Why don’t worker ants revolt?
The conditions that drive some species to evolve non-reproductive individuals are less strict than once thought.
Certain wasps, bees and ants live in highly organized social groups in which one member of a colony (the queen) produces all or almost all of the offspring. This form of social organization — called eusociality — raises an important question for evolutionary biology: why do individuals that forego the chance to reproduce and instead raise the offspring of others evolve?
One factor linked to the evolution of eusociality in insects is a system that determines the gender of offspring known as haplodiploidy. In this system, female offspring develop from fertilized eggs, while male offspring develop from unfertilized eggs. The queen mates with male insects and so she can produce both male and female offspring. On the other hand, the workers — which are also female — do not mate and therefore can only produce male offspring.
So, should these workers produce their own male eggs, or should all male offspring come from the queen? The answer to this question could depend on whether the queen has mated with a single male (monandry) or with multiple males (polyandry) because this affects how closely related the other insects in the colony are to each other. It is a widespread belief that monandry is important for the evolution of non-reproductive workers.
Jason Olejarz and co-workers developed a mathematical model that explores the conditions under which natural selection favours the evolution of non-reproductive workers. Contrary to the widespread belief, it turns out that non-reproductive workers can easily evolve in polyandrous species. The crucial quantity is the relationship between the overall reproductive rate of the colony and the fraction of non-reproductive workers present in that colony.
Olejarz and co-workers challenge the view that single mating is crucial for the evolution of non-reproductive workers. The study demonstrates the need for precise mathematical models of population dynamics and natural selection instead of informal arguments that are only based on considerations of genetic relatedness.
To find out more
Read the eLife research paper on which this eLife digest is based: “The evolution of non-reproductive workers in insect colonies with haplodiploid genetics” (October 20, 2015).
Read a commentary on this research paper by Michael Doebeli and Ehab Abouheif.
Listen to Martin Nowak discuss the benefits of eusocial organisation in episode 26 of the eLife podcast.
