Tuesday, January 19, 2010

When a termite is not a termite

Ever since entomology has existed as a science, termites have been honored with their own taxonomic Order. To explain, under the current system of taxonomic classification devised by Linnaeus and his proteges, all plants and animals (and other living things) are assigned to a Kingdom, Phylum, Class, Order, Family, Genus and species, in increasing taxonomic specificity. A house fly, for example belongs to the Kingdom Animalia, Phylum Arthropoda, Class Insecta, Order Diptera, Family Muscidae, and Genus and species: Musca domestica. The last two taxa, genus and species, together make up the scientific name of the insect.

Under this system, termites have always been viewed as distinct from other insect Orders, and assigned the well-known name "Isoptera". For many years it's been recognized that the "IBM" orders (Isoptera, Blattoidea, and Mantoidea: the termites, cockroaches and mantids), share Nymphs of Cryptocercus obtain nutrition from the anal secretions of the adult.  Image from Grimaldi and Engel, Evolution of the Insects, Cambridge University Press.many characteristics and are likely very closely related. A cockroach genus called Cryptocercus, for example, lives in a primitive colony with pale nymphs that resemble termites. These nymphs feed on the liquids exuded from the anus, like termites. Most interesting is that the anal feeding allows sharing of primitive protists (microorganisms) that reside in the hind gut and enable these cockroaches to digest cellulose.

In 2007, several Brits from the Natural History Museum in London published a paper, dramatically titled: "Death of an Order: a comprehensive molecular phylogenetic study confirms that termites are eusocial cockroaches". The paper claims to have proven that termites are, in fact, cockroaches...or at least their ancestors and all their closest relations are what we usually call cockroaches--in the Order Blattoidea.

Over the years I've heard pest management professionals and entomologists alike grumble about such taxonomic musical chair games. Vague mutterings like, "fools in ivory towers... just want to get their names on a paper... just want to mess things up... and this will all go away..." But, I'm sorry to report, there is method in this madness and it will probably not go away.

We all will need to get used to the old classification schemes being refined forever. The reason for the change is DNA--the same molecular tool that enshrined the CSI franchise and gave biologists new muscle. In addition to being a powerful anti-crime tool DNA has allowed us to infer the past in ways we never dreamed possible a few decades ago.

In the last couple of decades biologists have developed a number of sophisticated techniques for poking around in parts of DNA from animals and plants, reading the codes and using statistics to imply relatedness among organisms. The idea parallels theory that says your DNA is more likely to be similar with someone you are closely related to, say your cousin, than someone from another race who is only distantly related, going back much farther in human history.

These DNA-based studies allow today's systematists (those who study the evolutionary relationships between organisms) to build "family trees" for any animals they want. In the case of termites, systematists constructing the family tree for the IBM orders found that termites are direct relatives of cockroaches and fall squarely within the cockroach Order. An Order that is wholly contained inside another Order is called polyphyletic, and is not acceptable under a natural classification scheme.

All of this is more complicated than I can explain in a blog, but the end result is that most systematists today believe that termites don't deserve their own Order. Phooey. There is, however, disagreement over the level of name that termites deserve. For example, an Australian, Nathan Lo, and colleagues posted a rebuttal to the "kill the termites" paper listed above. They pointed out the long term acceptance of termites as an Order and the chaos that would ensue from demoting termites to lowly Family status. Apparently the issue has not been fully resolved, but will probably end up with termites being classified as something less than an Order, but higher than a Family.

I feel a little like Andy Rooney when I say that I hate unlearning something that I learned when my mind was fresh and impressionable. What I object to most, however, is how these new, molecular-based classification schemes don't help us learn insects in the real world as readily as the old system created by entomologists who actually watched and collected insects in the field. The gifted "gene jockeys" drawing their sophisticated "trees of life" sometime seem oblivious to the important biological and economic differences between termites and cockroaches. It's just easier to think of termites as different Orders and not as a superfamily or epifamily within an Order.

As for me, I am opting to put an asterisk next to the Isoptera titles in my slides. And I'm still calling them termites.

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