Light Pollution

Light pollution alters the cycle of natural light and behavior of many organisms (Le Tallec et al., 2013). Nocturnal species rely on natural light for cues for physiological behaviors, causing them to be severely impacted by light pollution as they are attracted to artificial light (Le Tallec et al., 2013). Light pollution can cause changes in reproductive cycles, migration patterns, locomotion, and general orientation/direction (Le Tallec et al., 2013). To fully understand the extent of light pollution’s impact on natural environments, mammals facing its consequences must be studied, like the grey mouse lemur.

Grey Mouse Lemurs

Grey mouse lemurs (Microcebus murinus) are small, nocturnal primates living in various parts of Madagascar (Zimmermann et al., 1998). Grey mouse lemurs have a specialized biological rhythm that defines their reproduction and locomotion activity (Le Tallec et al., 2016). Mouse lemurs have two annual reproductive states, an active sexual state where the mouse lemur is exposed to more than 12 hours of light (photoperiod) for a certain long period of time, and an inactive sexual state where the mouse lemur is exposed to less than 12 hours of light for a certain short period of time (Le Tallec et al., 2013). There is also a daily  locomotion rhythm that entails euthermy (normal body temperature) at night and hypothermia (lower body temperature) during the day (Le Tallec et al., 2013).

A Grey Mouse Lemur (Image: Blanchard Randrianambinina)

A study conducted by (Le Tallec et al., 2016) examined how 12 adult male mouse lemurs react to light pollution in mid-winter (shorter, inactive sexual period), and if this possibly resembles normal reproduction in a long-day, active sexual state. Melatonin production, testis size, body temperature, and locomotion were monitored. Results showed that in the times where the mouse lemurs were exposed to light pollution, their body temperatures were higher, testis size was higher, sexual activity was induced, and hormones were higher (Le Tallec et al., 2016). Melatonin secretion was also inhibited with the exposure to artificial light, causing changes in nocturnal behavior.

Another study on light pollution’s impact on grey mouse lemurs rhythm and behavioral patterns showed that exposure to artificial light caused increased body temperatures and active/resting phase delays in locomotion activity (Le Tallec et al., 2013). The time when the mouse lemur emerged from the nest and returned to the nest was much later when exposed to artificial light, but the total time they were out of the nest was shorter than the normal light (Le Tallec et al., 2013). Timing of foraging and feeding was later in the day when exposed to artificial light pollution (Le Tallec et al., 2013).

An example of light pollution a grey mouse lemur may be exposed to (Image: Mike Peel)

Possible Solutions

These two case studies show how light pollution can impact a plethora of behaviors in grey mouse lemurs, including reproduction, body temperature, and locomotion. This is yet another example of an unfortunate consequence from anthropogenic expansion and urbanization on wildlife.  To alleviate some of the light pollution affects on wildlife species like the grey mouse lemur, solutions to limit the strength of artificial light should be implemented. There are small solutions that if applied on a large scale, could help this problem. Using energy efficient light sources and time controls to regulate the amount of light can help limit the strength of impact on wildlife (Crawford, 1998). It is very difficult to fix the problem of light pollution in large urban areas, so there must be a conversation between important officials and organizations to determine laws and regulations of the amount of light used. Organizations like the International Lighting Commission (CIE) have already started theses discussions to address this issue, and hopefully more individuals will understand the significance of addressing this issue to save species like the grey mouse lemur.

References

All images were obtained from CreativeCommon

Crawford, DL (1998) Light pollution: The problem, the solutions. Preserving the Astronomical Windows 139, 13-16.

Le Tallec, Perret M, Thery M (2013) Light pollution modifies the expression of daily rhythms and behavior patterns in a nocturnal primate. PLoS ONE 8(11), 1-8.

Le Tallec T, Thery M, Perret M (2016) Melatonin concentrations and timing of seasonal reproduction in male mouse lemurs (Microcebus murinus) exposed to light pollution. Journal of Mammalogy 97(3), 753-760.

Zimmerman E, Cepok S, Rakotoarison N, Zietemann V, Radespiel U (1998) Sympatric mouse lemurs in north-west Madagascar: A new rufous mouse lemur species (Microcebus ravelobensis). Folia Primatol 69, 106-114.