Let Them Have Sex...Flowers, That Is!

Angiosperms have been around for a long time. More commonly referred to as the flowering plants that dominate the landscape today, they evolved sometime early in the Cretaceous Period about 130 million years ago when dinosaurs ruled and mammals were small and innocuous on the landscape. Remember that life on Earth has been around for 3.5-4.0 billion years, so these angiosperms are relative newcomers. If you condense the amount of time that life has been on Earth to a human just about to turn 30, these flowering plants would have just arrived in the last year or so! Their huge variety today ranges from the simple grasses to the delicate rose to the mighty oak. And they are ultimately the most important food source for most animals that exist today including insects, birds, and mammals...like us!

Flowering plants have been so successful because their method of reproduction is sexual and therefore mixes the genetic information from two plants when producing a seed. This leads to an ability to evolve efficiently and fill many ecological niches. Although many plants are wind pollinated, like most trees, grasses, and ragweed, many others require the services of insects for pollination, so the plant has to attract an insect. To do so it creates nectar and a showy flower. This is very costly for a plant so the rewards for this partnership must be significant for it to have persisted for so long and to become so diverse in its many expressions. That reward is the movement of pollen from one plant to another, without having to produce the enormous amounts of pollen needed for plants that are wind pollinated, and the mixing of genes through sexual reproduction.

Bird's Foot Violet on one of the bluff prairies in Hixon Forest

Flowers have both male and female parts. The male parts are the anther held aloft by the long filament and collectively called the stamen. It produces pollen. The female parts are the stigma that sits on top of the style leading to the ovary most commonly called the pistil or a carpel as in the following diagram. The stigma is where the pollen ends up for fertilization when it is carried from one plant to the next by wind or pollinating insects to then journey its way down the style into the ovary to unite with the ovule and eventually form a seed.

Many of us have read about the steep decline of insects across the globe with some estimates of a decrease in their populations by almost half in the last 40 years. We may have noticed this ourselves by seeing fewer insects hitting our windshields as we travel, fewer fireflies at night, or just noticing fewer bugs in our daily lives. This is very concerning because we need insects- they provide many services we depend on including pollination. Up to 75% of global crops and many of the plants in nature are pollinated by insects. One of the biggest drivers of this marked fall off in insect population is habitat loss. This is the "H" of HIPPO, which is an acronym coined by the late E. O. Wilson and stands for the main causes of loss of species- Habitat loss, Invasive species, Pollution in all of its forms including pesticides, Population increases (human) if coupled with increasing consumption and encroachment on the natural world, and Over-harvesting. Many also add climate change to the mix.

This insect decline has also been noticed by some plants. One plant has been shown to be adapting to fewer insects by becoming less dependent on cross pollination and more on self-fertilization. An article in the NY Times on Jan 4, 2024, "Flowers Are Evolving to Have Less Sex", describes a study about one common species in France, the field pansy, that is doing just that, in a process called "selfing": https://www.nytimes.com/2024/01/04/science/flower-sex-evolution-bees.html.

In this study, plants grown in identical conditions from older seeds that were stored in the 1990's (when there were more pollinators) were compared to ones grown from newer seeds from plants today. They found that self-fertilizing increased by 27 percent in the plants from new seeds compared to the old. The new plants also produced 20% less nectar and their flowers decreased in size by 10%. The researchers then exposed these two versions of the plant to bumblebees, and, as expected, the bees preferred the old plants with bigger flowers and more nectar compared to the new.

This changing interaction between plants and insects could go many ways. One could be for more plants to turn to self-pollination, like the field pansy, and put the breaks on investing in nectar and flowers that attract pollinators. This could then cause a further decline in insects that depend on that nectar and pollen and a negative self-reinforcing cycle could begin which could ultimately end with the pollinator-plant relationship being abandoned and with that would go the beautiful flowers we all admire. In the end, this path would not only cause pollinators to suffer but the plants as well by giving up sexual reproduction and its major advantages for adaptation. A second path could be for the flowers to respond to the lack of pollinators by increasing their production of nectar and the "attractiveness" of their flowers to better compete for the remaining pollinators, but this would be feasible only up to a certain point and for only a limited number of plant species.

One thing that can help with this situation right now is to give pollinators a boost by providing more habitat for the native flowers they know and need. Friends of the Blufflands hopes the work it has done restoring the bluff prairies and planting spring ephemerals will help! Thank you to all of our supporters and volunteers!

Here are a few native bees doing their work on some of these sites:

A metallic green sweat bee on Pussy-toes (Antennaria genus, species probably parlinii, maybe plantiginifolia) on a bluff prairie in Hixon

Probably a mining bee on Prairie Blued-eyed Grass (Sisyrinchium campestre) also on a bluff prairie in Hixon

Likely a cellophane bee on a Large-flowered Trillium (Trillium grandiflorum) in my backyard. Friends hopes to see these blooming one day in the spring ephemeral patch that was recently started on the north facing slope of Grandad Bluff