Termite evolution

At a casual glance --- whether in terms of external body morphology or apparent behavior and social organization --- termites appear to be closely related to ants. Actually, however, DNA analysis shows that members of the termite family (Isoptera), are much closer to cockroaches.

The differences between cockroaches and termites are numerous, but above all it is that the former have no specialized castes --- queens, workers, soldiers and so on --- while the latter do.

There are about 2,000 species of termites, and on June 1 Yves Roisin from the Free University of Brussels spoke at the Smithsonian Tropical Research Institute’s Tupper Auditorium about the ways that these have evolved and diversified.

One of the differences between ants and termites is the latter’s hemimetaboly, or development process that involves several moultings. Among the various termite species, individual development and the roles of different members of different castes vary, and in these variations Roisin believes that termite evolution can be traced.

Among termites there are three kinds of adults --- queens, kings and alates --- but all of these castes are not present in all species. Worker and soldier termites are all juveniles. Across the termite family there are males and females in all castes, but in most species the soldiers are either all male or all female. Workers sometimes evolve into soldiers, some soldiers are “born that way,” and no soldiers sexually mature. In many termite species workers and soldiers have distinct sub-specialties among themselves. Alates --- which disperse when it’s time to found a new termite colony --- do achieve sexual maturity, as do queens and kings. In some species there are pseudergates, or false workers, immature termites that go through an unspecialized worker phase while growing up.

One way to look at termite castes is to divide them into three groups: “reproductives,” which include kings, queens and alates; “dependent individuals,” which include larvae, nymphs and presoldiers; and the altruistic castes of soldiers, workers and false or temporary workers.

Roisin looks to foraging behavior as a key to the evolution of termite castes. There are species that live in and feed upon a single piece of wood; those that eat both of the wood in which they nest and from external sources as well; and those that nest in one place and find their food in another.

“It is likely that early termites were of the one-piece type,” the biologist opined, and then evolved into intermediate species and later into the advanced types that nest on one piece of wood and feed on others. He also proposes that species that live in large colonies evolved from those of smaller social groups, and that species with true worker castes evolved from those with unspecialized and often temporary helpers.

Studying the termites in Barro Colorado Island’s trees, Roisin finds that there are termites in both the canopy and at the ground level, with different species generally inhabiting the different niches. Way up in the treetops, he has found species that usually feed at the soil and wood interface munching away where debris collects in tree crotches or where epiphytes are rooted. Those observations will surely lead to further research and more insight into evolutionary processes.

In the question-and-answer period following Roisin’s presentation, what scientists don’t know about termites became even more apparent.

“We don’t know how a queen could decide to produce only males or only females,” he pointed out, although it’s apparent that somewhere in the life cycles of certain termite species, such a gender selection is made. Insects have no sex hormones, and neither sex changes nor workers systematically destroying eggs of one or the other gender have been observed among termites.

And what determines whether a larva becomes a worker or a soldier? “Nobody knows,” Roisin admitted.

Also in this section:
When the Americans brought their medicine to Panama
How figs keep wasps from cheating
Termite evolution
Biological climate control
Interpersonal violence as a public health issue

science

How termites evolved