onset, advanced awakening latency, and caused a reduction in total sleep duration. dLAN birds did not associate (physical association) with novel object and birds spent significantly lesser time on perch with novel object as compared to LD. In colour learning task, night illuminated birds took more time to learn and made more error, compared to LD. dLAN significantly altered the 24-h daily behavioral rhythm (amplitude and acrophase) of feeding, drinking, preening, and perch-hopping behavior. In particular, birds extended their feeding hours in the nighttime under dLAN, with no difference in total food intake. Birds under dLAN increased fattening and hence significantly increased body mass. Our results show that dim light at night altered feeding rhythm, caused decrease in sleep behavior, and negatively affected learning and memory performance in male zebra finches.

Night Migratory Songbirds Exhibit Metabolic Ability to Support High Aerobic Capacity during Migration

Aerobic metabolism in night migratory songbirds exhibit seasonal plasticity, which depends not only on annual life history stages (LHSs), viz., migratory/nonmigratory or breeding/nonbreeding, but also on the time of the day. Initially, we studied daily changes in behavior/physiology alongside aerobic metabolism intermediates using gas chromatography-mass spectrometry-based chemometric analyses of serum of migratory male redheaded buntings during low-energy wintering, that is, the nonmigrating LHS. Then, the metabolic phenotype of nonmigrating birds was compared with that of photostimulated migrating buntings, the latter representing the high-energy LHS. Diurnal changes such as daytime feeding and activity were reflected by increased fatty acid (FA, viz., palmitic, oleic, and linoleic acids) levels and protein catabolites, whereas higher night-time levels of short-chain FAs indicated lipolysis in night-fasted birds. High night-time levels of taurine, a sulfur amino acid, suggested the endogenous metabolite rendering an adaptive advantage to hyperglycaemic night migratory songbirds during the LHS with low daily energy expenditure. Conversely, migrating birds, largely night-active, exhibited higher circulatory FA, its mobilization, and increased aerobic catabolism, and the adipocyte-secreted lipid, palmitoylethanolamide (PEA), capable of activating the peroxisome proliferator-activated receptor α-PGCα axis, showed elevated levels throughout the day. PEA is known for anti-inflammatory and cannabinomimetic properties, and we show, for the first time, circadian changes in PEA levels in any migrating bird. Significantly higher levels of pyridoxal phosphate also suggested the bird's protective ability to combat metabolic stress through high aerobic capacity during migration. This study elucidates putative "serum biomarkers" with a protective role in stress accrued by enhanced aerobic capacity requirements at the organismal level.

Circadian Regulation of Mitochondrial Dynamics in Retinal Photoreceptors

Energy expenditure and metabolism in the vertebrate retina are under circadian control, as we previously reported that the overall retinal ATP content and various signaling molecules related to metabolism display daily or circadian rhythms. Changes in the fission and fusion process of mitochondria, the major organelles producing ATP, in retinal photoreceptors are largely dependent on light exposure, but whether mitochondrial dynamics in photoreceptors and retinal neurons are under circadian control is not clear. Herein, we investigated the possible roles of circadian oscillators in regulating mitochondrial dynamics, mitophagy, and redox states in the chicken retina and mammalian photoreceptors. After entrainment to 12:12-h light-dark (LD) cycles for several days followed by free-running in constant darkness (DD), chicken embryonic retinas and cone-derived 661W cells were collected in either LD or DD at 6 different zeitgeber time (ZT) or circadian time (CT) points. The protein expression of mitochondrial dynamin-related protein 1 (DRP1), mitofusin 2 (MFN2), and PTEN-induced putative kinase 1 (PINK1) displayed daily rhythms, but only DRP1 was under circadian control in the chicken retinas and cultured 661W cells. In addition, cultured chicken retinal cells responded to acute oxidative stress differently from 661W cells. Using pMitoTimer as a mitochondrial redox indicator, we found that the mitochondrial redox states were more affected by light exposure than regulated by circadian oscillators. Thus, this study demonstrates that the influence of cyclic lights might outweigh the circadian regulation of complex mitochondrial dynamics in light-sensing retinal cells.

Circadian disruption and divergent microbiota acquisition under extended photoperiod regimens in chicken

The gut microbiota is crucial for metabolic homeostasis, immunity, growth and overall health, and it is recognized that early-life microbiota acquisition is a pivotal event for later-life health. Recent studies show that gut microbiota diversity and functional activity are synchronized with the host circadian rhythms in healthy individuals, and circadian disruption elicits dysbiosis in mammalian models. However, no studies have determined the associations between circadian disruption in early life, microbiota colonization, and the consequences for microbiota structure in birds. Chickens, as a major source of protein around the world, are one of the most important agricultural species, and their gut and metabolic health are significant concerns. The poultry industry routinely employs extended photoperiods (>18 h light) as a management tool, and their impacts on the chicken circadian, its role in gut microbiota acquisition in early life (first 3 weeks of life), and consequences for later life microbiota structure remain unknown. In this study, the objectives were to (a) characterize circadian activity under two different light regimes in layer chicken (12/12 h′ Light/Dark (LD) and 23/1 h LD), (b) characterize gut microbiota acquisition and composition in the first 4 weeks of life, (c) determine if gut microbiota oscillate in synchrony with the host circadian rhythm, and (d) to determine if fecal microbiota is representative of cecal microbiota in early life. Expression of clock genes (clock, bmal1, and per2) was assayed, and fecal and cecal microbiotas were characterized using 16S rRNA gene amplicon analyses from birds raised under two photoperiod treatments. Chickens raised under 12/12 LD photoperiods exhibited rhythmic clock gene activity, which was absent in birds raised under the extended (23/1 LD) photoperiod. There was differential microbiota acquisition under different photoperiod regimes in newly hatched chicks. Gut microbiota members showed a similar oscillating pattern as the host, but this association was not as strong as found in mammals. Finally, the fecal microbiota was found to be not representative of cecal microbiota membership and structure in young birds. This is one of the first studies to demonstrate the use of photoperiods to modulate microbiota acquisition in newly hatched chicks, and show their potential as a tool to promote the colonization of beneficial microorganisms.

Circadian regulation of membrane physiology in neural oscillators throughout the brain

Twenty-four-hour rhythmicity in physiology and behavior are driven by changes in neurophysiological activity that vary across the light-dark and rest-activity cycle. Although this neural code is most prominent in neurons of the primary circadian pacemaker in the suprachiasmatic nucleus (SCN) of the hypothalamus, there are many other regions in the brain where region-specific function and behavioral rhythmicity may be encoded by changes in electrical properties of those neurons. In this review, we explore the existing evidence for molecular clocks and/or neurophysiological rhythms (i.e., 24 hr) in brain regions outside the SCN. In addition, we highlight the brain regions that are ripe for future investigation into the critical role of circadian rhythmicity for local oscillators. For example, the cerebellum expresses rhythmicity in over 2,000 gene transcripts, and yet we know very little about how circadian regulation drives 24-hr changes in the neural coding responsible for motor coordination. Finally, we conclude with a discussion of how our understanding of circadian regulation of electrical properties may yield insight into disease mechanisms which may lead to novel chronotherapeutic strategies in the future.

BMAL1 but not CLOCK is associated with monochromatic green light-induced circadian rhythm of melatonin in chick pinealocytes

The avian pineal gland, an independent circadian oscillator, receives external photic cues and translates them for the rhythmical synthesis of melatonin. Our previous study found that monochromatic green light could increase the secretion of melatonin and expression of CLOCK and BMAL1 in chick pinealocytes. This study further investigated the role of BMAL1 and CLOCK in monochromatic green light-induced melatonin secretion in chick pinealocytes using siRNAs interference and overexpression techniques. The results showed that si-BMAL1 destroyed the circadian rhythms of AANAT and melatonin, along with the disruption of the expression of all the seven clock genes, except CRY1. Furthermore, overexpression of BMAL1 also disturbed the circadian rhythms of AANAT and melatonin, in addition to causing arrhythmic expression of BMAL1 and CRY1/2, but had no effect on the circadian rhythms of CLOCK, BMAL2 and PER2/3. The knockdown or overexpression of CLOCK had no impact on the circadian rhythms of AANAT, melatonin, BMAL1 and PER2, but it significantly deregulated the circadian rhythms of CLOCK, BMAL2, CRY1/2 and PER3. These results suggested that BMAL1 rather than CLOCK plays a critical role in the regulation of monochromatic green light-induced melatonin rhythm synthesis in chicken pinealocytes. Moreover, both knockdown and overexpression of BMAL1 could change the expression levels of CRY2, it indicated CRY2 may be involved in the BMAL1 pathway by modulating the circadian rhythms of AANAT and melatonin.

Effect of Monochromatic Light on Circadian Rhythm of Clock Genes in Chick Pinealocytes

The avian circadian system is a complex of mutually coupled pacemakers residing in pineal gland, retina and suprachiasmatic nucleus. In this study, the self-regulation mechanism of pineal circadian rhythm was investigated by culturing chick primary pinealocytes exposed to red light (RL), green light (GL), blue light (BL), white light (WL) and constant darkness (DD), respectively. All illuminations were set up with a photoperiod of 12 light: 12 dark. The 24-h expression profiles of seven core clock genes (cBmal1/2, cClock, cCry1/2 and cPer2/3), cAanat and melatonin showed significant circadian oscillation in all groups, except for the loss of cCry1 rhythm in BL. Compared to WL, GL increased the amplitudes and mesors of positive elements (cClock and cBmal1/2) and reduced those of negative elements (cCry1/2 and cPer2/3), in contrast to RL. The temporal patterns of cAanatmRNA and melatonin secretion have always been consistent with the positive genes. Besides, GL advanced the acrophases of the positive elements, cAanat and melatonin, but RL and BL showed the opposite effect. Thereby, GL could promote the secretion of melatonin by enhancing the expressions of positive clock genes and repressing the expressions of negative clock genes.

Melatonin Regulates Daily Variations in Electric Behavior Arousal in Two Species of Weakly Electric Fish with Different Social Structures

Timing is crucial for social interactions. Animal behavior is synchronized with biotic and abiotic environment variables ensuring that the activity phase of conspecifics occurs during the same period of the day. As biological rhythms are embedded in the complex integrative control of the brain, it is fundamental to explore its interaction with environmental and social factors. This approach will unravel the link between external stimuli carrying information on environmental cycles and the neural commands for behavior, including social behavior, associated with precise phases of those cycles. Arousal in the solitary Gymnotus omarorum and in the gregarious Brachyhypopomus gauderio is characterized by a nocturnal increase in the basal discharge rate of electric behavior, which is mild and transient in G. omarorum and large and persistent in B. gauderio. In this study, we show that the major integrator of social behavior, AVT (arginine vasotocin), is not involved in the nocturnal increase of electric behavior basal rate in isolated animals of either species. On the other hand, endogenous melatonin, the major modulator of the circadian system, is responsible for the nocturnal increase in electric behavior in isolated individuals of both species.

Seasonally Changing Cryptochrome 1b Expression in the Retinal Ganglion Cells of a Migrating Passerine Bird

Cryptochromes, blue-light absorbing proteins involved in the circadian clock, have been proposed to be the receptor molecules of the avian magnetic compass. In birds, several cryptochromes occur: Cryptochrome 2, Cryptochrome 4 and two splice products of Cryptochrome 1, Cry1a and Cry1b. With an antibody not distinguishing between the two splice products, Cryptochrome 1 had been detected in the retinal ganglion cells of garden warblers during migration. A recent study located Cry1a in the outer segments of UV/V-cones in the retina of domestic chickens and European robins, another migratory species. Here we report the presence of cryptochrome 1b (eCry1b) in retinal ganglion cells and displaced ganglion cells of European Robins, Erithacus rubecula. Immuno-histochemistry at the light microscopic and electron microscopic level showed eCry1b in the cell plasma, free in the cytosol as well as bound to membranes. This is supported by immuno-blotting. However, this applies only to robins in the migratory state. After the end of the migratory phase, the amount of eCry1b was markedly reduced and hardly detectable. In robins, the amount of eCry1b in the retinal ganglion cells varies with season: it appears to be strongly expressed only during the migratory period when the birds show nocturnal migratory restlessness. Since the avian magnetic compass does not seem to be restricted to the migratory phase, this seasonal variation makes a role of eCry1b in magnetoreception rather unlikely. Rather, it could be involved in physiological processes controlling migratory restlessness and thus enabling birds to perform their nocturnal flights.

Genetic Correlates of Individual Differences in Sleep Behavior of Free-Living Great Tits (Parus major)

Within populations, free-living birds display considerable variation in observable sleep behaviors, reflecting dynamic interactions between individuals and their environment. Genes are expected to contribute to repeatable between-individual differences in sleep behaviors, which may be associated with individual fitness. We identified and genotyped polymorphisms in nine candidate genes for sleep, and measured five repeatable sleep behaviors in free-living great tits (Parus major), partly replicating a previous study in blue tits (Cyanistes caeruleus). Microsatellites in the CLOCK and NPAS2 clock genes exhibited an association with sleep duration relative to night length, and morning latency to exit the nest box, respectively. Furthermore, microsatellites in the NPSR1 and PCSK2 genes associated with relative sleep duration and proportion of time spent awake at night, respectively. Given the detection rate of associations in the same models run with random markers instead of candidate genes, we expected two associations to arise by chance. The detection of four associations between candidate genes and sleep, however, suggests that clock genes, a clock-related gene, or a gene involved in the melanocortin system, could play key roles in maintaining phenotypic variation in sleep behavior in avian populations. Knowledge of the genetic architecture underlying sleep behavior in the wild is important because it will enable ecologists to assess the evolution of sleep in response to selection.

Interactions between a Candidate Gene for Migration (ADCYAP1), Morphology and Sex Predict Spring Arrival in Blackcap Populations

Avian research has begun to reveal associations between candidate genes and migratory behaviors of captive birds, yet few studies utilize genotypic, morphometric, and phenological data from wild individuals. Previous studies have identified an association between ADCYAP1 polymorphism and autumn migratory behavior (restlessness, or zugunruhe), but little is known about the relationship between ADCYAP1 and spring migratory behavior. The timing of spring migration and arrival to the breeding ground are phenological traits which could be particularly favorable for establishing territories and acquiring mates, thus important to fitness and reproductive success. Here, we investigated how individual genotypic ADCYAP1 variation and phenotypic variation (wing length and shape) of blackcaps (Sylvia atricapilla) affect spring arrival date across nine natural populations in Europe. We hypothesized that longer alleles should be associated with earlier spring arrival dates and expected the effect on arrival date to be stronger for males as they arrive earlier. However, we found that longer wings were associated with earlier spring arrival to the breeding grounds for females, but not for males. Another female-specific effect indicated an interaction between ADCYAP1 allele size and wing pointedness on the response of spring arrival: greater allele size had a positive effect on spring arrival date for females with rounder wings, while a negative effect was apparent for females with more pointed wings. Also, female heterozygotes with pointed wing tips arrived significantly earlier than both homozygotes with pointed wings and heterozygotes with round wings. Stable isotope ratios (δ²H) of a subset of blackcaps captured in Freiburg in 2011 allowed us also to assign individuals to their main overwintering areas in northwest (NW) and southwest (SW) Europe. NW males arrived significantly earlier to the Freiburg breeding site than both SW males and females in 2011. NW females had more pointed wing tips compared to SW females, but no difference in ADCYAP1 allele size was found between the different migration routes.

Studying circadian rhythms in Drosophila melanogaster

Circadian rhythms have a profound influence on most bodily functions: from metabolism to complex behaviors. They ensure that all these biological processes are optimized with the time-of-day. They are generated by endogenous molecular oscillators that have a period that closely, but not exactly, matches day length. These molecular clocks are synchronized by environmental cycles such as light intensity and temperature. Drosophila melanogaster has been a model organism of choice to understand genetically, molecularly and at the level of neural circuits how circadian rhythms are generated, how they are synchronized by environmental cues, and how they drive behavioral cycles such as locomotor rhythms. This review will cover a wide range of techniques that have been instrumental to our understanding of Drosophila circadian rhythms, and that are essential for current and future research.

Avian circadian organization: a chorus of clocks

In birds, biological clock function pervades all aspects of biology, controlling daily changes in sleep: wake, visual function, song, migratory patterns and orientation, as well as seasonal patterns of reproduction, song and migration. The molecular bases for circadian clocks are highly conserved, and it is likely the avian molecular mechanisms are similar to those expressed in mammals, including humans. The central pacemakers in the avian pineal gland, retinae and SCN dynamically interact to maintain stable phase relationships and then influence downstream rhythms through entrainment of peripheral oscillators in the brain controlling behavior and peripheral tissues. Birds represent an excellent model for the role played by biological clocks in human neurobiology; unlike most rodent models, they are diurnal, they exhibit cognitively complex social interactions, and their circadian clocks are more sensitive to the hormone melatonin than are those of nocturnal rodents.