If flowers bloom a month earlier than usual – as they reportedly did last year in Maryland – what does that mean for bees? According to Will Plants and Pollinators Get Out of Sync? it could mean trouble. The story appears on NASA’s website and explains how plants and pollinators have co-evolved: “the two species time their cycles to coincide, for example, insects maturing from larva to adult precisely when nectar flows begin.”
Before we consider the implications, I’d like to dismiss the notion that the species got together over beers one evening to “time their cycles.” As the NASA correspondent undoubtedly knows, cycle-timing is entirely an accident of nature, an accumulation of evolutionary mishaps that include genetic mutations and selection. Rather than coincidental planning, pollination synchronization results from an exclusionary rejection. If, for example, a plant suffers a mutation which results in early blooming (say, a rewrite of the base pair in a gene that produces a protein benefiting from heat stimulation) and if no bees are around at the new earlier flowering time, the flower simply does not reproduce. There are no seeds and there is no next generation of similarly off-sync flowering plants. However, if there is also a type of pollinator bees that coincidentally suffers a genetic mutation resulting in an ability to rapidly build a large spring population, the mutated flower will have pollinators available to “meet up” with it. That plant will produce similarly inclined seeds and the bee colony with its tendency to build an early spring population will also thrive and spawn more early-risers.
Mutations are rare, nevertheless mutual coincidental genetic disruptions happen frequently amongst the billions of creatures involved. It’s a numbers game and the numbers are big. Each year, about one in ten million of each DNA base unit is altered during replication. This happens by exposure to natural radiation or chemical hazards. If there are over a hundred million individual seeds in a field (the number of alfalfa seeds produced in a quarter-section, for example), each year ten seeds in the field will suffer genetic damage to the coding affecting the proteins that result in early flowering. So, it does happen – and at a surprisingly fast rate when we consider the billions and billions of seeds produced each season around the world. This is how plant scientists genetically alter plants (unless they are “genetically engineering” by manipulating bits of genetic code). Plant scientists expose millions of seeds to high-level radiation, resulting in accelerated rates of mutation. Then they grow the resulting plants and measure the results: A brighter colour? A longer stem? A tastier fruit? Nature plays this same game over a longer period of time. Wild flowers in meadows and seeds in fields are nature’s genetic laboratory. (If you would like to understand mutation rates, this easy article by Toronto professor Larry Moran discusses estimating the rate of human mutations – which average about 150 genetic mutations per person each generation.)
What is the effect of a warmer climate on plant pollination? First, we know that temperature is not the only factor that determines when a plant will bloom. It is not even the most important factor. Length of day is. Photoperiodism is a fascinating subject. Plants have 15 different types of cell receptor that sense light. Humans, by the way, have just 3 and ours are stuck inside our eyeballs’ retinas – a plant’s eyes cover its entire body. The thing that triggers blossoming is the period of time between the last flash of “far red” at the time of the setting sun and the next full spectrum sunshine, the following morning. Greenhouse managers know this and they sometimes toy with the plants’ transducers, forcing off-season flowering, by exposing plants to artificial light.
But for this discussion, let’s assume ambient temperature actually triggers flowering – as it does in some plants. Will flowers and bees become “out of sync” because of climate change? According to this Independent newspaper article, “Higher temperatures may result in fewer bees, scientists claim”, the future is dire. “This is because the more out-of-sync pollinators and plants become, the more difficult it will be for each to find opportunities for pollination – potentially threatening a wide variety of plants, including crops of seeds or fruits, most of which depend on pollination,” says the Independent, adding “it will raise fears that popular foods such as apples and pears could be affected.” However, those popular foods (Pears are popular? Not in our house.) will survive because the orchard managers contract beekeepers to supply honey bees. If the season slides forward, the beekeeper will adjust his schedule, developing stronger colonies earlier. This has already happened in California’s almond groves where big colonies are required in February and beekeepers react by stimulating their bees in early January. Farmers will somehow manage. The ever-popular Bartlett pear will remain a staple food (in homes other than ours*). But wild bees and birds might not be so lucky, according to both common sense and the NASA article.
Hummingbirds are at risk. “Honeybees aren’t the only pollinators affected by climate change. Hummingbirds and other migratory pollinators may be even more susceptible if their seasonal migrations become out of sync with the flowering and nectar availability in their breeding habitat,” says NASA’s Earth Observatory website. I think the bottom line to this story is that humans, driven by profit and self-interest, will continue to enjoy juicy pears for generations to come, but the rest of the animal kingdom will be left to survive by the luck of evolutionary adaptation. Some species will adjust to the warmer climate, others will join the ranks of the extinct. Beekeepers will become more adept at manipulating colony populations to provide bees for commercially valuable crops while roadside asters (as seen in today’s photo, above) will mutate or perish. If man’s role in the changing environment fascinates you, you may like to read a piece I wrote for my Earth sciences blog, at this site.
* We do eat the occasional pear. It’s just hard to describe the fruit as popular.