It’s the birds, not the bees, that led to giant foxgloves in Americas
FOXGLOVES brought to the Americas 200 years ago by Britons have grown bigger because they are pollinated by hummingbirds instead of bees.
Scientists compared foxglove flowers brought to Colombia and Costa Rica with those in their native southern England and concluded that the flowers were up to a quarter larger in the South and Central American countries.
Introduced from the gardens of English engineers in the 19th century, the cone-shaped flowers have adapted to their new surroundings in just 85 generations, an unusually rapid evolution.
They grow at altitudes of 2,200m where the climate is similar to their native Britain, but flower all year round because of the lack of seasons.
In the UK they are pollinated by bees but in both American countries this is carried out by hummingbirds, which are better at pollinating longer flowers, said the study in the British Ecological Society’s Journal of Ecology. Researchers found the tube-shaped part of the flower which holds the nectar was 13 to 26 per cent larger in the Americas.
By counting pollen grains deposited inside flowers the researchers found that hummingbirds could bring in more than a bumblebee.
Lead author Dr Maria Clara Castellanos, of the University of Sussex, said it was rare to find a plant changing its shape in such a short period of time.
Other plants have evolved to self-pollinate, meaning they don’t need insects, when moved away from their native environment, but a rapid change in flower shape is more unusual.
“Evolution of flowers can happen quite quickly when you have strong selection, like in this case, where you have a new environment with the hummingbird.
“When facing new pollination environments, plants can actually be more resilient than you would expect. They quickly respond, but it still takes a couple of hundred years,” she said.
The finding also helps explain the wide diversity of flowers, even without human intervention, as it shows their ability to change in a new environment, leading to new sub-species specific to different parts of the world, the paper explained.
The scientists now plan to test the theory that the shift is directly caused by hummingbirds, by placing plants in mesh cages which exclude hummingbirds but allow bees to enter, in areas where the plants are pollinated by both.
There are no bumblebees in Australia so the experts now want to find out how the foxgloves there are pollinated. Other species have also evolved quicker than they would under natural conditions because of human intervention.
In 2018 a study found that elephants in Gorongosa National Park in Mozambique were evolving to become tuskless, due to their populations being decimated by ivory poaching.