We are more similar to insects than we commonly think: “Waste disposal, undertaking, child care, monarchies, slave trade, free riders, punishment, rebellions, architecture, agriculture, murder, cannibalism — social insects have it all and they did it 80 million years before we did.”
To do this they have to be altruistic and eusocial.
Altruistic — showing a disinterested and selfless concern for the well-being of others; unselfish.
Eusocial — living in a cooperative group in which usually one female and several males are reproductively active.
Insects main secret to being eusocial (super cooperative) is their ability to specialise: think workers, queens, scouts, etc.
This is weird — how does a species reproduce by increasing the ability to have sterile children? This was a struggle for Darwin too, but now conventional thinking is that having sterile castes of insects will help reduce time and energy wastage in insects.
The base ancestors of these insects would have been solitary individuals like we see some other species are, like some wasps that have no contact with their young.
The next step is when there is a little group of them that will share nest guarding duty or foraging.
Step 500 is a queen with specialised castes that do work, that look after children etc.
And yet bizarrely 1/50 insect species have this behaviour.
As an example we will take leaf-cutter (aka Atta) ants from South and Central America. Let’s see their team sheet!
- Queen (Largest 6)
- Soldiers (2nd row biggest)
- Trash Handlers
As you can see this is unlike anything we usually think of with animals. This diversity also leads to form some crazy looking ants and some with powers — like exploding in self defence!
How does this happen?
Well sex really. Animals (including us) do have variations within the genes — typically along male and female traits and this typically comes from differences in chromosomes - males have a XY chromosome pair when females have XX.
Ants also have chromosomes and gender but this isn’t how their traits grow. One main reason for this, every ant you have ever seen is almost always female.(Note: this isn’t true in bees.) Put simply, some insect reproduction is weird.
Haplodiploidy — this word is too much
Eusocial males insects do not have pairs of chromosomes. They just have single chromosomes.
Female insects do have pairs of chromosomes.
When a Queen lays an egg, the males will fertilise that egg. The egg will have one set of chromosomes from the Queen and will get another set from the males.
When a Queens egg doesn’t get fertilised — it will turn into a male. Yep. I am not making it up.
What this also means is that a male can never be a father, but he can be a grandfather.
It also means one lone queen can start a population.
How do they pick what caste to be?
Some social insect species can change at any point in their lifetime. Others are determined at birth.
Most will go through 4 stages of development — egg, larva, pupa and adult. It is hypothesised this development process is only possible due to eusocialism and hence any insects that do metamorphosis will have ancestor species which were eusocial.
It seems well cared for ants will go on to become queens and that some insects females can change with social pressure! It is a split of nature and nurture that trigger caste type and size seems to be a main player for what caste you may become — read about it here.
Back to being social
As there is less chance to pass ones genes on, social insects need to be more vigilant of who they are helping survive. Evolution dictates, that without a strategy for your genes survival, your genes wont survive and be passed on — and hence would disappear quickly.
Social insects need a way to ensure that those they are helping survive actually share genetic links. “Colony members will accept a seemingly unfair division of reproductive labor if their dominant nestmates are close relatives”. Most colonies do this with odour and visual recognition.
The conditions to which promote eusocialism can be described by Hamilton’s rule: br>c where
- b is the benefits of raising relatives young
- r is the strength of genetic relationship or similarity to the non-direct young you would look after (indirectly or directly)
- c is cost incurred by not breeding
So if raising young is really hard, they are highly related and there aren’t enough child bearing partners, the formula is heavily in favour of being eusocial. Conversely, if raising the young is easy, they aren’t related to you in anyway and there are numerous possible child bearing partners then you would move away from eusocialism.
Knowing this law causes an immediate problem. The first insects to be eusocial were likely just sharing a nest. The benefits in this scenario would be high but the r would be assumably very low and it would be unlikely that sterile specialisation would have occurred so the cost incurred from not breeding would be considerably high.
Potentially there was high pressure on the number of the population and hence staying in one location was beneficial — ie cost of not breeding was decreasing as it became more difficult to find partners as you may spend all your life trying to find a partner with no result.
When these groups stopped sharing nests but needed to move to having just one queen… like how did that work?!
Looking at paper wasps gives some insight. They are quasi-eusocial as the queen allows for some females to lay eggs as well as her and hence diversity of population was still reasonably large, and so long as there are males from that brood the linages would become linked.
How annoyed would you be if you pledge your life to your queen and find out that they weren’t actually related to you after all and hence your genes and life are wasted?
Researchers have recently proven that insects surfaces product complex hydrocarbons which provide identification.
It isn’t perfect as parasitic wasps can replicate that smell and can invade nests. As such, visual checking is also used.
At the end of the day, some insects still possess the ability to leave the colony as a female worker and transform into a queen and start their own colony.
So a summary
Basically, social insects are mental because they:
- do metamorphosis
- have a caste system
- have survived despite only 1 in an entire colony can lay eggs
- a single female can give birth to a brand new colony, without a male
- clean their nests, enact judgement on who is who and have a social structure with specialisms
- they worked all this out millions of years before any other animals
Oh and last thing. It isn’t just insects that are eusocial — naked mole rats are too.
You have a queen, multiple breeding males, a sterile work force, soldiers and something new — dispersers. These dispersers are the solution to over inbreeding of the mammals and are built to travel to find a new ‘family’.
The non-reproducing females appear to be reproductively suppressed, meaning the ovaries do not fully mature, and do not have the same levels of certain hormones as the reproducing females.
Inspired by Seirian Sumner’s “How did the social insects become social” from “What’s next? Dispatches on the future of science” 2009
Recently I began reading this book of science essays that were meant to assess the future. Seeming it is 10 years since the book was published, I thought it may be interesting to revisit these.