In addition, a few studies in humans reported a significant association between polymorphisms in circadian clock genes and ‘morningness–eveningness’ chronotypes, including a polymorphism in the promoter region of the period3 gene. For instance, twin studies found higher correlation of diurnal preference in monozygotic twins than in dizygotic twins, with the estimated heritability being as high as 40%. While plasticity plays an important role in diurnal preference, there is evidence for a strong genetic component underlying the variability seen among individuals. However, in experiments where the golden spiny mouse was the only species present, the mice immediately reverted to nocturnal behaviour. russatus) are two sympatric desert species that split their habitat, with the common spiny mouse being nocturnal and the golden spiny mouse being diurnal. For example, the spiny mouse ( Acomys cahirinus) and the golden spiny mouse ( A. Such “temporal niche switching” is undoubtedly associated with considerable plasticity that can lead to rapid changes in behaviour. Furthermore, many species shift their phase preference upon changes in environmental conditions. In addition, experimental conditions in the laboratory setting (particularly light and temperature) often fail to simulate the high complexity that exists in natural conditions. Laboratory studies have often focused on a single representative wild-type strain and ignored the population and individual diversity within a species. Īccumulating evidence suggests that diurnal preference within a species is far more diverse than previously thought. The visual system of most mammals is dominated by rods, yet lacks several cone photoreceptors that are present in other taxa where a nocturnal lifestyle is maintained. Two plausible systems that have been targeted for genetic adaptations driven by diurnal preference are the visual system and the circadian clock, the endogenous pacemaker that drives daily rhythms. Nocturnality and diurnality most likely evolved through different physiological and molecular adaptations. The nocturnality of mammals, for example, was explained by the nocturnal bottleneck hypothesis, which suggests that all mammals descended from a nocturnal ancestor. The fact that diurnality preference is usually similar within phylogenetic groups alludes to an underlying genetic mechanism. The genetic basis for such phase preference is largely unknown and is the focus of this study. Selection for activity during a specific time of the day is driven by various factors, including preferred temperature or light intensity, food availability and predation. Most animal species exhibit locomotor activity that is restricted to a defined part of the day, and this preference constitutes the species-specific temporal niche. The diurnal and nocturnal selection strains provide us with a unique opportunity to understand the genetic architecture of diurnal preference.Īlthough time is one of the most important dimensions that define the species ecological niche, it is often a neglected research area. 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. Our study demonstrates that genetic variation segregating in wild populations contributes to substantial variation in diurnal preference. This finding was congruent with behavioural experiments indicating that both light masking and the circadian pacemaker are involved in driving nocturnality. Other than one circadian clock gene ( pdp1), most differentially expressed genes were associated with either clock output ( pdf, to) or input ( Rh3, Rh2, msn). We used whole-genome expression analysis to identify differentially expressed genes in diurnal, nocturnal and crepuscular (control) flies. After 10 generations, we obtained highly diurnal and nocturnal strains. Using a highly diverse population, we performed an artificial selection experiment, selecting flies with extreme diurnal or nocturnal preference. However, a survey of strains derived from wild populations indicated that high variability among individuals exists, including flies that are nocturnal. Under laboratory conditions, Drosophila melanogaster is crepuscular, showing a bi-modal activity profile. The genetic basis underlying diurnal preference is largely unknown. Most animals restrict their activity to a specific part of the day, being diurnal, nocturnal or crepuscular.
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