Sunday, October 30, 2011

In matters of home, lichens follow their algal hearts

Many couples would probably agree that deciding on a place to live together is about as easy as tying your shoes using one hand and one foot- and that’s when the two parties are both human.  Consider what life is like for a lichen, a creature made up of organisms from two different kingdoms of life.  A lichen is a fungus that obtains nutrients from an algae growing inside of it- a symbiotic lifestyle that benefits the fungus, but not necessarily the algae.

It the past, biologists thought that it was the fungal partner who determined where the lichen grew, since it is the fungus that makes up most of the body of the lichen.  However, a new study in Molecular Ecology adds to the growing body of evidence that, it may actually be the algae who hold the reins.

When researchers at Charles University in Prague took samples of the DNA of Asterochloris algae living in Lepraria lichens from central Europe and California, they found that the most closely related algae were not the ones found living in the same species of lichen.  Instead, algae from different lichen species living in similar habitats were more closely related to each other.  For example, algae from lichens living in locations exposed to the sun and rain were more closely related to each other than they were to algae from lichens living in sheltered humid environments.

What this shows is that different algal species have preferences for different environments and if a fungal partner wants to live in a particular environment, it has to ally itself with an alga that also wants to live in that environment.  If the fungus attempts to grow somewhere that the alga doesn’t like, the alga will probably die, taking the fungus along with it.

Why is this biogeography?  Scale up the microclimatic preferences of the algae to the macroscale patterns of climate found across the earth.  Different algae have been found in lichens from the tropics versus the temperate zone versus more polar regions; and on a smaller scale, different algae are found in lichens at the tops of mountains than at their bases.  To figure what causes a lichen to live where it does, the most pertinent question may be, “Who’s your alga?”

You can find this article at:

ResearchBlogging.orgPEKSA, O., & ŠKALOUD, P. (2011). Do photobionts influence the ecology of lichens? A case study of environmental preferences in symbiotic green alga Asterochloris (Trebouxiophyceae) Molecular Ecology, 20 (18), 3936-3948 DOI: 10.1111/j.1365-294X.2011.05168.x

Monday, October 24, 2011

Floral gladiators evolve faster in South Africa than Rome

Gladiolus is latin for ‘little sword’, a fitting name for a plant whose flowers grow along giant spikes.  While these plants are ubiquitous in gardens across the United States, they actually are complete foreigners.  Of the 260 species around the world, almost all are from southern Africa, and none are from North or South America.

Even in the parts of the world where Gladioli are native, the distribution of their diversity varies hugely.  There are 106 species of Gladiolus in the Cape Floristic Region of South Africa and only 7 in the Mediterranean region of Europe, even though the Mediterranean region is 25 times larger than the Cape.  The two areas have similar climates and ecosystems, so what explains the 15-fold difference in diversity for these plants?

In evolutionary terms, making species is like making pancakes; to get more pancakes you either have to work longer or put more batter on the griddle and work faster.  Similarly, for there to be more Gladiolus species in southern Africa, either they have lived in southern Africa longer and have had more time for evolution to produce new species, or evolution of Gladioli proceeds faster in southern Africa than in Europe, so that new species are produced at a faster rate.

Luis Valente from the Imperial College in London and a group of international colleagues constructed a phylogenetic tree from 150 Gladiolus species from in Europe and across sub-Saharan Africa.  This ‘tree’ is like a family tree, showing how closely related all of the Gladioli are to each other.  By coloring the tips of the branches based on what region each species lives, the researchers were able to infer what region each of the ancestors used to live in, all the way back to the first Gladiolus.  From this information they could then calculate how long Gladioli have lived in different regions of Africa and Europe, as well as how quickly each of the branches of the tree found in these regions have produced new species.

So, which hypothesis explains the high Gladiolus diversity in the Cape- was it because of more time or faster evolution?  The answer, as it turns out for most questions in ecology, is both.  It is likely that the first Gladiolus species evolved in the Cape region and only much later did a Gladiolus species reach the Mediterranean and then evolve into the seven species found there.  Thus, Gladiolus in the Cape have had much more time to evolve than Gladiolus in the Mediterranean.  However, they’ve also done it faster- the rate of diversification has been 3-5 times slower in the Mediterranean than in certain parts of the Cape.

Just because Gladiolus appear to have diversified more rapidly in the Cape doesn’t mean that all plants follow this pattern.  In the group of plants called Dianthus (another flower that frequently shows up in people’s gardens), the pattern is just the opposite; Dianthus has evolved faster in the Mediterranean than in the Cape. 

You can find this article at:

ResearchBlogging.orgValente, L., Savolainen, V., Manning, J., Goldblatt, P., & Vargas, P. (2011). Explaining disparities in species richness between Mediterranean floristic regions: a case study in Gladiolus (Iridaceae) Global Ecology and Biogeography, 20 (6), 881-892 DOI: 10.1111/j.1466-8238.2010.00644.x

Sunday, October 16, 2011

Seeing evolution from space

A long long time ago, 25 million years, to be exact, the Andes Mountains in South America began to rise, and as they rose, all of the water in what is now Peru and Ecuador that used to flow northwest had to change directions and head east. This rainwater carried with it lots of dirt, creating a big mud-pie full of cations (i.e. plant nutrients) under a lake on the edge of the ocean.  But, the Andes kept rising and this mud-pie (called the Pebas Formation) drained of water as it was lifted up out of the ocean.  The Amazon River then started to flow east, carrying with it lots of nutrient-poor sand that covered up the Pebas formation.  But, the Andes kept rising, and now, instead of depositing sandy dirt on top of the ground, in the western Amazon the rivers carry dirt away, exposing the older Pebas dirt.  Today, the ground under the Amazon rainforest is like a half-eaten cracker.  In the west, crumby islands of nutrient-poor soil occur on top of the exposed nutrient-rich Pebas layer, but in the east, where erosion has not yet carried it away, the uneaten nutrient-poor soil reigns unmolested.

A human looking down from space upon the Amazon Basin would see a vast expanse of green and would probably wonder why this post just spent the last 200 words talking about dirt when the dominant feature of the Amazon is clearly trees.  The reason is, a special type of satellite imagery called Landsat, can look down from space upon that same vista and say- yup, those are trees, but here’s what kind they are. 

That’s where the geology becomes interesting to a biologist.  An international group of scientists, headed by Mark Higgins, has discovered that Landsat images of the western Amazon Basin show abrupt boundaries between one group of plants and another, and that these boundaries correspond exactly to the underlying geologic border between where the Pebas formation has been exposed and where it hasn’t.  By collecting soil and plant samples from either side of the satellite-predicted boundary, the researchers were able to show that different types of plants grow on the cation-rich soil of the Pebas than grow on the overlying cation-poor soils.

It may not seem like much of a leap to say that geology influences soils, which influence plants.  But, consider the fact that the geology of the Amazon has not remained constant through time.  Higgins and colleagues suggest that when rivers began to erode away the nutrient-poor soil and expose the nutrient-rich soil 5 million years ago, this created a new type of lifestyle for plants to adapt to and may have spurred the evolution of some of the biodiversity that is the signature of the Amazon.  Evidence for this includes the diversification during this time of a groups of plants called Inga that specialize on rich soil, as well as the fact that closely related bird and mammal species from eastern and western parts of the Amazon have only recently become separate species.

You can find this article at:

ResearchBlogging.orgM.A. Higgins, K. Ruokolainen, H. Tuomisto, N. Llerena, G. Cardenas, O. L. Phillips, R. Vasquez, & M. Rasanen (2011). Geological control of floristic composition in Amazonian forests Journal of Biogeography, 38, 2136-2149 DOI: 10.1111/j.1365-2699.2011.02585.x

Sunday, October 9, 2011

Bacteria... in every breath you take

In case you needed a more compelling reason to scoop your dog’s poop than the general good deed of not leaving behind a present for someone’s shoe to discover, consider the fact that what you leave behind on the ground doesn’t always remain on the ground.

One person is likely to breathe in 860,000 bacteria every day1.  Where do these bacteria come from?  What kinds of bacteria are they?  Does where you live affect the kinds of bacteria that are likely to be floating around in the air- and in your lungs?

Scientists from Colorado strained the air for bacteria in Chicago, Cleveland, Detroit, and Mayville, WI over the course of six weeks in the summer and six weeks in the winter in order to answer exactly these kinds of questions.  In 5,000 cubic meters of air (that’s how much a person breathes in about a year and a half) there were 200-300 different kinds of bacteria from at least seven different bacterial phyla.  Side note: Living things that are in different phyla are generally distantly related to each other: for example seas urchins belong to the animal phylum that is most closely related to the animal phylum containing humans- we last shared a common ancestor 600 million years ago.

Even though bacteria in the air were very diverse, the kinds of bacteria found in different cities didn’t vary much.  In fact, there was a much greater change within one city from summer to winter than between two different cities.  In the summer there were generally more bacteria in the air than in the winter, especially in Detroit and Cleveland.  The researchers found that the main sources of airborne bacteria during the summer are likely to be the soil and the surfaces of leaves.  Since leaves aren’t out in the winter and the ground is frozen, this probably decreases the input of bacteria into the air.

So, where do the bacteria found in winter air come from? Dog feces, most likely.  In the winter, but not in the summer, a kind of bacteria called Fusobacteria are very abundant in the air.  These bacteria are commonly found in canine guts, but not in humans or livestock.  Want to avoid the bacteria of fecal origin? Plan your trips to Cleveland or Detroit for the summer.  But to be fair, the origins of aerial bacteria for other cities have yet to be discovered.

1Assuming a constant breathing rate of 12 times per minute, inspiring 0.5 liters each time, with a concentration of 100,000 bacteria per cubic meter of air.

Your can find this article at:

ResearchBlogging.orgBowers, R., Sullivan, A., Costello, E., Collett, J., Knight, R., & Fierer, N. (2011). Sources of Bacteria in Outdoor Air across Cities in the Midwestern United States Applied and Environmental Microbiology, 77 (18), 6350-6356 DOI: 10.1128/AEM.05498-11

Saturday, October 1, 2011

Parasitic worms have center-leaning latitudes

Perhaps the most infamous puzzle in biogeography is the fact that places closer to the equator tend to have more species than places farther from the equator. Why is this true? 212 years have passed since Alexander von Humboldt first noticed this pattern, called the latitudinal diversity gradient, on his voyage to South America and scientists are still not in complete agreement on what causes it.

Not all living thing follow the latitudinal diversity gradient, either. In a paper published in Global Ecology and Biogeography in September, David Thieltges and colleagues discovered that, across Europe, a particular group of parasitic worms called trematodes actually has more species at moderate latitudes than in the south. Of course, since no part of Europe occurs in the tropics, the fact that the scientists didn’t find the traditional latitudinal gradient for trematode diversity in Europe doesn’t preclude its existence for the entire globe.

Trematodes might be bailing off of the latitudinal bandwagon because they aren’t free-living. These parasites must sequentially infiltrate at least two and often three different animals, (such as from a snail, to a fish which is then eaten by a bird) before they can lay thousands of eggs that will start their life-cycle over again. Because they are so dependent on finding hosts, the number of trematode species is more likely to be affected by how many different animal species are available to be parasitized, than aspects of the external environment that vary with latitude.

This is just what Thieltges and colleagues found when they looked at the diversity of animals that trematodes use as a final host (i.e. where they have sex and make eggs). Regions with higher final host diversity had greater trematode diversity. Surprisingly, it is only the variety in final host that matters; snail diversity does not affect trematode diversity, even though trematodes rely on snails to complete the first part of their life cycle.

So, just what is diverse, for trematodes? How many different kinds of worms are we talking, here? Thieltges’ source of information for his research was the book Limnofauna Europeae, compiled in 1978 by Joachim Illes, which catalogs pretty much all of the known animals that live in freshwater lakes, streams, and ponds in Europe. According to this book, the fewest number of trematode species occur in Iceland, at a whopping 9 species. And as for the most? You can find 322 trematodes out on the East European Plains. If this sounds like a lot, just consider the fact that at least 18,000 species of trematodes make the world their home.

You can find this article at:

Thieltges D.W., Hof C., Dehling D.M., Brändle M., Brandl R. & Poulin R. (2011). Host diversity and latitude drive trematode diversity patterns in the European freshwater fauna, Global Ecology and Biogeography, 20 (5) 675-682. DOI: