by David Malakoff
(
Abstract
The process of constructing the phylogenetic tree of life has become more contentious, as contradictions popped up between traditionally used measures of morphological similarity and more recently developed statistical comparisons of DNA sequence similarity. The healthy controversy, and an NSF initiative, may invigorate the field of taxonomy and systematics in time to help categorize the diverse biological resources of our planet.
Warning signs should be posted at many biology meetings these days. Caution! Tree of Life Undergoing Major Reconstruction: Watch for Falling Limbs. Dim lecture rooms have recently become conceptual construction sites. Scientists demolish stately, old evolutionary trees handcrafted from close study of organisms' anatomy, and they replace them with contemporary, high-tech designs manufactured from the computerized analyses of DNA molecules. Not a day goes by, it seems, without the appearance of a new paper proposing a major phylogenetic reshuffling - based on molecular findings - of some plant or animal's place in evolutionary history.
Like many renovation projects, however, this exercise in creative
destruction has made some of the contractors testy.
Hard hats are in order after some presentations as verbal brickbats fly
between the traditionally trained taxonomists - who painstakingly built the
existing trees by scrutinizing bone, shell, or leaf features - and their
increasingly cocky molecular colleagues. It's not unusual to hear a gene
jockey suggest that the newer approach, which involves statistically
comparing DNA chunks from organisms to determine which are related and which
evolved first, is scientifically superior to "subjective"
morphological techniques. But such claims are just "molecular
chauvinism," charge some morphologists, and downplay the inherent
subjectivity in interpreting genetic data. Both sides are able to point to
studies that support their point of view. While molecular approaches have
shown that some morphologically similar organisms are in fact genetic worlds
apart, blind faith in sequence analysis has also produced unlikely
phylogenetic trees that prompt peals of laughter from veteran morphologists.
As a journalist watching from the sidelines, I find the energetic debate
entertaining and, especially since it is sometimes bitter, newsworthy. More
importantly, however, I am hoping the conflict is a sign that the once
moribund discipline of systematic biology may be coming to life just when we
need it most. We are edging toward a biological catastrophe that threatens
to wipe out up to half of Earth's species in a geologic heartbeat.
Ironically, however, we don't really know much about what we risk losing
because there simply aren't enough taxonomists to discover and describe
unknown species - and perhaps even fewer systematists of any stripe to fight
about where they fit in the grand order of things.
So far, for instance, scientists have described less than 2 million of
Earth's estimated 14 million species. In even well-studied groups where most
of the species are known, such as birds and mammals, exact evolutionary
relationships remain mysterious and controversial. But almost nothing is
known of many more groups of organisms, from deep seafloor creatures to many
bacteria and plants, simply because there is nobody to study them. Around
the world there are probably less than 7,500 scientists engaged in the
Herculean task of documenting biodiversity, and many are nearing the end of
their careers with no replacements in sight.
Once this knowledge gap might have elicited knowing and worried looks - but
little action - from researchers in richer areas such as the medical
sciences. But today even drug makers have decided that there are quite
practical reasons to be interested in biodiversity and evolutionary history.
So-called "novel" genes, for instance, have become the gold
standard of drug development, with companies investing billions in trying to
find and exploit chunks of DNA that code for medically valuable compounds.
It has dawned on the smarter companies - such as Philadelphia's SmithKline Beecham - that having found an
organism, such as a bacteria, that carries one valuable gene, it might pay
to hire an evolutionary biologist who can identify its relatives, which may
carry similar genetic gold. So, for perhaps the first time in history,
taxonomists and systematists relegated to the nether reaches of their
college campuses and museums are being told that their work - which
experimental scientists sometimes dismissed as "stamp collecting"
or "pasting leaves on the tree of life" - has eminently practical
applications. It's about time.
But the morphology versus molecules debate suggests that beyond training a
new - and more valued - generation of biological stamp collectors, we must
train a new kind of systematic biologist: one who can synthesize both
traditional taxonomy and new genetic approaches into his or her work. This
kind of interdisciplinary training has long been one of the weak links in
American higher education, with its departmental boundaries and specialized
disciplinary kingdom building. Indeed, it was the perception that
taxonomists weren't real scientists that directly contributed to the current
shortage of trained experts: there was no incentive for graduate students of
the last three decades to devote much time to the subject, since it probably
wouldn't help them land a job.
That may still be true, given the precarious state of hiring at most
academic institutions. But on the coast of Maine, one can get a glimpse of
how the savvy taxonomist of the future may be trained - and how a little
federal money can provide a lot of incentive to take up the task of
inventorying life. At the University of Maine's Darling Marine Center in
Walpole, crustacean taxonomist Les Watling - a traditionally-trained
morphologist who has been openly critical of some molecular approaches - is
putting a few of his graduate students through a rigorous boot camp. It
teaches them to appreciate both gross anatomy and microscopic molecules: he
teaches the fine points of identifying key morphological characteristics;
the one-two punch is completed by Irv Kornfield, a master geneticist at
Maine's Orono campus.
Learning the two, equally intricate approaches can be exhausting, but it is essential, says Pilar Haye, a Chilean who is in the program. "You can't do this kind of work anymore from just one perspective," she says.
The program is made possible, in large part, by a special National Science Foundation program designed
to shore up taxonomy's declining ranks,
particularly outside the western, industrialized nations. Called the
Partnership for Enhancing
Expertise in Taxonomy (PEET), NSF officials say it is a modest effort to
return the foundation to its roots. More than 10% of NSF's first 97 grants
in 1952, notes PEET director James Rodman, were awarded for work in
systematic biology. Today, he says, far less than 1% of its funds are spent
on similar work. He argues that the 1952 "high water mark should again
be the goal."
So far, 31 researchers - including Watling and Kornfield - have won more than $15 million in PEET grants since the program started in 1995. And future grants, Watling believes, will increasingly go to research teams that marry morphology and molecules. "The problem has been that people perceive - and often present - [DNA-based trees] as fact, rather than theory," he says. "Challenging that perception and criticizing some of the sloppy techniques has been an important and useful activity. But the point of it all should be to see that the two techniques should be used together."
As a journalist, I will mourn the passing of the era when veteran taxonomists fought it out with the DNA upstarts. But the reality is that only a few extremists are left on the fringes of the debate. Most, like Watling, have rushed to the middle. The question now is whether they form enough critical mass to convince the powers that be that supporting systematics can help stave off two extinction threats. One threatens to deny us the scientists who are able to organize the world of life into some comprehensible form. The other would deny us the very species that we depend on and make so much of science worth doing.
David Malakoff is a freelance science writer in Bar Harbor, Maine. A graduate of the College of the Atlantic, he has written for Science, The Economist, PBS Online, ABCNews.com, and many other print and Web publications.
Andrzej Krauze is an illustrator, poster maker, cartoonist, and painter who illustrates regularly for HMS Beagle, The Guardian, The Sunday Telegraph, Bookseller, and New Statesman.
Endlinks
Journey into Phylogenetic Systematics - overview of the science of constructing the phylogenetic tree. An online exhibit at the University of California at Berkeley's Museum of Paleontology. See also their Phylogenetics Resources page.
NSF-PEET: WWW Resources in Systematics and Taxonomy - links to taxonomy, systematics databases, and related tools on the Web.
World Resources Institute - links to information on biodiversity prospecting, the economic use of genetic resources for sustainable development.
World Conservation Monitoring Centre - an information clearinghouse on maintaining species biodiversity. Provides links to databases of endangered species.
Taxonomy and Systematics at the University of Glasgow: Institutions and Internet Servers - links to taxonomy and biodiversity resources on the Web.
Biodiversity Information Network - biodiversity, taxonomy, and conservation links from Charles Sturt University in Australia.
Smithsonian Institution Natural History Web - extensive natural science links.
Biodiversity and Biological Collections Web Server - "information of interest to systematists and other biologists of the organismic kind." Links good though not very up to date. Site is searchable.