How birds are like islands (for lice)

Researchers document a new example of convergent evolution in bird lice.

In terms of evolution, islands are special.  The Galapagos Islands played a central role in the development of Darwin’s ideas on natural selection.  Alfred Wallace found the same inspiration while traveling among the islands of the Malay Archipelago.  With hindsight, it’s no surprise.  Island chains are great places to see how isolation and natural selection lead to the array of unique and exotic species that are found there.  Islands isolate groups of individuals from breeding with their counterparts on other islands and over time these isolated groups may diverge from each other, eventually leading to the emergence of new species.

Isolation doesn’t just occur on little bits of land in the middle of an ocean.  Lakes are like islands for fish.  The tops of mountains are like islands for alpine plants.

And birds can be islands, too — at least to lice — according to the work of Kevin Johnson and colleagues in a recently published paper in BMC Biology.

Think about it:  Since lice are tiny parasites that must stay put while feeding on their host, they will usually have an opportunity to mate only with other individuals that are hitching a ride on the same bird or when their host bird meets another bird carrying another potential lousy mate.  As a result, these isolated lice populations have a good opportunity to diverge and evolve into different species.  There are at least 2700 documented species of feather parasites that have evolved on these bird-islands.

But the really interesting part of their study is that they were able to determine, using molecular techniques, how the species of feather lice are related to each other.  In the process, they have added another example of convergent evolution to the textbooks.

In a nutshell, here’s how their story goes …

There are four general groups of lice: head, body, wing, and generalist.  Individuals within each of these groups tend to look alike.  Here’s a figure from their paper to demonstrate:

The particular form (morphological type) of each group is related to the “microhabitat” in which they live and the ways that the bird tries to get rid of the lice when they preen.  Wing lice will need to try and keep their ground as a bird’s beak is trying to pick them off, while head lice may have to avoid the same bird’s feet scratching to pry them off.

One reasonable hypothesis about how the many different species are related is that all the species that exist in the same microhabitat (and share the same morphological type) come from a common ancestor.  If true, then all the head lice would have arisen from one species of ancestral louse that was really good at living on the head of a bird.  If a group of head lice on a crow made their way onto a robin, a new species of head lice on robins might emerge.  Eventually, all the subsequent head lice (and all the head lice species we see today) would be related to each other and not as closely related to wing lice.

However, the genetics of lice do not follow this pattern.  The study documents many good examples where different species of lice on the same type of bird are more closely related to each other than you would expect.  In parrots, for example, the head, body, and wing lice are more closely related to each other than to the same kind of lice on other birds.

This appears to be another case to add to the long list of examples of convergent evolution, which means that different members of the same group (wing lice, for example) look alike because they experience a similar problem (preening by birds) not because they are closely related.

Check out the video on YouTube — it does a really nice job summarizing their findings and is narrated by the first author of the paper. (I wish more researchers would do the same!)

Thanks to Bug Girl’s Blog for tipping me off to this story.  Great for my introductory biology class.

Johnson, K.P., Shreve, S.M. & Smith, V.S. (2012). Repeated adaptive divergence of microhabitat specialization in avian feather lice, BMC Biology, 10 (1) DOI: 10.1186/1741-7007-10-52

Posted in Evolution, Organisms | Tagged , , , , , , , , , , | 2 Comments

If climate change leads to more powerful storms, greater ozone depletion will likely follow.

There’s a common misconception that climate change and the depletion of our ozone layer are closely linked. Actually, one survey reveals plenty of misconceptions about climate change:

“Majorities of Americans … incorrectly believe that the hole in the ozone layer, toxic wastes, aerosol spray cans, volcanic eruptions, the sun, and acid rain contribute to global warming.”

Climate change and ozone depletion are better thought of as distinct issues. Briefly …

  1. Climate change is happening because our planet is warming, caused predominantly by a rise in greenhouse gases (carbon dioxide, methane, nitrous oxide) in the atmosphere, which trap heat from escaping our Earth’s surface.
  2. Stratospheric ozone depletion is happening because there has been a rise in ozone-depleting substances. Since stratospheric ozone blocks a large amount of UV radiation, ozone depletion leads to more UV radiation reaching the Earth, which will cause harm to us and other living organisms.

However, a recent study published in Science by Anderson and his colleagues now provides a clear link between the two issues. Their study finds that strong storms have the ability to take moisture very high into the atmosphere, creating conditions that speed up the process of ozone destruction. If the frequency of convective storms were to increase, the amount of ozone in the stratosphere would decline … leading to higher amounts of UV radiation reaching the Earth’s surface. A press release explains the connection this way …

“In the system described by Anderson and his team, water vapor injected into the stratosphere by powerful thunderstorms converts stable forms of chlorine and bromine into free radicals capable of transforming ozone molecules into oxygen. Recent studies have suggested that the number and intensity of such storms are linked to climate changes, Anderson said, which could in turn lead to increased ozone loss and greater levels of harmful UV radiation reaching the Earth’s surface, and potentially higher rates of skin cancer.”

In more simplified terms …

Climate change = more powerful storms = more ozone depletion = greater UV radiation = higher cancer rates

This is a relatively long string of steps, but not uncommon when discussing atmospheric changes. We’re not dealing with a simple system, so it’s not a simple topic to try and explain. In addition, the way that climate change research is communicated in the media (and by scientists) isn’t always so clear. As one study of our society’s knowledge of climate change puts it:

“It is urgent that climate scientists improve the ways they convey their findings to a poorly informed and often indifferent public. “

It’s not surprising that there is confusion out there about how all the changes happening in our climate system are related to each other. Even though there is scientific certainty about the basic processes of climate change and ozone depletion, we’re still figuring out some of the complexities.

Read more … NYTimes article: Storms Threaten Ozone Layer Over U.S., Study Says

Anderson, James G., et al. “UV dosage levels in summer: increased risk of ozone loss from convectively injected water vapor.” Science 337.6096 (2012): 835-839.

Photo credit: NASA

Posted in Environmental Change | Tagged , , , , , , , , , ,

McKibben’s climate change math


Over the past few decades, Bill McKibben has been one of the more persuasive environmental writers chronicling the changes to our planet.  His recent article in Rolling Stone magazine continues his run.  The main point … we haven’t made much progress to address the serious threat of climate change:

“Since I wrote one of the first books for a general audience about global warming way back in 1989, and since I’ve spent the intervening decades working ineffectively to slow that warming, I can say with some confidence that we’re losing the fight, badly and quickly – losing it because, most of all, we remain in denial about the peril that human civilization is in.”

According to him, the forecast is not rosy and our collective will is not strong.

I’ve always appreciated his writing because he starts off with sound science and then tries to think through how it plays out in the very real game of politics, economics, and human nature that we all are engaged in.  I don’t always agree with everything he says, but he is able to make the science of global change a little more accessible to everyone.

In this article he concludes that the fossil fuel industry is blocking any progress that people are trying to make toward reducing our impact on the climate system.  His main argument rests on three numbers ….

  1. 2 degrees Celsius = The rise in global temperature we should stay below (we’ve seen about 0.8 degree rise so far).
  2. 565 Gigatons = The amount of carbon that can be added to the atmosphere to stay below a 2 degree rise.
  3. 2795 Gigatons = The amount of carbon stored in fossil fuel reserves is 2795 Gigatons (five times the amount in #2).

So, we are on a course to put five times the amount of carbon into the atmosphere than we should, if we want to keep the temperature of the planet from rising more than two degrees.

Of course, you could quibble with the numbers he selected (and a lot of people will), but when you look at them there is logic with the way that he chose them.  A two-degree rise doesn’t sound like a lot, but we’ve already seen big changes with less.  But he’s putting out an argument that we can talk about, based on numbers that you can check out for yourself, published somewhere among the heap of information we have amassed.

“If people come to understand the cold, mathematical truth – that the fossil-fuel industry is systematically undermining the planet’s physical systems – it might weaken it enough to matter politically.”

What we choose to do with the numbers is for us to discuss and decide.  It’s true that he often takes a gloomy approach to our situation on the planet.  But how would you rewrite the story and make it less so?

Posted in Environment, Environmental Change | Tagged , , ,

A few trends in environmental optimism

Photo source: Smoke Control Lantern Slide Collection, ca. 1940s-1950s.  Title: Corner of Liberty and Fifth Avenues, Pittsburgh, PA.

Industrial smoke, what’s optimistic about that?  It’s the fact that many of our old industrial towns are now much healthier to live in today compared with a half century ago.  The University of Pittsburgh has a great set of photos from the 1940s and 50s of Pittsburgh before the era of air quality legislation.  You can find them in their Smoke Control Lantern Slide Collection or on other sites that have set up slideshows with the photos.

I grew up just down from Pittsburgh on the Ohio River, and these photos remind me of the stories I occasionally heard by the older generations.  The skies of my hometown more than 50 years ago were often dark with the smoke that discharged from the coal-fired factories clinging to the riverside.  My grandmother used to say that you could sweep enough soot from your porch to fill dustpans and that washing your house would reveal its original color.

Today the skies of my hometown are mostly clear of the visible pollutants (like soot) and there’s also a lot less of the invisible ones (like sulfur dioxide).  By itself, this is a success story that we don’t often talk about, but we should.  China’s industrial pollution today follows the path of history that the US followed years ago.  In our case, a previous generation decided that some types of pollution were not tolerable and were able to fix them with the technologies of the time.  Of course, solving this particular smoke problem was probably driven by the desire to cure the health-related impacts of living in this region rather than a general concern for environmental health.  The deadly Donora Smog of 1948 that killed 20 people woke up the region to some of the real costs of industrial productivity.

Over the past few years, there seems to be a movement among some scientists, and conservationists who study and work on issues of environmental change to focus less on the gloomy aspects of their work and, instead, pay attention to the possible solutions we have before us.

Of course, there are those who will give you a heavy dose of “technology will fix everything” — just watch the TED talk by Peter Diamandis.   His basic message is that our lives today are better because of technology and they will continue to get better in the future, but he at least acknowledges that we have some big work to do:

“I’m not saying we don’t have our set of problems — climate crisis, species extinction, water and energy shortage — we surely do. [But] ultimately we knock them down.”

This is a little too reliant on technological fixes for me, but there is some merit to it.  We do have the ability to solve some environmental issues with our current knowledge … even climate change.  Take, for example, the argument from the Climate Mitigation Initiative  that we have the technological capability to substantially reduce our global greenhouse gas emissions.   We just need to agree on which direction to take and how to get there.

Science writer Keith Kloor has been recently making the case that we should shut the door on the depressing, pessimistic Green Traditionalist view of the world.  Instead, we should listen to the Green Modernists, whose members take a “pro-technology, pro-city, pro-growth” approach to solving environmental issues.

A similar sort of discussion is making its way through scientific circles.  For example, a prominent group of scientists who study global change issues recently wrote that their focus should shift toward studying “opportunities” that we have in solving global environmental issues rather than on the limits to the environment:

“A focus on planetary opportunities is based on the premise that societies adapt to change and have historically implemented solutions—for example, to protect watersheds, improve food security, and reduce harmful atmospheric emissions.”

Doing this requires that we accept the idea that humans have altered (and will continue to alter) the natural environment substantially and that we should not be so focused on trying to recreate an untouched, natural landscape.  Emma Marris takes this point of view in her book Rambunctious Garden.  She and some of her colleagues write about a different view of how we should approach the Big Changes we are seeing in the Anthropocene:

“The Anthropocene means that humans are having a large impact, but that doesn’t mean that we live in ‘an ecological hell.’”

and how we might address environmental changes:

“We can accept the reality of humanity’s reshaping of the environment without giving up in despair. We can, and we should, consider actively moving species at risk of extinction from climate change. We can design ecosystems to maintain wildlife, filter water and sequester carbon.”

So, can we effectively shift our focus toward the motivating force of solving problems and away from the debilitating fear of environmental collapse?  Will people pay attention if the headlines are less fearful?

Posted in Conservation, Environment, Environmental Change | Tagged , , , , , , , ,

Will nature inspire us on the Internet too?

Many of my nature-oriented friends and colleagues have some kind of story to tell about their close ties with the outdoors when they were growing up.  Sometimes when we get together we all moan about how “children these days” don’t get enough time romping around outside, experiencing mud and worms and streams and all of it.

My own childhood experience allowed me to go effortlessly from my backyard into miles of unbroken forest in the foothills of the Appalachian Mountains of West Virginia.  I spent my time swinging on vines, hiking to natural springs, and getting an up-close view of the creatures that lived there.  So naturally I get nostalgic about those times and want every kid to have that same experience.  What’s going to happen if they don’t and, instead, spend all their time looking at screens?

Carol Kaesuk Yoon makes a good case in an essay in the New York Times that children might be getting inspiration about nature from the Internet, it’s just different …

If the Internet is unavoidable and ubiquitous — and it is — then nature is following right along with it, shining out through screens everywhere. Young people are knowledgeable about organisms in a global way we could never have been as children. They may not often wander the local patch of forest — we won’t let them most of the time anyway — but they wander the natural world through the Internet.

Kids can see lemurs, pandas, lions, insects, and meerkats … in their exotic environments interacting with other creatures that we can’t see around us.  The Internet can be an extension of the smaller world that we live in on a daily basis.

Perhaps we can think of the globalization of information as a way of putting our own backyards in context.  We can now make our own connections about nature because we can see a greater range of our Earth’s biodiversity at the touch of a button (at least we can see the stuff that people have captured in pictures and videos).  Our backyards aren’t becoming less important, of course.  It’s still essential to get outside and experience the world firsthand.  What’s different is that we now we have easier access to the larger context in which to place ourselves and our local surroundings.

It reminds me of another important experience that encouraged me to become an ecologist and environmental scientist.  Sometime in the early 1980s, I watched the entire Life on Earth series.  It was narrated by David Attenborough, who alone has probably inspired millions of nature enthusiasts.  Life on Earth was some pretty captivating stuff and introduced me to the enormous range of biodiversity that I could never have seen as a kid in my extended backyard.  The series planted the seeds of the big questions of biology into my brain: “How did life first originate on our planet?” and “How did life evolve since then?”

So, maybe our greater access to the world can inspire us to understand it better?

Posted in Learning Science | Tagged , , , , , ,

Globalization is leading to greater biodiversity … in many regions, temporarily.

Most headlines about biodiversity follow the same storylines:  Species are going extinct at an incredible rate.   We are in the middle of the Earth’s sixth extinction event.  The number of endangered species keeps growing because of habitat loss and invasive species.

But Erle Ellis and his colleagues offer a slightly different perspective on the way in which our Earth’s biodiversity is changing.  In an article published by PLoS ONE, they look closely at an enormous amount of data on global plant biodiversity, separated into regions of the Earth.  Ellis describes one of their most surprising findings on his blog:

“The big story of plant biodiversity in the Anthropocene is not about loss at all.  Our model predictions indicate that human systems have caused a net increase in plant species richness across more than two thirds of the terrestrial biosphere, mostly by facilitating exotic species invasions.”

How can this be?  How can we be in the middle of the Earth’s sixth extinction event while the number of species (species richness) is increasing across most of the planet?  The answer lies in looking at how regional biodiversity is changing differently from global biodiversity as a whole.

Globalization has certainly led to a mixing of Earth’s biodiversity.  As we move ourselves and the stuff we want around the world at greater rates, we move more species around the world too.  We’ve been doing this for thousands of years, of course, but the pace has picked up dramatically over the past few decades.  Just think about the number of container ships unknowingly carrying plants, insects, fungi, bacteria and other organisms with them.

Before people started moving species around the planet in substantial numbers, organisms interacted with just a subset of the Earth’s inhabitant and evolved in ways that reflected their relatively isolated surroundings.  A different set of organisms inhabited each continent, island, and mountaintop, reflecting how these species interacted with each other and their environment.

Mixing together these different sets of species through our actions on a global scale is a huge centuries-long experiment unfolding before our eyes.  Most regions of the world are seeing a rise in the total species richness because the number of introduced species added is greater than the number of native species that have gone extinct so far.  Introduced and native species are coexisting for now, so the number of species in many regions has gone up.

However, this is very likely to be temporary as these new sets of interacting species “duke it out” and a subset of them go extinct.  This temporary stage is often referred to as our “extinction debt” — we’ll be paying the debt down in the coming decades.

As for global biodiversity, it is still declining.  There’s nothing new that this article says about that.

The bigger — and more interesting — argument that the authors make is that ecosystems today are vastly different from what we’ve seen in the past and that human activities rival geologic forces.  As Ellis writes, again on his blog:

“We set out on this work more than 3 years ago with the goal of testing a key hypothesis … that current global patterns of biodiversity are better explained by global patterns in human systems (populations, land use) than by the “natural” biophysical patterns of the Earth system (climate, geology).”

And they seem to do a good job of it, at least for plants.

In other words, one of the Big Changes in the Anthropocene that we are seeing is that human activities are becoming a major force shaping the composition of ecosystems.  The changes in biodiversity that we are observing are now so large that our current era will be recorded in the geologic record.


Ellis EC, Antill EC, Kreft H (2012) All Is Not Loss: Plant Biodiversity in the Anthropocene. PLoS ONE 7(1): e30535. doi:10.1371/journal.pone.0030535

Posted in Environmental Change, Organisms | Tagged , , , , , , , , , , , | 1 Comment

New species are found all the time, even in Europe.

How many species live on the planet today? No one knows.

How many species live in Europe today? No one knows that either. You would think that in one of the most densely-populated regions of the world (and the home of Linnaeus, father of our current taxonomic system) we would have an answer to this question. Unfortunately, we still have a long way to go toward cataloging life on Earth according to a recent study published in PLoS.

The authors of the study compiled a list of multicellular species that have been named over the past 250 years. This graph shows the cumulative number of species named in Europe since 1758:

The number of new bird species that are discovered each year leveled off in the late 1800s. That’s not surprising since a lot of people like to look for birds. They are also easy to find, catch, and compare with each other.

However, new species are continuously being found in most other groups of organisms. Overall, the total number of species that are named each year in Europe (panel A) continues to increase, with no indication that it is leveling off. On average, 770 new species have been described and named each year since the 1950s, which is about 2 new species each day. And this is just in Europe! Our knowledge of tropical biodiversity is incredibly poor.

What’s going on? For one, there is no overall plan for cataloging biodiversity. No one organization is in charge, so the process is inefficient.

Another reason for the slow progress is that there aren’t enough people with the skills to find and name new species. In fact, one of the most surprising findings of this study is that over half of all the new species documented each year are not professional taxonomists — in other words, these folks don’t have a paid position for doing this work. They are experts in identifying and naming new species, but they are either amateurs or retired taxonomists. The rate of finding new species would be much slower without their contribution, so encouraging more people to get out there to search would help speed things along.

So, what is needed is a plan and more people to do the work. Currently, the number of named species on the planet is around 1.9 million. But the estimated number is much, much larger. If the same rate of discovery continues, we’ll be in the dark for a long time:

“The frontiers of biodiversity exploration and discovery are generally considered to be in the tropics and if the actual number of species on the planet is 5–30 million, at the current rate several centuries will be necessary to describe and name them all.”

We’ve got our work cut out for us. And if we don’t know the number of species on the planet, there are a lot of species facing extinction that we don’t even know exist.


Fontaine B, van Achterberg K, Alonso-Zarazaga MA, Araujo R, Asche M, et al. (2012) New Species in the Old World: Europe as a Frontier in Biodiversity Exploration, a Test Bed for 21st Century Taxonomy. PLoS ONE 7(5): e36881. doi:10.1371/journal.pone.0036881

Posted in Conservation, Organisms | Tagged , , , , , , , , | 8 Comments