Sunday, December 30, 2012

Of Mice and Oogonial Stem Cells

Note: This program first aired on Deecmber 29, 2012.

I was asked by a listener recently, if female chickens are born with all of the eggs they will lay over the course of their lives, like human females are. This made me wonder if all females have this characteristic, if that is a distinguishing feature of being female—that the cells that become the gametes form in the embryo, and are not replenished as the individual matures. Conventional wisdom states that we females have a set amount of eggs (more than likely more than we will release in the reproductively active period of our lives), we do not make more as we go along. This is in contrast to males, who are able to continually replenish their supply of gametes.

We need to pause for a moment and return to high school biology, and revisit the concepts of meiosis and mitosis. Our cells have two sets of DNA in them, one from our mother and one from our father. That DNA is in the form of chromosomes. Mitosis is simple cell division, we get two cells when we started with one. The chromosomes in the cell all line up, split in half, and each half then replicates itself in the new cell; each new cell ends up with two sets of chromosomes, just like the parent cell had. Meiosis is cell division that results in the formation of gametes. What makes gametes special is that they have only one set of DNA in them, a mash up of DNA from the mother and the father. In meiosis, the chromosome pairs line up, swap DNA and then get separated from each other into two separate cells. Then the chromosomes themselves split in half, and the halves end up in two more cells, yielding a total of four cells from the original one, each with a single set of genetic information. That is what makes gametes gametes, they have only one set of DNA and they need to join with another gamete cell to get a full set of genetic information, enough to make a new individual. The traditional thinking has been that , at least in mammals, meiosis occurs in the ovaries of the embryo. As a female’s reproductive organs are forming, meiosis is going on, and all the eggs the female is going to have are formed then.

Before we get to the chicken issue, I have to break it to you that the conventional wisdom here has been shown to be wrong. As early as 2004, researchers discovered that in mice, the females seemed to be able to maintain a supply of healthy living eggs, even when fed toxins that would kill their follicles. This meant that the mice could generate new eggs, a discovery that flies in the face of the conventional understanding that mammals are born with the only eggs they will ever have. Since then researchers have identified the stem cells in human ovaries, called oogonial stem cells, that do the same thing for us. These oogonial stem cells are able to undergo meiosis at any point and produce new oocytes or eggs. What isn’t clear is if these oogonial stem cells are just a back up system, or if they share responsibility for egg production with the original meiotic cells in the ovary.

So, on to chickens. It turns out this is a very difficult question to answer definitively. Most of the literature refers to the “all the eggs you’ll ever make” phenomena as occurring in either mammals, or “higher animals ” (which by the way are apparently all vertebrates except fish). There is, thus far, no evidence of oogonial stem cells in chickens, but that doesn’t mean they aren’t there, it just means no one has looked, which is a different thing altogether. Likewise, this conventional wisdom principle has likely been laid like a blanket on top of our knowledge of all “higher animals”, meaning, it is unlikely that scientists have studied the embryos of every species close enough to declare that all higher animal females are always born with all their eggs. To be fair, closely related things usually behave in closely related ways, so this blanket technique may not be as imprecise as I am making it sound. We do know that certain worms continually make new oocytes, so it is not unheard of in that natural world, but chickens are closer to the higher animals than to round worms.

The final word? I suspect that chickens, like humans, make most of their eggs during the development of the embryo, and may, like humans, potentially retain the ability to generate new eggs as needed. This question illustrates nicely, the limits of our knowledge, and way we construct what we know, or think we know about the natural world. Thanks Greg, and keep your questions coming.


From Science Daily, a digest of the original study from Massachusetts General Hospital and the University of Edinburgh, demonstrating that female mice can grow new eggs:

National Geographic’s take on the same study:

Need a review of mitosis and meiosis? Check out this nice slide show from the good folks at PBS:

A bit here on the traditional take on female oocyte development:

Whoa. Here’s a scientific article about what can regulate meiosis in chickens!!

The truth? Its complicated…

Winter Solstice

Note: This program first aired on December 22, 2012.

6:12  am, Friday December 21, 2012. That’s the local time of the occurrence of the winter solstice. Yes, we tend to think of the solstice as a day, but astronomically, it is a moment in time. At that moment, the planes of the earth’s orbit and axis are perpendicular to one another, with one pole pointed towards the sun and one pointed away from the sun as much as possible. On the winter solstice, here in the northern hemisphere, this day will have the longest night of darkness and the shortest day of light of any in our 365 day trip around the sun, simply due to the angle of the axis of earth’s rotation. The sun’s arc in the sky will be at its lowest, and the location of its rise and set will be the furthest south along the horizon. Once we have passed this point in our orbit, the days gradually begin to lengthen (you and the plants won’t notice until at least February), the sun’s rise and set will edge further north along the horizon, and the sun will creep higher in the sky each day, all as we move along the ellipsis and the axis of earth’s rotation slowly moves parallel with the plane of the orbit (this occurs at the equinoxes).

We call the winter solstice the start of the winter season, but plants and animals (and us) have been responding to the drop in temperatures and the decreasing amounts of sunlight for some time now. Starting with the shortening days of late summer and fall, plants begin their period of outward dormancy. Leaves senesce (or die back or fall off) and the living tissue of the plant becomes limited to the roots and perhaps the above ground stalk. This limits the damage the cold and lack of water can do to the plant. Most seeds are fully developed by this time and should be being dispersed throughout the environment. Animals have three ways to deal with the rigors of winter; they can leave or migrate, hibernate or “tough it out”. Again, as early as late August, observant bird watchers can see birds flocking and preparing to leave our area for warmer, lower latitude environments.   When it gets truly cold as winter really begins, many animals enter a state of torpor, with marked drops in metabolic activity. This decreases their physiologic needs, allowing them to wait out the challenging conditions of winter. Hibernation is the most commonly used term for this, but the phenomenon actually encompasses a spectrum of dormant like behaviors. Of course many animals just tough it out, relying on their stores of body fat and whatever food they can find in the winter, to remain fully active..

Humans have been observing the cycles of the natural world for as long as we have been on this planet. And as the natural order draws in and appears to pause at the cold and dark time of the year, humans have created rituals of observance that inscribe these natural patterns on human culture as well. Black Friday not withstanding, many of our holiday traditions throughout the year are based on early pagan celebrations tied directly to the solar cycles of solstice and equinox. Traditions include contemplative rituals that reflect the quiet and dark of the year, and rituals that celebrate the return of the light. So as we enter these last few days of the frantic modern holiday season, take a moment to reflect on where this frenzy of visiting and parties, family time and gift giving came from—our ancestors, who had all the time in the world to watch the path of the sun and the arc of the moon, and who knew this earth with an intimacy we can’t even fathom today. It is my belief that this level of deep deep knowledge is healing, restorative, and as the events of the last week have shown us, we are deeply in need of this. This holiday and solstice season, honor those that have come before us and pause and pay attention, noticing where the sun comes up and where it drops below the horizon. Do this every day and by February, you will be ready as that extra light creeps into your life. Happy Solstice everyone.


Straight from the horse’s mouth:

Ask an Astronomer--

Cute teacher website from the state of Michigan:

There is so much great new age info out there on the pagan rituals as they relate to modern holidays and solar cycles. Google it and you’ll find lots of wild and wacky and very interesting reading.

This is the best show I’ve ever heard on the symbolism of solstice and our winter holidays: (spoiler alert: Santa is a Shaman…)

Islands in the Intertidal

Note: This program first aired December 15, 2012.

If the intertidal zone can be considered one of the most rigorous habitats on the planet, due to its consistent inconsistency, part time ocean, part time land, then tide pools are the oasises in the intertidal zone’s deserts.  A tide pools is like an island. An island is a little piece of land, terrestrial environment, surrounded by water, a physiologically hostile environment (at least to the land based organism on the island). A tide pool is the same thing in reverse—an oasis of habitat stranded in a larger hostile environment.

As a general concept, tide pools allow organisms to live further away from the contiguous coastal ocean than they “normally” would; further away meaning higher up the intertidal zone. The pools provide a little piece of sea like habitat in the middle of a dry beachfront or rocky shore. Of course, all tide pools are not created the same, and it would be a misconception to think that they perfectly recreate the conditions found subtidally. No, tide pools, though they do offer marine organisms a more desirable situation than simply being stranded on a rock in the sun at low tide, do present their own set of physiologic challenges and inconsistencies to the plants and animals that call them home.

The further away a tide pool is from the low tide line, the less like the ocean it tends to be. And the smaller or lower volume a tide pool is, the more easily its environmental parameters can stray from those found in the mother ocean as well. The shape of the tide pool matters too—a big wide but shallow tide pool may have a high volume of water but that water will have a wide surface area in contact with both the atmosphere and the underlying substrate, both vectors for change of the physical parameters of the pool. Finally, the tidal cycle itself varies. Sometimes of the month the tide is low during the hottest sunniest part of the day, at other parts of the monthly tidal cycle, the intertidal zone is covered during this time. The organisms that live in this environment must be endlessly and admirably flexible, dealing with dramatically different parameters on a daily basis.

All of this is to illustrate the main point, that though tidepools are typically characterized by their height in the intertidal zone, no two tidepools are the same, and the high and low characterizations I’m about to talk about need to be taken with a grain of sea salt.

The higher the tide pool is in the intertidal zone, the further it is from the contiguous coastal ocean and the longer the organisms that live in it are castaways “on the island”. The temperature of these pools can vary greatly, as air temperatures vary much more than ocean temperatures due to the differences in the physical properties of air and water. In winter these pools get colder than the ocean, in summer they get much warmer. The salinity can vary much more than the ocean as well; when it rains or snows, the salinity in a high tidepool can drop dramatically as the sea water is diluted by fresh water precipitation. When the sun is intense and the water is easily heated, salinities can increase as evaporation takes place. Even the pH of a high tidepool varies. At  night the pool can experience low pHs (acid conditions) because the organisms in the pool are respiring and producing carbon dioxide, which when dissolved in water, creates carbonic acid. During the day, the photosynthetic organisms in the tide pool will photosynthesize and take up carbon dioxide, which causes the pH to increase and the water to become less acidic. High tide pools tend to have lower biological diversity because of the wide range in physical parameters.

Tide pools that are closer to the ocean, have less variation in all those parameters, because they are replenished by the contiguous coastal ocean sooner and more often than the higher tidepools. As a result, the lower tidepools exhibit higher biodiversity and host communities that look more like neighboring subtidal zones. The closer the island is to shore, the more like shore it will look.

Thursday, December 6, 2012

Tide Pool Fanatic

Note: This program first aired December 1, 2012.

Looking through an old resume recently, I noticed that I listed “tidepool fanatic” on my list of other skills and interests. Seriously, and it got me the job too. And I am not the only one; there are millions of us*, you can find us pawing through seaweed, looking under rocks, and staring into tide pools every time we go to the edge of the sea. The organisms we find in the intertidal zone are our windows to the mysteries of life under the ocean surface. Twice daily the veil is pulled back and the tribe of the curious gathers to explore the unknown.

The intertidal zone is the area at the edge of the ocean that is regularly covered and uncovered as the tide rises and falls each day. Places like Maine, with high tidal ranges have a large and diverse intertidal zone. Places like Florida, with very small tidal ranges have minimal intertidal diversity. The intertidal zone is populated with marine organisms, meaning organisms adapted to live in the salty aquatic environment we call the ocean. These are some of the toughest organisms in the world, and this is why: imagine yourself as a land based, air breathing being, having to survive, day after day, totally submerged in sea water half of the time. This would certainly challenge your physiology, to put in nicely. This is the kind of challenge (albeit in the opposite direction) that organisms in the intertidal zone face twice daily, every day. As organisms dependent on the ocean’s water, they are stranded out of it for some, if not most of their lives.

Consider the benefits of the ocean, if you are a marine organism that is. Being submerged in water means that you can breathe; water brings with it food for many organisms, water provides a medium for motility (and breeding and hunting), water provides environmental stability in terms of temperature, salinity and pH, in short, the intertidal zone comes alive at high tide. Consider the difficulties of living in the terrestrial environment, if you are a marine organism. You can’t breathe air (with a few exceptions), the temperature and salinity can fluctuate dramatically with season and weather events, you can’t eat, and you could easily dry out. If you are algae, you just have to lay there as you fell. Its rather undignified when you think about it. Clearly, these organisms would be much better off if the tide just came in and stayed in.

Or so we think. The reality is that the organisms we see in the intertidal zone live in this marginal environment because they get outcompeted (which is just the scientific word for bullied) in the sub tidal environment. The intertidal organisms do better in that incredibly stressful intertidal zone, because they evolved physiologic and structural adaptations that protect them from drying out, suffocating, cooking and freezing. Subtidal organisms just can’t do that. Take them out of water and they die.

I have huge respect for the resilience of the intertidal organisms. They eke out a living in a consistently inconsistent habitat, organisms of the ocean that can exist on land, at least temporarily. This sounds pretty significant, but how different is it from our own situation? We humans are predominantly visual animals, yet, we evolved in and exist in an environment that grows dark for half of the time we are in it, effectively negating our primary sense. So perhaps the achievement of the intertidal organisms isn’t as amazing I led you to believe. I don’t care, you’ll still be able to find me staring into the nearest tide pool, imagining the scene when the tide comes in and all of the organisms live the fullest expressions of their lives. Perhaps that is why so many of us love the edge of the sea. Its rhythms of activity and rest, and abundance and famine so readily mirror our own.

*Full disclosure: this is a complete guess.


Oh there are so many books on the intertidal environment! Though it is old, I still love the Sierra Club Naturalist’s Guide to the North Atlantic Coast (Cape Cod to Newfoundland) by Michael and Deborah Berrill.

Don't Call It a Comeback: Wild Turkeys in New England

Note: This program first aired on November 24, 2012.

Come November, many minds in America start daydreaming about the bird that could have been our national symbol, the Turkey. Amazingly, that bird you buy in the grocery store or order from your local farm is the same species as those wonderful prehistoric baby dinosaurs you see in flocks along the roadside or in the fields as you drive to work.

Wild turkeys are found throughout the lower 48 states and into parts of Mexico. The species is actually comprised of 6 sub species, separated by geography. All of the sub species are derived from the southern Mexican wild turkey (Meleagris gallopavo gallopavo). This is the species that the Aztecs of Mesomerica and the Anasazi of the desert southwest were known to have domesticated, one of the few “New World” organisms that lent itself to agriculture. Interestingly, this Aztec domesticated turkey was then brought to Europe by Spanish conquistodors and gained popularity there.  It was further selectively bred in Europe and then came back to the new world with the colonists, who had no idea that there was already a wild turkey waiting for them here in colonial North America.  The sub species we see here in Maine is the Eastern Wild Turkey; Meleagris gallopavo silvestris), and as a sub species it is able to interbreed with the domesticated turkey.

Wild Turkeys were once abundant throughout New England, but the spread of agriculture during the colonial period up through its peak in the 1800’s, combined with unrestricted hunting nearly exterminated the species in our area. Most New England states went from being almost entirely forested at the time of European colonization to being 60 to 90 % cleared for cropland and pasture. This clearing of the land strongly decreased diversity across the landscape and obliterated wild turkey habitat. Turkeys need mixed woodland with nut bearing trees like oaks and beeches as a food source. They roost high in trees at night to avoid nocturnal predators. Young turkeys need dense shrubbery for cover and lots of insects to feed on to fuel their rapid growth. A patch work of diverse northern hardword forest is ideal for them, and that is what has been regenerating in much of New England since agricultural clearing peaked in the 19th century.

The turkeys we see around today are a result of reintroduction programs throughout the northeast.  Maine’s reintroduction program started in 1977 and 78, with 41 turkeys from a wild population in Vermont, followed by 70 more Connecticut turkeys in 1987. From those 111 birds come the 50 to 60,000 we have in the state today. That is a phenomenal recovery, and speaks clearly to the importance of habitat restoration in the field of conservation biology. When released from the pressure of unregulated hunting and total habitat destruction, wild turkeys are able to thrive, achieving population numbers and ranges that are likely higher and wider than the precolonial population. So if you are partaking in the traditional turkey feast some time this holiday season, take a moment to reflect on the marvelous resilience of the bird you are eating.


Maine Inland Fisheries and Wildlife info:

Vermont also has some nice things to say about wild turkeys:

The Lewiston Sun Journal article on wild turkeys in Maine:

Yep, he really did say that: Ben Franklin, though he never made a public fuss about it, did think the turkey to be a more respectable bird than the eagle.

Nice article in Wired magazine, regarding new research on the domestication of turkeys in North and Meso America

Jared Diamond Guns, Germs and Steel—learn all about the few species that native North Americans were able to domesticate (and why that bad luck doomed them).