Kudzu: It’s worse than you thought. The invasive plant now covers more than 7 million acres in the United States, mostly in the Southeast but not limited to there. Besides overrunning trees as it spreads like wildfire, the vine also brings another danger: In a study in the Proceedings of the National Academy of Sciences, Jonathan Hickman sounds the alarm that kudzu could cause a spike in ozone, polluting the air.

Ozone, of course, is a good thing when it’s high in our atmosphere, blocking some of the sun’s harmful radiation. But down on the surface of the planet, ozone isn’t such a good thing. It can cause respiratory problems in people and harm plants’ ability to absorb carbon dioxide; it also is a major constituent of smog.

Kudzu’s contribution to ozone levels works like this: Like other members of the pea family, or legumes, Kudzu grabs nitrogen from the air and puts it into the soil. There microbes convert nitrogen into nitrous oxide, one of the pollutants that also comes from automobile exhaust. That gas escapes from the soil and into the air, and undergoes reactions that lead to the creation of ozone [Discovery News].

When this reaction happens on a small scale it’s not a big problem. However, there’s getting to be so much kudzu in the U.S. that Hickman decided to measure what its ozone contribution might be. So his team studied the soil of Madison County, Georgia, picking some areas where kuzdu had invaded and some where it had not. In the kudzu-ed areas, he says, nitrous oxide emissions were double that of the kudzu-free areas.

To drive home the point, Hickman and his colleagues ran a simulation in which kudzu spread over the entirety of its region except for soils in the city or those used in agriculture. Crunching those numbers, the team estimated a dramatic increase—35 percent—in the number of days that would register an atmospheric ozone level in excess of the safe limit set by the Environmental Protection Agency.

That’s a pretty extreme scenario; kudzu alone isn’t going to drive up ozone pollution by a third. Even with kudzu stretching out ever further, its present contribution to ozone is most likely a minor one, Hickman says, but the ozone potential is one more reason to loathe the vine.

He acknowledged that any soil used to grow nitrogen-fixing plants or were fertilised for agricultural reasons would result in an increase in gases involved in the formation of ozone. “But in those cases, we are doing these things for necessary reasons — namely food production,” he observed. “In the case of Kudzu, it is an undesirable plant that is spreading over a large area in the south-east US” [BBC News].

It’s also an undesirable plant that people brought to America on purpose, making it not just a poster child for invasive species, but also for importing a foreign organism to try to fix some other problem in an ecosystem.

Kudzu (Pueraria montana) is a rapidly growing vine native to Asia that was introduced to the United States in 1876 at the Centennial Exposition in Philadelphia as an ornamental plant and later promoted to farmers in the Southeast as a means of controlling soil erosion by the U.S. Soil Conservation Service during the 1930s [LiveScience].

Related Content:
DISCOVER: The Truth About Invasive Species
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80beats: Should Humans Relocate Animals Threatened by Global Warming?
80beats: Globalized Pollution: Asian Smog Floats to American Skies
80beats: Today’s Biggest Threat to the Ozone Layer: Laughing Gas

Image: flickr / SoftCore Studios

Since its launch in 1990, the Hubble Space Telescope has taken… let’s see… <counting on fingers>… carry the two… about a gazillion pictures of the sky. Not all of them are gorgeous, and not all of them are news-breaking, but an awful lot are really cool but don’t get any press.

That’ll change now. The folks at the European Space Agency side of Hubble Central have created a new feature: the Hubble Picture of the Week. This is pretty much what it sounds like: a new, way cool picture posted once a week. They’ve posted the first three already, like this one:

Click to embiggen. That’s the planetary nebula IC4634, a star that was once much like the Sun, but is now at the end of its life, throwing off great gusts of gas in its final paroxysms before fading away as a white dwarf.

The galaxy image above is another one, NGC 2082, a pretty, face-on spiral about 60 million light years away. I worked on Hubble data for a long time, and I saw a lot of images that should be seen by more people, but there simply wasn’t a way to do it back then. With this new HST PotW, I bet a lot of those will get wider acknowledgment now.

Tip o’ the lens cap to astronomer, my friend, and sometime dance partner Lars Christian Lindberg.

I was going to write something up about Mount St. Helens, which erupted 30 years ago today. But then The Big Picture went and did an incredible retrospective of it, so I’ll just send you there. Here’s a taste:

If you’ve ever wondered what my nightmares are like, you’re looking at one.

I’ll add that a few years ago, when I still lived in California, I flew up to Seattle for a meeting. I literally gasped out loud when I saw the volcano out my window. I stared at it for as long as it was visible. The whole story was laid out clearly for anyone to read it: the side of the caldera was collapsed, and I could see the long run out from the lahar, the mudslide that followed the eruption. Even nearly three decades later the devastation was incredible. Over 3 cubic kilometers (0.67 cubic miles) of rock and ash blew out of the volcano that day.

You can read about the details of the event on the USGS site and on their 30th anniversary page. It’s a hair-raising story. [Edited to add: This NASA series of pictures is also way cool.]

And by the way? The volcano is still active. Have a nice day.

Image credit: USGS.

Orac has a great post skewering an ambitious gambit over at Age of Autism: One Julie Obradovic lectures us there on how to actually save the vaccine program. Much of the advice has to do with accepting the incorrect premises of the vaccine skeptics, and humoring them. All of Orac's criticisms are on target, but I actually thought Obradovic wrote one thing worth listening to--at least if we take the more abstract point out of the biased context in which she introduces it. It is this:
Additionally, [vaccine skeptical parents] don't take kindly to propaganda or threats, and they most definitely don't like to be insulted. Telling them their choice is to go with the scientific side is juvenile in its approach, suggesting that any parent who researchers [sic] both sides of the debate, personally knows someone with a different experience, and disagrees with the one size fits all approach to vaccination is by default, non-scientific. Brilliant. Well, they actually are unscientific when they do this. However, it probably is true that the confrontational, "you're clueless and irrational approach" is unlikely to unclog their minds or shatter their misconceptions. Why? Human beings just don't work that way. We have vast bodies of social science ...

Mutations are as you know a double-edged sword. On the one hand mutations are the stuff of evolution; neutral changes on the molecular or phenotypic level are the result of from mutations, as are changes which enhance fitness and so are driven to fixation by positive selection. On the other hand mutations also tend to cause problems. In fact, mutations which are deleterious far outnumber those which are positive. It is much easier to break complex systems which are near a fitness optimum than it is to improve upon them through random chance. In fact a Fisherian geometric analogy of the affect of genes on fitness implies that once a genetic configuration nears an optimum mutations of larger effect have a tendency to decrease fitness. Sometimes environments and selection pressures change radically, and large effect mutations may become needful. But despite their short term necessity these mutations still cause major problems because they disrupt many phenotypes due to pleiotropy.

But much of the playing out of evolutionary dynamics is not so dramatic. Instead of very costly mutations for good or ill, most mutations may be of only minimal negative effect, especially if they are masked because of recessive expression patterns. That is, only when two copies of the mutation are present does all hell break loose. And yet even mutations which exhibit recessive expression tend to generate some drag on the fitness of heterozygotes. And if you sum small values together you can obtain a larger value. This gentle rain of small negative effect mutations can be balanced by natural selection, which weeds does not smile upon less fit individuals who have a higher mutational load. Presumably those with “good genes,” fewer deleterious mutations, will have more offspring than those with “bad genes.” Because mutations accrue from one generation to the next, and, there is sampling variance of deleterious alleles, a certain set of offspring will always be gifted with fewer deleterious mutations than their siblings. This is a genetics of chance. And so the mutation-selection balance is maintained over time, the latter rising to the fore if the former comes to greater prominence.

The above has been a set of logic inferences from premises. Evolution is about the logic of life’s process, but as a natural science its beauty is that it is testable through empirical means. A short report in Science explores mutational load and fitness, and connects it with the ever popular topic of sexual selection, Additive Genetic Breeding Values Correlate with the Load of Partially Deleterious Mutations:

The mutation-selection–balance model predicts most additive genetic variation to arise from numerous mildly deleterious mutations of small effect. Correspondingly, “good genes” models of sexual selection and recent models for the evolution of sex are built on the assumption that mutational loads and breeding values for fitness-related traits are correlated. In support of this concept, inbreeding depression was negatively genetically correlated with breeding values for traits under natural and sexual selection in the weevil Callosobruchus maculatus. The correlations were stronger in males and strongest for condition. These results confirm the role of existing, partially recessive mutations in maintaining additive genetic variation in outbred populations, reveal the nature of good genes under sexual selection, and show how sexual selection can offset the cost of sex.

Additive genetic variance just refers to the variation of genes which affect the phenotype by independent and usually small effects which sum together to produce the range of variation of the trait. Imagine for example that the range of variation in height within the population was 10 inches, and that there were 10 genes which varied, and that each gene exhibited co-dominance. One could construct a model where every gene pair could add 0, 0.5 or 1 inch to the height independently, so that the maximum height could be constructed by adding 10 inches to the baseline and 1 inch per locus, and the minimum height by adding no inches to the baseline when each locus is homozygous for null alleles.

Mutations can be conceived of in the same manner, with each mutation being a new variant which changes trait value. Even if most of the impact of a mutation is masked there is a small effect in the heterozygote state, and this may serve as a fitness drag. The range in mutational load can then naturally be analogized to additive genetic variance, in this case the trait under consideration ultimately being fitness, mediated through life history and morphological phenotypes.

In this report they focused primarily on the weevil’s ability to obtain resources and transform those resources into size, which correlates with greater sexual access for males and fecundity for females (ergo, greater fitness). They bred various outbred and inbred lineages across families of these weevils, because these sorts of crosses gauge the impact of masked deleterious alleles, which will manifest in homozygote state more often between related pairs who share mutations than unrelated ones. They found a correlation of -0.24 between inbreeding and breeding value; in other words the more inbred the pair the fewer offspring. The impact of these recessively expressed alleles is mitigated in heterozygous individuals, but because of the non-trivial impact the number of these alleles within an individual will determine its fitness all things equal.

Interestingly when background variables were controlled males tended to show the greatest fitness drag due to inbreeding depression. This would comport with models of sexual selection where males justify their expense (because they can not bear offspring) within the population by serving as the perishable dumping grounds of bad genes. In particular in a polygynous population a few healthy males with good genes could give rise to most of the next generation, and so providing the balance of selection to the background mutational rate.

Of course mating patterns vary between taxa. The more reproductive skew there is, in particular for males, the more recourse selection has every generation to dump deleterious alleles via selection. In contrast monogamous populations will have less power to expunge mutations in this fashion because there is more genetic equality across males, the bad will reproduce along with the good, more or less. Therefore a breeding experiment of weevils may have more limited insight than these authors may wish to admit. Geoffrey Miller’s The Mating Mind attempted to take the insights of sexual selection and develop a model of human evolutionary history, but it does not seem that this theory has swept all before it. Only time will tell, but until then more breeding experiments can’t help but clarify where theory goes wrong or right.

Citation: Tomkins, J., Penrose, M., Greeff, J., & LeBas, N. (2010). Additive Genetic Breeding Values Correlate with the Load of Partially Deleterious Mutations Science, 328 (5980), 892-894 DOI: 10.1126/science.1188013