Termite Research
Termites are one of the most
important recyclers of woody debris in tropical ecosystems. Therefore, factors affecting
termites can have ramifications for the ecosystem as a whole. We use the
Caribbean termite, Nasutitermes acajutlae as our research animal. Nasutitermes
acajutlae live in large arboreal colonies that can contain more than
500,000 individuals. Only a few individuals within a colony reproduce. All
other colony members perform tasks such as rearing the offspring of the
reproductives, defending the colony against invaders and foraging. Sterile
female N. acajutlae become workers, building nests, enclosed foraging
trails, feeding larvae and other castes. Sterile males become soldiers, with a
nozzle-shaped proboscis that shoots a sticky defense compound. Reproductives
are produced and released once a year after the first heavy rain in the fall.
These winged "alates" find mates and found new colonies. This species
is wide-spread in the Caribbean and is the most common forest termite on many
islands, including the US Virgin Islands. My research on N. acajutlae
has two main components: ecological and immunological.
Termite Ecology and Behavior
The study island. Most of our ecological and behavioral work is conducted on St. John, U.S. Virgin Islands. St. John is small (49.2 km2), and steep with max. elevation of 370 m. It is considered to be a tropical dry island, with rainfall below 130 cm per year and temperatures generally ranging between 70-95 F. St. John is sparsely populated (< 4000) and 2/3 of the island is a national park (Virgin Islands National Park). Nasutitermes acajutlae colonies occur in all areas of the island, although densities vary depending on habitat (Jeyasingh and Fuller, 2004). While on St. John, we typically stay at the Virgin Islands Environmental Resource Station (VIERS), on Lameshur Bay.
Effects of parasitism. We are examining the effect of a thorny-headed worm (Phylum Acanthocephala) on N. acajutlae morphology, behavior and population biology. The termite is the intermediate host of the parasite (the host in which the parasite is a larva) and is passed to its definitive host (in which it reproduces) when the termite is eaten. Infected termites are much lighter in color than uninfected termites. They also behave differently, spending more time in exposed locations than unparasitized termites. These changes make parasitized termites more susceptible to predation (Fuller et al 2003). We are also examining the impact of parasitism on the entire termite colony. The number of infected foragers can be high (30% is common). We have shown that parasitized colonies have lower reproductive success of unparasitized colonies (Fuller and Jeyasingh 2004). We are in the process of further documenting behavioral changes associated with parasitism such as foraging and feeding of nestmates.
Effects of habitat. Nasutitermes acajutlae is unusual in that it occurs in many
different habitats. This situation has provided us with an opportunity to
examine whether factors such as differential levels of food (woody debris),
competition (e.g., with fungus) and predation (e.g., by anoles) impact
colonies. We are conducting a long-term monitoring study of 100 colonies in 5
different habitats (mangrove swamps, wetlands, dry forests, rain forests and
areas with sparse vegetation such as beaches) to determine whether the factors
mentioned above are correlated with differences in colony growth, survival and
reproduction. Analysis of the first 5 years of this study indicates that each
factor may be important and that their relative importance varies by habitat
(Jeyasingh and Fuller 2004).
Dispersal. This work is part of a collaboration with L.W.
Harris and Dr.
Elizabeth Walsh, at the University of Texas, El Paso. We are using a
genetic technique (AFLP) to examine patterns of termite dispersal on the island
of St. John.
Termite
Defenses Against Pathogens
Immunology. We are examining the relationship between habitat,
colony size and immune response. We are focusing on various aspects of immunity
including melanization, lytic ability of hemolymph, encapsulation and susceptibility
to fungal pathogens. We have just begun this work/
Defenses Against Fungi. We are examining whether termite secretions can
deter fungal growth. Thus far, our studies have supported the findings of
Rebeca Rosengaus and her collaborators – soldiers inhibit fungal growth and may
defend colonies against invasion.
Funding
This
project was funded in part by the generous support of Earthwatch Institute,
the Howard
Hughes Medical Institute and
Murray State University.