Cardinal robes

As winter marches towards spring, two male northern cardinals have set up territories in our yard, keeping an eye on their mates but not getting along with each other.  They watch, emblazoned against a blue sky, from a favorite perch in bare trees. Catching sight of each other they ‘see red’, puffing up scarlet robes which get more brilliant as the breeding season approaches.

Why does red stand above all others, sometimes a sign of menace, sometimes a symbol of courage, and often expressing the power of joy and passion?

Cardinal
Cardinal in our yard

Red brake lights, red stop lights, red London buses, red light district, red planet, Redcoats, Red Army, red flags, cardinal bishops, Coca-Cola … the list goes on.  A color so intense it seems to sear the back our brain, where circuits originating in the red cone receptors of the retina are processed in the visual cortex. Would red convey a smaller emotional charge if blood was blue or fire green?

There’s nothing in a color beyond a wavelength – apart from how the brain perceives it. Hot peppers come in green as well as red, and red letter days and red herrings are fairly benign! Most mammals lack the red cone, seeing gray instead, but they are capable of as much passion as any primate or bird that has full color vision.  Bulls charge at a waving ‘gray’ flag.

To ask how a bird gets as hot as a cardinal is like asking for a Just So story – How the leopard got his spots … How the camel got his hump? Well, it’s the diet, dum-dum, because everyone knows, “We are what we eat.”  And looking around the yard, there is ostensible evidence everywhere.  Holly and Nandina bushes tempt hungry birds with dangling crimson berries.  But wait, biologists seldom answer a simple question with a straightforward story. Most of the intensity in these berries is from anthocyanin pigments which are not absorbed intact into the bloodstream. If berries are not wholly responsible, perhaps birds get their color from something else in their diet – like insects.  Errh … not the cactus juice-sucking insects that gave us cochineal for the pantry and for dyeing the tunics of Redcoat officers.

Most old sayings become threadbare in the light of research, and with a few exceptions there is no simple relationship between what we eat and how we look because of the rumbling process of metabolism going on inside.  Otherwise some of us would look like … well, I leave that to your imagination.

Nandina
Nandina

What then lends cardinals their color – and to so many wonders in nature, from fall leaves to appetizing vegetables?  Bugs Bunny would say that carrots are a good place to begin nibbling:

“Oh, carrots are divine, you get a dozen for a dime …”

Nearly two hundred years ago, a German student, one Heinrich Wickenroder, extracted from carrot juice a “yellow fatty oil with carotin” which dissolved in ether but not in water.  He won praise from his professors who thought it might fend off gut parasites, which were rampant in those days and still all too common in domesticated animals and wildlife.  Over time, his discovery expanded into a family of related molecules from plants, called carotenoids, including lycopene, lutein, and beta-carotene, which is the precursor of vitamin A. If I was asked to score my favorite molecules, carotenoids would be in the top ten beside DNA and chlorophyll.

Carotenoids are needed for photosynthesis, so they are almost ubiquitous in the plant kingdom, from whence we satisfy our own needs.  They prevent blindness, promote fertility, inhibit cancer, block oxidation, boost immunity, and make dandies of our avian friends in the yard.  I love the biological symmetry: carotenoids make plumage conspicuous in birds and give the power of vision so their mates and rivals recognize it and we can enjoy it (in fact, vitamin A is only responsible for the rod cells). Because we can’t make these virtuous molecules in our bodies but have to absorb them from our diet, the food police keep heaping more fruit and veg on our plates.

Northern cardinals obtain their supply from an omnivorous diet of berries, seeds, and insects, while American goldfinches subsist on strictly vegetarian fare.  When Cornell ornithologists reduced red carotenoids in the diet, cardinals grew pale, and goldfinches turned orange when yellow carotenoids were deficient. But changing diets didn’t go as far as switching their colors because the gut is wise to the vagaries of nature (and researchers) by converting one type of molecule to another.  It’s obvious that diet alone can’t explain everything because female cardinals eating the same food are so much drabber than males.  It takes testosterone to make a male hot.

Red grouse are hardly that.  A game bird looking like a large cardinal in the open heather would soon end in a vixen’s den or on a Scottish table. But the males have a small red comb, a token that performs the same service as the cardinal’s feathers.  Since grouse are plagued by roundworms and ticks, ornithologists wondered whether treating the males with anti-helminthic drugs could improve their breeding performance as well as their overall health. They did.  After ridding them of parasites, the birds absorbed more vitamins from their food which, in turn, increased the color intensity of their combs.  The little red flag on their heads was more attractive to the hens, who thought they would make healthier partners.  Female cardinals get the same message. They can’t be hoodwinked by a frail male because carotenoids painting the breasts of males bursting with blushing pride make honest birds of them.

Next Post: A Death Observed

A Dog’s Dinner

Banana Joe stole the show!

No, not the LA radio presenter, I mean the affenpinscher from Attleboro who won Best in Show last week at the Westminster Dog Show in NYC.

I’m not a pooch person, prefer big mushy dogs, but Joe the affenpischer who looks like a cross between a toy and a monkey is easy to love. And a monkey dog he is (ein Affe, a monkey). Like monkeys, Joe and our Golden enjoy a banana, which is not so surprising if you consider it is a perfectly natural food for their cousins – wolf packs in Minnesota and Alaska.  Erhh!

We changed their dietary preferences after the first wolf cub was adopted by a human family.  I ought to pause to correct myself because dogs can’t express preferences any more than I could as a London schoolboy. It is only a slight exaggeration to say that we were served Dickensian gruel for school lunch. I remember peering through the kitchen window at the cooks watching over steaming vats of bubble and squeak made from yesterday’s left-overs and stirring custard thick as tar but not so smooth. It was ‘Hobson’s choice’, or, in other words, no choice at all, just as it has always been for our dogs.

Until the food industry realized there was a canine market, most dogs had to make-do with human left-overs, living hopefully for a bone flung their way with a morsel of meat on it.  As members of the Order Carnivora, their ancestors enjoyed a high protein diet before they were domesticated around 10,000 years ago (some put it earlier). Neolithic people were then switching from hunting and gathering to agriculture, growing various cereal crops in the Old World, sweet potato, corn and beans in the New, and – yes – bananas in New Guinea.  Growing-their-own enabled them to form settlements with greater food security, and afterwards their diet became much richer in starch. So did the dogs’.

A new study of whole genome resequencing shows what an impact this change had on canine genetics. There are not as many genetic differences between dogs and wolves as you might think from their manner and appearance, but significant differences were found between genes involved in brain function and the digestion of starchy and fatty foods.  It seems that a genetic bottleneck occurred in the early prehistory of domestication. Animals with gene variants that favored compliant behavior and efficient starch digestion squeezed through, and those survivors became the founders of modern dogs. The wild-type wolf genes disappeared because dogs lacking genes that were better adapted to the new life were either kicked out for bad behavior or didn’t thrive on the new diet. Lying at your fireside is an example of how we sculpt the evolution of species.

Lilah
Lilah’s turn

Now to sweeter talk. Sweet is one of our five senses of tastes, but long before we celebrated it by inventing confectionary it was probably beneficial for distinguishing between good and bad food. Since wolves will occasionally eat vegetable matter it’s not surprising that they share the same sweet taste receptor gene, Tas1r2, as ourselves, and dogs inherited it from them.  Other mammals can taste sweetness too – raccoons and of course bears – but not all. Cats can’t taste it because their Tas1r2 is pseudogenized (meaning it doesn’t function), and likewise in sea lions, otters, dolphins, and hyenas.  Since they are flesh-eaters that swallow their food whole there’s no time for tasting and therefore no point in having a sweet taste receptor. But biologists who love to tell a commonsense story are often embarrassed by an ugly fact that threatens a beautiful theory. We might expect a species that sips its food to have a well-developed sense of taste, but apparently vampire bats don’t have a sweet tooth in their heads.

Now back to bananas and Banana. Our dog, Lilah, has a more discerning palate than her owner because she turns her nose up at green bananas which are just full of starch but she will happily chomp on yellow ones in which much of the starch has been converted to sugar.  We throw away overripe bananas but, given the chance, she will gorge on them knowing they have the most sugar.  The French clearly know their bananas too because their grocery stores have premium prices on fruit with brown skins.  Belle banane.

Banana Joe deserved a better reward. He was taken to a swanky Manhattan restaurant where he was served filet mignon to celebrate victory. I expect he was glad to leave starch behind for a day if only to prove he is still a card-carrying carnivore.

Next Post: Cardinal robes

Winter bee-line

T.S. Eliot was wrong: February is the cruelest month, not April.

When one of our sister bee hives in the Yorktown churchyard was opened recently the entire colony was found to have died. Several thousand bees were strewn across the frames and base. Our local expert warned that this is a tough time of year for bees, which can starve to death despite having honey in the comb or kindly keepers who leave candy for them. Sometimes, he told us, they starve within inches of plenty.

This sad news put me in mind of a teacher’s favorite story when I was a fifth grader in England. A hundred year ago, Captain Robert Scott leading a small band of Antarctic explorers was returning to base feeling dejected after being beaten to the Pole by Norwegians.  During a ferocious blizzard they froze to death just eleven miles from the safety of a depot, their bodies still entombed to this day in the Ross ice shelf which is slowly migrating to the sea.

I always thought Captain Oates played a supremely heroic role before their final camp because he walked out to his death so that his frost-bitten legs wouldn’t slow the party down. That’s another reminder of the life of a bee, who lays down her life for the colony with one, and only one, sting. Altruism in nature was something that used to stick in the gullet of evolutionary theorists like a fish bone, but it’s not such a mystery in bees because they are genetically-related. Self-sacrifice makes genetic sense if it helps siblings to survive. But to think that each bee is as much an individual as, say, a dog or ourselves is misleading: a hive is more like a superorganism with different castes of bees playing roles equivalent to the organs and limbs of our bodies. Put that way, I don’t feel so guilty when I accidentally squash a few of the ‘girls’ putting the lid back on their hive.

Perhaps self-sacrifice in bees is more like the shedding of a lizard’s tail after it is grabbed by a predator. On second thoughts, that’s not such a brilliant analogy.  Bees are not genetically identical, like clones, because although they are all derived from the same bag of genes in the queen the genes have been reassorted by meiosis in eggs.

Bee
Bee up close

Our surviving hive is thriving (the other was mysteriously evacuated last September). On warm days foragers leave for polligrinations over several square miles of territory. They return with payloads of nectar and golden sacs of pollen stuck to their body, which are passed to nursemaid bees to feed the larvae. Even in mid-winter they find flowers when I can’t see any.

While most insects and other cold-blooded creatures hibernate to conserve energy, bees are busy whenever the temperature rises above the forties. It’s imperative! Already sensing the longer days, they have started to expand their colony in a race against time. The hive needs more workers; it must raise numbers from a few thousand to forty thousand or more so it can manufacture enough honey to store for next winter (and for us!).

The queen lays up to 1,000 eggs per day, about one every minute. Like poker played for high stakes, she goes all in. It takes 42 days for an egg to grow into an active worker, so she is fully employed now preparing the hive for the large flows of nectar starting in March. Now when I see a hive standing cold and silent I know the heart of the superorganism is beating fast while almost everything around is in the deep sleep of winter.

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 Knight Bruce has lent me a grand observatory hive; and I am going to watch.

Letter from Charles Darwin to his son, Willy (May 26, 1858)

Next Post: A Dog’s Dinner

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