Our spring is slow in coming.
Remember that old saying, April showers bring May flowers? Several snow-showers in mid-late April proved that our impatience was not hurrying the season along.
Mallards on my pond swam together in pairs, the paired male vigorously chasing off would-be interlopers. By the last week of April, females rarely appeared on the pond, so I knew they were tending their eggs. An immature eagle swept over the house roof and down past the front windows so suddenly that all of us in the house were startled out of our chairs. It flew on down and over the pond, missed its prey, made two more tries, but failed to nab a duck. Mink and otter visited the pond, looking for little fish.
The hummers are finally here, in some parts of town, although not yet at my place. Ruby-crowned kinglets (known as RCKIs or “Rickies”) are singing, after a late start. I wonder if those late arrivers were delayed by the volcanic ash clouds that interrupted air-traffic in the Pacific Northwest. A few big queen bees are flying and now there are blueberry flowers to feed them. There are some reports of bears out there, looking for food. And, in the warm spots, the brilliant yellow spathes of skunk cabbage shelter the spikes of flowers, all initially in female-phase.
Frogs have been calling. Columbia spotted frogs gather in some of the dredge ponds in the upper Mendenhall Valley; we usually see eggs and tadpoles there later. Wood frogs are reported from the big beaver pond on the Outer Point Trail where we’ve found them in previous years, and observers in other years have seen eggs and tadpoles there too.
The Boy Scout Trail has been rather quiet. One day, we found several huge horse clam shells on the tide line, all lined up several yards apart. That was a puzzle — why did they wash up on the last tide and why were they so spaced? One specimen still had both shells linked together by a nice hinge; when I took it home to inspect, the dried hinge parts fell out as two hard lumps; the connection between them and the shells had disappeared. I would like to know more about how those hinges work.
On another day, we stopped for a snack on a convenient beach log. Soon came a mooching raven, who stood around hopefully. We obliged, of course, throwing a few nuts in its direction, one at a time. The raven shattered almonds and pepitas with the tip of its bill and scavenged all the tiny bits. If we tossed a really small fragment, that bird could spot where it landed, although we could not.
We may be waiting impatiently for a nice spring season, but for many plants, the clock has already been partly set. Flowering plants need to make their flowers and seeds at seasons that are favorable for pollinators and seed maturation. That’s “why” they flower when they do. But “how” they manage it is another question.
How do plants decide when to flower? Most folks would think first of the lengthening days of spring and warming temperatures. Such environmental conditions are surely important. But for many plants, there’s another essential timing device. Botanists call this “vernalization.” The term is derived from a Latin word (vernal) for springtime, so vernalization means getting ready for spring. Specifically and physically, this means the requirement of a period of cold (but not freezing) temperatures before the plant is ready to respond to day length and temperature. The length of the cold period and the degree of coldness can vary among species, in most cases probably reflecting the conditions to which the species is normally exposed. That same exposure to cold induces plant dormancy for the winter, giving the plant a rest period.
Vernalization appears to be an epigenetic phenomenon, modifying gene expression without changing the genes themselves. Many studies have examined the molecular basis of vernalization, which in some species involves turning off a gene that inhibits flowering, but in others, it turns on a gene that activates the flowering process. There are several modifications of those two procedures and perhaps other molecular pathways too. (But let’s not get lost in all the molecular processes!)
Vernalization must be repeated in every generation, because it is not inherited. Just the ability to make these epigenetic modifications is heritable. It is a good example of something for which plants are well-known: phenotypic plasticity, or producing different phenotypes in different conditions—changing leaf shapes or sizes, or branching patterns, or numbers of sucker shoots, or stem diameter, or various physiological processes, and so on.
Epigenetic regulation of genes is particularly well-developed in plants, although it is known in animals too. Plants can’t move around to find suitable conditions for growth and reproduction, although many animals can. So having a means of adjusting gene expression to prevailing conditions is thought to be especially useful for plants. Unlike many animals (vertebrates, at least), in which organ and tissue formation are determined largely in the embryo stage of development, plants can continually produce new organs and tissues from meristems (like stem cells, able to develop into many different things). Epigenetic processes allow plants to modify themselves, to some degree, as the season progresses, fine-tuning gene expression in order to accommodate unpredictable environments.
Many plants of the temperate zones, with strong seasonal changes, require a winter before they prepare for spring. However, apparently most of the studies have been done with domestic species—fruit trees and shrubs (e.g., apples, cherries, blueberries), cereal crops (wheat, rice), garden vegetables (cabbage, carrots), and flowers (tulips, crocus). So we are left to extrapolate those findings to native plants in their usual environments.
A further question is How will climate warming upset the usual seasonal patterns of vernalization and flowering? Then there will be subsequent effects on pollinators and seed set, with further consequences for seedling recruitment to the population and for seed-eating and fruit-eating animals. Upsetting the seasonal pattern of flowering leads to upsets of the chains of interactions.
• Mary F. Willson is a retired professor of ecology. “On The Trails” appears every Wednesday in the Juneau Empire.