Ultraviolet polarized light pollution and evolutionary traps for aquatic insects

Abstract

When animals are misguided by evolved behavioural cues to preferentially make mistakes, they are caught in an evolutionary trap. Aquatic insects rely heavily on polarized light cues to locate bodies of water necessary for oviposition and mating. However, where artificial objects (e.g. asphalt, buildings) are at least as effective at polarizing light as natural water bodies, aquatic insects may instead prefer to oviposit on those surfaces where there eggs fail to hatch. These objects are known to create evolutionary traps by polarizing light in the visible range (390–700 nm), yet their potential for creating evolutionary traps via the reflection of ultraviolet (UV) wavelengths (<380 nm) remains largely unknown. We surveyed the natural and artificial environment to understand the properties of objects that can polarize natural and artificial sources of UV light and conducted a multiple-choice field experiment to test the importance of UV polarized light in guiding habitat selection behaviour in six families of aquatic insects. We found that UV polarized light was associated with natural water bodies, was a common component of the man-made environment created by sunlight reflecting off vehicles, buildings and solar panels during the day, and originating from lamplight with a UV component at night. One of the six families of aquatic insects we examined was preferentially attracted only to UV polarized light sources, indicating that UV polarized light is a cue used in habitat selection. These results highlight a quantitatively new type of ecological light pollution capable of creating evolutionary traps for polarotactic insects at night, or even during the day.