People living closer to the equator have darker skin due to higher UV radiation, and this is passed down through generations of people having higher levels of melanin, but is the same true for flowers? Researchers at the University of Pittsburgh say yes, but it’s not noticeable to the human eye.
“Pigmentation patterns getting darker towards lower latitudes is ... an ecological rule called ‘Gloger’s Rule’, and it’s been formulated towards animals, so this is kind of the first extension of this ecological rule to plants,” said researcher and grad student Matt Koski.
Although flowers do not appear darker, pollinators such as bees see the ultraviolet light in addition to the visible spectrum. When examining flowers in the UV spectrum, flowers have a dark "bull's eye" near pollen and nectar rewards. The researchers found that the bull’s eyes were larger closer to the equator.
The larger bull’s eye helps the flower to absorb the sun’s ultraviolet light, and leads the researchers to believe that without a large bull’s eye a flower would be damaged.
“In the lab we exposed flowers to UV, and protected flowers from UV, and measured pollen viability to find that UV radiation does damage pollen viability, and that having higher pigmentation can protect the pollen from UV damage,” said Koski.
The damage to the pollen is what they believe drives natural selection so that flowers with bigger bull’s eyes are more common closer to the equator.