Cardinals: why they’re red and their ability to act as PFAS sensors

Birds are enviable. Although they can’t integrate the Lambert function, they’re far more musical than rappers and far more in tune than most of us. They build nests without mortgages and fly despite COVID. In fact they will always fly without having to sit, without hoping for a window seat. We can only dream of the true bird’s eye view; it’s at modest heights, unlike that of Icarus, and it shifts with a wavy motion as every bird surfs on an invisible medium.

On Monday, I was on my skis and with a camera strapped over my shoulder. A passerby complained about how the squirrels who were stealing from the sunflower seed-filled feeder were scaring away the cardinals. After a lap around the woods, the squirrels were gone, and I decided to hide behind some reeds and wait for the cardinals to appear. It didn’t require much patience because a woodpecker and chickadee appeared in the meantime.

Here’s the first arrival.

Ever wonder why cardinals are red?

The source material for the red pigments are carotenoids from their diet. Carotenoids are yellow, orange, and red pigments synthesized by plants from basic isoprene units ( 5 carbons). The most common carotenoids in North American human diets are α-carotene, β-carotene, β-cryptoxanthin, lutein, zeaxanthin, and lycopene. Of these 6, are four non-red pigments that are also part of the cardinal diet. They are the following.

Some mutant cardinals, which are yellow in color, can only oxidize the oxygen-hydrogen group to a a double-bonded oxygen. Since the keto group’s π bonds are not conjugated with the rest of the π bonds, the gap in energy levels for electrons isn’t reduced enough to change the color of the molecules to red. Here are the compounds the mutants form.

Red cardinals, unlike their yellow counterparts, do not lack a ketolase enzyme known as CYP2J19. What this enzyme does is attach a keto group in the right place to conjugate the rest of the π bonds, forming the following reddish pigments:

Cardinals can be used to monitor Per- and polyfluoroalkyl substances (PFAS) in a certain region because they don’t migrate, and the birds’ large size means you can take blood samples without harming them. PFAS are a group of man-made compounds that have been manufactured since the 1940s to act as water repellents and to serve a variety of functions in industry. The class of compounds, due to their strong C-F bonds, are very persistent in the environment and can accumulate in the human body over long periods from consistent exposure to very small concentrations. There is evidence that exposure to PFAS can lead to adverse human health effects. Concentrations of the following types of PFAS: PFOS, perfluoroheptanoic acid (PFHpA), and perfluorononanoic acid (PFNA) in rivers correlate strongly with human population density. So the research group of Marie C. Russell hypothesized that they would find a higher concentration in the blood serum of cardinals in Atlanta than in those of the Big Island in Hawaii. Surely, enough they measured significantly higher median concentrations of four PFASs and significantly higher detection frequencies of seven PFASs in the cardinals from Atlanta.

One third of all birds in Atlanta are carriers of the West Nile virus. One of the reasons that the transmission rate to humans is very low could be the presence of cardinals. Cardinals, even though infected with the virus, have immune systems that greatly reduce the amount of virus circulating in their blood. It’s why cardinals are dubbed as “supersuppressors”. But given that in higher concentrations, PFAS can compromise immune systems, it’s one more reason that concentrations of PFAS should not be allowed to keep bioaccumulating. Otherwise cardinals may no longer protect us.

Sources:

• Carotenoid pigments in a mutant cardinal: implications for the genetic and enzymatic control mechanisms of carotenoid
  metabolism in birds The Condor 105:587–592
• Genetic basis for red coloration in birds https://www.sciencedirect.com/science/article/pii/S0960982216304018
• Per- and polyfluoroalkyl substances in two different populations of northern cardinals https://doi.org/10.1016/j.chemosphere.2019.01.112
• Micronutrients. Oregon State University. https://lpi.oregonstate.edu/mic/dietary-factors/phytochemicals/carotenoids
• Cardinals and West Nile Virus https://www.cidrap.umn.edu/news-perspective/2016/08/cardinals-may-protect-people-west-nile-virus 

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Zebra Finches At a STEM Conference

In the spring of 2016, I attended a STEM conference. Expanding the acronym as science, technology, engineering and math doesn’t shed too much light on the intentions and philosophy of STEM.  The premise is that math, science and technology subjects should not be taught in isolation; there should be more integration and emphasis on applications. All of this is largely inspired by the job market’s need for a larger number of better-trained people in these specialised fields. It all seems reasonable as long as the approach is not taken to an extreme.

A society, regardless of its bent, functions best when a wide range of talents are cultivated, even if they seem to serve no practical purpose. Similarly, we have a healthier situation in schools and colleges when educators don’t sail on the same ship. There was at least one organiser at the conference who shared my views because a particular lecture went against the grain of STEM.  95% of the auditorium featuring the lecture was empty and attended mostly by the speaker’s university students, a couple of bird-lovers and a little cluster of Canada Wide Science Fair attendees. Rudely, the latter group even walked out before it ended. But if you stick to the premise that attendance at public events is very often inversely proportional to its quality, you don’t worry about numbers.

Parentese or “baby talk“ is far from being just indulgence on the part of parents. In humans it helps draw attention from babies and promotes the learning of speech. Regardless of language, there are universal characteristics of parentese. Voice pitch is modulated; speech is slower, more repetitive and more attention-grabbing than adult-talk.

Image of baby zebra finch from http://www.singing-wings-aviary.com/zebrafinches.htm

A similar situation arises in a small Australian bird known as the zebra finch. For those of you unfamiliar with the small bird, one of its distinguishing characteristics is its song, which is reminiscent of the squeaky sound of a rubber duckie. With their form of baby talk, adult zebra finches change their vocalisations when singing to young birds. They slow them down and use more repetition. The juvenile finches in return pay more attention to such songs than to those used between adults. In their young lives, they use the simpler versions. With time, in the physical presence of adults, the chick’s song converges with that of their tutor. When zebra finches were isolated and exposed to mere recordings, they developed different songs.

The social interaction between tutor and chick stimulates communication between the midbrain’s ventra legmental area (VLA) and regions of the cerebrum. The VLA is partly a reward centre and uses dopamine.  When humans acquire language, neural bridges of that type are also made. In case of the finch, the evidence for such a pathway comes from the fact that in the absence of tutor’s physical presence, a marker for gene expression of catecholamines (which include dopamine) remained inactive.

Another revelation which made my morning was that the zebra finch researcher had originally majored in economics, reinforcing my notion that to get to an island you don’t have to board any specific boat.

Fertility Kits and Giraffes

On the sixth human chromosome, there is a gene that codes for the glycoprotein leuteinizing hormone (LH), produced by the brain’s anterior pituitary gland. LH is less known for the role it plays in male testosterone production, and more on the minds of women who are trying to conceive. Its concentration peaks like a sole stalagmite only at the time of ovulation. When this happens, it stimulates the release of an egg from the ovary.

Unlike some other animals, humans cannot directly rely on their senses to detect the hormone. To see signs of  its presence in urine, they have to use ovulation kits* which contain antibodies that bind to LH. A study of 155 cycles from 35 women revealed that LH surges mostly between midnight and early morning (37% between midnight and 4 AM, and 48% 4 and 8 AM)

Jacobson’s organ, a.k.a the vomeronasal organ, in snakes, giraffes and other animals is capable of detecting LH. In giraffes, the organ is at the base of its nasal cavity. The male takes the female’s urine into its mouth. If LH is detected, the signal travels directly to the brain’s amygdala, one of the centers of emotional learning. The excited giraffes subsequently engage in a slow neck-rubbing form of foreplay before the male mounts its mate.

The pair mating in the adjacent picture belongs to reticulated giraffes, one of four species that can be distinguished from their different spots. The latter do not only serve as camouflage against their background by breaking their overall outline. The blood vessels and sweat glands under each spot keep them cool from either the Sub-Saharan or southern African heat.

Source: Giraffe Conservation Foundation

An estimated one million giraffes roamed the African continent in the 1700s. There are now only 110 000 due to deforestation, fragmentation of their habitats, war and poaching. A single 2000 pound giraffe yields up to 650 pounds (295 kg) of meat, but sometimes they are killed only for their tales, a status symbol in some cultures.

A giraffe’s stomach like that of the cow has four chambers. Leaves, which serve as their main food, enter the first chamber. Then coarse bits are regurgitated, chewed again and re-swallowed. Finally the cud passes through the three other chambers and through an 82-foot ( 25 meter) large intestine.

According to fossil evidence, 6-20 million years ago, ancestors of the giraffes had not yet evolved their characteristic long necks. In This View of Life, Stephen Jay Gould points out that Darwin finally used the giraffe’s neck in a discussion of natural selection in 1868, nine years after he explained the evolutionary mechanism. Each small increase in length, he said, would improve access to leaves. But he recognized that he was speculating about the supposed gradual elongation and necessary accompanying changes in anatomy.  Without a knowledge of genetics, Darwin had not discounted Lamarck’s version, unlike the story told in science magazines and high school textbooks.

*Some tests also measure another hormone — estrone-3-glucuronide (E3G)

Sources:

Detection of ovulation, a review of currently available methods https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5689497/

Histological features of the vomeronasal organ in the giraffe, Giraffa camelopardalis. https://www.ncbi.nlm.nih.gov/pubmed/28094892

https://giraffeconservation.org/giraffe-species/

Giraffes. National Geographic. October 2019

Gould, Stephen Jay. The Tallest Tale. Natural History. May 1996.