The benefits of monogamy in humans (even if it has fallen out of style recently) are easy to see. Given the very long period of time that human children take to grow up and become self-sufficient, having both parents around to help raise them is obviously a good thing.
For many monogamous insects, however, the benefit is far less clear. This is especially the case with termites, which evolved from cockroaches.
Cockroaches are not at all monogamous, so why did the termite evolve to have just one breeding pair per colony, and how did it happen?
That is what a team of researchers led by Professor Nathan Lo of the University of Sydney investigated, and they published their fascinating results in Science.
They looked at termites and woodroaches, which are something of a midpoint between termites and roaches in that they live in smaller colonies, but they do have one breeding pair. In a statement on the study, Lo said:
“Our study shows how their DNA changed first as they specialised on this poor-quality diet and then changed again as they became social insects. The surprising result is that termites increased their social complexity by losing genetic complexity. That goes against a common assumption that more complex animal societies require more complex genomes.”
The genetic makeup of any animal is constantly changing with each generation. As the termites progressed over time, they evolved to do things like grooming each other in order to help keep pathogens out of the colony.
This is extremely important when living in large groups since a disease could destroy them all if left unchecked. For cockroaches, which live mostly on their own and are not monogamous, being exposed to a disease is much less risky since it would likely only kill a very small number of them.
Upon analysis, the team found that cockroaches have 2-4 billion base pairs of genes in their DNA, compared to termites that have about one billion.
Some of the loss of genes comes from the fact that termites transitioned to eating only wood. They acquired microbes that could break down cellulose in wood into useful nutrients, which meant they didn’t need the genes to process other types of foods.
In addition, they found that termite sperm all but lost their tails. In species with strict monogamy, this is not uncommon since there is no evolutionary advantage for a sperm to be able to swim fast, given that there is no competition from other members of the species. Lo explained:
“It’s energetically costly to produce a lot of sperm with tails.”
The team believes that the termites evolved to be monogamous first, and then lost the tail on their sperm over the following generations. In the statement, Lo said:
“This loss doesn’t cause monogamy. Instead, it’s a strong indicator that monogamy had already evolved. Once monogamy was locked in, there was no longer any evolutionary pressure to maintain genes involved in sperm motility.”
When a species like termites or bees has just one breeding queen, or a king and queen couple, the colony is at risk of ending if something happens to them, creating a single point of failure.
To combat this, these insects have developed ways to make replacement breeders, which is also how new colonies are formed. With bees, the colony feeds the larvae a special ‘royal jelly’ that gives them the nutrients needed to become a queen.
Termites take something of the opposite approach. Most larvae are fed lots of food so that they can develop into productive members of the colony fast, but they don’t have the ability to reproduce.
When it is time for a new queen or king, they will be fed smaller amounts of food, which allows them to develop more slowly. This extra time allows for the proper development needed for reproduction.
If you thought that was interesting, you might like to read about the mysterious “pyramids” discovered in Antarctica. What are they?