Walking in the South or Central American mountains, you might find an unexpected immigrant among the otherwise unfamiliar plants, the spectacular but common foxglove (Digitalis purpurea).
While it is sometimes nice to see an old friend when you are away from home, the foxglove does not naturally occur outside Europe and was introduced to South and Central America by English colonists, probably as an ornamental garden plant.
Even more surprising than coming across this staple of European cottage gardens in the temperate mountains of Colombia or Costa Rica, you might see it being pollinated by a hummingbird.
When plants are introduced by humans to new locations where they have never been before, they often arrive without the diseases and insect herbivores that they would have evolved with in their native range. Without these natural enemies to slow them down, plants can increase rapidly and become invasive and damaging to native biodiversity and human health or economic activities. Examples of these harmful invaders include Japanese knotweed, rhododendron or Gunnera in Ireland.
However, when invasive plants are moved, they might also leave behind the essential animal pollinators or seed dispersers that enable them to reproduce and spread. In this situation they can either rely on self-pollination, where a plant can pollinate itself, or co-opt the local pollinators in its new location.
Hummingbird beaks
Hummingbirds in Colombia and Costa Rica have found the foxglove to their liking, using the sugar-rich nectar to keep their energy levels up. Hummingbirds’ long beaks and tongues are able to access the nectar at the base of the bell-like flowers. In Europe, foxgloves are usually pollinated by long-tongued bumblebees, which fly and then crawl to the back of the flower to access the nectar.
In Europe the foxglove flowers narrow sharply towards the back, which means only bumblebees with long tongues can access the nectar. This system makes sure that the pollen is deposited on bumblebees, which then move it from plant to plant to fertilise the female ovules and make seeds. Foxglove flowers in Colombia and Costa Rica are subtly different to their European cousins and have evolved to have a wider flower base, enabling the larger hummingbirds to access the nectar.
Native South and Central American insect pollinators are not as effective at pollinating foxgloves as European bumblebees, so the flower shape may have evolved rapidly (over just 85 generations) to take advantage of the locally available hummingbird pollinators.
Human transport of thousands of species outside of the places where they have evolved is having profound ecological effects on the communities they are moved to. We also have increasing evidence that invasive species can change their own, and other species, evolutionary pathways.
Altering evolution
Human actions have, for a very long time, altered the course of evolution. The first crop plants evolved in tandem with human farming practices. Most grass species will “shatter” or drop their seeds when ripe so that they are dispersed to new areas to grow, whereas crop plants such as wheat and rye are “non-shattering” and retain ripe seeds on their heads. The genes for “non-shattering” seeds were preferentially passed on to new generations as it made the grains easier to harvest. Some of the harvested seed was stored, saved and planted in the next season.
The evolution of plants and animals can happen rapidly, but it is neither assured nor inevitable. For every example of evolutionary adaptation to change, there are many of extinction. Rapid changes, such as the intensification of agriculture, introduction of invasive species or climate change, will have profound consequences for millions of species, both through evolutionary dead ends leading to extinction as well as the emergence of new evolutionary solutions.
Studies such as the foxglove-hummingbird partnership give us some insight into the new world of interactions and adaptations that will be part of species’ survival with humans. They are a reminder that our actions now get written into the genetic code of living organisms for generations to come.
Yvonne Buckley is an ecologist, Irish Research Council laureate and professor of zoology at Trinity College Dublin