Clausen, Keck, Hiesey

To continue a bit of theme, I mentioned that there were some different ways to approach biology, and that old-school systematists with their breadth of knowledge about the diversity of life are getting harder and harder to find. This is something I also bring up in my introductory biology course, where we discuss how biologists do their work, and I mention that one distinction you can find (which is really a continuum and frequently breached) is that there are bench scientists and field scientists, and they differ in multiple ways. Bench scientists tend to be strongly reductionist, tend to focus on one or very few species, and may study just one specific, highly inbred lab strain of a species, and try to minimize environmental variables. Variation is noise that interferes with getting at basic mechanisms. Field scientists, on the other hand, argue that the simplicity of the lab is unrealistic, that the proper study of organisms has to be done in the messy complexity of the real world, and think that variation, rather than being uninteresting noise, is fascinating stuff, the meat and potatoes of evolution. Both points of view have their place, and speaking for all biologists, I think we appreciate the power and necessity of both approaches. The money seems to mostly go to the bench guys, though, which does unfortunately skew the field as a whole.

Another point that has come up here now and again is the idea of “teaching the controversy.” Creationists would have you think that the teachable controversy lies between that Intelligent Design nonsense and the entrenched monolith of the science establishment. This is not the case. There are good and interesting and fruitful controversies within biology, and these are the domains within which we like to engage our students, not in that evidence-free malarkey that the ideologues of the Discovery Institute like to disgorge in their press releases.

One example: I recently stumbled across a wonderful paper by Nunez-Farfan and Schlichting (2001), a retrospective of the work of Clausen, Keck and Hiesey, that highlighted both the value of a broad-ranging synthetic approach to biology, and also discussed a real and pending controversy in biology, the nature of species and the interaction between environment and phenotype.

Clausen, Keck, and Hiesey ought to be familiar names. Their work is definitely familiar to any of us who teach introductory courses; they produced classic examples, which are often splashed across the pages of our textbooks with some names buried in fine print at the end of the chapter. They were a team of biologists at the Carnegie Institution in Stanford who did multidisciplinary work on the adaptedness of plant populations in the 1930s, 1940s, and 1950s, at the time of the neo-Darwinian synthesis. Here’s the abstract to the paper:

The studies of Clausen, Keck, and Hiesey (CKH) have been widely cited as exemplars of ecotypic differentiation in textbooks and in the primary literature. However, the scope of their findings and achievements is significantly greater than this. In this paper we analyze the research program of CKH, highlighting their major findings during the years when the modern synthesis of evolution was taking shape. That synthesis, curiously, drew little from their examples, although their studies at the Carnegie Institution represent conceptual and methodological work that is still relevant. The works of CKH not only embodied the principles of the nascent synthesis, but often provided needed supporting data. Their classic work, especially on Achillea and Potentilla, produced abundant evidence on population differentiation of many quantitative traits and plant phenotypes, as well as demonstrating the now commonly reported distinction between environmental and genetic determination of traits. Their ecological genetic investigations of quantitative traits in plants were in sharp contrast to contemporaneous animal studies on adaptation that focused on discrete polymorphisms—with correspondingly little influence of the environment on phenotypic expression. Of utmost importance was the demonstration by CKH of adaptive differentiation by natural selection and their approaches to understanding the genetic structure of populations.

Clausen, Keck, and Hiesey ran a long term project titled Experimental Studies on the Nature of Species (ESNOS) which studied variation in plant populations in California. One of their best known studies was on clinal variation in the yarrow, Achillea. They examined this species along a transect that ran from the Pacific coast well up into the Sierra Nevada range; as the diagram below shows, these plants exhibited a characteristic pattern of variation in the different environments, with taller plants in the San Joaquin valley and shorter plants at high altitude.

Note that this is a tiny fraction of the huge amount of data collected. In addition to measuring plant height in the yarrow, they also examined 181 other species, measured multiple parameters, looked at cytology and genetics, and studied hybrids in the lab and in the wild.

One important idea they pursued was that of reaction norms: how a particular genotype interacts with its environment to produce a phenotype. They did this by the relatively easy experiment of cloning the plants, or growing them from cuttings. If you took a healthy, tall plant from the San Gregorio lowlands and planted one cutting at Stanford (sea level), one at Mather, partway up the Sierras at 4600 feet, and a third at Timberline at 10,000 feet, how would they fare? How about cloning a plant from the top of the mountains and trying to grow it at sea level?

Clones of Achillea collected at 5 sites at different elevations (San Gregorio, Knight’s Ferry, Aspen Valley, Tenaya Lake, and Big Horn Lake) were planted at garden sites at 3 different elevations (Stanford, Mather, and Timberline).

They were early and thorough supporters of the idea that phenotype and adaptation cannot be separated from their interactions with the environment. This was and still is somewhat controversial in population genetics (controversial in the sense that it is difficult to assess and actually use in research, but not so in that any population ecologist will admit that it is an important issue). Nunez-Farfan and Schlichting cite one understated criticism Clausen and Keck made of the standard models in population genetics:

Taking note of the Fisher-Wright controversy, they argue that, given that “the genetic systems these formulas assume are far too simple to represent correctly the operation of actually existing systems,” in natural populations, it was “premature to discuss the relative merits of formulas that are designed to by-pass a detailed genetic analysis.”

One of the great things about reading their work is that they directly confronted the complexity of biological systems, recognizing that the traits they studied were not only under the influence of the environment, but were polygenic and that the genes involved were pleiotropic. Despite butting heads (in a calm and scholarly way) with the leading lights of the neo-Darwinian synthesis, though, nowhere in their work will you find any dissent from the fact of evolution. If anything, their understanding of the variation and fluidity of populations in nature reinforced the idea that species are not fixed and are interlinked by heredity.

Nunez-Farfan J, Schlichting CD (2001) Evolution in changing environments: the “synthetic” work of Clausen, Keck, and Hiesey. Q Rev Biol. 76(4):433-57.