The Evolution of Colonial Insects

It was originally proposed by sociobiologist E. O. Wilson in the 1970s that eusocial communities evolved because they were just one big, happy family. That the  workers didn't care about forgoing reproduction because they and their sisters were so closely related that it didn't matter if she or her sister reproduced. This may be the case, but how did they get to this point?

Figure 1 - Offspring and sibling relatedness with monogamous and polyandrous relationships.

One current theory, the monogamy hypothesis (Boomsma 2007) says that if a female mates with only one individual during her entire life - that is, strict lifetime monogamy - her progeny will be equally related to their siblings and to their own offspring (Figure 1). From here the potential for caste evolution begins to arise as some individuals could opt out of mating to help a dominate reproductive to produce more offspring. Natural selection will favour cooperation in any situation where it is more efficient to raise siblings than offspring, and this could start paving a path towards eusociality.

Researchers led by William Hughes of the University of Leeds in England examined 267 eusocial species of bees, wasps and ants and found that the insects evolved from monogamous conditions, which maximize a group’s degree of relatedness (Hughes 2008). When Hughes's group examined the distribution of monogamous versus polygamous species among the eight branches of the family tree in which eusociality had independently evolved, the researchers concluded that each branch had started with a monogamous species.

In a lot of monogamous species, the death of a partner would mean the individual would start looking for a new mate, which would affect relatedness as family members would be much more related to their offspring than their sibling. This would lower the chances for altruism and ultimately hinder the evolution of eusociality. The death of a partner in a strict lifetime-monogamous relationship obviously presents a large problem in the development in eusocial colonies, and is something that will be covered in a future post. Stay tuned!

References:

Boomsma JJ. Lifetime monogamy and the evolution of eusociality., 2009, Philos Trans R Soc Lond B Biol Sci. 2009;364(1533):3191–3207. doi:10.1098/rstb.2009.0101

Edward O. Wilson, Social Insects, 1971, Science (New York, N.Y.). 172: 406. PMID 5550494  

Hughes WO, Oldroyd BP, Beekman M, Ratnieks FL, 2009, Ancestral monogamy shows kin selection is key to the evolution of eusociality. Science 320: 1213–1216. pmid:18511689 

Figure:
Altruism, Spite and Greenbeards, https://science.sciencemag.org/content/327/5971/1341, 29/03/20