Termite Research:
Termites are one of the most important degraders
in tropical ecosystems; they are thought to be responsible for as much as 20%
of carbon mineralization. Numerous studies document the composition of termite
communities and their role in ecosystems. However, only a few studies have
examined the factors that affect the fitness of individual termite colonies. We
are examining two of these factors: habitat variation and parasitism. We study
colony success in 6 habitats across the island of St. John, USVI: developed land,
dry forests, mangrove lagoon, moist forests, sparse vegetation (beaches), and
woodlands. We are also examining the impact of a thorny headed worm (Phylum
Acanthocephala) and other parasites on termite colonies and are beginning a new
project to determine how fungus interacts with termites.
The termite we study, Nasutitermes acajutlae,
builds arboreal nests that are easy to find and measure. Three types (castes)
of termites can be found inside nests. Soldiers (non-reproductive males) have
pointed heads with which they squirt out a sticky defense compound. This
compound is used to defend the colony against predators such as ants and
lizards. In addition to being responsible for colony defense, soldiers lead
workers to new food sources. Workers (usually non-reproductive females) build
the termite nest out of fecal material, build covered trails to food sources,
forage and bring back the food to feed nestmates. The final type of termite is
the reproductive caste. These individuals (both males and females) produce all
of the other insects in the colony. When young, reproductives have wings and
are called alates. Alates fly out of the nest to find a mate and start a new
colony. For an excellent overview of termites of the world: http://www.utoronto.ca/forest/termite/termite.htm
The SCAP students on the termite team participated in 3 projects
this year:
First, they helped monitor > 100 termite colonies in 6 habitats across the island of St. John. We have been monitoring these colonies yearly since 1998. We have been testing two hypotheses: that colonies in different habitats have differential fitness and that parasitized colonies have lower fitness than unparasitized colonies (see Fuller and Jeyasingh 2004, Insectes Sociaux 51: 215-220 and Jeyasingh and Fuller. In press. Ecological Entomology). We examine colony survival, growth and reproduction as measures of fitness. We also use the measurements to determine which colonies to include in further projects.
Second, SCAP students tested the hypothesis that termite soldiers are less susceptible to parasitism by pathogenic fungus than termite workers, as suggested in studies by Rebeca Rosengaus. Work by 2003 SCAP students showed that fungus grew faster from workers than from soldiers. However, we could not distinguish between 2 hypotheses, which we tested this year. Hypothesis 1: Workers are the primary foragers, therefore are exposed to fungus more frequently. Hypothesis 2: (same as the initial hypothesis) soldiers inhibit fungal growth. We tested this hypothesis by mixing worker and soldier extracts and placing them in different combinations on growth media. To see the results, see the PowerPoint presentation by the termite team.
Third,
we tested aggression between termites. Previous research by Fuller et al.
(Fuller et al. in press. Journal of Insect Behavior) and the 2002 SCAP termite
team, showed that St. John termites are not aggressive toward other termites from
St. John. This lack of aggression is highly unusual for termites. It is
possible that termites across St. John are genetically similar to each other,
thus can’t tell each other apart. This could happen if termites can interbreed
with any other termite colony on an island. However, we predict that they will
have a hard time moving between islands because they are poor fliers and water
should serve as a barrier to movement. Thus we predicted that termites would
recognize termites from a different island. We put termites from St. John and
St. Thomas together to observe aggression during SCAP, and termites from St.
John and Tortola after SCAP. Although we still didn’t observe any aggression,
we did see an increase in exploratory behaviors the further from St. John we
traveled.
Research
by the fish crew has focused on two aspects of reef fish ecology. The first concerns the influence of
ectoparasites on the behavior of Caribbean reef fishes, especially
damselfishes. The second area of focus
is the tradeoff between spawning and territory defense in damselfishes. These are briefly summarized below.
1)
Most research on the determinants of the diel (daily) activity patterns and the
distribution of fishes on coral reefs has focused on the role of food and
predators. One factor that has been
virtually ignored is the role of ectoparasites, particularly gnathiid isopod
larvae, and the cleaner fishes and shrimps that remove them. Gnathiid isopod larvae live in the
substratum and emerge to find and suck blood from host fish. They are the most common ectoparasite on
reef fishes in the Caribbean, and are the preferred food of cleaner
fishes. Our research on yellowtail damselfish
(Microspathodon chrysurus) in Barbados has revealed a strong early
morning peak in the timing of visits to cleaner fishes and shrimps. This is significant because cleaning can
therefore compete with reproduction, which also occurs during the early
morning. In fact, we have observed females and males interrupting reproductive
activities to visit cleaners, suggesting that removal of parasites is an
extremely important activity. In an
effort to quantify this potential tradeoff, we have examined the diel (time of
day) emergence patterns of gnathiid isopods during the course of the day, their
diel variation in attachment onto fishes, and the whether this variation
corresponds with variation in interactions with cleaner fishes and
shrimps. Because they are more common
at our study sites and easier to catch, most of our fish work on St. John has
focused on smaller damselfishes in the genus Stegastes. Our results thus far indicate dawn peaks in
gnathiid emergence, infestation onto fishes, and the time fish spend
interacting with cleaners. Much of these data were obtained with the help of
SCAP students from the 2002 and 2003 teams and in collaboration with Spencer
Chambers of Murray State University, and Drs. Karen Cheney and Isabelle Côté http://www.uea.ac.uk/~b102/at the
University of East Anglia in the United Kingdom (see Chambers & Sikkel,
Carib. J. Sci. 38: 37-43 and Sikkel et al. 2004, Animal Behaviour 68:
241-247).
In 2004, with the help of Murray State undergraduates Jeremy Mathenia and Collin Schaumburg, we further examined whether gnathiid loads on caged fish vary during the diel cycle. In particular, we wanted to determine whether dawn peaks in infestation were due to high but relatively constant rates of infestation at night, or were due to an increase during the day-night transition. When we examined gnathiid loads on fish held in cages for 2-3 hour intervals, we found that loads were higher during this transition period than during any other time during the day or night. We further found that nocturnal loads
were
lowest during periods of no moonlight. To view these results, see the 2004 fish
team’s Power Point
presentation (1.9 mb).
2)
Female damselfish spawn in nests of males who subsequently care for the eggs
until hatching. In territorial species,
this creates a conflict between spawning and territory defense, whereby absence
during spawning may mean an increase in intrusions by other fish. Spawning occurs just after first light, a
time when intruder pressure is relatively low.
Still, some intrusions do occur and females often make trips to their
territory during spawning, possibly to deter intruders. However, there appears to be a lot of within
and between-species variation in the pattern of these trips among the five
species of Stegastes that are common at our St. John study sites: in
some species, females make trips about every two minutes while others make only
one or two trips. Thus, one of our
goals is to determine the causes of this variation. This project is linked to similar work conducted in Barbados in
collaboration with Dr. Donald Kramer http://www.mcgill.ca/biology/faculty/kramer/
of McGill University. Thus far, SCAP students (2002 and 2003) have helped
quantify variation in spawning tactics among species in Lameshur and Haulover
Bays.
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