An experiment found that selfing” monkeyflower plants lost 13 percent to 24 percent of their genetic variation compared to another group that were propagated by bumble bees. 

Genetic variation is important to respond to changes in nature or the overall environment. The good news is that they used bumblebees and though they claim they are in decline, evidence does not show that, so the plants are not at short term risk. Even better, pollination is not done by bumblebees alone, there are over 25,000 species of just bees, and lots of other insects pollinate. An experiment outside a closed greenhouse would show that.

The real risk is not a change in one bee population in some areas, but self-pollination itself. Adopting self-pollination can endanger a plant species long-term survival, because a lot can grow wrong, as in the experiment where genetic variation was lost in nine generations. 

The controlled greenhouse experiment used yellow monkeyflower plants, a common wildflower found in the Western U.S., in which a group of plants were isolated from pollinators - in this case bees. At first the non-bee plants produced few seeds, then they produced a lot as they adapted to self-pollinate. The flowers changed as well with their male and female reproductive parts, the tops of their stamens and pistils, moving closer together to allow for the easier transfer of pollen.

While the selfing plants continued to reproduce, they lost genetic variation compared to a control group that were visited by bumble bees.

Adaptation is key to explaining these declines, the authors note. In selfing populations, a favored genotype will spread if it has an advantage, but so do all other mutations it carries, simply because they are lucky enough to reside in that plant’s genome. This phenomenon of “genetic hitch-hiking” is much less pronounced when bees visit plants because offspring are a mix of their parents’ genetic variability.

“Strong inbreeding fundamentally altered the consequences of adaptation,”said Jeremiah Busch, a Washington State University evolutionary biologist and lead author on the study. What will be key to learn is if and when the loss of genetic variation leads to population collapse.