Researchers have measured decreased flight-to-light responses in moths from urban areas with historically high light pollution. This direct example of Darwinian selection could be hurting the ecological role of moths as pollinators and food sources.
Most of us have witnessed nocturnal insects incessantly bouncing off streetlights and lamps, seemingly oblivious to the futility of their efforts. But could this bizarre activity have greater consequences than occasionally inconveniencing a relaxing evening?
Previous studies have shown that in an era of increasing light pollution and expanding urban area, nocturnal insects are at increased risk of fatality caused by artificial lights.
But researchers in Switzerland have recently published evidence of a more profound consequence of increased insect mortality due to artificial light: the evolution toward reduced flight-to-light behavior in city-dwelling moths compared to their rural brethren.
While this may seem to be a pretty obvious cause-and-effect result (going toward light kills moths, so they’ve adapted to go toward light less), it has important implications.
First, some background on the methods of their study.
As their test subjects, the researchers used the widely-distributed ermine moth (Yponomeuta cagnagella). They gathered moths from low-light rural areas and from high-light urban areas that had been urbanized for many decades and were spatially independent from one another.
Flight-to-light experiments were conducted in a controlled lab setting using the offspring of their collected specimens in order to control for environmental influence. Using over 1000 individuals, they quantified the number of moths from each location (rural vs urban) that were attracted to an artificial light source.
Their results showed that urban moths, whose forebears had experienced high levels of light pollution, had a significantly reduced flight-to-light behavior compared with those from pristine dark-sky habitats.
The reduced attraction to light sources exhibited by urban moths is most likely a direct result of Darwinian selection by decreasing their likelihood of being killed by manmade light.
However, the authors suggest that this also comes with unintended consequences, such as a reduced mobility. This could negatively affect foraging as well as colonization ability.
Additionally, nocturnal insects are a significant source of plant pollination and the primary food source of many vertebrates. A significant evolutionary change such as an impairment of flight-to-light behavior could thereby potentially cause unforeseen changes to the local food web.
This is certainly not the first negative consequence of human-induced evolutionary change in nature. However, since flight-to-light is a commonly observed phenomenon it shows that even ordinary and seemingly inconsequential disruptions can have notable effects.