The Genetics of Eusocial Insects

The Genetics of Society
Claire Asher and Seirian Sumner
1 January 2015

Link to Article: http://www.the-scientist.com/?articles.view/articleNo/41704/title/The-Genetics-of-Society/
Link to Eusocial Insects explained: http://es.rice.edu/projects/Bios321/eusocial.insect.html

Eusocial insects are recognized by three defining characteristics:
1) The mother conducts care of the young
2) Insects from sterile castes aid the reproducing organism
3) There are overlapping generations. This allows for older generations of offspring to help younger generations.

While Darwin was developing his theory of natural selection, he encountered altruistic insects. Darwin wondered how different behavioral traits were expressed through genes and why some insects were subordinate to others of the same species. He also wondered how a single ancestor led to the development of "social" castes in eusocial insects.

One hypothesis proposed was that a solitary insect lived as a single mother. This mother then laid eggs and foraged for food to feed her offspring. Upon reaching maturity, offspring would forage and reproduce on their own, resulting in the conventional non-eusocial insect. Eusociality developed when offspring remained at the nest with their mother past adulthood. When the mother reproduced again, the first generation of offspring would help their mother raise the newer generation. As the helper insects began to take on specific roles in the nest, the mother, not having to provide food for the new generation, would focus solely on reproduction while the other generations would forage for food and subsequently become workers. The newly evolved phenotype, "the queen", had the exclusive responsibility of reproduction while foraging and laborious behavior was taken on by workers. Thus, creating a eusocial insect society with social castes.
.
The hypothesis is supported by the recent discovery of shared genes between "queen" and "worker" insects across all species. These genes have been shown to code for behavioral traits which explains the shared eusocial behavior traits: queens reproduce while workers complete laborious tasks of the nest.

Shared genes are further expressed through phenotypic differences; for example, a queen ant is over 10 times the size of a leaf-cutter ant. Scientists believe that sometime during the evolution of eusocial insects, regulatory elements called microRNAs controlled the genotypes of organisms through gene regulation and protein production and from these genotypes, the ensuing phenotypes. Researchers have concluded that this phenomenon was not entirely a product of natural selection as there are many molecular level happenings that affect the regulation of genes and the production of proteins. However, one reason eusocial insects exist is because the division of labor results in a more efficient society. This is interesting because eusocial societies resemble primitive human societies with the basic division of labor and social hierarchy.

This article relates to both the last unit on molecular biology as well as the current unit on evolution. Through evolution, eusocial insects are prevalent because the micro-societies they created were more efficient than those of other insects. This development might have resulted in more offspring (higher fitness) and led to the social structure becoming widely seen. Additionally, the article relates to molecular biology because it addresses regulatory elements that control gene expression. This ultimately results in different insect social castes.