NH Notes: Exploding Termites – Sacrifice for the Good of the Whole Organism

There are over 2800 species of termites that have been identified.  They are all social insects with division of labor among individuals in a single colony much like ants and bees.   The social insects are truly amazing organisms with many very sophisticated types of behavior that allow them to complete complex tasks that non individual insect could complete themselves.   The social insects have been extensively studied to understand how colonies are maintained and grow and how diseases bacteria and fungi are transmitted socially.  Much of this research is very practical because of the economic importance of social insects for pollination of plants or as pests of humans.   The behavior, genetics and reproduction of social insects is highly varied and complex and most people probably find them very perplexing.   One of the stranger behaviors of termites was reported this past week and a summary can be found in this note in Nature.  This report contains a description of exploding termites!  How, and probably more intriguing, why  would a termite explode and commit suicide?

The smaller worker termites with the blue abdomens are the ones that have chemicals stored up that can be released by busting their abdomen open and mixing the substance with salivary material to make a toxic substance that will kill an invading enemy. The larger termites in the picture are soldier termites.

Researchers found that workers of a single tropical species of termite were observed with a bluish abdomen that appeared to be used as a defensive mechanism.   They researchers hypothesized that the workers with the most blue abdomens had the most toxin and that they would be more willing to explode themselves in order to spray their enemies with the contents of their abdomens.   They tested their ideas by introducing typical enemy termites into an arena with workers with various colored abdomens and the ones with the bluest were the most willing to commit suicide. They also found that an extract from these termites was an effective poison capable of killing the attacker not just slowing it down.  There are many other termite species that produce chemicals in their abdomens that can be used in defense though not always through self-sacrifice but most of these seem to be less effective.  Closer examination of the blue phenotype termite workers reveals that they are likely the oldest workers so it seems that the blue crystals have build up over their lifetime and so if they reach old age they become the most effective weapons.  The researchers reason that when old a termite worker has worn down its jaws and is an ineffective forager for food and it can’t feed the rest of the termite colony and thus has little use to the colony.  These elderly termites rather than simply leaving the nest to die or be killed, which can happen in some social groups, accumulate a toxin over their life-time and then become willing to sacrifice themselves in defense of the rest of the body.  I say “willing” because the researchers found that workers with less blue abdomens, and thus are probably younger and less toxic, were found to be much less likely to commit suicide in the presence of an enemy.  That they do this and their is a benefit to the colony seems apparent, but I am sure that this will still leave many perplexed by these odd behaviors of social insects.

One simple way to understand the biology of  social insects is to imagine a colony as a single large multicellular organism in which the individual ants/termites of the colony are akin to the cells of single multicellular organism.   The cells in your body have specific jobs. For example as many as 1 in 10cells (immune specific cells and epidermal cells) are involved in defense against foreign invaders or other rogue cells (eg. cancer) of the body, other cells transmit electrical signals (nerves), others are sensory organs and others carry oxygen (red blood cells) etc…   In a colony there of termites there are typically workers, soldiers, males and queens.   There may be many specialized workers and soldiers in a colony further subdividing the various duties that must be performed.   Workers typically do the feeding for the colony and then share the food that they have processed with all the other termites that can’t get food for themselves.  Queens obviously are involved in reproduction but they also produce behavior and developmental altering hormones that are thought to be passed throughout the colony by the shared feeding allowing for communication of signals much like hormones released by cells in an animal body are used to communicate and direct other cells in the body.

A termite mound in Australia. A large colony of termites produced this mound. Image credit: Wikipedia

One can think of soldiers and these old workers  as the immune system of the termite colony.  Soldiers do not produce food, nor can they participate in reproduction, and they are produced by hormonal influences from the queen.  This is very much like the immune cells of an animal whose sole job is protection of the body even if it means their death.   These exploding workers are just a more dramatic example of an altruistic behavior.  The worker did productive work as a forager for food and feeder of the rest of the colony but now that they are less effective in old age they become immune “cells” for the whole body.  You and I have suicide cells called neutrophils. When they encounter possible invasive hosts like bacteria from a puncture wound they lyse  themselves to expose the toxic chemicals they had stored in special containers in the cells. These chemicals then can kill bacteria and any of your cells in the area.  The results is the destruction of large numbers of cells in local area.  Its is a sloppy, first line of defense in which you not only give up those specific cells but also kill thousands of your “innocent” cells in the death zone for the sake of saving the rest of the organism(this can create the puss that can ooze from a insect bite or other wound).   These exploding workers are doing something very similar as I am sure that they not only take out the enemy but at times kill some of the other colony members in a form of friendly fire.   The “individuals” of a termite colony or ant colony then are more like cells of single organism. There is no individualism in a social insect just like there is no individualism in a multicellular organism.   A cell of an animal that wishes to do what it wants is actually destroyed by the immune system of an animal because it can be very dangerous for the whole organism to allow individual cells to take on jobs that they aren’t supposed to do. You don’t want your skin cells to try to become brain cells.  The end result of cells that “rebel” against the organism is often cancer – cells that divide indiscriminately inside tissues that normally is under control.   Individuals in a social insect colony that exhibit unexpected behavior or lose their sense of self (all members of a colony have a chemical that identifies them as being members of that colony) are killed by other members of the colony to protect that colony for the same reasons.  Social insects are remarkable organisms that that continue to astound and amaze as we learn more about them.

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