Field pansy (Viola arvensis) Photo By Ivar Leidus – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=127273286

Dear Readers, you might have come across a story about this little plant in the press this week, and no wonder. Field pansies can be found across Europe, western Asia and North Africa, and normally they are pollinated by long-tongued bumblebees such as Bombus terrestris, the buff-tailed bumblebee. However, these bees have suffered a 33% decline in the regions of study (around Paris, France), and so scientists wondered if, and how, the plants were adapting.

Producing nectar is very expensive for a plant – it requires a lot of resources to generate all that sugar. Furthermore, the plant then has to attract the bees, by using petal shape and colour and perfume to advertise that there is food available. Insect pollination is the most precise way for the plant to pass on its genetic material, so if there are enough pollinators, it’s worth it. However, when there aren’t enough bees around, the plant has another strategy that can be deployed.

Pansies are capable of something called ‘selfing’ – self-pollination. In this case, the plant fertilises itself, so it doesn’t need a pollinator. Plants that adapt to doing this can reduce their nectar load, and they no longer need the flashy advertising signals (one reason why plants that are wind-pollinated, such as grasses, don’t bother with such a palaver). Scientists used something called resurrection ecology to look at populations of field pansy in the same locations in the past, and compared them to the plants of today. They found that today’s pansies are 27% more likely to be self-pollinating compared with the plants of only 30 years ago, and that the plants, as expected, have lost some of the characteristics that made them attractive to bees.

This is an extraordinary example of rapid evolution to meet changing conditions, but there is a sting in the tail. The problem with self-pollination is that the offspring are all clones of the parents. This is ok while the conditions that the plant grows in remain the same, but the great advantage of cross-pollination is that you get variation in each generation. Then, when some ghastly disease or drought or rainstorms or bitter cold appear, at least some of the youngsters will survive (hopefully). If everyone is identical, everyone could be wiped out.

The web of life is complicated. In a way, it’s great that pansies are capable of self-pollination (not all plants are), but it is likely to reduce the genetic diversity in those particular populations, making them more vulnerable, as we’ve seen. This feels like an important study, and I hope that it will be replicated in other places to see what’s going on. And yet, we continue to use neonicotinoid pesticides which have a devastating effect on bees, bumblebees in particular. Humans might be the most intelligent species on the planet, but we seem, unlike the pansies, to have no survival instincts whatsoever.

Rant over.

Buff-tailed bumblebee queen (Bombus terrestris) Photo Holger Casselmann, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons