2.25.26

Pollination matters

A Mexican petunia in the bagged self-pollination treatment.

The activities are as follows:

Pollination is one of nature’s most important processes. Without pollen moving from one plant to another, many plants would not be able to produce fruits or seeds. Without pollination, we wouldn’t have food like apples, strawberries, or even chocolate! But not all pollination works the same way. Some plants rely on pollinators like bees and butterflies, while others can reproduce without any help at all. Scientists are still exploring why plants have these different strategies.

As a science teacher, Cynthia is always looking for ways to bring real science into her classroom. To learn more about the work of scientists, she joined a summer research program. While there, she had the opportunity to design and carry out a study on pollination in a plant species, Mexican petunia.

Mexican petunias are a flowering plant found in gardens, parks, and wild spaces. They have bright purple flowers. This plant has two ways it can be pollinated, called pollination methods. First, insect pollinators visit and move pollen. When pollen is moved from one plant to another, this is called outcrossing. Second, these plants can self-pollinate, meaning pollen from a single flower can pollinate that same flower. 

Pollination methods make a big difference for plants. Outcrossing mixes the genetics of two different plants together, which creates new genetic combinations that may help offspring survive and thrive. In contrast, self-pollination means the genetics of the plant are the same as the parent plant and no new genetic combinations are made. Plants that use self-pollination don’t need to rely on pollinators, however many times the seeds they produce are not viable and are not able to grow. 

Cynthia predicted that outcrossing would produce the most fruits and seeds, and flowers that relied on self-pollination would produce fewer seeds. She designed a garden experiment where she could control how Mexican petunias were pollinated. To set up her study, she used four different treatments. 

Bagged – Cynthia put mesh bags around the petunia flowers. This prevents pollination from other plants, so this treatment shows whether flowers are able to successfully self-pollinate on their own.

Open pollination – Cynthia left these flowers open to visits from insects. These plants could be self-pollinated or outcrossed.

Self-pollinated by hand – Cynthia hand-pollinated these flowers using pollen from another flower on the same plant. This treatment shows whether the plant produces fruit when the flowers are self-pollinated by hand.

Outcrossed by hand – Cynthia hand-pollinated these flowers with pollen from a different Mexican petunia plant. These plants are all outcrossed.

Cynthia monitored the Mexican petunia plants in her four treatments for three weeks. She checked the flowers every few days to see which ones developed fruit. If a flower made a fruit, she counted the number of seeds per fruit. In the open pollination treatment, a few times the fruit opened and launched out its seeds before Cynthia could count them, meaning she could get fruit data from the flower, but not a seed count. At the end of her experiment, she had collected data on percent fruit development, or the chance of successful development of a fruit from a flower, and the number of seeds produced within those fruits, called seed count.

Featured scientist: Cynthia Nuñez from Florida International University

Flesch–Kincaid Reading Grade Level = 8.8

12.8.25

The science of stamen loss

A pollinator visiting a mustard flower, drinking nectar and picking up pollen from anthers.

The activities are as follows:

Plants and animals have adaptations, or traits that help them survive and pass on more of their genes to the next generation. Flowers are a key adaptation for plants because they help the attract pollinators and reproduce.

Flowers come in many different shapes, sizes, colors, and forms. While flowers as a whole are an adaptation, traits within flowers are often adaptations themselves. For example, different flower colors attract different types of animals to the plant. Some flowers make nectar that gives animals a food reward for visiting. Other plants have small flowers with no petals so that pollen can be easily picked up and travel by wind.

Many of the animals that visit the plant serve as pollinators. Pollinators help plants reproduce by bringing reproductive parts together. Pollination happens when pollen from the stamen reaches the stigma. This is needed for seeds to form. By moving pollen, pollinators help plants make more seeds. More seeds lead to more plants in the next generation. Small differences in flower traits can change which plant is the most successful at reproducing and setting seed.

Jeff is a scientist studying a very particular flower shape seen in plants of the mustard family. Most plants in this family have flowers with 4 long stamens and 2 short stamens. No other plants have this shape, and no one knows why! The short stamens are a particular mystery.

Jeff wanted to see why mustards might have these short stamens. He thought that short stamens are an adaptation because they make it harder for pollinators to reach the pollen, so that more pollen would be left over for later pollinators. This might be beneficial because the first pollinator visiting the flower wouldn’t be able to take all the pollen, leaving none for the following visitors. If his hypothesis was correct, he predicted that short stamens would have less pollen removed with each pollinator visit compared the long stamens.

Members of the Conner Lab taking measurements of pollen found on the anthers of short and long stamens.

To collect his data, Jeff and other scientists in his lab needed to measure how much pollen was removed by pollinators on short and long stamens. To do this, they grew mustard plants in the greenhouse and let them flower. This made sure no pollinators could visit the plants before the experiment. Next, they exposed the plants to the three most common pollinators for mustards – bumblebees, small bees, and syrphid flies. To test honeybees, plants were put into flight cages with bees inside. To test small bees and syrphids, plants were put outside. Pollinators chose the flower to visit. After each visit, the lab counted the pollen on the visited flower. They then compared it to the amount of pollen on a flower that was not visited. They used these values to calculate the percent pollen removed. This was repeated for short and long stamens.

Featured scientists: Jeff Conner (he/him) from the W.K. Kellogg Biological Station. Written with Kirsten Salonga, Justice High School, Research Experience for Teachers.

Flesch–Kincaid Reading Grade Level = 7.6

Additional teacher resource related to this Data Nugget:

The data featured in this activity has been published. If you are interested in having students read primary scientific literature, they can complete this Data Nugget and then explore the full study here: