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First Collaborative Power Points
Now we will talk about Pheromones
Multicellular organisms use chemicals to send messages from one cell to the next.
-There are two major types of chemical messengers
-Hormones - Chemical messages inside of the body
-Pheromones - Chemical messages outside of the body
Termites
Termites and the Use of Trail Pheromones
Chemical communication is perhaps the most ancient means of communication in the animal world. Animals send and receive chemical messages that hold information about food location, danger, territory, and mates. Chemical messages are private, effective in darkness, long-lasting, and they may operate over long distances. Reliance on chemical communication ranges from not-at-all in some species to extreme in others.
Humans, for example, live in a sensory world dominated by acute, 3-dimensional color vision. Other mammals such as mice and deer rely heavily on chemical communication to interact with conspecifics. The insects are particularly well-known for pheromone production and their acute olfactory ability. The most spectacular insects in terms of pheromone use are highly social species such as honeybees, ants, and termites. Their body compartments are loaded with pheromone-secreting glands and their antennae have many olfactory neurons that are highly-sensitive to airborne signals.
Termites live in highly organized societies that are built around physical castes and defined divisions of labor. The key castes that maintain and defend the colony are the workers and soldiers, respectively. As the name implies, soldiers are devoted to colony defense and have the anatomy to repel invaders. Workers do routine nest maintenance and are responsible for finding and retrieving food. After a foraging worker finds a food source, it deposits a trail pheromone on the ground as it returns to the nest. The trail pheromone represents a temporary signal that nest-mates may follow to that same food source. If subsequent workers also find food, they reinforce the signal by taking the same path back to the nest while depositing their own trail pheromone. As the food source dries up, the specific trail back to the nest is no longer used and the pheromone signal dissipates.
Dissipation below olfactory detection limits eliminates the chemical trail which reduces the likelihood of workers wasting time investigating unproductive foraging areas.
A great deal is known about the chemistry, concentration, and glandular source of trail pheromones used by ants. Among the ants, trail pheromones are mixtures of volatile substances that include diverse chemical structures secreted from multiple glands.
An odd but interesting discovery is that ink from certain ball-point pens contains volatile substances that seemingly mimic trail pheromones of termites. If a line is drawn on paper, a worker termite will follow it, stopping only when the line ends. Google termite trail following and select video to see termites orienting to ink trails.
Our Lab
This lab is an opportunity to gain understanding and appreciation for the world of chemical communication by termites. You will join one of several lab groups that will be designing and executing their own unique experiment(s). No two groups will have the same research design or do the same work. A good strategy for each group would be to do some background reading before reconvening for a barnstorming session. This is a difficult lab because you are not being told what to do. The prelab lecture along with this lab handout will provide some basic background information.
When formulating the design, each group should make decisions about
- Hypotheses/Objectives/Questions
- Dependent and independent variables
- Ways of quantitatively measuring behaviors
- Replication and sample sizes for each type of test
- Needed number of pre-chilled (= anesthetized) termites
- Production and use of termite odors
- Possible use of ink
- Backup or alternative ideas to ensure use of the entire lab period
- Special requests for needed equipment or supplies the following will be present on lab day
- Dissection tools
- Brushes for manipulating termites
- Solvents (water, propanol, other?)
- Timers
- Rulers and calipers
- Ink pens
- Super glue
Group Goals
After gaining some background knowledge, each group should meet and create a research design. The design should investigate some aspect of pheromone use and/or chemical communication by termites. The termite available in lab will be Reticulitermes.
Research topics of interest might include
- Trails laid by walking workers
- Manipulation of odor plume
- Antennae manipulation
- Trail-following accuracy
- Termite body parts as odor sources
- Extracts of body parts (head-thorax-abdomen) as odor sources
- Feces as odor source (trail pheromone?)
- Soldiers vs workers
- Continuous vs intermittent trail
- Height above trail
- Rotten wood and/or fungi from rotting wood as a termite attractant (you supply
the wood/fungi)
Strong research designs will be those that show real creativity, involve replicated quantitative data that permit statistical analyses, and are grounded in biological
Each group will submit one lab report. Because the written report will involve co- authors, expectations are very high. It will be difficult to do well without substantial data analyses, interpretation, and presentation in the form of figures and tables. You will need to cite and use primary sources.
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