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Recent studies on birds have shown that offspring begging and parental provisioning covary at the phenotypic level, which is thought to reflect genetic correlations. However, prenatal maternal factors, like yolk testosterone, may also facilitate parent-offspring coadaptation via their effects on offspring begging and development. In fact, maternal effects are thought to adjust offspring phenotype to the environmental conditions they will experience after birth, which are in turn strongly dependent on the levels of parental provisioning. Using cross-fostering experiments in canaries, we tested the role of maternal effects on parent-offspring coadaptation from two different approaches. First, we analyzed whether females deposit yolk testosterone in relation to their own or their partner's prospective parental provisioning, measured as the rate of parental feeding to foster nestlings. Second, we investigated whether females deposit yolk testosterone in relation to costs they incurred when raising a previous brood, as this likely impinges on their capacity to provide parental care in the near future. However, from the results of both experiments we have no evidence that canary females deposit yolk testosterone in order to match offspring begging to the levels of care they and/or their partners provide. We therefore found no evidence that yolk testosterone facilitates parent-offspring coadaptation. In addition, our results suggest that the functional consequences of yolk testosterone deposition may relate to hatching asynchrony since it primarily varied with egg laying order.

Global warming has substantially changed the environment, but the mechanisms to cope with these changes in animals, including the role of maternal effects, are poorly understood. Maternal effects via hormones deposited in eggs, have important environment-dependent effects on offspring development and fitness: thus females are expected to adjust these hormones to the environment, such as the ambient temperature. Longer-term temperature variation could function as a cue, predicting chick rearing conditions to which yolk hormone levels are adjusted, while short-term temperature variation during egg formation may causally affect hormone transfer to eggs. We studied the effects of ambient temperature on yolk androgens (testosterone and androstenedione) and thyroid hormones (thyroxine and triiodothyronine) in great tits (Parus major) using data from unmanipulated clutches from a wild population and from aviary birds (ad libitum food) exposed to different experimental temperature treatments during five years. Both in the wild and in captivity, longer-term pre-laying ambient temperature was not associated with clutch mean yolk hormone levels, while the way androstenedione and thyroxine levels varied across the laying sequence did associate with pre-laying temperature in the wild. Yolk testosterone levels were positively correlated with short-term temperature (during yolk formation) changes within clutches in both wild and captivity. We also report, for the first time in a wild bird, that yolk thyroxine levels correlated with a key environmental factor: thyroxine levels were negatively correlated with ambient temperature during egg formation. Thus, yolk hormone levels, especially testosterone, seem to be causally affected by ambient temperature. These short-term effects might reflect physiological changes in females with changes in ambient temperature. The adaptive value of the variation with ambient temperatures pre-laying or during egg formation should be studied with hormone manipulations in different thermal environments. (C) 2016 Published by Elsevier Inc.

Maternal hormones deposited in the egg can provide a powerful model for the study of maternal effects. The differential amount of maternal hormones in the yolk of freshly laid eggs is assumed to represent differential maternal allocation. However, some evidence suggests that these amounts do not reflect maternal allocation that in fact takes place before ovulation. We compared the amounts of a wide array of gonadal steroids and their metabolites in the yolk of pre-ovulatory follicles with those of freshly laid eggs of rock pigeons using mass spectrometry. We found that between the follicle and egg stages the levels of progesterone increase whereas androstenedione and testosterone decrease in which the strength of decrease was dependent on the laying order of the egg. For conjugated estrone the change between follicle and egg differed in direction for first and second laying position yielding a significant interaction effect. For conjugated testosterone the interaction did not reach but was close to significance. This extremely early steroid metabolism was not due to maternal enzymes in the yolk as indicated by incubation of pre-ovulatory yolks treated with proteinase-K, a protein digesting enzyme. The results have significant consequences for the functional and evolutionary interpretation as well as experimental manipulation of hormone-mediated maternal effects.

In birds, mothers can affect their offspring's phenotype and thereby survival via egg composition. It is not well known to what extent and time-scales environmental variation in resource availability, either via resource constrains or adaptive adjustment to predicted rearing conditions, influences maternal effects. We experimentally studied whether egg and yolk mass and yolk hormone levels respond to short-term changes in food availability during laying in wild great tits (Parus major). Our treatment groups were: 1) food supplementation (mealworms) from the 1st until the last egg; 2) food supplementation from the 1st first until the 5th egg, where the effect of cessation of the supplementary food treatment could also be studied; 3) no food supplementation (controls). We analysed both nutritional resources (egg, yolk and albumen mass), and the important developmental signals, yolk androgens (testosterone and androstenedione), and for the first time in a wild population, yolk thyroid hormones (thyroxine and 3,5,3’-triiodothyronine). Egg mass is a costly resource for females, androgens most likely non-costly signals, whereas thyroid hormones may be costly signals, requiring environmental iodine. In the food supplemented group egg, yolk and albumen mass increased rapidly relative to controls and when food supplementation was halted, egg and albumen mass decreased, indicating rapid responses to resource availability. Yolk androgen and thyroid hormone levels were not affected by food supplementation during laying. Thyroxine showed an increase over the laying sequence and its biological meaning needs further study. The rapid changes in egg mass to variation in within-clutch food availability suggest energetic/protein/nutrient constrains on egg formation. The lack of a response in yolk hormones suggest that perhaps in this species the short-term changes in resource availability during egg laying do not predict offspring rearing conditions, or (for thyroid hormones) do not cause systemic changes in circulating hormones, and hence do not affect maternal signaling.

Melanin-based plumage ornaments have been shown to play an important role in male-male competition, but also influence inter-sexual communication. Consequently, ornaments may be associated with reproductive effort of both males and females. Females mated to males with larger melanin ornaments may acquire access to better territories or benefit from increased paternal care. Here we investigated whether the melanin-based breast-band of male and female Bar-throated Apalis Apalis thoracica is a signal of information about its bearer and is associated with male and female reproductive effort. Breast-band size was a highly variable morphometric trait in both sexes, but only in males was it associated with body mass. We then assessed whether male and female breast-band size predicted maternal and paternal investment. Egg mass increased with male breast-band size, but decreased with female breast-band size. Whether females adjust maternal hormone allocation in response to their partner's ornamentation remains a contentious issue. We found that yolk testosterone and androstenedione concentrations were not predicted by male ornamentation or body mass. Finally, males with larger breast-bands provided their mates with more food, allowing those females to spend more time incubating. Reproductive effort of both parents is therefore predicted by their own and their mate's ornamentation in Bar-throated Apalis, and thus breast-band size potentially acts as a signal of reproductive performance in both sexes. These results highlight the need for more comprehensive analyses of a relationship between melanin-based ornaments and fitness, incorporating multiple behavioural variables associated with reproductive effort.

Animal personality traits emerge developmentally from the interaction of genetic and early environmental factors. Maternal hormones, such as androgens (testosterone, T and androstenedione, A4), transferred to embryos and egg yolks may simultaneously organize multiple behavioural and physiological traits. Whereas previous studies demonstrated an association between the mother's personality and yolk androgen levels, the independent effects of the male partner's personality and pair combination are unknown. We test this association using an ecological model species for personality research, the great tit (Parus major) using multiple approaches: 1) a wild population, 2) a randomly-mated captive population, and 3) an experimental study with (dis)assortatively mated pairs from lines selected for fast exploration/boldness or slow exploration/shyness. Egg androgen concentrations were associated with variation in female personality traits, and the experimental data suggested that this is independent of male personality: experimental females from slow-shy line tended to have higher egg T concentrations than females from the fast-bold line, with no effect of male personality. Shy females from the wild population had higher egg A4 concentration than bold females. However, in the correlative data yolk hormones were linked with male personality, as well as the interaction between female and male traits and yolk androgen levels: Male handling responsiveness correlated negatively with egg A4 concentration in wild birds. In randomly-mated birds, pairs that were mated assortatively for personality had lower egg T concentrations than disassortatively mated pairs. Given that egg androgens are known mediators of avian personality, our results suggest that maternal hormones might contribute to the heritability of personality, may be sensitive to the social context of mating, and act as key drivers of individual differences. This article is protected by copyright. All rights reserved.

Exposure to light at night increases alertness, but light at night (especially short-wavelength light) also disrupts nocturnal physiology. Such disruption is thought to underlie medical problems for which shiftworkers have increased risk. In 33 male subjects we investigated whether short-wavelength attenuated polychromatic white light (

Birds can manipulate offspring sex ratio under natural and experimental conditions and maternal hormones have been shown to be involved in this process. Studies also provided evidence for the presence of sex specific concentrations of yolk hormones in avian eggs. These findings led to the suggestion that yolk hormones could influence genetic sex determination in birds. However, in previous studies, yolk hormone concentrations and egg sex were studied in incubated eggs, although incubation of the eggs and embryonic development can alter yolk hormone concentrations and measured sex ratio. This study is the first to determine a wide array of egg components and hen body weight in relation to the sex of the egg in unincubated eggs. Egg parameters studied were yolk concentrations of testosterone, estradiol, androstenedione, progesterone, dihydrotestosterone, and glucose, and egg weight and dimensions. In addition, we studied the associations among all measured parameters. Associations were found between a number of yolk hormones (progesterone associated with testosterone, estradiol and androstenedione; androstenedione with testosterone; dihydrotestosterone with estradiol and androstenedione) as well as between yolk testosterone and egg length and egg weight. There were no significant overall differences between male and female chicken eggs in any of the measured egg parameters. However, there were a few interactions such as the interaction of egg sex with dihydrotestosterone and with hen body weight which predicted estradiol levels and an interaction of estradiol levels with egg width for predicting sex of egg. Their biological relevance need, however, further study. (c) 2013 Elsevier Inc. All rights reserved.

Thyroid hormones (THs) - triiodothyronine (T3) and thyroxine (T4) - are essential for embryonic development in vertebrates. All vertebrate embryos are exposed to THs from maternal origin. As maternal TH levels are known to be essential to embryonic development, the natural variation of maternal THs probably represents a pathway of maternal effects that can modify offspring phenotype. However, potential fitness consequences of variation of maternal TH exposure within the normal physiological range and without confounding effects of the mother have never been experimentally investigated. We experimentally manipulated the levels of yolk T3 and T4 within the physiological range in a species in which the embryo develops outside the mother's body, the Rock Pigeon (Columba livia) eggs. Making use of the natural difference of yolk testosterone between the two eggs of pigeon clutches, we were also able to investigate the potential interaction between THs and testosterone. Elevated yolk TH levels enhanced embryonic development and hatching success, and reduced body mass but not tarsus length between day 14 and fledging. The yolk hormones increased plasma T4 concentrations in females but reduced it in males, in line with the effect on metabolic rate at hatching. Plasma concentrations of T3 and testosterone were not significantly affected. The effects of treatment did not differ between eggs with high or low testosterone levels. Our data indicate that natural variation in maternal yolk TH levels affects offspring phenotype and embryonic survival, potentially influencing maternal and chick fitness. (C) 2016 Elsevier Inc. All rights reserved.

Reproduction in vertebrates is an energy-demanding process that is mediated by endogenous hormones and potentially results in oxidative stress. The primary aim of this study was to quantify the relationship between oxidative stress parameters (antioxidant capacity and levels of reactive oxygen metabolites) and circulating testosterone and cortisol in a common and widespread teleost fish, the brown trout (Salmo trutta. L). Results show that trout with higher testosterone levels prior to spawning have higher levels of oxidative damage at the time that they spawn (although by the time of spawning testosterone levels had dropped, leading to a negative relationship between testosterone and oxidative damage at that time). Cortisol levels were not directly related to oxidative damage or antioxidant capacity, but concentrations of this hormone were positively related to levels of fungal infection, which was itself associated both with lower antioxidant capacity and lower levels of oxidative damage. These results highlight the complexity of interactions between different components of the endocrine system and metabolism and suggest that caution be used in interpreting relationships between a single hormone and indicators of oxidative balance or other fitness proxies. (C) 2012 Elsevier Inc. All rights reserved.

Exposure of mothers to risk of predation can induce phenotypic changes in offspring as shown in several species. We previously found that cross-fostered great tit (Parus major) chicks of females exposed to increased predation risk were smaller and lighter, but had faster wing growth than control cross-fostered chicks, possibly improving predator-escaping abilities. Here we examined the possible role of maternal steroids deposited in eggs as an underlying mechanism. We collected eggs from female great tits under either experimentally increased predation risk (PRED) or control treatments (CON) and analyzed the concentration of testosterone, androstenedione, and progesterone in the yolks. PRED eggs contained lower levels of testosterone than CON eggs, but levels of androstenedione and progesterone did not differ. The smaller size and mass of chicks found in the previous study may thus be explained by the lower testosterone concentrations, since yolk testosterone is known to boost growth and development. Alternatively, testosterone may act as a modulator of differential investment into morphological traits, rather than a simple growth enhancer, explaining lower body mass in conjunction with the accelerated wing growth. This could possibly occur concurrently with other hormones such as corticosterone. (C) 2012 Elsevier Inc. All rights reserved.

The effect of artificial dawn during the last 30 min of sleep on subsequent dissipation of sleep inertia was investigated, including possible involvement of cortisol and thermoregulatory processes. Sixteen healthy subjects who reported difficulty with waking up participated in random order in a control and an artificial dawn night. Sleep inertia severity was measured by subjective ratings of sleepiness and activation, and by performance on an addition and a reaction time task measured at 1, 15, 30, 45, 60, and 90 min after waking up at habitual wake up time at workdays. At all intervals, saliva samples were collected for cortisol analysis. Sleep electroencephalogram was recorded during the 30 min prior to waking up; core body temperature and skin temperatures were recorded continuously until 90 min after waking up. Subjective sleepiness was significantly decreased and subjective activation increased after waking up in the artificial dawn condition as compared with control, in which lights were turned on at waking up. These effects can be explained by effects of artificial dawn on skin temperature and amount of wakefulness during the 30 min prior to the alarm. Artificial dawn accelerated the decline in skin temperature and in the distal-to-proximal skin temperature gradient after getting up. No significant effects of artificial dawn on performance, core body temperature, and cortisol were found. These results suggest that the physiology underlying the positive effects of artificial dawn on the dissipation of sleep inertia involves light sleep and an accelerated skin temperature decline after awakening.

The timing of work and social requirements has a negative impact on performance and well-being of a significant proportion of the population in our modern society due to a phenomenon known as social jetlag. During workdays, in the early morning, late chronotypes, in particular, suffer from a combination of a nonoptimal circadian phase and sleep deprivation. Sleep inertia, a transient period of lowered arousal after awakening, therefore, becomes more severe. In the present home study, the authors tested whether the use of an alarm clock with artificial dawn could reduce complaints of sleep inertia in people having difficulties in waking up early. The authors also examined whether these improvements were accompanied by a shift in the melatonin rhythm. Two studies were performed: Study 1: three conditions (0, 50, and 250 lux) and Study 2: two conditions (0 lux and self-selected dawn-light intensity). Each condition lasted 2 weeks. In both studies, the use of the artificial dawn resulted in a significant reduction of sleep inertia complaints. However, no significant shift in the onset of melatonin was observed after 2 weeks of using the artificial dawn of 250 lux or 50 lux compared to the control condition. A multilevel analysis revealed that only the presence of the artificial dawn, rather than shift in the dim light melatonin onset or timing of sleep offset, is related to the observed reduction of sleep inertia complaints. Mechanisms other than shift of circadian rhythms are needed to explain the positive results on sleep inertia of waking up with a dawn signal. (Author correspondence: m.c.gimenez@rug.nl)

In oviparous species like birds, eggs provide the direct environment in which embryos are developing. Mothers may adjust different egg components in different ways in reaction to environmental cues either to adjust offspring development or because of constraints. In this study, we investigated the effects of food quality and quantity before and during egg laying on three different aspects of egg quality: macro-nutrients (egg and yolk mass), androgens (testosterone and androstenedione), and thyroid hormones (3,5,3'-triiodothyronine, T3 and l-thyroxine, T4), using the rock pigeon (Columba livia). As expected, egg and yolk mass were significantly reduced for the eggs laid under the poor-food condition, indicating a maternal trade-off between offspring and self in allocating important resources. We did not find any significant change in yolk testosterone or their within-clutch pattern over the laying sequence. This is consistent with the fact that, in contrast with nutrients, these hormones are not costly to produce, but does not support the hypothesis that they play a role in adjusting brood size to food conditions. In contrast, we found that T3 levels were higher in the egg yolks under the poor-food condition whereas the total T4 content was lower. This change could be related to the fact that iodine, the critical constituent of thyroid hormones, might be a limiting factor in the production of this hormone. Given the knowledge that food restriction usually lead to reduction of circulating T3 levels, our results suggested that avian mothers can independently regulate its concentrations in their eggs from their own circulation. The study demonstrates that environmentally induced maternal effects via the egg can be a result of a combination of constrained resources and unconstrained signals and that thyroid hormones might be an interesting case of both. Therefore, this hormone and the interplay of different maternal effects on the offspring phenotype deserve much more attention. ispartof: Ecology and Evolution vol:6 issue:2 pages:397-411 ispartof: location:England status: published

Bright light can influence human psychophysiology instantaneously by inducing endocrine ( suppression of melatonin, increasing cortisol levels), other physiological changes ( enhancement of core body temperature), and psychological changes ( reduction of sleepiness, increase of alertness). Its broad range of action is reflected in the wide field of applications, ranging from optimizing a work environment to treating depressed patients. For optimally applying bright light and understanding its mechanism, it is crucial to know whether its effects depend on the time of day. In this paper, we report the effects of bright light given at two different times of day on psychological and physiological parameters. Twenty-four subjects participated in two experiments ( n = 12 each). All subjects were nonsmoking, healthy young males ( 18 - 30 yr). In both experiments, subjects were exposed to either bright light ( 5,000 lux) or dim light

The mammalian retina contains both visual and circadian photoreceptors. In humans, nocturnal stimulation of the latter receptors leads to melatonin suppression, which might cause reduced nighttime sleepiness. Melatonin suppression is maximal when the nasal part of the retina is illuminated. Whether circadian phase shifting in humans is due to the same photoreceptors is not known. The authors explore whether phase shifts and melatonin suppression depend on the same retinal area. Twelve healthy subjects participated in a within-subjects design and received all of 3 light conditions—1) 10 lux of dim light on the whole retina, 2) 100 lux of ocular light on the nasal part of the retina, and 3) 100 lux of ocular light on the temporal part of the retina—on separate nights in random order. In all 3 conditions, pupils were dilated before and during light exposure. The protocol consisted of an adaptation night followed by a 23-h period of sustained wakefulness, during which a 4-h light pulse was presented at a time when maximal phase delays were expected. Nasal illumination resulted in an immediate suppression of melatonin but had no effect on subjective sleepiness or core body temperature (CBT). Nasal illumination delayed the subsequent melatonin rhythm by 78 min, which is significantly ( p= 0.016) more than the delay drift in the dim-light condition (38 min), but had no detectable phase-shifting effect on the CBT rhythm. Temporal illumination suppressed melatonin less than the nasal illumination and had no effect on subjective sleepiness and CBT. Temporal illumination delayed neither the melatonin rhythm nor the CBT rhythm. The data show that the suppression of melatonin does not necessarily result in a reduction of subjective sleepiness and an elevation ofCBT. In addition, 100 lux of bright white light is strong enough to affect the photoreceptors responsible for the suppression of melatonin but not strong enough to have a significant effect on sleepiness and CBT. This may be due to the larger variability of the latter variables.

The effect of artificial dawn during the last 30 min of sleep on subsequent dissipation of sleep inertia was investigated, including possible involvement of cortisol and thermoregulatory processes. Sixteen healthy subjects who reported difficulty with waking up participated in random order in a control and an artificial dawn night. Sleep inertia severity was measured by subjective ratings of sleepiness and activation, and by performance on an addition and a reaction time task measured at 1, 15, 30, 45, 60, and 90 min after waking up at habitual wake up time at workdays. At all intervals, saliva samples were collected for cortisol analysis. Sleep electroencephalogram was recorded during the 30 min prior to waking up; core body temperature and skin temperatures were recorded continuously until 90 min after waking up. Subjective sleepiness was significantly decreased and subjective activation increased after waking up in the artificial dawn condition as compared with control, in which lights were turned on at waking up. These effects can be explained by effects of artificial dawn on skin temperature and amount of wakefulness during the 30 min prior to the alarm. Artificial dawn accelerated the decline in skin temperature and in the distal-to-proximal skin temperature gradient after getting up. No significant effects of artificial dawn on performance, core body temperature, and cortisol were found. These results suggest that the physiology underlying the positive effects of artificial dawn on the dissipation of sleep inertia involves light sleep and an accelerated skin temperature decline after awakening.

In this paper we examine the relationship between melatonin suppression and reduction of sleepiness through light by comparing three different data sets. In total 36 subjects participated in three studies and received 4 h of bright light either from midnight till 4:00 hours (experiments A and B) or from noon till 16:00 hours (experiment C). In experiment A (night-time light, partial illumination of the retina, pupil dilated) subjects were exposed to either 100 lx of ocular light on the temporal, 100 lx on the nasal part of the retina, or

Light can influence physiology and performance of humans in two distinct ways. It can acutely change the level of physiological and behavioral parameters, and it can induce a phase shift in the circadian oscillators underlying variations in these levels. Until recently, both effects were thought to require retinal light perception. This view was challenged by Campbell and Murphy, who showed significant phase shifts in core body temperature and melatonin using an extraocular stimulus. Their study employed popliteal skin illumination and exclusively considered phase-shifting effects. In this paper, the authors explore both acute effects and phase-shifting effects of ocular as well as extraocular light. Twelve healthy males participated in a within-subject design and received all of three light conditions—(1) dim ocular light/no light to the knee, (2) dim ocular light/bright extraocular light to the knee, and (3) bright ocular light/no light to the knee—on separate nights in random order. The protocol consisted of an adaptation night followed by a 26-h period of sustained wakefulness, during which a 4-h light pulse was presented at a time when maximal phase delays were expected. The authors found neither immediate nor phase-shifting effects of extraocular light exposure on melatonin, core body temperature (CBT), or sleepiness. Ocular bright-light exposure reduced the nocturnal circadian drop in CBT, suppressed melatonin, and reduced sleepiness significantly. In addition, the 4-h ocular light pulse delayed the CBT rhythm by -55 min compared to the drift of the CBT rhythm in dim light. The melatonin rhythm shifted by -113 min, which differed significantly from the drift in the melatonin rhythm in the dim-light condition (-26 min). The failure to find immediate or phase-shifting effects in response to extraocular light in a within-subjects design in which effects of ocular bright light are confirmed strengthens the doubts raised by other labs of the impact of extraocular light on the human circadian system.