Current and future research

Research on termite colonial physiology is continuing on two broad fronts:

Study of wind- and temperature-driven gas exchange in the architecturally simple mounds of Trinervitermes trinervoides. Click here to see more details
Study of the links between soil transport, morphogenesis and patterns of gas exchange in the mounds of Macrotermes michaelseni. Click here to see more details.

The study site
Our study site was located near the small town of
Kamieskroon, roughly 400 km north of Cape Town, in the
picturesque region of South Africa known as Namaqualand (right).
This region is famous for its spectacular spring
displays of wildflowers. To botanists, however, Namaqualand
is better known as part of the Succulent Karoo, one of the world's
most exotic and speciose botanical regions. The flora of the
Succulent Karoo is exceptionally diverse, with a high degree of endemism and unique plant forms, drawn mostly from a few families of plants.
The study site itself is located at high elevation in the Kamies Mountains, which consist mostly of recently exposed granitic domes, with truly magnificant vistas. The soils are correspondingly sandy and well drained, which support robust populations of Trinervitermes. Top

The species
Trinervitermes trinervoides is a member of the subfamily
Nasutitermtidae, distinguished by the modification of the
head capsule into a nozzle-like device which the termites use
to spray intruders with a noxious fluid. It builds nests
consisting of honeycombed cells constructed from soil
cemented into place by anal and oral secretions of the
workers. Especially in sandy soils, the termites build a
mound that rises above the nest. These mounds can be
quite large - in parts of southern Namibia, they reach
heights of 2 meters or so. More common are relatively
low dome-shaped mounds that are 1-1.5 meters tall. Top

Experiments & preliminary results

Field work focused on three major questions:

Do the structures of the internal air spaces show any evidence of the "bucket-brigade" soil transport proposed as the principal driver of mound morphogenesis among the more advanced macrotermitines?
Do winds drive flows of air within the mounds of Trinervitermes as they do in mounds of Macrotermes?
What are the relative strengths of natural convection (driven by temperature gradients within the mound) compared to forced convection (driven by wind) in driving ventilation of the mound?

Field work was recently completed on this project and the results are being prepared for publication. Following is a precis of the results so far:

The internal air spaces within the Trinervitermes mound are not strongly differentiated. However, air spaces are comparatively more voluminous at the mound's center than at its periphery, indicating a rudimentary bucket-brigade soil transport mechanism in operation.
Wind strongly drives air flows within the mound, consistent with the capture of wind energy and its transformation to pressure according to the Bernoulli principle.
The mound is undermined by a network of large tunnels that comprise scorpion burrows. There is no gas exchange between the air spaces of the scorpion burrows and the termite mound.
The daily march of insolation imposes large temperature gradients on the mound throughout the day. These appear to have little effect on patterns or rates of gas movements within the mound. The mound's gas exchange seems driven most strongly by its interaction with wind. Top

Wind- and temperature-driven gas exchange in mounds of Trinervitermes trinervoides.

Trinervitermes trinervoides is a widely-distributed termite that builds a simple dome-shaped or columnar mound (pictured above). Unlike the more complex Macrotermes and Odontotermes mounds, Trinervitermes mounds are simple in construction, and so not exhibit any strong differentiation of tunnel types. The intent of this work is to use these simple mounds as a comparison to the structurally complex mounds of the macrotermitines, in the hope they will illuminate the selective forces that drove the evolution of the macrotermitine's very sophisticated structures.
This research was supported by the Earthwatch Institute, and by the contributions of time and money by the volunteers of EarthCorps.

Mound morphogenesis and emergent homeostasis in colonies of Macrotermes michaelseni

This work continues our main project in understanding the superorganismal physiology of Macrotermes colonies. The problem addressed here is concerned with understanding the link between termites' building behavior, how it is influenced by local conditions of atmospheric composition, and how perturbations of architecture or environment affect the gas exchange properties of tunnel networks built by termites.

Our principal experimental method is to induce termites to build tunnel networks in large-diameter PVC pipes implanted into the mound. We are undertaking detailed analysis of the structures of these tunnel networks by 3D reconstruction of plaster casts of the tunnels. An animation of a tunnel network is available for viewing by clicking here (2 MB).

These building arenas, as we are calling them, will be used for experimental perturbations of the local atmosphere. These perturbations will take many forms, including altering the distribution of pressure within the tunnel network, modification of the local composition of the tunnel atmosphere, and analysis of the gas exchange properties of the tunnel networks.

These experiments will provide, for the first time, a complete picture of all the elements of social homeostasis - building behavior, local conditions and physiological function - and how they relate to one another.

This work is sponsored by the National Science Foundation.