Sunday, April 7, 2013

Evolutionary Rescue, Pappy Van Winkle, and Next-Level Smokin-Hot Secret Sauce

Many years ago, when Mike Kinnison and I were office mates in Seattle, we started a list of “words we should use more often.” These were usually esoteric English words that we had encountered in some publication and decided were just too cool to be used so infrequently. I can’t remember all of the words but consanguineous was certainly one of them. I did use consanguineous in at least one paper but, sadly, it did not precipitate a particularly far-reaching or long-lasting meme. But what if I had tried harder? What if I had insisted that my fellow graduate students use the word in their papers – or bribed them to do so? What if I had used it in all of my own papers? What if I had extorted (or bribed) each visiting seminar speaker to use it in their talks? This is precisely the experiment currently being conducted by the Jen Schweitzer and Joe Bailey labs at the University of Tennessee.

While visiting UT for a seminar last week, I met with Joe and Jen’s students. At the end of our meeting, the students casually mentioned that they had come up with a series of phrases that should be introduced into the scientific lexicon – and they pointed out that I could help their cause by using the phrases in my seminar later that day. I immediately thought back to consanguineous and its ignominious continuance in anonymity. Maybe I here had a new chance to save some cool lost word or phrase from the dustbin of academia. I would be glad to help, I told them, what are the phrases? They pointed to the chalkboard behind me, where I read:

“Next level shit”
“Smokin’ hot right now”
“There ain’t no secret sauce”

Hmmm – not quite what I was expecting and perhaps not so deserving as consanguineous but, then again, who am I to quash enthusiasm and ambition. The meme does not stop here. After presenting some genetic data in my talk, I pointed out that the particular genetic markers (microsatellites) I used were rather old school, and that what we really needed to answer the question was some “next level shit.” I then pointed out that what is “smoking hot right now” (actually I had forgotten the phrase and needed some prompting) is RAD-tag based SNP discovery – for which I conveniently had some results in my next slide. Two phrases down, one to go: the hardest one. I struggled to think of an appropriate use for “there ain’t no secret sauce” and eventually realized, while looking at my conclusions, that this was precisely the spot.

Now, I can’t say that I will continue to use these phrases in all my talks, but I do feel I have done my part and that, should the meme not take off, I will at least have given it the "old college try.” If it does take off, I suggest that consanguineous should be next. In fact, I anticipate that all of Jen and Joe’s students will now feel obliged to use it in their talks. (It means “of the same blood” and so can be used in relation to ancestry or relatedness.)

Jen and Joe holding court in the Smokies.

During my visit, I stayed with Jen and Joe, who kept me well fed (home-made crab cakes, gumbo, and cherry pie), well beveraged (beer, wine, and – in a rare treat – a drink of 23-year-old Pappy Van Winkle’s Family Reserve Bourbon), and well entertained (Emmylou Harris, Rodney Crowell, and Richard Thompson at the historic Tennessee Theater). Joe even let me beat him at ping pong on his home court. I stayed through Saturday to see some sights in the nearby Smoky Mountains, a major biodiversity hotspot. Joe and Jen both had field courses to teach in Cade’s Cove – a mountain valley in the Smokies – and so I tagged along. Both courses – one graduate and one undergraduate – were to collect data at a series of deer exclosures. 

Deer exclosure - or Hendry enclosure?

At one site, Mark Genung and Joe showed me a dead hemlock tree and then found a hemlock sapling that was covered with an invasive scale insect. This insect has apparently decimated hemlock populations on a massive scale. This brought to mind many seemingly parallel instances: Dutch elm disease, myxomytosis in Australian rabbits, phyloxera in European grape varietals, sudden oak death, white nose syndrome in bats, tuberculosis in native Americans, the Black Death in Europe, mountain pine beetles, chestnut blight, and chytrid fungus in amphibians. In each case, an emerging disease – often (maybe always) an invasive, or at least spreading, species – decimates native populations that are not resistant.

What I find interesting about these catastrophes is that they rarely cause species extinctions – except perhaps for chytrid fungus. Instead, the massive declines are arrested short of extinction and the native species either carry on at a much lower abundance or ultimately recover. The interesting question for me is why extinction does not occur. Three possibilities come to mind. First, success of the disease may be frequency dependent, such that its impact or ability to spread greatly decreases as the host becomes rare. This makes some sense as the spread of a disease often depends on the number of nearby susceptible hosts – and so a decline in population density of hosts will decrease the chance that the remaining individuals will be infected. Second, hosts may evolve resistance – as long as genetic variation in resistance exists, then the individuals that survive and reproduce will increase the frequency of resistant genes. In fact, massive mortality events are expected to drive the fastest rates of evolution – because they can impose the strongest selection. Third, the disease may evolve to be less severe, as would befit its continued existence. I have no idea which of these effects is most important in any of the above examples, but it seems to me an important eco-evolutionary question in the context of evolutionary rescue.

Evolutionary rescue is the idea that when environmental change results in maladaptation that causes a population decline, adaptive evolution might reduce maladaptation and thereby arrest the population decline and allow recovery. Evolutionary rescue is generally thought to be most effective for organisms with short life spans, such as bacteria, viruses, or some weeds and insect pests. This makes good sense because these short-lived and numerous organisms presumably have high genetic variation and mutation rates and thus greater evolutionary potential. But it seems to me that large and long-lived organisms, such as trees, have something else going for them. In particular, high mortality can eliminate all but the few mature individuals that are most resistant, which – owing to their very high reproductive output (a birch tree can produce 15-17 million seeds per year) – have the potential to rapidly recover population size. I am not saying that bacteria and viruses don’t have the advantage in evolutionary rescue, merely that the supposed disadvantage to long-lived organisms might sometimes be partly offset by a combination of extremely strong selection and high potential reproductive output in survivors. For more about evolutionary rescue, see the recent PTRSB special issue.

A Tennessee Turkey strutting its stuff.
Well, that’s it for now. I hope to enjoy the rest of my day in the airport of some city that ends in “ville” (Tennessee has more than 50 such cities and towns – more than any other state) and some city that ends in “ark” before finally making it home to that city that ends in “real”.

In the Newark Airport, is it the Earl himself? Or maybe a descendent, perhaps basking in the glory of his ancestor - or protesting the lack of royalties.

1 comment:

  1. Yeah, bring that next level shit


On second thought...

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