Thursday, January 29, 2015


thescientist |  Eusocial insects are among the most successful living creatures on Earth. Found in terrestrial ecosystems across the globe (on every continent except Antarctica), the world’s ants alone weigh more than all vertebrates put together. Bees are key pollinators of major crops as well as many other ecologically important plants. Termites construct thermoregulating homes that can dominate the landscape, and that are inspiring new energy-efficient skyscraper designs. The organization and collective decision making of eusocial insects is even yielding new insights into human behavior and what it means to be part of a society. But one of the biggest unanswered questions in our understanding of these complex insect groups is how a single genome can produce such diverse and contrasting physical and behavioral forms, from egg layers, provisioners, and caretakers to soldiers.

In a eusocial colony, reproduction is dominated by one or a few individuals adapted to egg laying, 
while their offspring—colony workers—display physical and behavioral adaptations that help them perform their subordinate roles. These phenotypic adaptations can be extreme. A leafcutter ant queen is 10 times larger than her smallest workers, for example.  (See photograph below.) And some carpenter ant species have evolved a “kamikaze” caste, born with a self-destruct button that causes the insect to explode upon colony attack, killing itself and covering the invading animals in toxic chemicals. Remarkably, differences in the behavior and morphology of insect castes are usually generated through differences in the expression of identical sets of genes. (There are a few cases of genetically determined castes, but this is the exception, not the rule.)

We are now entering a new era of research into eusocial insects. For the first time, scientists are investigating the molecules that underlie eusocial behavior at a depth that was previously unimaginable. New, affordable sequencing technologies enable scientists to examine how genes across the entire genome are regulated to generate different caste phenotypes, the roles of DNA methylation and microRNAs in this differential expression, and what proteins are synthesized as a result. This burgeoning area of research, dubbed “sociogenomics” in 2005 by Gene E. Robinson,1 is revolutionizing our understanding of the evolution of eusociality from a solitary wasp-like ancestor to the million-strong colonies we see today. New work is yielding insights into how genomes interact dynamically with the physical and social environment to produce highly adapted, specialized castes with remarkable phenotypic innovations. These findings are, in turn, illuminating the importance of gene regulation and epigenetics in controlling behavioral plasticity across the animal kingdom.