Evolution: Termite evolution: which came first?, tiny critters, ancient lineage

http://en.allexperts.com/q/Evolution-3839/Termite-evolution-first.htm

The type of protists you're naming in the termite intestine are flagellates in the genera Trichonympha and Personympha.  They belong to a very ancient lineage that evolved long before insects were even on the planet.  However, these species themselves were not present before termites.  In fact, termites and their flagellate mutualists *coevolved*.

It is most likely that ancestral termites ate more than just wood.  Like many insects in this group, they were herbivorous, and ate soft parts of plants as well as the occasional wood bit that just passed through.The hypothesis about the origin of the mutualistic relationship between the insect and the protist would go something like this:The ancestral termite-like insect ingested protists along with its diet of plant material, since those protists might also have been feeding on the plant matter.  If some of those protists happened to be feeding on wood bits because they were able to produce enzymes that dissolved the cellulose, these might have been ingested, too.It's not unusual for protists and other microorganisms to take up residence inside other, larger organisms.  Sometimes they become commensal (gaining benefit for themselves, but not harming the host), parasitic (gaining benefit for themselves at the expense of the host), or mutualistic (gaining benefit for themselves and also benefitting the host).  Which type of relationship will evolve depends on the genetic changes that take place from generation to generation in both host and resident partner.In the case of the termite, if the protists were able to stay in the gut unharmed (which again, is not uncommon), they may have provided an immediate benefit to the host insect by providing digestive services that other termites who didn't ingest those protists didn't have.  This, ostensibly, could give the protist-hosting termite ancestors an energy advantage, allowing them to reproduce more and leave more genes to the succeeding generations.

---SPSmith