We were among the members of honeybee genome project between 2005-2007, but did not find time to continue working on social insects since then. Hymenopteran insects are fascinating. It is a rare place in nature, where you see the emergence of social behavior.
Even more unusual is that eusociality developed independently and multiple times in hymenopteran and isopteran (now Termitoidae) insects (corrected by james alberts), but nowhere else among other insect orders. Nobody discovered a queen mosquito or social crab yet. Naturally, we looked for ‘social genes’ by comparing the bee genome with the human genome and excluding genes from flies and mosquitoes. That simple analysis did not give us any lead. Even though our honeybee Nature paper was titled Insights into social insects from the genome of the honeybee Apis mellifera, sadly the only insight we got was that a single genome provided no insight. Baylor continued with the sequencing of wasp genome, but by then we were too busy and too bored to leave.
All that changed in 2010, when the availability of next-gen sequencing made many ant genomes available. Readers will enjoy a very nice comparative paper that came out in Genome Research few months back from some of our ex-bee collaborators and others.
Genomes of eusocial insects code for dramatic examples of phenotypic plasticity and social organization. We compared the genomes of seven ants, the honeybee, and various solitary insects to examine whether eusocial lineages share distinct features of genomic organization. Each ant lineage contains ~4,000 novel genes, but only 64 of these genes are conserved among all seven ants. Many gene families have been expanded in ants, notably those involved in chemical communication (e.g., desaturases and odorant receptors). Alignment of the ant genomes revealed reduced purifying selection compared to Drosophila without significantly reduced synteny. Correspondingly, ant genomes exhibit dramatic divergence of non-coding regulatory elements, however extant conserved regions are enriched for novel non-coding RNAs and transcription factor binding sites. Comparison of orthologous gene promoters between eusocial and solitary species revealed significant regulatory evolution in both cis (e.g., CREB) and trans (e.g., Forkhead) for nearly 2000 genes, many of which exhibit phenotypic plasticity. Our results emphasize that genomic changes can occur remarkably fast in ants, as two recently diverged leaf- cutter ant species exhibit faster accumulation of species-specific genes and greater divergence in regulatory elements compared to other ants or Drosophila. Thus, while the “socio-genomes” of ants and the honeybee are broadly characterized by a pervasive pattern of divergence in gene composition and regulation, they preserve lineage-specific regulatory features linked to eusociality. We propose that changes in gene regulation played a key role in the origins of insect eusociality, whereas changes in gene composition were more relevant for lineage-specific eusocial adaptations.
The ecodevoevo blog wrote an insightful description of the paper that is worth taking a look.
Characteristics of eusocial insects, ants, bees and aculeate or stinging wasps of the order Hymenoptera, include reproductive division of labor, cooperative brood care, and overlapping generations. Simola et al. compared the genomes of seven ants, the honeybee and various solitary insects to try to identify genomic features that were common to the eusocial insects, even though these ants and the bee are from evolutionarily independent lineages and differ in various significant respects. The question was whether they had enough in common to elucidate the genomic basic of eusociality.
This paper is a goldmine of information about ant genomes, their structure and evolution. For example, the authors write that many ‘taxonomically restricted genes’ (TRGs) are found in ant genomes, but they did not find a “social toolkit” of conserved protein coding genes for eusociality. They found that Hymenoptera have a greater number of taxonomically restricted genes than do solitary insects, and that they evolved faster. They identified gene families that expanded or constricted depending on, e.g., the diet of a particular ant species, and they found fairly insignificant differences between the immune genes of ants and solitary insects. Distinct methylation patterns were found in ant genomes. And much more.
Did they find shared genomic features responsible for eusociality? They identified 64 genes conserved among the 7 ant lineages they analyzed, but these genes are not expressed in a caste-specific pattern, so can’t explain the phenotypic plasticity of these insects. Nor do they encode any known protein domains. Thus, the authors write, “These results suggest that a broad “social toolkit” of conserved de novo protein-coding genes is not a requirement for eusociality.”
The discussion ends with -
Sofware rather than hardware-dependent social behavior is what makes humans so unique, and that it can occur (if our surmises are right) without genetic programming makes us so interesting as well.