Light Masking in the Field: An Experiment with Nocturnal and Diurnal Spiny Mice Under Semi-natural Field Conditions

Effects of chronic light cycle disruption during adolescence on circadian clock, neuronal activity rhythms, and behavior in mice

The advent of artificial lighting, particularly during the evening and night, has significantly altered the predictable daily light and dark cycles in recent times. Altered light environments disrupt the biological clock and negatively impact mood and cognition. Although adolescents commonly experience chronic changes in light/dark cycles, our understanding of how the adolescents' brain adapts to altered light environments remains limited. Here, we investigated the impact of chronic light cycle disruption (LCD) during adolescence, exposing adolescent mice to 19 h of light and 5 h of darkness for 5 days and 12 L:12D for 2 days per week (LCD group) for 4 weeks. We showed that LCD exposure did not affect circadian locomotor activity but impaired memory and increased avoidance response in adolescent mice. Clock gene expression and neuronal activity rhythms analysis revealed that LCD disrupted local molecular clock and neuronal activity in the dentate gyrus (DG) and in the medial amygdala (MeA) but not in the circadian pacemaker (SCN). In addition, we characterized the photoresponsiveness of the MeA and showed that somatostatin neurons are affected by acute and chronic aberrant light exposure during adolescence. Our research provides new evidence highlighting the potential consequences of altered light environments during pubertal development on neuronal physiology and behaviors.

When night becomes day: Artificial light at night alters insect behavior under semi-natural conditions

Light is the most important Zeitgeber for temporal synchronization in nature. Artificial light at night (ALAN) disrupts the natural light-dark rhythmicity and thus negatively affects animal behavior. However, to date, ALAN research has been mostly conducted under laboratory conditions in this context. Here, we used the field cricket, Gryllus bimaculatus, to investigate the effect of ALAN on insect behavior under semi-natural conditions, i.e., under shaded natural lighting conditions, natural temperature and soundscape. Male crickets were placed individually in outdoor enclosures and exposed to ALAN conditions ranging from <0.01 to 1500 lx intensity. The crickets' stridulation behavior was recorded for 14 consecutive days and nights and their daily activity patterns were analysed. ALAN impaired the crickets' stridulation rhythm, evoking a change in the crickets' naturally synchronized daily activity period. This was manifested by a light-intensity-dependent increase in the proportion of insects demonstrating an intrinsic circadian rhythm (free-run behavior). This also resulted in a change in the population's median activity cycle period. These ALAN-induced effects occurred despite the crickets' exposure to almost natural conditions. Our findings provide further validity to our previous studies on ALAN conducted under lab conditions and establish the deleterious impacts of ALAN on animal behavioral patterns. TEASER: Artificial light at night alters cricket behavior and desynchronizes their stridulation even under near-natural conditions.

Wild mice in an urbanized world: Effects of light at night under natural and laboratory conditions in the single-striped grass mouse (Lemniscomys rosalia)

Urbanization, and the accompanying artificial light at night (ALAN), can disrupt the activity of animals. Such disruptions at the base of a food web can ripple through the ecosystem. Most studies of ALAN are performed in the laboratory. Thus, we lack basic information about the circadian responses of animals under natural environmental conditions to fully evaluate the impact of ALAN. We studied the behaviour and activity of wild-caught, peri-urban single-striped grass mice (Lemniscomys rosalia) under a natural treatment and in a standard laboratory treatment, including dim light at night to mimic conditions that they could experience. The species exhibited predominantly crepuscular activity under all experimental treatments. It showed the highest level of activity under the natural treatment, whereas ALAN significantly suppressed its activity. Males were more active than females under all experimental treatments. The marked changes in activity under ALAN is of particular concern since global change in combination with urbanization can lead to a change in vegetation density and composition that will decrease the number of suitable microhabitats and expose small mammals to novel habitat changes. We suggest that the single-striped mice could become vulnerable because of urbanization, leading to impacts on its ecosystem broadly.

Exposure to a nocturnal light pulse simultaneously and differentially affects stridulation and locomotion behaviors in crickets

It is crucial for living organisms to be in synchrony with their environment and to anticipate circadian and annual changes. The circadian clock is responsible for entraining organisms’ activity to the day-night rhythmicity. Artificial light at night (ALAN) was shown to obstruct the natural light cycle, leading to desynchronized behavioral patterns. Our knowledge of the mechanisms behind these adverse effects of ALAN, however, is far from complete. Here we monitored the stridulation and locomotion behavior of male field crickets (Gryllus bimaculatus), raised under light:dark conditions, before, during, and after exposure to a nocturnal 3-h pulse of different ALAN intensities. The experimental insects were then placed under a constant light regime (of different intensities); their behavior was continuously monitored; and the period of their daily activity rhythms was calculated. The light pulse treatment induced a simultaneous negative (suppressing stridulation) and positive (inducing locomotion) effect, manifested in significant changes in the average level of the specific activity on the night of the pulse compared to the preceding and the following nights. The transition to constant light conditions led to significant changes in the period of the circadian rhythms. Both effects were light-intensity-dependent, indicating the importance of dark nights for both individual and population synchronization.

Fitness consequences of chronic exposure to different light pollution wavelengths in nocturnal and diurnal rodents

Use of artificial at night (ALAN) exposes the world to continuously increasing levels and distribution of light pollution. Our understanding of the adverse effects of ALAN is based mostly on observational or laboratory studies, and its effects are probably underestimated. Demonstration of direct experimental fitness consequences of ALAN on mammals is missing. We studied the effects of chronic light pollution at different wavelengths on fitness and glucocorticoid hormone levels under semi-natural conditions in two closely related species: the nocturnal common spiny mouse (Acomys cahirinus) and the diurnal golden spiny mouse (Acomys russatus). Our results clearly demonstrate the adverse effects of ALAN exposure on the fitness of both nocturnal and diurnal species, manifested by changes in cortisol levels and reproductive timing, reduced reproductive output and reduced survival, which differed between species and wavelengths. In A. russatus exposure to blue ALAN had the strongest effect on fitness, followed by white and yellow ALAN exposure. In A. cahirinus the results are more complex and suggest it suffered from the combined effects of ALAN and competition. Our research shows that light pollution presents a real threat to both nocturnal and diurnal species, affecting the species fitness directly and through interspecific interactions. Worryingly, these effects are probably not limited to spiny mice. The clear adverse effects we documented, as well as the differences between wave lengths, contribute to our ability to present science-based recommendations to decision makers regarding the use of artificial light at night. Such information and guidelines are highly important nowadays when lighting systems are being replaced to promote energy efficiency.

Exposure to Artificial Light at Night and the Consequences for Flora, Fauna, and Ecosystems

The present review draws together wide-ranging studies performed over the last decades that catalogue the effects of artificial-light-at-night (ALAN) upon living species and their environment. We provide an overview of the tremendous variety of light-detection strategies which have evolved in living organisms - unicellular, plants and animals, covering chloroplasts (plants), and the plethora of ocular and extra-ocular organs (animals). We describe the visual pigments which permit photo-detection, paying attention to their spectral characteristics, which extend from the ultraviolet into infrared. We discuss how organisms use light information in a way crucial for their development, growth and survival: phototropism, phototaxis, photoperiodism, and synchronization of circadian clocks. These aspects are treated in depth, as their perturbation underlies much of the disruptive effects of ALAN. The review goes into detail on circadian networks in living organisms, since these fundamental features are of critical importance in regulating the interface between environment and body. Especially, hormonal synthesis and secretion are often under circadian and circannual control, hence perturbation of the clock will lead to hormonal imbalance. The review addresses how the ubiquitous introduction of light-emitting diode technology may exacerbate, or in some cases reduce, the generalized ever-increasing light pollution. Numerous examples are given of how widespread exposure to ALAN is perturbing many aspects of plant and animal behaviour and survival: foraging, orientation, migration, seasonal reproduction, colonization and more. We examine the potential problems at the level of individual species and populations and extend the debate to the consequences for ecosystems. We stress, through a few examples, the synergistic harmful effects resulting from the impacts of ALAN combined with other anthropogenic pressures, which often impact the neuroendocrine loops in vertebrates. The article concludes by debating how these anthropogenic changes could be mitigated by more reasonable use of available technology - for example by restricting illumination to more essential areas and hours, directing lighting to avoid wasteful radiation and selecting spectral emissions, to reduce impact on circadian clocks. We end by discussing how society should take into account the potentially major consequences that ALAN has on the natural world and the repercussions for ongoing human health and welfare.

The genetic basis of diurnal preference in Drosophila melanogaster

Background

Most animals restrict their activity to a specific part of the day, being diurnal, nocturnal or crepuscular. The genetic basis underlying diurnal preference is largely unknown. Under laboratory conditions, Drosophila melanogaster is crepuscular, showing a bi-modal activity profile. However, a survey of strains derived from wild populations indicated that high variability among individuals exists, including flies that are nocturnal.

Results

Using a highly diverse population, we performed an artificial selection experiment, selecting flies with extreme diurnal or nocturnal preference. After 10 generations, we obtained highly diurnal and nocturnal strains. We used whole-genome expression analysis to identify differentially expressed genes in diurnal, nocturnal and crepuscular (control) flies. Other than one circadian clock gene (pdp1), most differentially expressed genes were associated with either clock output (pdf, to) or input (Rh3, Rh2, msn). This finding was congruent with behavioural experiments indicating that both light masking and the circadian pacemaker are involved in driving nocturnality.

Conclusions

Our study demonstrates that genetic variation segregating in wild populations contributes to substantial variation in diurnal preference. We identified candidate genes associated with diurnality/nocturnality, while data emerging from our expression analysis and behavioural experiments suggest that both clock and clock-independent pathways are involved in shaping diurnal preference. The diurnal and nocturnal selection strains provide us with a unique opportunity to understand the genetic architecture of diurnal preference.

Season dependent effects of urban environment on circadian clock of tree sparrow (Passer montanus)

Great efforts have been made recently to understand the effect(s) of urban environments on the circadian and seasonal physiology of wild animals, but the mechanisms involved remain largely unknown.

Circadian and photic modulation of daily rhythms in diurnal mammals

The temporal niche that an animal occupies includes a coordinated suite of behavioral and physiological processes that set diurnal and nocturnal animals apart. The daily rhythms of the two chronotypes are regulated by both the circadian system and direct responses to light, a process called masking. Here we review the literature on circadian regulations and masking responses in diurnal mammals, focusing on our work using the diurnal Nile grass rat (Arvicanthis niloticus) and comparing our findings with those derived from other diurnal and nocturnal models. There are certainly similarities between the circadian systems of diurnal and nocturnal mammals, especially in the phase and functioning of the principal circadian oscillator within the hypothalamic suprachiasmatic nucleus (SCN). However, the downstream pathways, direct or indirect from the SCN, lead to drastic differences in the phase of extra-SCN oscillators, with most showing a complete reversal from the phase seen in nocturnal species. This reversal, however, is not universal and in some cases the phases of extra-SCN oscillators are only a few hours apart between diurnal and nocturnal species. The behavioral masking responses in general are opposite between diurnal and nocturnal species, and are matched by differential responses to light and dark in several retinorecipient sites in their brain. The available anatomical and functional data suggest that diurnal brains are not simply a phase-reversed version of nocturnal ones, and work with diurnal models contribute significantly to a better understanding of the circadian and photic modulation of daily rhythms in our own diurnal species.

Chronobiology of interspecific interactions in a changing world

Animals should time activities, such as foraging, migration and reproduction, as well as seasonal physiological adaptation, in a way that maximizes fitness. The fitness outcome of such activities depends largely on their interspecific interactions; the temporal overlap with other species determines when they should be active in order to maximize their encounters with food and to minimize their encounters with predators, competitors and parasites. To cope with the constantly changing, but predictable structure of the environment, organisms have evolved internal biological clocks, which are synchronized mainly by light, the most predictable and reliable environmental cue (but which can be masked by other variables), which enable them to anticipate and prepare for predicted changes in the timing of the species they interact with, on top of responding to them directly. Here, we review examples where the internal timing system is used to predict interspecific interactions, and how these interactions affect the internal timing system and activity patterns. We then ask how plastic these mechanisms are, how this plasticity differs between and within species and how this variability in plasticity affects interspecific interactions in a changing world, in which light, the major synchronizer of the biological clock, is no longer a reliable cue owing to the rapidly changing climate, the use of artificial light and urbanization.This article is part of the themed issue 'Wild clocks: integrating chronobiology and ecology to understand timekeeping in free-living animals'.

Two sides of a coin: ecological and chronobiological perspectives of timing in the wild

Most processes within organisms, and most interactions between organisms and their environment, have distinct time profiles. The temporal coordination of such processes is crucial across levels of biological organization, but disciplines differ widely in their approaches to study timing. Such differences are accentuated between ecologists, who are centrally concerned with a holistic view of an organism in relation to its external environment, and chronobiologists, who emphasize internal timekeeping within an organism and the mechanisms of its adjustment to the environment. We argue that ecological and chronobiological perspectives are complementary, and that studies at the intersection will enable both fields to jointly overcome obstacles that currently hinder progress. However, to achieve this integration, we first have to cross some conceptual barriers, clarifying prohibitively inaccessible terminologies. We critically assess main assumptions and concepts in either field, as well as their common interests. Both approaches intersect in their need to understand the extent and regulation of temporal plasticity, and in the concept of 'chronotype', i.e. the characteristic temporal properties of individuals which are the targets of natural and sexual selection. We then highlight promising developments, point out open questions, acknowledge difficulties and propose directions for further integration of ecological and chronobiological perspectives through Wild Clock research.This article is part of the themed issue 'Wild Clocks: integrating chronobiology and ecology to understand timekeeping in free-living animals'.

Experimental illumination of natural habitat--an experimental set-up to assess the direct and indirect ecological consequences of artificial light of different spectral composition

Artificial night-time illumination of natural habitats has increased dramatically over the past few decades. Generally, studies that assess the impact of artificial light on various species in the wild make use of existing illumination and are therefore correlative. Moreover, studies mostly focus on short-term consequences at the individual level, rather than long-term consequences at the population and community level-thereby ignoring possible unknown cascading effects in ecosystems. The recent change to LED lighting has opened up the exciting possibility to use light with a custom spectral composition, thereby potentially reducing the negative impact of artificial light. We describe here a large-scale, ecosystem-wide study where we experimentally illuminate forest-edge habitat with different spectral composition, replicated eight times. Monitoring of species is being performed according to rigid protocols, in part using a citizen-science-based approach, and automated where possible. Simultaneously, we specifically look at alterations in behaviour, such as changes in activity, and daily and seasonal timing. In our set-up, we have so far observed that experimental lights facilitate foraging activity of pipistrelle bats, suppress activity of wood mice and have effects on birds at the community level, which vary with spectral composition. Thus far, we have not observed effects on moth populations, but these and many other effects may surface only after a longer period of time.

The first observation of seasonal affective disorder symptoms in Rhesus macaque

Diurnal animals are a better model for seasonal affective disorder (SAD) than nocturnal ones. Previous work with diurnal rodents demonstrated that short photoperiod conditions brought about depression-like behavior. However, rodents are at a large phylogenetic distance from humans. In contrast, nonhuman primates are closely similar to humans, making them an excellent candidate for SAD model. This study made the first attempt to develop SAD in rhesus macaque (Macaca mulatta) and it was found that short photoperiod conditions could lead monkeys to display depressive-like huddling behavior, less spontaneous locomotion, as well as less reactive locomotion. In addition to these depression-related behavioral changes, the physiological abnormalities that occur in patients with SAD, such as weight loss, anhedonia and hypercortisolism, were also observed in those SAD monkeys. Moreover, antidepressant treatment could reverse all of the depression-related symptoms, including depressive-like huddling behavior, less spontaneous locomotion, less reactive locomotion, weight loss, anhedonia and hypercortisolism. For the first time, this study observed the SAD symptoms in rhesus macaque, which would provide an important platform for the understanding of the etiology of SAD as well as developing novel therapeutic interventions in the future.

Diurnal rodents as an advantageous model for affective disorders: novel data from diurnal degu (Octodon degus)

Circadian rhythms are strongly associated with affective disorders and recent studies have suggested utilization of diurnal rodents as model animal for circadian rhythms-related domains of these disorders. Previous work with the diurnal fat sand rat and Nile grass rat demonstrated that short photoperiod conditions result in behavioral changes including anxiety- and depression-like behavior. The present study examined the effect of manipulating day length on activity rhythms and behavior of the diurnal degu. Animals were housed for 3 weeks under either a short photoperiod (5-h:19-h LD) or a neutral photoperiod (12-h:12-h LD) and then evaluated by sweet solution test and the forced swim test for depression-like behavior, and in the light/dark box and open field for anxiety-like behavior. Results indicate that short photoperiod induced depression-like behavior in the forced swim test and the sweet solution preference test and anxiety-like behavior in the open field compared with animals maintained in a neutral photoperiod. No effects were shown in the light/dark box. Short photoperiod-acclimated degu showed reduced total activity duration and activity was not restricted to the light phase. The present study further supports the utilization of diurnal rodents to model circadian rhythms-related affective change. Beyond the possible diversity in the mechanisms underlying diurnality in different animals, there are now evidences that in three different diurnal species, the fat sand rat, the grass Nile rat and the degu, shortening of photoperiod results in the appearance of anxiety- and depression-like behaviors.

Light pollution modifies the expression of daily rhythms and behavior patterns in a nocturnal primate

Among anthropogenic pressures, light pollution altering light/dark cycles and changing the nocturnal component of the environment constitutes a threat for biodiversity. Light pollution is widely spread across the world and continuously growing. However, despite the efforts realized to describe and understand the effects of artificial lighting on fauna, few studies have documented its consequences on biological rhythms, behavioral and physiological functions in nocturnal mammals. To determine the impacts of light pollution on nocturnal mammals an experimental study was conducted on a nocturnal primate, the grey mouse lemur Microcebus murinus. Male mouse lemurs (N = 8) were exposed 14 nights to moonlight treatment and then exposed 14 nights to light pollution treatment. For both treatments, chronobiological parameters related to locomotor activity and core temperature were recorded using telemetric transmitters. In addition, at the end of each treatment, the 14^th night, nocturnal and feeding behaviors were explored using an infrared camera. Finally, throughout the study, body mass and daily caloric food intake were recorded. For the first time in a nocturnal primate, light pollution was demonstrated to modify daily rhythms of locomotor activity and core temperature especially through phase delays and increases in core temperature. Moreover, nocturnal activity and feeding behaviors patterns were modified negatively. This study suggests that light pollution induces daily desynchronization of biological rhythms and could lead to seasonal desynchronization with potential deleterious consequences for animals in terms of adaptation and anticipation of environmental changes.

Chronobiology by moonlight

Most studies in chronobiology focus on solar cycles (daily and annual). Moonlight and the lunar cycle received considerably less attention by chronobiologists. An exception are rhythms in intertidal species. Terrestrial ecologists long ago acknowledged the effects of moonlight on predation success, and consequently on predation risk, foraging behaviour and habitat use, while marine biologists have focused more on the behaviour and mainly on reproduction synchronization with relation to the Moon phase. Lately, several studies in different animal taxa addressed the role of moonlight in determining activity and studied the underlying mechanisms. In this paper, we review the ecological and behavioural evidence showing the effect of moonlight on activity, discuss the adaptive value of these changes, and describe possible mechanisms underlying this effect. We will also refer to other sources of night-time light ('light pollution') and highlight open questions that demand further studies.

Effects of circadian phase and melatonin injection on anxiety-like behavior in nocturnal and diurnal rodents

Animals show daily rhythms in most bodily functions, resulting from the integration of information from an endogenous circadian clock and external stimuli. These rhythms are adaptive and are expected to be related to activity patterns, i.e., to be opposite in diurnal and nocturnal species. Melatonin is secreted during the night in all mammalian species, regardless of their activity patterns. Consequently, in diurnal species the nocturnal secretion of melatonin is concurrent with the resting phase, whereas in nocturnal species it is related to an increase in activity. In this research, we examined in three diurnal and three nocturnal rodent species whether a daily rhythm in anxiety-like behavior exists; whether it differs between nocturnal and diurnal species; and how melatonin affects anxiety-like behavior in species with different activity patterns. Anxiety-like behavior levels were analyzed using the elevated plus-maze. We found a daily rhythm in anxiety-like behavior and a significant response to daytime melatonin administration in all three nocturnal species, which showed significantly lower levels of anxiety during the dark phase, and after melatonin administration. The diurnal species showed either an inverse pattern to that of the nocturnal species in anxiety-like behavior rhythm and in response to daytime melatonin injection, or no rhythm and, accordingly, no response to melatonin.

The ecological impacts of nighttime light pollution: a mechanistic appraisal

The ecological impacts of nighttime light pollution have been a longstanding source of concern, accentuated by realized and projected growth in electrical lighting. As human communities and lighting technologies develop, artificial light increasingly modifies natural light regimes by encroaching on dark refuges in space, in time, and across wavelengths. A wide variety of ecological implications of artificial light have been identified. However, the primary research to date is largely focused on the disruptive influence of nighttime light on higher vertebrates, and while comprehensive reviews have been compiled along taxonomic lines and within specific research domains, the subject is in need of synthesis within a common mechanistic framework. Here we propose such a framework that focuses on the cross-factoring of the ways in which artificial lighting alters natural light regimes (spatially, temporally, and spectrally), and the ways in which light influences biological systems, particularly the distinction between light as a resource and light as an information source. We review the evidence for each of the combinations of this cross-factoring. As artificial lighting alters natural patterns of light in space, time and across wavelengths, natural patterns of resource use and information flows may be disrupted, with downstream effects to the structure and function of ecosystems. This review highlights: (i) the potential influence of nighttime lighting at all levels of biological organisation (from cell to ecosystem); (ii) the significant impact that even low levels of nighttime light pollution can have; and (iii) the existence of major research gaps, particularly in terms of the impacts of light at population and ecosystem levels, identification of intensity thresholds, and the spatial extent of impacts in the vicinity of artificial lights.

Acute behavioral responses to light and darkness in nocturnal Mus musculus and diurnal Arvicanthis niloticus

The term masking refers to immediate responses to stimuli that override the influence of the circadian timekeeping system on behavior and physiology. Masking by light and darkness plays an important role in shaping an organism's daily pattern of activity. Nocturnal animals generally become more active in response to darkness (positive masking) and less active in response to light (negative masking), and diurnal animals generally have opposite patterns of response. These responses can vary as a function of light intensity as well as time of day. Few studies have directly compared masking in diurnal and nocturnal species, and none have compared rhythms in masking behavior of diurnal and nocturnal species. Here, we assessed masking in nocturnal mice (Mus musculus) and diurnal grass rats (Arvicanthis niloticus). In the first experiment, animals were housed in a 12:12 light-dark (LD) cycle, with dark or light pulses presented at 6 Zeitgeber times (ZTs; with ZT0 = lights on). Light pulses during the dark phase produced negative masking in nocturnal mice but only at ZT14, whereas light pulses resulted in positive masking in diurnal grass rats across the dark phase. In both species, dark pulses had no effect on behavior. In the 2nd experiment, animals were kept in constant darkness or constant light and were presented with light or dark pulses, respectively, at 6 circadian times (CTs). CT0 corresponded to ZT0 of the preceding LD cycle. Rhythms in masking responses to light differed between species; responses were evident at all CTs in grass rats but only at CT14 in mice. Responses to darkness were observed only in mice, in which there was a significant increase in activity at CT 22. In the 3rd experiment, animals were kept on a 3.5:3.5-h LD cycle. Surprisingly, masking was evident only in grass rats. In mice, levels of activity during the light and dark phases of the 7-h cycle did not differ, even though the same animals had responded to discrete photic stimuli in the first 2 experiments. The results of the 3 experiments are discussed in terms of their methodological implications and for the insight they offer into the mechanisms and evolution of diurnality.

Circadian rhythms and depression: human psychopathology and animal models

Most organisms (including humans) developed daily rhythms in almost every aspect of their body. It is not surprising that rhythms are also related to affect in health and disease. In the present review we present data that demonstrate the evidence for significant interactions between circadian rhythms and affect from both human studies and animal models research. A number of lines of evidence obtained from human and from animal models research clearly demonstrate relationships between depression and circadian rhythms including (1) daily patterns of depression; (2) seasonal affective disorder; (3) connections between circadian clock genes and depression; (4) relationship between sleep disorders and depression; (5) the antidepressant effect of sleep deprivation; (6) the antidepressant effect of bright light exposure; and (7) the effects of antidepressant drugs on sleep and circadian rhythms. The integration of data suggests that the relationships between the circadian system and depression are well established but the underlying biology of the interactions is far from being understood. We suggest that an important factor hindering research into the underlying mechanisms is the lack of good animal models and we propose that additional efforts in that area should be made. One step in that direction could be the attempt to develop models utilizing diurnal animals which might have a better homology to humans with regard to their circadian rhythms. This article is part of a Special Issue entitled 'Anxiety and Depression'.

The effect of the lunar cycle on fecal cortisol metabolite levels and foraging ecology of nocturnally and diurnally active spiny mice

We studied stress hormones and foraging of nocturnal Acomys cahirinus and diurnal A. russatus in field populations as well as in two field enclosures populated by both species and two field enclosures with individuals of A. russatus alone. When alone, A. russatus individuals become also nocturnally active. We asked whether nocturnally active A. russatus will respond to moon phase and whether this response will be obtained also in diurnally active individuals. We studied giving-up densities (GUDs) in artificial foraging patches and fecal cortisol metabolite levels. Both species exhibited elevated fecal cortisol metabolite levels and foraged to higher GUDs in full moon nights; thus A. russatus retains physiological response and behavioral patterns that correlate with full moon conditions, as can be expected in nocturnal rodents, in spite of its diurnal activity. The endocrinological and behavioral response of this diurnal species to moon phase reflects its evolutionary heritage.