Research into juvenile garden orb weaving spiders in Melbourne shows light reduced their ability to climb and hunt
Light pollution is shrinking the brains of city-dwelling spiders in ways that could affect their ability to climb and hunt, according to new research.
The study published in the journal Biology Letters found exposing juvenile garden orb weaving spiders to light pollution reduced their brain development, particularly in an area used for vision.
Co-author and University of Melbourne professor Therésa Jones, who researches the ecological effects of light pollution on invertebrates, said the changes in brain structure could potentially impede spiders’ ability to do everyday things, like foraging and navigating their complex environments.
Light pollution was likely bad news for the spiders, she said, with implications for people too.
“This long history we have with light cycles is now being completely changed, and the impacts that we’re seeing in wildlife are mirroring some of the impacts we’re seeing in the medical fields and in the human literature,” she said.
Prof Jones said both humans and spiders produced melatonin at night time, an important chemical that acted as an antioxidant and driver of day-night rhythms. Light pollution interfered with these processes, impacting reproduction, survival, immune function and a whole suite of physiological processes, she said.
Spiders provided a model for understanding effects of light pollution, she said. “Yes, it’s got eight legs … obviously we can’t take a human and scoop their brains out and CT them, but we can use spiders to start looking at some of the impacts.”
Prof Jones has been researching the ecological effects of artificial light at night for more than a decade. She said the study was the first globally to measure the effect of light pollution on invertebrate brain structure.
Lead author and University of Melbourne researcher Nikolas Willmott collected 20 female and 10 male juvenile garden orb-weaving spiders from dark sites across Melbourne.
The spiders were placed in specialised labs and fed with crickets twice weekly, with half exposed to light conditions equivalent to standing under a street lamp.
Once the spiders had matured – 35 days for males and 50 days for females – the scientists froze them and removed their brains.
Jones said the spiders were beautiful and quite chunky in size, with bodies measuring up to 3 cm and legs stretching even further. But their brains were “teeny”, roughly equivalent to the size of a ballpoint pen nib.
Using micro CT scanners – a smaller, and higher resolution version of the kind used for humans – the team measured and analysed the spiders’ brains.
In the group exposed to artificial light conditions, they found a section of their brains called the primary visual pathway was smaller, compared to the control spiders.
Dr Loren Fardell, an ecologist who studies the effects of light pollution at the University of Queensland, said artificial light from street lamps, houses and cities had many effects on wildlife.
Night pollution could distract animals from normal responses and mislead them in ways that disturbed their movement and orientation, she said. This was particularly a problem during a hatchling stage of sea turtles or migration stages of birds or moths, for example.
“A lot of Australian animals are nocturnally active and are strongly affected by artificial lights at night altering their perception of natural light cycles,” she said.
She said many local councils in Australia were now implementing warm low-level light, reducing hours of light use, and designating dark areas and parks, she said. Households could help too, by minimising outdoor lighting and closing curtains, to stop indoor lights from shining outdoors.