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article imageEssential Science: Artificial light disrupts wallaby reproduction

By Tim Sandle     Dec 28, 2015 in Science
Perth - Humans are steadily "lighting up" the natural environment. However, new evidence shows artificial light disrupts animals' normal rhythms. This affects both defensive and mating behaviors.
The discombobulating effect of artificial light in wild animals has been reinforced by a new study published about wallaby populations on an Australian naval base. The wallabies are subjected to 10 times the light intensity their cousins in the bush would received, and this alters mating behavior and carries serious long-term consequences.
Gas light and street scene recreated at the RAF Museum  Hendon.
Gas light and street scene recreated at the RAF Museum, Hendon.
The effect of artificial light has been previously documented, although the full extent of the alterations to behavior continue to be gathered. The easiest creatures to be studied were moths. To illustrate the effect of artificial light on the natural world, it is worth looking at moth experiments in more detail.
Information about light and moths continues to be gathered. In April 2015, a paper was produced which showed how artificial light makes moths less wary of predatory bats, making moths more vulnerable in urban areas (see: Royal Society Open Science's article "Light-emitting diode street lights reduce last-ditch evasive manoeuvres by moths to bat echolocation calls.") A related study demonstrated artificial light led to female cabbage moths no longer producing a male-attracting pheromone; instead producing one that repelled potential mates. This finding was published in the journal Ecological Entomology, in a paper headed "Artificial night lighting disrupts sex pheromone in a noctuid moth."
Moth on flower
Moth on flower
With larger creatures, new research shows artificial illumination can cause both males and females to alter behavior. The highlighted study on Tammar wallabies (Macropus eugenii) at the naval base has revealed how artificial light leads to the mammals changing their seasonal patterns, most specifically when it comes to mating. These wallabies, also known as dama wallabies or darma wallabies, are small nocturnal macropod marsupials (around the size of a rabbit.) The naval base is located on Garden Island (Western Australia), 35 kilometers southwest of Perth.
Summarized by Science News, the study revealed how the light disrupts the timing of the natural breeding season, leading to the wallabies mating far later than they would do so if they lived in the Australian bush (with births peaking in April.) The consequence is that mothers miss the peak season for birth and struggle to meet their joeys’ demands for milk given that the best plants are no longer available, resulting in a higher death rate.
The swamp wallaby is the only living representative of the genus Wallabia. They are preyed upon by f...
The swamp wallaby is the only living representative of the genus Wallabia. They are preyed upon by feral cats and foxes.
The observations about the wallabies was made by a research group led by Kylie Robert of La Trobe University in Melbourne, Australia. Data was gathered over a five year period.
The reason why anthropogenic light is a problem is because all animals receive cues from the patterns of daylight and night. The researchers note that part of the brain called the hypothalamic suprachiasmatic nuclei is a timekeeping system that works on the basis of being a biological clock, set by photic cues perceived by the retina and regulated by the hormone melatonin.
When night arrives and light, generated from human activity, continues to shine, this disrupts the natural and seasonal rhythms (circadian oscillations) by affecting the production of pineal hormone melatonin. Through this disruption, the types of behaviors potentially affected include:
Emergence time,
Weakened immune systems,
Reduced cognition,
Foraging behavior,
Survival behavior,
Timing of reproduction.
The timing of reproduction was the area selected for the wallaby study. Over time, much of the vegetation on island where the study was made has been replaced with illuminated buildings, footpaths and roads. Those areas unaffected by the built environment, are affected by the lights of the structures.
Given the push for more "environmentally friendly" low energy light, the researchers are concerned that an extension of high-brightness white light-emitting diodes will exacerbate the problem for mammals like wallabies.
The research is published in the journal Proceedings of the Royal Society B. The paper is headed "Artificial light at night desynchronizes strictly seasonal reproduction in a wild mammal."
The study is one of the first to connect artificial light at night with induced changes in mammalian reproductive physiology, and it should open up a new field of biological inquiry given the extension of artificial light into the environment (which is at a global rate of around 6 percent per year.)
Women are economically active in the night life of Lagos as seen in this photo of a woman selling ro...
Women are economically active in the night life of Lagos as seen in this photo of a woman selling roasted yam at night.
There may also be implications for humans, with this type of research, given how shift work has been shown to affect human health through the disruption of circadian rhythms. Circadian rhythms are widely thought to affect every cell in the human body and disruption has been implicated in obesity and cancer. The body clock can be disrupted, such as through long-haul flights or by those undertaking nightshifts (as Digital Journal has reported on previously.)
This article is part of Digital Journal's Essential Science series. Other articles in the series are "Space-food for astronauts made from bacteria"; "Health effects of antibiotic use"; "Graphene makes improved night vision tech"; "Personalized medicines, the health innovation”; “Power paper can store electricity”; and "Why some rainbows are completely red."
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