Pond lilies and dandelions

two yellow flowers with very different life histories

A cool, damp day in mid-July, not very summery, but I strolled around the lower loop at Eaglecrest with a friend, just to see what we could see.

The showy white-bracted inflorescences of dwarf dogwood (bunchberry) were just past their prime but still pretty. A small black moth with white wing-bars visited the flowers of Tofieldia (so much easier to say than “sticky false asphodel”, its cumbersome common name). Cloudberries and blueberries were developing. The tall ‘candles’ of the white bog-orchid sent their delicate fragrance into the air, and thousands of tiny pink flowers of bog cranberry dotted the mosses.

Some of the dandelion stems had reached extraordinary lengths; several were over two feet tall, including one that was close to three feet tall. After flowering, the stems elongate as the seeds mature, increasing the likelihood of rising above the surrounding herbaceous vegetation to let the wind-borne seeds disperse on their little parachutes. A few shooting stars still bloomed, but most of them had seed capsules maturing. Like the dandelions, this species seems to elongate its stems as the seeds mature, so a breeze can reach them and shake the seeds from the fully mature, split capsule.

The ponds were decorated with the leaves and flowers of yellow pond lily. The yellow cup of the flower is formed by sepals; the actual petals are smaller and inside the sepalous cup. The ovary is shaped like a bottle, with a bulbous base, a neck, and a flat disc on top. The disc is the stigma, which receives pollen that can fertilize the ovules in the base of the ovary. Around the base of the ovary are the numerous anthers, containing pollen.

Photo by Bob Armstrong

Although pond lily flowers are self-compatible, they seldom receive pollen from themselves, because stigma and anthers do not mature simultaneously. The stigma matures early, just as the flower begins to open, and visiting insects can enter the barely-open flower, perhaps depositing cross-pollen from another plant. Pollen from that flower may be distributed to other flowers later. The flower is said to smell like stale brandy—alluring to certain insects. UV patterns may add to the attraction: the stigmatic disc and sepals absorb UV and look dark, while the stamens (or maybe just the anthers) reflect UV, making a bright circle around the stigma. Nectar is produced on the petals near the base of the cup; that’s a nice reward for visitors.

Who are these visiting insects? In some places, mostly flies, but other populations may be pollinated by beetles or by bees and hoverflies. All that regional variation indicates that a closer look is needed for our pond lily populations.

The flowers we saw had been open for a while and were probably past the female-receptive phase. They had dozens of small flies covering the anthers, but we don’t know if those flies eventually would visit another lily flower. On the inner surface of the sepals were lots of very tiny insects we couldn’t begin to identify, but they were not likely to be pollinators.

Except for Steller’s jays hopping over the muskegs and squawking from the pines, bird life was quiet. Juncos chipped continually, as if they had young ones nearby.  A hermit thrush sang, but rather rustily. And calls from high in the canopy sounded like young sapsuckers, maybe.

A highlight was spotting a small adult toad, probably at least a year old, as it sought cover under some leaves. Do toads breed at the elevation of the lower loop or did this one hop up from some distant pond down below?

Complex Life Cycles

The life cycle of a bird or mammal is relatively simple: once it is born (or hatched), development proceeds directly to an adult form. All along the way, although there are developmental changes, you can easily tell that the animal is a bird or a mammal.

But for most animals, the life cycle is more complex. An individual makes one or more major transformations during its lifetime; this is called metamorphosis.  For example, think of a toad tadpole, living in water and eating vegetation, versus an adult toad, living on land and eating insects. Think of a caterpillar, worm-shaped and crawling and chewing vegetation vs. a butterfly, flitting about and sipping nectar. Or a mussel larva, drifting on the sea currents vs. an adult, inside a shell and stuck onto a rock.

The different phases of such life cycles are so different as to be quite unrecognizable. Indeed, it took Europeans a long time to realize that flies were not spontaneously generated from rotting meat but that the little white maggots ultimately gave rise to flies. Careful observation of maggots over a time period and meticulous dissections eventually revealed this secret in the 1600s, but even in the 1800s the idea was still controversial.

How is metamorphosis accomplished? It is regulated by hormones. Across much of the animal kingdom, metamorphosis is orchestrated by thyroid hormones. From mussels and flatworms to toads and fishes, thyroid hormones are the primary controllers of reorganizing the body and its physiology, although each kind of animal has its own variety of thyroid hormone.

However, the arthropods (such as insects and crustaceans), and their distant relatives called nematodes (round worms), do it differently. These groups diverged from the rest of the animal kingdom around five hundred million years ago. Both arthropods and nematodes have hard body coverings that have to be molted so that the soft-bodied animal inside can grow. For these animals, metamorphosis is typically controlled by a balance of two hormones: one regulates the molting process and the other controls the transformation of the body.

Scientists generally agree that the first insects, roughly five hundred million years ago, hatched from egg directly to an adult form and did not undergo metamorphosis. Silverfish still don’t, but other insects typically do. Somehow, a separate juvenile phase was ‘invented’. There are two basic patterns. The first to evolve was a partial metamorphosis (technically hemimetabolic), in which the juvenile form bears some resemblance to the adult, with articulated legs and sometimes similar body shape. This is the pattern used by dragonflies, grasshoppers, aphids, and their relatives. Much later, perhaps almost three hundred million years ago, a more radical form of metamorphosis evolved, technically called holometabolic, in which the juvenile looks and behaves totally unlike the adult form. This is the life cycle pattern used by beetles, flies, butterflies, and their relatives.

The holometabolic life cycle presumably evolved from the hemimetabolic cycle, but the steps involved are still being discussed by scientists. In any case, the holometabolic life cycle has been wildly successful in terms of numbers of species that exhibit it. Holometabolic insects comprise as much as sixty percent of all animals on earth and maybe about eighty percent of all insect species.

Different phases of a complex life cycle commonly have different ecological roles, and the combination of roles varies among types of critters. In most cases, all the life stages feed, although the diet may vary. For insects and toads, the larval phase is generally devoted to accomplishing growth by feeding on an abundant resource, while the other phase, typically an adult, accomplishes reproduction and dispersal. For many aquatic invertebrates, such as mussels and anemones, the larval phase disperses and the settled adult phase reproduces. Some life cycles have more than two distinct phases. For example, barnacles have one larval stage that disperses, a second one that does not feed but is in charge of settling on a substrate, and the adult phase, which reproduces. A salamander in eastern North America has an elaborate arrangement: the larva grows in water, the pre-adult phase grows on land and disperses, and the adult phase reproduces in water.

Blow fly and eggs. Photo by Bob Armstrong
Blow fly larvae. Photo by Bob Armstrong

What might be the advantages of having separate juvenile and adult forms in a life cycle? Not surprisingly, this too is a matter for discussion. For one thing, separate forms can exploit different environments and evolve specializations for those environments, becoming ever better at using the resources there. Furthermore, juveniles and adults are not competing for the same resources. It also becomes easy to partition the costly activities of living, for example, separating the energetic costs of growing from those of reproducing.

With such advantages, that leaves open the question of why don’t more animals do this! Perhaps the right mutations didn’t happen or, if they did, a suitable niche was not available. Or perhaps for some animals there are constraints imposed by other aspects of their life history, such as perhaps a necessity of both nurturing and teaching offspring? As usual, the ‘whys’ are harder to answer than the ‘hows’.

Twice-told Tales

Juneau-style

I have borrowed this title from nineteenth-century writer Nathanial Hawthorne, because (like his book) this essay is mostly a collection of previously-reported short stories, bringing together a few of the special ones from our little expeditions over the years.

— Perseverance Trail: We were coming down the trail, just below the Horn (where two benches provide a view of Snowslide Gulch). Some distance ahead of us there appeared a large black lump, followed by two smaller black lumps, moving slowly up the trail. Ooooops! What now?! Steep cliff up on our right, steep cliff down on our left, and nowhere to go but back. So we quietly backed up a hundred yards or so to the Horn and waited. And there they came, mom and two cubs.

First we tried going up on the little rubble slope on the inside of the curve, to allow the bears plenty of room between us and the railing. But mom took one look at us on the rocks and turned around, heading back down the trail. Then she hesitated and looked back, as if she really wanted to continue upward. So we all scuttled into a corner of the fence behind the benches. Ah! Much better! The family came back uphill and sauntered past us—Mom completely calm and owning the trail, the kids a bit skittish. Everybody was well-behaved.

–Gustavus: We stopped to braid some stems of sweetgrass, just to see how it worked, with no ambitions to construct a basket. As we bent over our task, we heard thundering hoofbeats, getting rapidly closer. Turning around, we saw a galloping female moose, with a gangly little calf that managed to keep up with her. They were so intent on getting away from whatever startled them that they ignored us and passed by, barely thirty feet away, and off they went, full tilt.

–Granite Basin trail: We watched two bear cubs sliding down a snowy avalanche chute, tumbling head first and tail first. Then they climbed back up to do it again…and again. After watching her offspring, mom joined in the fun, and made several (somewhat more decorous) slides too.

–On a beach somewhere near Sitka: It’s always fun to find hermit crabs, sometimes a tiny one that can hide in the tip of a big whelk shell, or one wearing a wee periwinkle shell (seemingly uselessly) on the end of its abdomen. In the shallow water by this beach, we found dozens of hermit crabs scrabbling to and fro. They came in all sizes and there weren’t enough empty shells to go around. So there were battles going on everywhere, with one crab trying to pull another out of its shell. As soon as one extracted an owner and moved in, it was subject to attempted evictions. It didn’t seem to matter if the shell was the right size for the attacking crab…maybe any shell was better than none.

–North Douglas boat ramp: Crows had been foraging on mussels and other shellfish. We often see them do this, dropping their prey onto the beach in hopes of breaking the shell and exposing the fleshy interior. Very often, the substrate is too soft to be effective. But at the paved boat ramp, although it sometimes required two or three drops, the strategy worked very well—except when some of the crows chose to sit on the sidelines and wait for their hard-working companions to do the foraging and shell-dropping, then raced out to snitch the meat without doing the work.

–Cowee Meadows: As two of us strolled quietly on a bank above some lower ground, we suddenly heard some loud snorting and thrashing of brush from a thicket below us. Oh-oh! Our eyebrows and the hair on the backs of our necks went up. We couldn’t see the source of the ruckus, so we didn’t learn if the perpetrator was guarding a carcass or just feeling cranky, but we didn’t stay around to meet this annoyed beast and very carefully and discretely retreated down the trail.

–Berners Bay: A sizable troop of young sea lions approached our group of kayakers. They seemed to be very curious, eye-balling us with their heads raised up and talking loudly among themselves. They made several approaches, sometimes coming within twenty feet or so of a kayak. Another time, a humpback whale eased up to the surface right next to my kayak, close enough that I could have touched it. I’m sure the great beast knew I was there and was just visiting.

Another time there, right in front of the cabin, a humpback whale rose straight up with its mouth wide open, engulfing a dinner of herring. Escaping fish cascaded down from both sides of the mouth, a glittering stream (like liquid mercury, said one observer) in the sunshine.

–Glacier Bay: We were parked on a beach, sunning ourselves after a trip up the East Arm. The rising tide pushed some oystercatchers up the beach toward us…parents and two chicks. They stopped just a few feet in front of us and ignored us, giving us a great look at them, until we (unfortunately) had to move on.

–Gustavus: A friend and I had looked in several places here in Juneau for a particular kind of fern, a weird one called moonwort. We had failed and needed help. So we took the ferry, the good old LeConte, to Gustavus. We had to take the same ferry back to Juneau, so there was a short turn-around time. A naturalist friend met us and led us down the beach a few dozen yards, and said ‘There it is’. Finally we saw this elusive plant, and since then we have seen it and a related species in the Gustavus area and found it near the glacier visitor center. The ferry ride was good too!

–Eaglecrest: Plodding up from Hilda Meadows on snowshoes, we followed the trail of an otter all the way from Hilda Creek, up the hill along a Hilda tributary to the divide, thence to one of the sources of Fish Creek. That critter knew where it was going.

–Spaulding trail in late winter: A raven flew overhead and dropped something—thud—onto the snow next to us. It was a wad of moss and tiny twigs, but why would that make a thud? It was an old robin’s nest, mud-walled inside the moss-and-twig mix, and frozen solid. Now the question became—was that raven bombing us, as message, or just playing games?