Global Warming disrupts the timing of flowers and pollinators

As the temperatures rise, different organisms respond differently. Some migrate to higher latitudes or altitudes. Others stay put but change the timing of reproduction and other seasonal activities. As a result, ecosystems get remodeled.

So, for instance, insect pollinators and flowers they pollinate may get out of sync.

Animals tend to use photoperiod as a major clue for seasonal timing, with temperature only modulating the response to some extent.

Plants, on the other hand, although they certainly can use photoperiod, are much more strongly influenced by temperature. Non-biologists who have only heard abot vernalization in the context of discussion of Lysenko may not be aware that this process is not bunk pseudoscience, but a target of active research:

Flowers are the reproductive organs of plants and are responsible for forming seeds and fruit. As their name implies, biennials complete their life cycles in two years, germinating, growing and overwintering the first year. The second year, the plants flower in the spring and die back in the fall.

That biennial strategy, Amasino explains, arose as flowering plants, which first evolved some 100 million years ago during the age of the dinosaurs, spread to fill the niches of nature. Spring blooming confers numerous advantages, not the least of which is leafing out and flowering before the competition.

But how do the plants know when to flower?

"If you carve out that niche, you need to get established in the fall, but you need to make darn sure you don't flower in the fall," Amasino says. In the case of biennials, "the plants can somehow measure how much cold they've been exposed to, and then they can flower rapidly in the spring niche."

Exposure to the cold triggers a process in plants known as vernalization, where the meristem - a region on the growing point of a plant where rapidly dividing cells differentiate into shoots, roots and flowers - is rendered competent to flower.

In a series of studies of Arabidopsis, a small mustard plant commonly used to study plant genetics, Amasino and his colleagues have found there are certain critical genes that repress flowering.

"The plants we've studied, primarily Arabidopsis, don't flower in the fall season because they possess a gene that blocks flowering," Amasino explains. "The meristem is where the repressor (gene) is expressed and is where it is shut off."

The key to initiating flowering, according to the Wisconsin group's studies, is the ability of plants to switch those flower-blocking genes off, so that they can bloom and complete their pre-ordained life cycles.

But how that gene was turned off was a mystery until Amasino and his group found that exposure to prolonged cold triggered a molecular process that effectively silenced the genes that repress flowering.

So, if the plants respond to temperature by changing the timing of flowering and insect retain the same timing (although they mave migrate away), there will be no flowers around when the insects are looking for them, and no insects buzzing around when the flowers need to be pollinated.

This recently got some experimental support:

"Climate change is already affecting ecological systems and will continue to do so over the coming years, providing a particularly relevant topic for this session," said Inouye.

For instance, Earthwatch volunteers in the Rocky Mountains helped Inouye document that global warming affects lower altitudes differently than higher ones. As a result, animals exposed to earlier warm weather may exit hibernation earlier and birds responding to earlier spring weather in their wintering grounds may flock north while there are several feet of snow on the ground, risking starvation.

"Already the difference in timing between seasonal events at low and high altitudes has negatively influenced migratory pollinators, such as hummingbirds, which overwinter at lower altitudes and latitudes," said Inouye. "If climate change disturbs the timing between flowering and pollinators that overwinter in place, such as butterflies, bumblebees, flies, and even mosquitoes, the intimate relationships between plants and pollinators that have co-evolved over the past thousands of years will be irrevocably altered."