Night-time light pollution makes flightless crickets more drought resistant

Abstract

Since the turn of the 20th century, when human street lighting really took off, the nocturnal world has been bathed in light. While this is great for people, the illumination has proved a menace for some creatures, confusing body clocks and sending migratory species off course. And it wasn't clear how nocturnal light pollution might impact the ability of animals to cope with other threats, such as climate change. Knowing that some creatures are capable of adjusting their physiology to survive environmental conditions that would otherwise prove challenging, Alyssa Bonfoey and colleagues from the University of the Pacific, USA, had an ideal animal in mind – the variable field cricket (Gryllus lineaticeps) – to find out how light pollution affects an animal's ability to withstand heatwaves and drought. ‘The adult cricket exists in two forms – some can fly to disperse away from stressful environments while others are flightless, but instead focus on reproduction’, says Zach Stahlschmidt. Together with Bonfoey and Jessica Chen, Stahlschmidt decided to find out how nocturnal light pollution might affect the ability of these crickets to cope with a lack of water and higher temperatures.Illuminating developing crickets during the day with sunlight-simulating bulbs before turning the lights off at night, Bonfoey then switched some of the crickets to dimmer, more orangey lightbulbs at night, similar to dim street lighting, until the crickets developed into adults. Then, she transferred the crickets to individual homes for an additional 5 days as the newly emerged females spontaneously followed one of two different growth patterns: some crickets were unable to fly, ramping up their fertility instead, while other crickets were capable of flight but had poorer fertility. Bonfoey next checked how well both groups of crickets coped with drought when she removed their water supply, in addition to seeing how long the crickets could withstand a brief 45°C heatwave before they toppled over.Surprisingly, crickets that had grown up with nocturnal light pollution were larger and heavier than crickets that had grown up with completely dark nights. Yet, the crickets that had experienced light pollution struggled to deal with the heat, toppling over more swiftly than the crickets that developed in complete nocturnal darkness. However, the nocturnally illuminated flightless crickets were better prepared when drought set in, holding out for 10 days on average before succumbing to dehydration, in contrast to the flight-enabled crickets, some of which could only survive for 2 days without water.So, it seems that nocturnal light pollution is a problem for developing variable field crickets, making it harder for them to withstand heatwaves as adults. However, some of the crickets may be more resilient to other aspects of climate change, as nocturnal light pollution seems to improve the ability of the flightless insects to survive drought. The team suggests that nocturnal light could reduce the effects of hormones that regulate water use, allowing the flightless crickets that grew up with light pollution to better conserve their water stores, making them more able to withstand drought. However, they point out that the flight-enabled crickets have stronger body clocks, which probably makes them less susceptible to the effects of nocturnal light pollution in general.