Science Questions

Why do some species have thousands of sterile individuals?

Sat, 5th Jun 2010

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Question

Eric Taylor asked:

If the point of reproduction is to pass your DNA to the next generation, why do some organisms such as ants, bees, or termites produce thousands of† individuals that have no chance of reproducing?

 

This seems to me to be a terrible waste energy. The queen basically becomes a helpless baby factory, unable to care for her own young, find food or even leave the nest†in many cases. So she must expend even more energy to produce workers to care for her young and herself.

 

This seems to me to be a huge evolutionary DISadvantage,† But it worked†because there are†several different organisms that do this.

 

Eric in Portland, Oregon, USA

Answer

We posed this question to Elva Robinson from the University of York...

Elva -   In some species of ants, there are workers that are completely sterile although in many species of ants, bees and termites, the workers can actually reproduce a bit, but not as much as the queen.  This posed a problem for Darwin when he was thinking about evolution by natural selection because usually, evolution should move individuals towards the best chance of passing on their own genes directly to the next generation.  Obviously, sterile worker ants can't do that.  But they are, of course, very closely related to the queen who is their mother, and actually, because of ant genetics, they're more closely related genetically to their mother than we are to our own mothers, because ant genetics work slightly differently.  So, this means that their genes will be passed on to the next generation through their siblings, through their sisters, the future queens of other colonies, and through the males that that colony produces.

Chris -   So itís less "selfish gene", itís more that the genes will go on, but you have to be there to help the genes flow from somebody else.  But because you're closely related to them doesnít matter?

Elva -   Yes and we call it kin selection; acting in the interests of the family when itís very closely related.  There are also big efficiency benefits for these ant colonies because of the way they organise their division of labour.  So they can very efficiently help their siblings to reproduce.

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Bees & ant colonies are superorganisms:
the colony is the individual entity, its members are not individuals but components of a larger organism.

So asking "why don't worker bees reproduce" is a bit like asking "why doesn't my nose give birth to another nose".


RD, Fri, 23rd Oct 2009



Because if your eyes and mouth did the same, you'd be two faced.

As RD wrote, you are referring to superoganisms. Each individual has a specific part to play in the order of the superorganism's existance. Don_1, Sat, 24th Oct 2009

This does not answer the question. I want to know how this situation came about in an evolutionary sense.

  It's like answering the question "What is the origin of life?" with "panspermia". Panspermia simply explains how life came to Earth. It doesn't tell us how it came about. mountaineirc1969, Fri, 30th Oct 2009

I think the evolution of colony insects can only be theorised. Finding fossil evidence might not be possible. So here is my theory.

Most insects have the capability for each individual to hunt, forage, defend themselves, build a nest, attract a mate and reproduce. But they can only perform each function to a degree (except reproduction). Insects need to reproduce in high numbers because they are very highly predated. The chances of an individual insect actually surviving long enough to mate and pass on its genes, are not good.

It seems that temperature has a great deal to do with which type of colony insect will emerge from the egg. By laying eggs at a specific temperature producing only infertile males, a female would have a swarm of individuals with no desire to mate. Therefore, these individuals would probably not have any desire to make off to find a mate. They would stay with the female. Thus the female would have produced her own protection, since there is always safety in numbers.

By laying eggs at different temperatures, the female may have discovered that slightly different males would result. Now the female can produce soldiers, hunter/gatherers, nurserymen, builders etc. Since they will all share the same genetic code, but are infertile, they must now protect their gene pool by providing all the female's (or Queen's) needs.

My suggestion is that this did not originally happen by design, since the temperature was responsible, but that it was recognised by the females and they used it to their advantage. Could an insect be so intelligent? Why not, they continue the practice today, so that must indicate they have the intelligence.

Don_1, Fri, 30th Oct 2009



There can be natural selection for altruistic behaviour, (self-sacrifice, working for nowt), if the genes for this behaviour benefit the community who share those genes.

http://en.wikipedia.org/wiki/Gene-centered_view_of_evolution#Individual_altruism.2C_genetic_egoism RD, Fri, 30th Oct 2009

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