Gene regulation underlies the evolution of social complexity in bees

May 14, 2015, University of Illinois at Urbana-Champaign
A new study offers insights into the genetic changes that accompany the evolution of social complexity in bees, including honey bees. Credit: L. Brian Stauffer

Explaining the evolution of insect society, with sterile society members displaying extreme levels of altruism, has long been a major scientific challenge, dating back to Charles Darwin's day. A new genomic study of 10 species of bees representing a spectrum of social living - from solitary bees to those in complex, highly social colonies - offers new insights into the genetic changes that accompany the evolution of bee societies.

The new findings are reported in the journal Science.

By sequencing and comparing the genomes of ten bee species that vary in , the researchers made three important discoveries.

"First, there is no single road map to eusociality - the complex, cooperative social system in which animals behave more like superorganisms than individuals fending for themselves," said Gene Robinson, a lead on the study who is a professor of entomology and director of the Carl R. Woese Institute for Genomic Biology at the University of Illinois. "In this study, we found that independent evolutionary transitions in social life have independent genetic underpinnings."

The second insight involved changes in the evolution of gene regulation: As social complexity increased, so did the speed of changes to parts of the genome involved in regulating gene activity, located in the promoters of the genes, the researchers report.

By contrast, evolution seems to have put the brakes on changes in many parts of the genome that code for the actual proteins, Robinson said. Similarly, there was an increase in DNA methylation as social complexity increased, which also means enhanced gene regulatory capacity, he said.

"It appears from these results that gene networks get more complex as gets more complex, with network complexity driving social complexity," Robinson said.

A third major finding was that increases in social complexity were accompanied by a slowing, or "relaxation," of changes in the genome associated with natural selection. This effect on some genes may be a result of the buffering effect of living in a complex, interdependent society, where the "collective genome" is less vulnerable to dramatic environmental changes or other external threats, Robinson said.

"These results demonstrate once again that important new insights into evolution can be obtained by using genomes as history books," Robinson said. "We have now learned what have occurred during the of the bees, notable for their elaborate societies and essential pollination services."

Explore further: Bumblebee genomes give insights into threats to pollinators

More information: Genomic signatures of evolutionary transitions from solitary to group living, Science, … 1126/science.aaa4788

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1 / 5 (1) May 14, 2015
Gene regulation is nutrient-dependent and pheromone-controlled in the honeybee model organism, which links our 1996 review of RNA-mediated cell type differentiation to insects via Elekonich and Robinson (2000). Robinson is a co-author of this published work.

The link to life history transitions in the honeybee model organism is in Elekonich and Roberts (2005) and the link from honeybees to humans is in my 2012 and 2013 reviews.

See also: How a well-adapted immune system is organized http://www.pnas.o...950.full

In 1996 we wrote: "Small intranuclear proteins also participate in generating alternative splicing techniques of pre-mRNA and, by this mechanism, contribute to sexual differentiation in at least two species, Drosophila melanogaster and Caenorhabditis elegans... That similar proteins perform functions in humans suggests the possibility that some human sex differences may arise from alternative splicings of otherwise identical genes."
1 / 5 (1) May 14, 2015
Others seem likely to continue their attempts to link biodiversity to mutations and evolution. Serious scientists know that the honeybee model organism is linked to humans via nutrient-dependent pheromone-controlled fixation of RNA-mediated amino acid substitutions that differentiate all cell types in all individuals of all species from microbes to man.

http://www.ncbi.n...3960065/ Nutrient-dependent/pheromone-controlled adaptive evolution: a model
"The honeybee already serves as a model organism for studying human immunity, disease resistance, allergic reaction, circadian rhythms, antibiotic resistance, the development of the brain and behavior, mental health, longevity, diseases of the X chromosome, learning and memory, as well as conditioned responses to sensory stimuli (Kohl, 2012)."

The honeybee model organism links ecological variation to ecological adaptions via RNA-mediated cell type differentiation, not via mutations.
1 / 5 (1) May 14, 2015
See also: "Non-CG DNA hydroxymethylation and alternative mRNA splicing in honey bees" http://www.biomed...4/14/666 (2013) was co-authored by Gene Robinson.

Conclusion: "Our identification of GO categories related to protein phosphorylation that were enriched for genes with methylated splice junctions is consistent with a similar finding in a recent study of species-specific alternative exons [45]. The authors present evidence that argues that alternative splicing is used to alter protein phosphorylation, which can alter protein stability, subcellular localization, activity, and other properties [45]. Further research is needed to determine the mechanism by which splice junction methylation and hydroxymethylation affect mRNA splicing."

Phosphorylation appears to link the fixation of RNA-mediated amino acid substitutions to the stability of organized genomes in all genera, via conserved molecular mechanisms in the honeybee model organism.

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