Abstract
Circadian rhythms can synchronize to environmental time cues, such as light, temperature, humidity, and food availability. Previous studies have suggested that these rhythms can also be entrained by social interactions. Here, we used Drosophila melanogaster as a model to study the influence of socio-sexual interactions on the circadian clock in behavior and pacemaker neurons. If two flies of opposite sex were paired and kept in a small space, the daily activity patterns of the two flies were clearly different from the sum of the activity of single male and female flies. Compared with single flies, paired flies were more active in the night and morning, were more active during females’ active phase, and were less active during males’ active phase. These behavioral phenotypes are related to courtship behavior, but not to the circadian clock. Nevertheless, in male-female pairs of flies with clocks at different speeds (wild-type and per S flies), clock protein cycling in the DN1 pacemaker neurons in the male brain were slightly influenced by their partners. These results suggest that sexual interactions between male-female couples can serve as a weak zeitgeber for the DN1 pacemaker neurons, but the effect is not sufficient to alter rhythms of behavioral activity.
Highlights
The circadian clock synchronizes with several environmental stimuli in order to precisely predict 24-h environmental changes
As reported previously [30], there is a sex-specific difference in daily activity patterns, as females were more active than males during the daytime
To determine whether the nocturnality in male-female pairs is mediated by the circadian clock, we paired male and female per01 arrhythmic mutants, in which the circadian feedback loops stop due to the lack of a functional per gene [31]
Summary
The circadian clock synchronizes with several environmental stimuli in order to precisely predict 24-h environmental changes. Other environmental factors that are not directly generated by the Earth’s rotation, but are generated by consequences of circadian rhythms in ecological systems, are often discussed as potential zeitgebers. One of these elusive factors is social interaction [1,2,3]. It would be advantageous for animals to predict the timing of any 24-h rhythms that might occur in, for instance, mutualism, parasitism, competition, or predator-prey interactions. Some animals may have evolved circadian clocks that use social stimuli as zeitgebers
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