Evolution of the flowers: Better inbreeding than being eaten

The colorful variety of flowers is due to the co-evolution of flowers and their pollinators.

Originally, all flora depended on wind or water in order to be able to reproduce sexually.

It wasn't until insects began to romp around in flowers that they carried pollen from one plant to another with increasing reliability.

Most flowers offer a reward for this service, such as nectar.

If they woo very specific guests - sometimes also birds and small mammals - with colors, shapes and scents, they can achieve particularly efficient pollination.

For flower visitors, specializing in certain flowers can in turn have the advantage of having to share this food source with fewer competitors.

However, pollinators are not always the only driving force behind the evolution of flower colors and shapes.

Scientists working with Zachary Cabin and Nathan Derieg from the University of California in Santa Barbara have observed that sometimes hungry herbivores are also involved.

Their research subject was a columbine native to the Rocky Mountains called

.

The five outer petals of this Colorado state flower are usually blue.

A long spur containing nectar glands hangs down only from the five inner, mostly white ones.

Butterflies from the hawkmoth family stick their even longer proboscis into this cornucopia and feast on the sweet contents while hovering in front of the flower.

In 1897, a columbine mutant was described that had replaced its five white, spurred petals with five more blue, spurless ones.

Since such plants offer no nectar to their visitors, it was to be expected that they would soon disappear from the scene.

But far from it, the mutant has multiplied magnificently and, a hundred years later, also established itself south of the first site of discovery on a meadow in Reynolds Park.

Cabin and his colleagues took a closer look at this population of

, in which about 25 percent of the plants are currently spurless.

As the researchers report in the journal Current Biology, as expected, the mutants lose out in pollination.

It is true that hawkmoths, like bumblebees, head for both types of flowers.

But unlike bumblebees, which harvest and carry pollen, the moths are only useful as pollinators when there is a normal flower.

They leave a spurless mutant without depositing pollen on the stigma or taking it with them from the stamens.

Therefore, such plants are likely to be more dependent on self-pollination.

Analysis of their DNA has confirmed that they actually show a trend towards inbreeding.

Surprising evolutionary advantage of spurless mutants

Surprisingly, despite this disadvantage, the mutants develop fruit significantly more frequently than normal flowers.

Environmental factors such as exposure to light or soil moisture do not seem to play a role here, as both variants grow evenly distributed, sometimes only a few centimeters apart.

However, aphids and mule deer show a pronounced preference for normal columbine flowers: the deer eat the whole flower;

Aphids are usually content with just sucking on the ducts of the stalk.

In doing so, however, they often inhibit the growth of the flower and cause it to wither prematurely.