You’re not entirely what you think you are!

…the many microbes inside us, and how they shape our lives

Usually I write about things that I like to imagine that I know at least a bit about. Today is an exception. I have little background in this subject, but some recent readings got me so interested that I’m writing about microbes—bacteria and viruses, which are too tiny to see without fancy equipment but which could be said to rule the world. The implications for medical matters of some relatively new information are enormous.

There are way more kinds of microbes, with lots more genetic diversity, than all other organisms on earth. The numbers are so big that most of us can’t really comprehend them. It turns out that microbes are involved with almost everything we are and do! Mind-boggling!

For starters, each of us harbors a couple of pounds of bacteria (as well as trillions of the even-smaller viruses, of which more, presently). We are all familiar with the idea that bacteria can cause unpleasant diseases, but many bacteria are actually beneficial. Some live on our skin, where they can help keep harmful bacteria at bay. Many live in our digestive tracts, where they perform major feats of breaking down food into usable particles. Bacteria produce helpful enzymes too, such as one that allows a baby to extract nutrition from milk—reportedly, no human gene encodes an enzyme that can do this.

Having the right assortment of resident bacteria can, at least sometimes, help determine if one is obese, diabetic, has high blood pressure or multiple sclerosis, for example, or if one escapes these conditions. Bacteria that affect metabolism may even be involved with the condition of autism, or the avoidance of same. It may become possible to combat a nasty sort of bacteria with the proper application of another one, which outcompetes or destroys the first one. The previously unsuspected roles of bacteria in many human ailments—or in our avoidance of them—are just starting to be explored, and the medical implications for treatments are fascinating.

Now consider viruses for a moment. Viruses consist of a small protein shell and usually just a few genes. They make their living, so to speak, by invading the cells of other organisms and taking control of the metabolic machinery in those cells, forcing the cell to make more viruses. However, the process of replication is sloppy, with lots of mutations, and if two viruses occur together in one cell, they may exchange genetic material. So new versions of viruses are emerging all the time. Sometimes the new versions find an opportunity to invade entirely different species, jumping from bird to human, or pig to primate.

Inside the cell, reproduction of the invading virus may be extremely rapid, eventually exploding the cell and releasing viral offpring. Flu viruses and the common-cold virus work this way. Other viruses don’t kill the host cell, but they speed up cell division and cause the host cell to make more cells. That’s the makings of a possible cancer. Whether or not a cancer actually develops, however, depends on many factors, including the specific kinds of cells involved and if a previous exposure has already alerted the immune system.

Surprisingly, viruses may offer a way to treat some bacterial infections. Many, perhaps most, viruses attack bacteria, and they are commonly host-specific, attacking only one kind of bacterium. These viruses are called bacteriophages, or phages, for short. So there is hope that medical treatments with phages might help control some bacterial infections. Of course, the bacteria can mutate, and some would probably become phage-resistant (just as happens with antibiotics). But phages can evolve too and might acquire a mutation that overcomes resistance by bacteria.

What really ‘blew me away’ was learning a little about retroviruses, which insert their genes into the DNA of the host cell. These viruses can cause host DNA near the insertion to make proteins, in effect turning on host genes that had been turned off, and cancer can sometimes result. But not inevitably!

After a retrovirus inserts itself into the host DNA, the host’s immune system may inactivate it or mutations may cripple it. The inserted but inactive retrovirus can spread harmlessly through the host as the host’s body makes new cells (which it does frequently). If the retrovirus gets into an egg or sperm cell, it can be passed on to offspring and to future generations.

We now know that this has happened many, many times in the long history of life on earth. Viruses have been around for billions of years. Retroviruses are found in all kinds of vertebrates, from fishes to humans. In fact, about eight percent of DNA in humans comes from retroviruses that long ago inserted themselves into our ancestors’ DNA!

Even crippled retroviruses can be dangerous, if a mutation re-activates them, or if they insert new copies of themselves into the host genome. So, not surprisingly in this co-evolutionary arms race, humans (and probably other animals too) have evolved at least a few means of defense, by producing certain proteins that disable the retrovirus’ process of replication.

It turns out that retroviruses are essential to human (and perhaps most mammalian) reproduction. Most species of mammals, including humans, feed a growing fetus by means of a placenta. A particular retrovirus plays a critical role in the development of a placenta, without which a fetus would quickly starve to death.

So, in effect, you are not entirely what you probably thought you are. In addition to truly human DNA from your parents, you are partly an assortment of good, neutral, and bad bacteria, some resident and some transient, and good, neutral, and bad viruses, some of them buried in your DNA. In short, each of us is an ecosystem (living in an environment that itself is a gigantic ecosystem). Just think: ecosystem management applied to medicine!

Walking Gustavus beaches

predator leavings, big snails, and boring clams

A recent walk with two friends on some of the great sandy beaches of Gustavus provided several observations of interest. The four-footed friend probably had the advantage of us mere humans, because she could sniff many messages that were beyond our ken. Nevertheless, the curious-naturalist humans found much to see and discuss.

A line of wolf tracks followed the upper edge of the sand, steadily headed…somewhere. One huge wolf scat held remains of a murre, probably scavenged from a carcass, and another was made up mostly of clay, with a few feathers. Do wolves self-medicate with clay, as some birds do (to counter toxins in their food)?

There was evidence that predatory birds had feasted on murres, mallards, and a loon. Owls and eagles undoubtedly accounted for some of these avian remains. But also, perched on a log within distant binocular range was a slim, gray bird that we thought might be a peregrine falcon. Some owl pellets held the bones of voles, including skulls with teeth, which made identification of the prey relatively easy. A set of vole molars looks, on the grinding surface, like a row of tightly packed triangles; this is quite different from the cusped molars of deer mice, for example. Perhaps I needn’t have bothered to look closely, though: I was interested to learn, from a well-known naturalist in Gustavus, that deer mice are scarce over there, for reasons undetermined.

Scattered along the sand were several strongly ridged, giant snail shells, the biggest whelks I’ve ever seen. These specimens were four or five inches long, but they are said to reach a length of seven inches or so. They belong to the genus Neptunea, but the species name is still undetermined, thanks to some taxonomic confusions. They hang out in the sediments but emerge to travel, feed, and lay their eggs. Neptuneas make their living by drilling (with their file-like radulas) into the shells of other molluscs and slurping out the contents, eating polychaete worms, and by scavenging dead and dying critters. Females produce masses of egg capsules that are spread over rocks and in rocky crevices. Each capsule contains about two thousand eggs, but many of these are not fated to become juvenile snails, because they are eaten by their siblings. After developing inside the protective capsule for many months, well-fed young snails emerge.

Clam shells were everywhere, mostly horse clams. But on one beach we found deeply arched clam shells, each with a pronounced internal projection, for muscle attachment, near the hinge. This beast was entirely new to me, so my learning curve took a jump. These clams are called piddocks (Zirfaea pilsbryi). Piddocks and some other bivalve molluscs burrow into the substrate using their shell as augers; piddocks make their tunnels in clay, sand, or even rock (!). The sharp, jagged teeth on the front part of the shell slowly rasps away, back and forth, as the piddock rotates, eventually making a full circle, only to start over on the next round. Their tunnels can be over a foot long, so their siphons (or the so-called neck: the paired tubes, one of which is used for breathing and drawing in food particles, and the other for excreting wastes) are substantial. If the piddock is eating well and grows as it slowly burrows, the first part of the tunnel becomes too small for the clam to back out, and it can only go forward.

Piddock (Zirfaea pilsbryi). Photo by K. Hocker

I am not a marine biologist of any sort, but I love finding out more about this unfamiliar world.

Tricky flowers

…clever little arrangements for pollination

Most of our wild flowers are wide-open structures, just letting all the sexual parts hang out. Think of nagoonberry or cloudberry, asters, avens, silverweed, wild roses, geranium, anemones, and so on—all of these just present the sexual organs to whatever insect happens to land there. The smaller flowers of angelica and cow parsnip and their relatives do the same, but present the flowers in flat-topped bunches, making a good-sized landing platform for a visiting insect. It is then a relatively simple matter for an insect to walk around, picking up pollen from one flower and carrying it to another. Columbine and fernleaf goldthread dangle the sex organs loosely, downward or outward, where a visitor just bumps into them, when in search of nectar deeper in the flower.

Some of our flowers, however, are a bit more complex, requiring a visiting insect to do a little work or behave in a particular way. In these species, the sexual parts are typically enclosed within the flower—concealed in various ways. Here are some examples:

Lupine. Photo by Bob Armstrong

Lupine: Bees pry open the flower, and when they depress the lowest, keel-like petal, out pop the stigma (to receive pollen, if the bee carried any) and the anthers (containing pollen to be deposited on the bee and carried to another flower).

Twayblade orchid: A visiting tiny bee or fly pokes into the miniscule flower, bumping into a projection that releases a sticky gob that pulls out clumps of pollen. The pollen is stuck onto the insect’s face or head until another flower is visited and the pollen is inserted there.

Violet: Down in the heart of the flower, the stigma is encircled by closed anthers, packed tightly together (the technical term is ‘connivent’—conjuring up mental images of conniving and scheming deviously (!). A visiting insect displaces the stigma, pushing it to one side and perhaps depositing pollen, and only then do the anthers open, releasing pollen to be picked up and carried away by the insect.

Bog cranberry. Photo by Bob Armstrong

Blueberry, cranberry, shooting star, wintergreens (and tomato): Although the flowers differ in shape, all depend on what is called ‘buzz pollination.’ A visiting bee vibrates certain flight muscles (and buzzes), which causes pollen to shake down on the bee. If the bee already had pollen on its body, from another flower, it is brushed off onto the stigma.

Bunchberry/dwarf dogwood: the tiny flowers are clustered together, surrounded by white, petal-like bracts. Ripe flower buds open suddenly and the anthers explode their pollen into the air or onto an insect, when a tiny projection on one of the four petals is triggered, perhaps by an insect.

Lady-slipper orchid/moccasin flower: These flowers are doubly devious. They offer no nectar to insect visitors, who nevertheless prospect around inside the ‘slipper’, in hopes of a reward. But once inside that slipper, they cannot get out—except by squeezing through a tight opening at the back of the flower, where the sexual organs just happen to be located, convenient for pollen deposition and pick-up.

Bog laurel. Photo by Bob Armstrong

Bog laurel: When the flower opens, the anthers are held in little pockets on the faces of the petals, with slim filaments linking them to the center of the flower. This species is normally pollinated by bumblebees: when the bee lands on a flower, the anthers spring out of their pockets and dust pollen on the bee. The springing mechanism is reported to be very sensitive, so perhaps even small insects, coming in search of nectar, can spring the anthers free, but it is unclear if the pollen would land on their bodies and if they would be effective pollinators.

All these clever little arrangements are a small sample of the ingenious contrivances for pollination exhibited by flowers in more southerly latitudes, about which whole books have been written. The world of flowers is far more complicated than one might expect.

Where to put freshly-laid eggs

…a panoply of nest types

Most people would answer: In a nest, of course! But it is a tad more complicated than that. For instance, there are some mammals in Australia and New Guinea that produce milk to nourish their young, but they lay eggs and care for them until they hatch. The duck-billed platypus lays its eggs in a burrow, where the two eggs stick to each other and to the female’s fur while the female incubates with her tail wrapped around the eggs. In a sense, the female herself is the nest, and the burrow houses the female. In contrast, a spiny echidna puts her single egg into a pouch, like that in which marsupials (e.g., kangaroos) keep their offspring, until it hatches. So echidna females carry their eggs with them as they forage.

But birds typically don’t carry their eggs around; they put them in special places. It would be easy to guess that birds don’t lug their eggs around because they are basically flyers (although some have reverted to walking) and it could be very awkward to tote eggs while flying. But sungrebes in Latin America are able to fly while carrying chicks in pockets under their wings, so why not eggs too? Furthermore, even though they did not fly, lots of dinosaurs made nests: fossil eggs have been found in ancient nests, sometimes with a presumed parental dinosaur fossilized nearby. That leaves open the question of why birds usually have nests for eggs.

One possibility is that it would be hard to fly with more than about two eggs in some pocket and having a nest would allow the production of larger clutches of eggs. Some birds lay large clutches of six or eight eggs, or even more. Having more offspring could mean that at least some might survive to adulthood and produce the next generation.

Bird nests come in a huge array of forms. Some birds, such as most shorebirds, just make a little scrape in the soil or sand, sometimes adding bits of stone or grass. Others build substantial piles of vegetation in marshes or in trees. Some weave complex chambers or hanging bags, some make a sketchy latticework of sticks, and others build cup-shaped nests of various fibers. Some birds build nests of mud, shaped in various ways, and even of their own saliva (think: bird nest soup!). Some birds nest in cavities made by other creatures, and others carve their own cavity from a tree or earthen bank. And all that just begins to indicate the variety of nests used by birds.

Barn swallow nest. Photo by Bob Armstrong

Even among our local birds, the variety of nests is impressive. Some examples: Barn swallows stick a little ledge of mud pellets to a wall and line it with feathers. Cliff swallows take it one step farther and build a gourd-shaped mud nest with a narrow entrance. Juncos make a grass-lined cup on the ground, while hermit thrushes make a mossy nest in a shrub or small tree. Killdeer and spotted sandpipers carve out shallow saucers in the sand. Ducks generally make downy bowls on the ground, but some have taken to tree cavities. Woodpeckers chisel their own nesting cavities in trees, but tree swallows, nuthatches, and chickadees depend on old woodpecker holes for their nests. Solitary sandpipers take over abandoned robin nests and great horned owls often use old nests of red-tailed hawks.

Ruby-crowned kinglet nest. Photo by Katherine Hocker

Although some kind of nest is the norm for breeding birds, there are some oddball birds that don’t make nests. For example, emperor penguins put the single egg on the feet of the incubating male, and a fold of feathery belly skin drapes down to cover the egg; the male can actually shuffle around on the ice while holding his egg safely on his feet. Fairy terns in the South Pacific perch their single eggs on a bare branch, somehow keeping them from falling off. Cliff-nesting seabirds often just balance their eggs on a ledge.

Once the eggs are in a basket, so to speak, there is an inevitable constraint on the behavior of the parents. They (or at least one of them) are now tied to a specific place for a certain period of time while the eggs are incubated and, in many cases, while the chicks are growing up. Being tied to a central place that is the focus of activity gives human nest-searchers many clues about finding scattered nests; we commonly just try to follow songbird adults as they carry nesting material or food to the central place. Nest predators are likely to do the same thing: jays and ravens and crows are strongly suspected to do so, for example, and weasels and foxes surely can do the same.

A few birds avoid the central-place focus by dumping eggs in the nests of other birds, often other species. American cowbirds, Eurasian cuckoos, African indigobirds and honeyguides, and some ducks, for example, have become brood parasites, letting other birds rear their chicks. The foster parents still have the central-place focus, of course, but the brood parasites have dispersed their eggs among several foster parents and at least diffused the potential problem.

When parent birds are central-place foragers during incubation and chick rearing, the nest needs to be located within range of a sufficient food supply. Few songbirds fly more than a few hundred yards from the nest to find food, although American Dippers sometimes fly a mile or more along a stream. An extreme contrast is seen in some seabirds, such as albatrosses. For example, the Waved Albatross of the Galapagos Islands may fly more than sixty miles from its nesting site to find food; other species may fly even farther. The interval between chick-feeding trips may be several days, for some kinds of shearwaters, because the parents are ranging so widely over the ocean in search of food.


…a story of acid and eggshells

Our mothers and dentists tell us to drink our milk because calcium helps build strong bones and teeth. Of course we are not the only beings for whom calcium is critically important. Rodents often chew cast-off deer or moose antlers and the bones of dead animals to obtain this essential element. Corals build their protective shells of calcium carbonate—the basic component of coral reefs. The shells of mollusks and crustaceans have high proportions of calcium; think of snails, clams, oysters, mussels, shrimp and crabs, for example.

Birds need lots of calcium for building eggshells. The calcium requirements of domestic chickens have been well studied, and commercial diets for laying hens are calcium-enriched. But until recently, virtually nothing was known about the calcium needs of wild birds – and even now there is still much to be learned.

However, it is well known that acidic conditions lower the availability of calcium in water and soil, and by the 1990s the effects of acid rain (from industrial effluents) on forest and lakes in eastern North America and western Europe were clearly evident. Then avian ecologists began to wonder if acidification also affected nesting birds, which have high calcium requirements: ninety-eight percent of the dry weight of eggshells consists of calcium carbonate, some of which is gradually absorbed by the growing embryo.

Some birds, notably species with large bodies such as ptarmigan and geese, are capable of storing extra calcium in their bones, building up their calcium supplies well before the nesting season and then depleting that storehouse during egg formation. But small-bodied birds, such as songbirds, generally can’t do this, so they have to obtain the needed calcium at the time of egg laying and chick rearing. Spiders and sawfly larvae reportedly provide more calcium than flies or butterfly and moth caterpillars, which in turn provide more than aphids and beetles.

But sometimes none of these provide enough calcium for egg-laying females. Nesting birds commonly search far and wide for sources of calcium, sometimes at a considerable distance from their nests. Many small birds consume eggshells, crushed bone, or calcareous grit to supplement the diet. Some food items can provide high levels of calcium; for instance, snails, millipedes, and woodlice (isopods), but their calcium content decreases and they also become less abundant on acidified soils.

Several studies have now shown that low calcium supplies can be limiting to avian reproduction. Negative effects can include smaller clutches, delayed egg-laying, thin eggshells, shell defects, smaller eggs, lower hatching success, and slower chick growth. Evidence of calcium limitation has been found in many kinds of small birds, such as woodpeckers, swallows, chickadees, nuthatches, flycatchers, and dippers. Experimental supplementation of calcium, by providing crushed eggshells or bone in the diet, may eliminate such negative effects. Adding lime to acid soils can lead to more abundant snails and, thus, better reproductive success and even higher densities of nesting birds.

Calcium limitation sometimes can be found in areas without acid rain; for example, the well-known effects of DDT leading to pathologically thin eggshells and poor hatching success was due, in part, to the effect of that poison on calcium metabolism. And tree swallows normally consume low-calcium prey and have improved nesting success when the diet is supplemented.

Calcium availability is even important in determining the amount of spotting or speckling on bird eggs. Historically, spots on eggs have been assumed to provide some sort of camouflage, tending to disguise temporarily untended eggs. However, another kind of explanation of egg speckles is also possible: when calcium is scarce, eggshells tend to have weak spots. Many birds reinforce these weak spots with reddish or brownish pigments (byproducts of blood synthesis), creating the speckled appearance. Evidence for this explanation includes the observation that individuals of some species nesting in areas with limestone bedrock (and therefore good calcium supplies) produce eggs with few or no speckles, while individuals of the same species nesting in nearby non-limestone areas lay very speckled eggs. There may be still other explanations for speckled eggs, but a comprehensive explanation of egg pigments across all bird species awaits future synthesis.

Is all of this relevant to Southeast? Probably, but the exact relationship remains to be determined. Here, our soils tend to be very acidic, with low calcium content. But cedar trees, especially yellow-cedar, accumulate calcium in their tissues; old, senescent foliage falls to the ground, enriching the calcium supply in the soils below these trees and reducing the acidity there, thus creating little hot spots of calcium, so to speak.

These observations raise several questions in my mind. For instance, do nesting birds in Southeast suffer signs of calcium deficiency? Or do they have access to good calcium sources—and if so, what are they? Are bird eggs in Southeast more speckled than eggs of the same species elsewhere? Do nesting birds in forest with cedar trees show fewer signs of calcium limitation that those in forests without cedars? If so, does the decline of cedar forests in Southeast have repercussions for avian nesting success and density?


…often overlooked, but very important fish

This male stickleback is fanning his nest. Photo by Bob Armstrong

Last summer, I did a little fish trapping (with a permit) in some of the ponds in the Dredge Lake area. The most common fish in my traps were three-spined sticklebacks. These tiny fish-lets get no attention from most people, because they have no ‘value’ for sport or commercial fishing, but they are exceedingly interesting biologically and very important scientifically. The research literature on this species is vast, so this short essay provides only a sampling.

The three-spined stickleback is found in both marine and fresh waters; the marine form is anadromous, breeding in fresh water but returning to the sea. These fish are very small, seldom as much as three inches long, at least in fresh water. The males acquire bright colors in the breeding season, blue eyes and usually a red belly and sides. Intensity of the red color is an indication of health, and intensely red males are commonly preferred by females. In some populations, however, males have black breeding colors, or part black and part red; black males may not be preferred by females, but they are good fathers. Males build tubular nests of plant debris and invite females to lay their eggs there. The males then care for the several hundred eggs, fanning them to increase oxygen availability, guarding them, and so on, for about a week. It seems that males with the most intense breeding colors and males who court too long or too vigorously don’t have enough energy left to be good fathers—they invest more in getting eggs than in taking care of them once they have them.

They feed on all sorts of small aquatic organisms and, in doing so, can affect the composition and productivity of the entire lake ecosystem. In some lakes, there are benthic populations that exploit food that’s found near the bottom and limnetic populations that exploit food such as zooplankton that’s found in open water. These populations are genetically distinct from each other and differ morphologically in the position of the mouth and eyes, for instance.

Sticklebacks are an important source of food for many animals. Their many predators include fish (including their own species), birds, otters, and dragonfly larvae. To some degree, sticklebacks can protect themselves physically. The marine form has well-developed lateral plates and erectable back and pelvic spines. The spines help protect the fish, partly because the erected spines make the fish larger, in effect, so small-mouthed predators are less likely to attack, and partly because predators are more likely to release them after being stabbed by the spines. Otters are reported to eat the fish but leave a little heap of spines on the ground. Bird predators may be able to manipulate their prey so that the spines are made ineffective (But very young sticklebacks don’t have these spines; they develop as the fish grows—starting to appear when the young fish reaches about one centimeter in length.) The bony lateral plates provide another form of predator protection, rather like armor. These protective devices seem to work best against predatory fishes and apparently do not help much against dragonflies.

Marine sticklebacks have repeatedly invaded fresh water systems all up and down the coasts. When they do so, these protective devices are reduced or lost, in nearly every freshwater system these fish inhabit. Without the lateral plates, the fish make quicker starts to escape from an approaching predator, such as a loon or merganser. So there is a tradeoff between armored protection and ability to escape by fleeing. Pelvic spines are often much reduced in lakes that lack predatory fishes, particularly when the lake water is low in calcium (it takes calcium to build bones and spines). If predatory rainbow trout are introduced to these lakes, populations of these poorly protected sticklebacks decline.

Most predators are not capable of wiping out whole populations of sticklebacks, but just winnow out the slow or poorly protected ones or those that live in a particular habitat. However, one predator seems to be responsible for driving several stickleback populations to extinction. This rapacious predator is the northern pike, which was foolishly introduced to Alaskan lakes in the 1990s. In some lakes, no sticklebacks are left. A few other lakes, with deeper water, still have sticklebacks, mostly the limnetic forms, largely because the deep water gives them some space to escape from the pike.

These little ‘no-account’ fish are scientifically important for at least two reasons. One is the speed at which freshwater adaptations are acquired. The classical view of evolution is that it is very slow, requiring thousands of years. Yes, some evolutionary changes have taken a long time. But the sticklebacks provide one example (of an increasing number) of very rapid evolution, with morphological changes occurring in just a few years. For example, Middleton Island was uplifted by the 1964 earthquake, creating new beaches and ponds. Sticklebacks from the sea have colonized those freshwater ponds and lost their pelvic spines and lateral plates. Sticklebacks recolonized one Alaskan lake in the 1980s. In 1990, most of the fish still had lots of lateral plates. But by 2001 (less than twenty years after arriving and only eleven years after the first sampling), most of the fish had few lateral plates.

Interestingly, the genes involved in these changes are not always the same in every freshwater system, indicating that there are multiple ways of achieving the same adaptation. In fact, different populations of sticklebacks in different freshwater systems are often quite different genetically, and probably really represent different, very closely related, species. The dynamic evolutionary changes in these populations offer scientists wonderful opportunities to study both pattern and process of evolution and species formation.

Another reason these fish are scientifically important is that the entire genome has been sequenced, so we know the precise composition of their DNA. It turns out that about 70% of their genes are just like ours. This is likely to have medical implications: If we learn which genes control what features in the fish, there is then a possibility that some of those genes also control similar features in humans. For example, if certain genes control the loss of bony plates and spines in the fish, could those genes perhaps be involved in human bone deterioration (as in osteoporosis)?


a productive meander on Gold Ridge

As I slowly meandered up the Gold Ridge trail above the tram, a grouse stepped out of the brush and strode calmly up the trail ahead of me. We walked together but apart for many yards. Next to the trail, a young marmot sat with its head out of its burrow, watching the approaching trail-walkers. As the grouse drew near, the youngster hurriedly pulled back underground. When the grouse passed by, the marmot crept out a little way and carefully watched the bird go on up the trail until it was out of sight. The marmot was quite unconcerned about the human standing next to the burrow—the big worry seemed to be the grouse! Maybe the young marmot had never before seen such a bird, while the humans were too common to warrant a second thought?

Fall is in the air, although it is only the middle of August. (Surely, it’s too soon??? I’m not ready for this!) Alder leaves are brown and crumpling; cottonwood leaves are bronzed. Robins are flocking on beaches and in blueberry patches, and warblers of several species keep company while searching for bugs in the shrubs. Fireweed has gone to seed, spectacularly. During our recent spell of sun, the fluff on the seeds was showing off, especially when backlit. I’ve noticed some visitors admiring the display of open seed pods; they didn’t know what it is, but they saw how pretty it can be. I like to look closely at the open pods (when they are dry) that still contain seeds; they and their fluff are arranged very artistically, arching across between the open sides of the pod. Of course, to the amusement of my hiking companion, I had to help the breeze blow some seeds away to their destiny.

It was a perfect fall day on the ridge. A few hawks migrated along the ridgetops and ravens cavorted in the breeze. The dwarf willows had gone to seed, making mats of seed-bearing white fluff against the dark green of the leaves. Most plants with wind-dispersed seeds bear them high above the ground, where the wide can reach them, but somehow the prostrate dwarf willows must manage to send their seeds aloft despite being so close to the ground. Many of the wildflowers were past blooming too, although we found some louseworts, blue harebells, yellow arnicas, lavender fleabanes, and lots of yellow groundsel. Most of the monkshood flowers were the usual intense purple, while others were purple veined with white.

The best show was stands of the sky-blue broad-petaled gentian. Under sunny skies the flowers opened, and we looked attentively for visiting bumblebees. No luck—the bees were visiting the groundsels, fleabanes, and arnicas. August had seen drenching downpours for days and days, so this was perhaps the first chance for these alpine gentians to open and be pollinated. Did they miss their chance this year?

Photo by Bob Armstrong

Juvenile marmots were out foraging in many places, intent on filling up before hibernation. One juvenile carried a mouthful of dry grass for a hibernation bed. The few adults we saw were lounging on rocks in the warm sun, letting the kids do the work.

Part of the Parks and Rec hiking group went on up Gastineau Peak, while the rest of us found a cushy spot for lunch at the end of Gold Ridge. The marmots could keep their rocks—we chose a springy cushion of mountain heather on which to sprawl and soak up the rays. It doesn’t get much better than that!

Well, perhaps some cookies….

Apical dominance

which leader will lead?

Did you ever wonder how it happens that spruce trees typically have such nice, conical tops? The uppermost shoot, called the leader, produces a particular hormone that suppresses growth in the branches below, most effectively in the branches nearest the leader. The effect dwindles to negligible on the lowermost branches. Voilá! –a conical top to the tree.

If the leader is damaged—chewed by a porcupine, or invaded by an insect, or cut off, the next-lower branches rapidly start to grow, and the damaged tree-top may now display two or three new leaders, until one of them might eventually take over. The dominance of the leader at the apex is disrupted, allowing lower branches to grow more. A similar but usually smaller effect may occur on the end of branches.

The effect of that suppressive hormone is countered by another hormone, one that encourages growth. The balance between the two hormones differs among species of plants, so not all plants grow with conical tops. But one can see the same phenomenon in other trees: for example, look at the cottonwood trees that have been decapitated to prevent them from growing up into the power lines. The remaining branches grow well and begin to reach upward more than before the top was removed.

The strength of apical dominance and the effects of release from that dominance vary among species, although very few general patterns have been discerned (such as effects of habitat, geography, climate, or life history). And the evolutionary pressures that govern both the strength of apical dominance and the effects of its release have been little studied. So I’ll just present a few examples here, to illustrate some of the variation and complexities.

Herbivory, by grazing and browsing animals, often crops off the tops of a plant, ending the dominance effect and leading to branching, which frequently increases the production of flowers and fruits (this is why gardeners commonly pinch off the tops and ends of branches, making a plant bushier and potentially more fruitful). But this begs the obvious question: if branchi-ness is good for the reproductive output of the plant, why was apical dominance so strong, suppressing the branches? Presumably, there are other advantages associated with apical dominance. For example, if the plant allocates resources not to branches but to good vertical growth, this can be advantageous by reaching more light and increasing the survival of the plant, which would eventually lead to greater lifetime reproduction. That option might over-ride the advantages of short-term increased fruit production in most circumstances. Nevertheless, the ability to respond to release, if herbivory occurs, is itself a useful trait. In other words, the evolutionary fitness of a plant may be better with strong apical dominance in the absence of herbivory, but better with release when herbivory occurs.

The club moss (Lycopodium) grows along the ground, sending up short vertical shoots. If the main upright shoot dies, dominance is reduced, and lateral spread increases. The horizontal growth then eventually reaches a new location and a new upright shoot forms there. A living, dominating shoot is successfully exploiting a good site, but when it fails and releases lateral growth, the individual plant as a whole may survive by reaching a new site. In short, the dominance is advantageous in certain circumstances but not in all.

In a species of fireweed (Epilobium in some taxonomies), strong apical dominance leads to good seed production and good seed dispersal (by wind) in areas where competition for light is severe, giving an advantage to good vertical growth and reduced branching. However, this only works where soil nutrients are sufficient to support such growth; in poor sites, which cannot support good growth, the potential advantages of apical dominance may be negated. Again, the advantage of apical dominance is seen in certain circumstances, in this case related to resources.

The relationship between resource availability and the effects of apical dominance are seen also in bearberry (Arctostaphylos uva-ursi). Here (in contrast to fireweed), apical dominance is weak in rich habitats, the plants are much-branched, and the plant is exploiting its present location to the fullest possible extent. In resource-poor habitats, apical dominance is strong, as the plant allocates its limited nutrients to growing in situ: release from apical dominance, perhaps by herbivory, leads to increased branching, increasing the chances of the plant stretching out to find a better site.

These few examples serve to emphasize that multiple factors interact to determine the strength of apical dominance and the consequences of release from that dominance. No wonder that researchers have yet to find general patterns in the ecology of apical dominance. The physiology is well understood; now to learn the whys and wherefores!

Mate choice (1 of 2)

…it’s complicated!

When a female wood frog, ready to mate, arrives at a small pond full of singing males, she is jumped by the nearest male, who grabs her around the neck and locks his thumbs together, so he cannot be dislodged. She apparently has little or no choice in the matter—it is first come, first served.

But in many vertebrates, females can and do choose their mates. Sometimes choice is based, at least partly, on the male’s property—his territory, defended against other males and providing nest sites or food sources or protection from weather. For example, male yellow-headed blackbirds carve out territories in a marsh. When females arrive, they cruise around, checking out each male and his property. One of the factors determining their choice of mate is the availability of suitable nest sites at the edges of clumps of cattails or bulrushes—the more edges he owns, the more females he gets.

Males of a wide variety of insects present females with nuptial gifts of food, and females select males on the basis of the size of the gift. The female gains energy for egg production, at least, and if the ability of males to find good gifts is hereditary, she also may get good genes for her offspring.

Sometimes females base their choices on the qualities of the male himself. It might be his song, or the vigor of his courtship dance, or his colors. For example, in the Lower Forty-eight, the size and brilliance of male plumage pattern is the basis for choice by female house finches. Male house finches have red feathers on the head and chest. Females prefer males with intense red coloration and large red chest patches. The red pigment is carotenoid-based, and carotenoids come from the bird’s diet, so the red depends on what the male has eaten (and his ability to convert components of food to red pigment). Thus, house finch females may be choosing males that are the best foragers or have the most efficient metabolism.

A small warbler called a yellowthroat nests in marshes and shrubby swamps. Males have black masks and yellow chests. Careful research has shown that yellowthroat females have marked preferences, but that these preferences differ from region to region: In Wisconsin, females like males with bigger black masks, but in New York, they like ‘em with bigger yellow chest patches. What the females get from making these choices is not clear.

Female preferences also affect the ability of males to obtain extra-pair copulations (many socially monogamous birds engage in very active mating activity outside the pair bond). Mountain bluebirds, for instance, vary in the intensity of blue plumage, and males with brighter blues are more successful in attracting extra-curricular females. Similarly, intensely colored male tree swallows and yellow warblers are preferred by females that copulate with males outside their pair bond.

The bowerbirds of New Guinea and northern Australia have gone a step farther, by transferring the signals to females from themselves to elaborate structures (bowers) that a built solely for the purpose of attracting and courting females. Different species construct bowers in differing shapes—avenues, towers, huts—and decorate them with colorful objects. Each species uses different kinds and colors of objects; some like blue, some like white or yellow, and so on. Within each species, female bowerbirds cruise around and visit the bowers of the males and judge each male on the construction and decoration of his bower. After she makes her choice and mating takes place, she goes off to build a nest and rear chicks by herself.

What’s the payoff to females for making these choices? In some species, there is a direct benefit in terms of resources such as nest sites or food. In other cases, males with brighter colors turn out to be better providers for the offspring. When males do no parental care, females might at least get good genes for their offspring. And in other cases, choosing a ‘sexy’ male might mean that the sons of the choosing female will also be sexy and successful in attracting females. The so-called sexy-son hypothesis obviously requires that the attractive characteristics are genetically based and inheritable.

Of course, male animals make choices too. Males of some species choose on the basis of color or pattern, just as females do. For instance, for whatever reason, male barn owls prefer to mate with females that have lots of lovely black spots on their white breasts. However, in many vertebrates, males seem to be somewhat less choosy than females.

When female creatures choose males, we do not suppose that the choices are conscious in the human sense. (Nor can we say that all human female choices are necessarily conscious!). All that is required is that there is variation among males and that females can discern the differences and act accordingly.

The result of mate choice (and of the competition to be chosen) is, in the big picture, an incredible diversity of color and form in the animal kingdom—diversity that is not directly related to making a living or simple survival but, instead, is related to mate selectivity and being attractive to the opposite gender.

Mate choice

part 2 of 2

Last week I wrote about female animals making choices of mates on the basis of the male’s property, nuptial gifts, songs and dances, or physical appearance. Those choices occur before copulation (in animals with internal fertilization: sperm meets egg inside a female) or spawning (in those with external fertilization: sperm meets egg outside the female). However, there are also some much subtler forms of female mate choice that have been revealed by recent research. These choices occur during or after copulation or spawning.

Here are a few examples: In some fruit flies, sperm size varies and females discriminate against small sperm—and thus against males that make small sperm. In ducks and fruit flies, preliminary studies suggest that females may be able to kill sperm that come from copulation with unwanted males. Females can eject sperm after mating in certain damselflies, flour beetles, flies, and songbirds, ridding themselves of undesired sperm and leaving themselves then available for a preferred mate.

One of the best-studied examples comes from a free-ranging population of chickens, of a breed similar to the red jungle fowl that is the ancestor of domestic chickens. Roosters maintain a strong dominance hierarchy among themselves, and hens prefer to mate with high-ranking roosters. These males provide hens with better courtship feeding, protection from predators, and protection from sexual harassment by subordinate males. Dominant males leave more descendents than subordinate males, because they mate more often. Dominance is heritable, so their sons are likely to be preferred partners also.

Subordinate males, however, obtain some copulations by forcing the hens to mate, even when the hens resist. When accosted by a subordinate male, hens make a distress call, which induces dominant males to disrupt the copulation attempt. In addition, even if the subordinate male achieves copulation, hens can eject his sperm immediately, even before he dismounts from her back. Then she is free to mate with a preferred, dominant male and the dominant male’s sperm can fertilize her eggs.

When female salmonid fishes release their eggs during spawning activity, the eggs are accompanied by ovarian fluids that can affect sperm swimming speed, longevity, and motility. Arctic charr females can change the composition and effect of their ovarian fluid, depending on just what male is trying to fertilize her eggs. Different females of rainbow trout may produce ovarian fluid with differing effects on sperm motility, and thus some females may be able to be choosier than others.

It is even possible that plants may be able to mate selectively with certain individuals. It is well known that many plants are self-incompatible—that is, they reject pollen from themselves or from genetic relatives (which share their genes). But, in addition to this common form of selectivity, experiments have indicated that some plants discriminate among the pollen grains of different unrelated pollen donors (males), thus allowing only certain males to fertilizes the ovules.

These kinds of subtle interactions that occur during or after mating have only been discovered rather recently. Many more possibilities in this hot research area are now being studied in a wide variety of organisms. The take-home message from these studies is that females are not necessarily passive receptacles for sperm, but at least in some cases they are able to exert what is called cryptic female choice.