Chronobiology by moonlight

Abstract

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.

Keywords: communication; foraging; light pollution; lunar cycle; predation; reproduction.

Figure 1.

Mechanisms underlying moonlight effects on overt physiological and behavioural rhythms. The lunar month is associated with a 29-day moonlight-dark cycle with a peak during full Moon and a trough during new Moon. The solar day is associated with a 12 L : 12 D cycle. The interaction between the Earth's rotation and the Moon's orbit around the Earth leads to the lunar day, associated with a 28.4-hour moonlight-dark cycle on days in which moonlight is intense enough. The 12 L : 12 D cycle entrains (black solid arrow) circadian clocks that generate circadian rhythms. The lunar day moonlight-dark cycle could potentially entrain (red solid arrow) the circadian clock. The 29-day moonlight-dark cycle entrains (blue solid arrow) circalunar month clocks that generate circalunar month rhythms. Every light environmental cycle exerts masking (dashed arrows) on the expression of biological rhythms.