Sunday, July 20, 2014

The Ten Principles of the Hologenome

Source: Charis Tsevis, Science News
(Update - June 12, 2015: For newly updated principles, see this blog post - What are Holobionts and Hologenomes?)

So recently I've been thinking a lot about the principles of the hologenome. From a summer workshop at the Munster Graduate School of Evolution in Germany to various dialogues with luminaries, there is a palpable interest in what is and what is not the hologenome. From reading The Hologenome Concept by the Rosenbergs and their conceptual papers to a coming NESCENT workshop on the ecology and evolution of the host-associated microbiota, I am now taking stock of what I've stored in the attic thus far and trimming it down to make it useful for everyone. I have also set up a FaceBook community page on the Hologenome for anyone who would like to join the discussion. I anticipate that Ill publish this list in a journal at some point, but for now it is most valuable here and at once.

These are my Ten Principles of the Hologenome.

1. The hologenome is a unit of selection that incorporates the genomes of the holobiont - host genome, cytoplasmic organelles, and host-associated microbiome. These three compartments of variation can cooperate or clash to forge a unit of selection whose importance grows as we probe the functions and specificity of the host-associated microbiome. 

2. The hologenome is comprised of microbial parasites, mutualists, and commensals - all sources of variation that selection can act against or with.

3. The hologenome is best understood in terms of equating a microbe in the microbiome to a gene in the genome - if a gene can be selected for in the genome, a host-associated microbe can too. If a gene is neutral, a microbe can be too. If a gene comes and goes in the genome (i.e., recombination), a microbe can too.

4. The hologenome is not a superorganism, metagenome, organ, or the only unit of selection. It is an assembly of genomes of diverse organisms, some of which is essential to holobiont fitness.

5. The hologenome is a body of scholarship that fits squarely into genetics and multi-level selection theory.

6. The hologenome does not change evolutionary biology, but upgrades it to incorporate the microbiome as part of the genetic variation subject to selection.

7. The hologenome fits seamlessly into all canonical mechanisms of evolutionary change, namely genetic variation, intergenomic disequilibria (i.e., mitochondria and host genome), maternal transmission to some extent, and selection.

8. The hologenome reboots Lamarckian evolution (microbial acquisition) into neo-Darwinian evolution.

9. The hologenome variation arises not only from genetic variation, recombination, mutation, but also new microbial acquisition, microbe amplification, and extensive horizontal gene transfer.

10. The hologenome exemplifies the postmodern synthesis of various disciplines, including the unification of evolutionary biology, genetics, and microbiology. 


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