The Sahara is the world largest desert, and getting larger. It threatens to creep ever further to the south and turn arable land in desert wasteland. The nations in its path have an idea, though: We’ll build a fence. Of trees.

The “Great Green Wall” would be a tree band that spans the breadth of northern Africa, 9 miles wide and nearly 5,000 miles long, from Senegal at the western edge near the Atlantic to Djibouti on the eastern edge near the pirate-infested Gulf of Aden. It may sound too dreamy or crazy to ever go forward, but this week at a meeting in Chad about desertification, the Global Environment Facility backed the belt idea with $119 million. Chad’s minister of environment, Hassan Térap, says it can be achieved:

When asked if the long-discussed but yet-to-be funded Green Wall initiative was too ambitious, Térap told IRIN: “We have to attack the problem, long ignored, through vision, ambition – and trees. What is wrong with ambition?” [IRIN Africa].

To bridge the east-west expanse of Africa, the wall would pass through Burkina Faso, Chad, Djibouti, Eritrea, Ethiopia, Mali, Mauritania, Niger, Nigeria, Senegal and Sudan. But while those nations have discussed such a huge project before, little has been done. Now, though, with the $119 million divided between the constituent countries, perhaps the planting will go on.

Older people in N’Djamena – where the conference is being held – talk anecdotally about how the capital city has become a dustbowl over the last 20 years as the Sahara Desert has encroached southwards. The country has made efforts to plant a green belt of trees around the capital, and tens of thousands of young trees are being grown in nurseries on the outskirts of the city, she says [BBC News].

It’ll take more than money to get the wall going. Project leaders must now decide which trees to plant—preferably native, drought resistant ones. They’re considering 37 species.

Red tape may hold back the green wall, but the idea itself is no crazier than others proposed to counter Saharan sprawl. Here at 80beats we’ve covered proposals to set up vast irrigation and desalination plants to turn the desert green, and using a bacterium to bind the sand grains together as a rather different kind of “wall.”

Related Content:
80beats: To Save the Planet from Global Warming, Turn the Sahara Green
80beats: Can Bacteria Create a Cement Wall To Hold Back the Sahara
80beats: Happy News: Indonesia Won’t Slash-And-Burn Forests for Next 2 Years
DISCOVER: How To Make a Desert

Image: flickr / kashmir

I have good news about podcaster, skeptic, musician, friend, and fellow bald guy George Hrab: his latest album, "Trebuchet", has finally hit the streets!

Yay! This collection of songs runs quite the range, from topics skeptical to sad to even, yes, cosmological annihilation. I refer you to the song listed in the upper right of the above picture, track number 11, entitled "Death from the Skies" (noting also the book displayed in the bottom right corner in said above picture). That song features music by Geo and a litany of astronomical destruction (and their odds of occurring) by me, your host. That was a lot of fun to do, and I’m proud and honored to be on an album made by my friend.

The delightful Donna, aka Brickgrrl, aka MsInformation, has more info on the album, and the entire album can be downloaded on Geo’s podcast feed. You can download it at iTunes, of course, but I suggest going to CDBaby, which also has the download but where you will soon be able to order the physical, actual CD, which you should, because a) it comes with liner notes which are epically cool, 2) one lucky customer will win a Golden Ticket providing them with a free house concert by Geo (!) and γ) it puts some money in Geo’s pocket, which deserves it.

To give you an idea of just how clever this epidermically bepated man is, check out this time lapse video he made of how he created the album cover:

Geo’s been making the rounds of the podcasts, too. For example, you can hear an interview with him on this week’s Skepticality (with bonus interview of horror writer, equally balded, and friend-of-BA Scott Sigler).

Go ahead: buy the album, listen to the interviews, check out those links. It’s spring, it’s Friday, and it’s not like you’re gonna get any work done today anyway.

Some damselfish have sensitive stomachs, but they certainly aren’t in distress. They can hold their own, researchers have recently determined, by diligently farming their preferred algae crops.

It shouldn’t come as a surprise that Stegastes nigricans–otherwise known as the “dusky farmer fish”–has a bit of a green fin, but researchers rarely see such dedication to farming chores in a marine animal. They watched as this fish yanked out less digestible types of algae from their crops and threw them aside to make room for their preferred varieties, like the delicious red Polysiphonia.

As reported by Discovery News, researchers at Ehime University looked at 320 territories of 18 damselfish species from coral reefs from Thailand to the Great Barrier Reef. Though the fish in different locales preferred different regional algae flavors, they all exhibited a drive to cultivate. Hata and colleagues also raised similar crops themselves without the fish. They were no match for the fish farmers, and their crops soon overflowed with unwanted algae weeds.

They published their findings online today in BMC Evolutionary Biology. Researchers believe that the relationship is beneficial to the algae too and call it “cultivation mutualism.” Besides raising their own plots of land, the fish also fought for their turf, raising their pitchforks, so to speak, against sea urchins and other fish.

Related content:
Discoblog: This Fish Has Seen the Enemy, and It Is Him
Discoblog: The Curious Case of the Immortal Jellyfish
Discoblog: Can a Dead Fish Prove that Modern Brain Studies Are Bunk?
Discoblog: Fish that Climb? New Catfish Scales Rocks with Pelvic Fins

This is a guest post from Melissa Lott, a dual-degree graduate student in Mechanical Engineering and Public Affairs at the University of Texas at Austin. Her work includes a unique pairing of engineering and public policy in the field of energy systems research. Melissa has worked for YarCom Inc. as an engineer and consultant in energy systems and systems design. She has previously worked for the Department of Energy and the White House Council on Environmental Quality for the Obama Administration. She is a graduate of the University of California at Davis, receiving a Bachelor’s of Science degree in Biological Systems Engineering. Melissa is also the author of the blog Global Energy Matters: Energy and Environment in Our Lives.
It has been almost two months since the Deepwater Horizon oil rig exploded and sank to the ocean floor in the Gulf of Mexico. Since then, a continuous stream of oil has contaminated our ocean and coastline, resulting in the worst environmental disaster in U.S. history. Efforts have been made to stop the flow of oil, but the solutions with the highest likelihood of success ...

Twelve years have passed since Pfizer’s little blue pill for erectile dysfunction, Viagra, hit the market. The pill became so popular and ubiquitous that subsequent attempts by drug companies to make a libido-booster for women invariably drew the moniker “female Viagra.” Those attempts have failed, but today the Food and Drug Administration is considering approval for a new contender—a drug that has stirred up plenty of controversy.

The drug is called flibanserin, and the company is a German one, Boehringer Ingelheim. The first problem with evaluating the daily oral pill is figuring out whether it really has an effect that appears in trials.

The flibanserin data involved about 2,400 women treated with either flibanserin or a placebo for about six months. The agency said the two groups showed an increase in their number of sexually “satisfying” events but didn’t show a boost in a sexual-desire score. The “overall response rate… is not particularly compelling,” the FDA said, even though many of the differences in response rates between the two groups were statistically significant [Wall Street Journal].

About 15 percent of the women on the drug quit taking it because of side effects, like nausea and dizziness. That’s about twice as many as quit the placebo.

Secondly, there’s the regimen. A man need only take Viagra in advance of sexual activity, but a woman on flibanserin would have to take it every day.

Lastly, there’s the issue of “hypoactive sexual desire disorder” itself: what it is, and how it merits treatment.

“It’s a fairly complicated area, unlike in men’s sexual dysfunction where there’s a major mechanical concern,” said Dr. Elizabeth Kavaler, a urologist at Lenox Hill Hospital in New York. “In women there’s no mechanical concern, so if she’s not having a successful sex life, where is the problem?” [CBS News].

“There is no dispute that some women have a depressed level of sexual desire that causes them anguish,” The New York Times says. But there are plenty of doctors with concerns that this kind of drug is creating a problem to make money on the solution.

“This is really a classic case of disease branding,” said Dr. Adriane Fugh-Berman, an associate professor at Georgetown University’s medical school who researches drug marketing and has studied the campaign. “The messages are aimed at medicalizing normal conditions, and also preying on the insecurity of both the clinician and the patient” [The New York Times].

It seems unlikely that flibanserin will pass muster this time around. An FDA background document (pdf) for today’s meeting recommends against approval. The FDA’s Reproductive Health Drugs Advisory Committee will debate the drug today, and the agency as a whole typically follows its lead. But even if they say no, the “female Viagra” candidates will continue to emerge. If for no other reason, because Viagra showed just how much money there is to be made.

UPDATE: This afternoon the FDA committee voted unanimously against flibanserin, saying that it did not do enough good to justify the side effects.

Related Content:
DISCOVER: The Science of Great Sex at 80
DISCOVER: The Era of Nanoparticle Drugs Begins with an Erection Cream
80beats: Viagra Helps Women Combat the Sexual Side Effects of Antidepressants
80beats: FDA: We’re Going To Regulate Those Personal Genetics Tests, After All

Image: Wikimedia Commons

The Tangled Bank gets a three-page review in the latest issue of Evolution, the world’s leading journal on evolutionary biology. The reviewers, Judith Bronstein and Peter Reinthal of the University of Arizona, have very kind things to say. Here are a few of the passages that made me smile:

Each chapter reads more like a compelling narrative or a first-rate newspaper article than as a (classically, rather dry) textbook. Zimmer is a skilled essayist; he manages to be engaging without being pedantic or condescending…Zimmer’s appealing and provocative writing style should be extremely successful at introducing evolutionary thinking into the nonmajors student population that often avoids sciences in general, and evolutionary biology in particular….

Even casual readers will immediately appreciate the eye-catching presentation of The Tangled Bank. Drawings are large, full-color, simple, and well-labeled, and so informative that they have helped keep the verbiage to a minimum. They will be integral to students’ comprehension of the material. Photographs are more sparsely used, but the exceptionally high-quality and informative drawings did not make us miss them. We consider the graphics to be a major selling point of this text….

The book does an excellent job of synthesizing and summarizing complex innovations. Zimmer is unusually successful at helping to untangle the complex story of evolution of life on earth by blending paleontology, comparative anatomy, phylogenetics, molecular genetics, and many other disciplines, in a manner that is both entertaining and accessible….

The back cover of The Tangled Bank is plastered with enthusiastic encomiums by several dominant figures in evolutionary biology and science education today. Among other features, they point out the quality and compelling nature of its writing and illustrations, and its ability to capture the ferment of this rapidly moving scientific field for a nonmajors audience. As instructors with many years of experience teaching evolution topics to undergraduates, we agree. Carl Zimmer’s approach is a rather radical departure from most textbooks. But we fully expect it to rivet reluctant students’ attention, and that is exciting indeed.

It’s just a fact that contemporary human evolutionary genetics has relied upon its potential insights into disease to generate funding, support and interest. I don’t think that this is much of a silver lining when set next to the suffering caused by disease, but it’s a silver lining nevertheless. Therefore findings which would be of interest in and of themselves are able to push to the front of the line because of possible medical relevance. A new paper in PLoS Genetics illustrates the relationship between what seem like esoteric evolutionary insights and diseases of importance to the medical community. It takes a look at the gene whose disruption results in the horrible illness cystic fibrosis, CFTR, and uncovers some interesting genetic patterns of possible evolutionary relevance. The paper is The CFTR Met 470 Allele Is Associated with Lower Birth Rates in Fertile Men from a Population Isolate. From the author summary:

Cystic fibrosis (CF) is the most common lethal recessive disorder in European-derived populations and is characterized by clinical heterogeneity that involves multiple organ systems. Over 1,600 disease-causing mutations have been identified in the cystic fibrosis transmembrane regulator (CFTR) gene, but our understanding of genotype–phenotype correlations is incomplete. Male infertility is a common feature in CF patients; but, curiously, CF–causing mutations are also found in infertile men who do not exhibit any other CF–related complications. In addition, three common polymorphisms in CFTR have been associated with infertility in otherwise healthy men. We studied these three polymorphisms in fertile men and show that one, called Met470Val, is associated with variation in male fertility and shows a signature of positive selection. We suggest that the Val470 allele has risen to high frequencies in European populations due a fertility advantage but that other genetic and, possibly, environmental factors have tempered the magnitude of these effects during human evolution.

The high frequency of alleles which result in cystic fibrosis is something of a mystery. Basic population genetic theory tells us that lethal (at least in the pre-modern era) recessive traits should be extant only at very low frequencies so that most of the deleterious alleles are “masked” by normal copies. The ?F508 mutation is found in 1 in 30 people of Northern European descent (you see somewhat different ratios, but all in the same ballpark). That means that assuming a random mating Hardy-Weinberg Equilibrium a touch more than 0.1% of offspring would exhibit the disease due to the coming together of the ?F508 allele in a homozygote state, not a trivial proportion when you consider that the fitness of these individuals converges upon zero.

In this paper they don’t get at ?F508 and the other disease causing alleles directly. Rather, they find that one particular SNP has a strong effect on fertility, as well as having a relationship in some contexts to disease implicated alleles. Not too surprising considering that cystic fibrosis is associated with infertility. I presume that the overarching logic is that understanding the genetics of CFTR in its details will give us a better picture of its internal architecture and the various networks and pathways which result in its proper, or improper, function.

CFTR spans ~200,000 base pairs, but in the paper the authors focus on a few regions of interest within a sample from the American Hutterite community. In particular there is the 5-thymidine (5T) repeat allele at the 3′ splice site of intron 8, a variant which interferences with the proper transcription of exon 9. Then there is TG repeat (TG) on intron 8 and an SNP on exon 10, rs213950. In the latter case the two alleles result in the amino acids methionine and valine respectively at the 470th position (Met470 and Val470). Both of these variants have an effect on the 5T allele, increasing its penetrance in relation to the outcome of cystic fibrosis. The Met470Val mutation’s molecular genetic implications are double-edged outcome; Val470 results in a CFTR protein which matures more quickly, but with lower activity compared to the Met470 allele. Since 5T reduces splicing efficiency one could intuit why the presence of Val470, with its result of lower activity of the protein, might have a a deleterious effect when the two are found in conjunction.

The paper approaches cystic fibrosis sideways because the focus on Met470Val means that they’re looking at a secondary variant from a medical perspective; a modifier, not the primary agent. But from an evolutionary perspective there’s a lot to dig into! First, let me jump to the discussion, where they seem to admit the modest current medical relevance of this paper:

Lastly, there has been a long-standing debate as to whether disease-causing CF mutations, such as ?F508, confer a fertility advantage to healthy carriers…Unfortunately, the results we report here do not provide insight into this question. The most common CF causing mutations in Europeans (i.e. ?F508, G542X, N1303K, W1282X) and the most common mutation in the Hutterites, M1101K…all reside on haplotypes carrying the ancestral, Met470 allele in exon 10…the 9T allele at the polyT locus, and (by inference) the TG10 or TG11 alleles…Therefore, any positive fertility effects of the Val470 allele would not be expected to affect the frequencies of the common CF disease-causing mutations in European populations.

A haplotype just refers to a sequence/correlation of alleles along the genome. You know that DNA consists of a string of base pairs, AGCGCTGAGCGCAA…. If there is variation at the first and last positions in the sequence above, and if the alternative variants at the two loci do not associate randomly but exhibit high correlations along a physical sequence, then there may be a haplotype of the variants. In the case of this paper the three regions of mutations combine to form the haplotypes. Tables 1 & 2 show the frequencies of alleles and haplotypes within their Hutterite sample.

Table 1 lays out the frequencies of each allele within the sample, while table 2 illustrates the frequencies of combinations of these alleles. The haplotypes.

The next two figures show the major finding, the association between Val470 and higher fertility in Hutterite men (not women). Remember that p-value = 0.05 is the normal bar for statistical significance. The ticks in the second figure are 95% intervals.

Do I need to emphasize how important it is that the alleles have a correlation with reproductive outcomes? Changes in gene frequencies are driven by variations in reproductive outcomes, whether random or systematically correlated with phenotypes. Drift or selection. Traits strongly tied to reproduction often have low heritabilities because all the variation on such traits quickly disappear because of selection’s homogenizing power. It is interesting that in this case they’re implying that there’s heritable variation in reproductive outcomes, as they know a priori that selection should have expunged the variation, all things equal.

Here’s a more stark figure which illustrates the association between haplotype and fertility in a more stepwise fashion:

OK, so how does this vary across populations? The next figure comes straight out of the HGDP browser:

The variation on Met470Val exhibits an African/non-African difference. I assume that the variation in the non-African segment (compare the Tuscans to the Russians for example) is mostly noise because of the small sizes of some of the HGDP sample groups. The 0.10 frequency in the San sample is intriguing. I’ve never heard anyone assert that the HGDP San had likely non-Africa admixture, so existence of Val470 in this southern African group suggests to me that its appearance among non-Africans is not simply a random act of history (i.e., the outcome of the Out of Africa event and bottleneck). There may be common relaxations of ecological constraints on novel adaptation as one moves away from the tropics, or, new selective pressures.

I wanted to highlight the nature of the haplotype variation earlier because the authors ascertain the possibility of natural selection driving Val470 up in frequency among non-Africans using haplotype based tests of natural selection. In the figure below panel A shows the haplotype blocks. The short of it is that Val470 has a much longer haplotype than Met470, which stands to reason if Met470 was the ancestral state around which a lot of variation had crept in through drift (LCT, the gene which has a derived variant which confers lactase persistence has a very long haplotype on the selected allele because it rose in frequency faster than recombination and mutation could break apart the distinctive genetic profile of the original copy). Panel B shows extended haplotype homozygosity (EHH), while D shows iHS (integrated haplotype score). The latter is to some extent an elaboration of the former, able to detect selective sweeps which have not come close to fixation as those best detected by EHH. Panel C has Fst between African and non-African populations. Fst is a statistic which summarizes between-population variance. It is 0.43 for Met470Val, while genome-wide it’s 0.11. Both the Fst and iHS values for the SNP are on 5% tails of the distribution, illustrated by panel E.

The Fst differences, along with suggestions of homogeneity across the genetic scale for the allele, Val470, which confers reproductive fitness, strongly points to the possibility of natural selection. But the reproductive differences they found were large; why is Met470 still around? In the discussion there throw out some possibilities:

In fact, given the large fertility effects observed in the Hutterites, it is surprising that the Val470 allele has not gone to fixation in non-African populations. However, there might be several reasons why this has not occurred. First, the combined data on fertility effects of the Val470 allele indicate that this allele can be associated with both increased and decreased fertility, depending on genetic background. In the presence of the 5T allele at the intron 8 polyT locus, Val470 increases the risk of CBAVD and male infertility…In the absence of the 5T allele (as in the Hutterites), the Val470 allele is associated with increased male fertility relative to Met470. Although the mechanism of this interaction is obscure, it provides one example of counteracting variation that could increase the time to fixation of the Val470 allele. Second, as mentioned above, the Val allele could also be deleterious in certain environments, such as in the presence of specific pathogens or the 5T allele, as a result of its pleiotropic effects in other organ systems. Third, the fertility advantage we observed is restricted to males; we found no such association in Hutterite women…This would further slow the spread of the allele as there would be no selection advantage in half of all Val carriers. Lastly, this study was conducted in a population living under optimal conditions for reproductive success, including excellent nutrition and abundant food, access to modern health care, and negligible maternal mortality. Thus, estimates of fitness effects based on Hutterite fertility rates are likely inflated compared to the effects in human populations throughout most of evolutionary history, when competing selective pressures were likely more prevalent. Taken together, the lack of fixation of the Val470 alleles in populations outside of African may not be inconsistent with the fertility effects observed in the Hutterites, but rather suggestive of antagonistic effects of other genetic variations or environment factors that tempered these effects during most of human evolution.

Remember that we’ve seen for a while now that loci which exhibit signatures of positive natural selection are often not fixed to 100%. Why not? There have been many explanations offered, and the ones above fall into the general categories mooted. Looking at a relatively isolated population in a snapshot form may not give us a full impression of what’s going on. On the other hand, the Hutterite genetic uniformity presumably eliminates many of the confound signals which might otherwise obscure associations, so there are pluses and negatives to this sample. And of course evolution occurs over time, and peaking at slices tells us what it tells us, no more, no less. This is a place to start, but I bet it will make more sense once we have a better grasp of the distribution of dynamics across the genome. Scientific understanding often proceeds in a piecewise fashion, but the sum is greater than the parts as the sum often exhibits a structure of variation which allows us to squeeze more juice from the parts.

Citation: Kosova G, Pickrell JK, Kelley JL, McArdle PF, Shuldiner AR, Abney M, & Ober C (2010). The CFTR Met 470 allele is associated with lower birth rates in fertile men from a population isolate. PLoS genetics, 6 (6) PMID: 20532200